HK1208780A1 - Method for prevention of formation of abnormal flavor in raw milk or pasteurized milk, and pasteurized milk processed by the method - Google Patents

Abstract

[PROBLEMS] To provide a method for preventing the formation of abnormal flavor in raw milk or pasteurized milk and to provide pasteurized milk for use in the production of milk having good quality and flavor. [MEANS FOR SOLVING PROBLEMS] During the course from the milking to the pasteurization in the milk processing process, a treatment for reducing the dissolved oxygen concentration is performed. The treatment is carried out within 72 hours after milking. After the treatment is completed, the dissolved oxygen concentration is maintained at a low level until the pasteurization is started. The prevention of the formation of abnormal flavor means the prevention of one or more of the spontaneous generation of oxidized odor in raw milk, the formation of and/or increase in a hexanal, the generation of heated odor, and the formation of and/or increase in a sulfide.

Description

Raw milk, method for inhibiting peculiar smell in sterilized milk and sterilized milk treated by the method

The present application is a divisional application of application No. 200680021543.5, application date 2006, 6/14, entitled "method for suppressing off-flavor in raw milk and sterilized milk, and sterilized milk treated by the method".

Technical Field

The invention relates to a method for inhibiting peculiar smell in raw milk and sterilized milk and the sterilized milk treated by the method.

More specifically, the present invention relates to a method for suppressing the off-flavor in raw milk and sterilized milk by suppressing so-called spontaneous oxidation odor caused by spontaneous oxidation of raw milk called soybean odor (also called cardboard odor), suppressing the generation and/or increase of carbonyl compounds such as hexanal which are causative substances of spontaneous oxidation odor, suppressing heat odor which is a problem of the quality or flavor of sterilized milk, and suppressing the generation and/or increase of sulfides which are causative substances of heat odor. Also, relates to a pasteurized milk treated by the method for suppressing the peculiar smell.

In the present invention, "raw milk" includes raw milk (raw milk before sterilization) containing raw milk (raw milk in a state of being squeezed from a cow), raw milk or raw milk, and a milk fluid that is subjected to supercooling or heating without affecting the quality or flavor thereof.

In the present invention, the term "sterilized milk" includes not only raw milk subjected to sterilization but also all milk fluids of raw milk or raw milk of mammals subjected to sterilization.

In the present invention, the term "immediately after milking" includes within 3 hours from the start of milking, in addition to the time of milking. That is, the time when the composition of the raw milk collected immediately after the milk expression is made uniform by stirring or the like is included, for example, when the extruded raw milk is collected in a tank provided in a pasture. In general, the time required to immediately cool the extruded raw milk to a temperature of about 5 ℃ takes about 2 hours.

Background

The peculiar smell of the raw milk is harmful to the good impression (image) of 'nature', 'delicious', 'nutrition/function' of the milk. This will reduce the consumption of milk and ultimately adversely affect the overall dairy industry.

A typical off-flavor that causes a problem in the quality or flavor of raw milk is a so-called spontaneous oxidation odor caused by spontaneous oxidation of raw milk. Spontaneous oxidative odors include bean odors (also known as cardboard odors), closed odors, metal odors, animal tallow odors, grease odors, fish odors, and the like.

The mechanism of formation of spontaneous oxidation odor is not known in detail, but it is known that carbonyl compounds such as hexanal are typical causative substances.

Spontaneous oxidative odor occurs with time during cold storage even in raw milk that is sufficiently hygienic-managed and has no abnormal quality of bacteria. At this time, the amount of carbonyl compounds such as hexanal in the raw milk increases.

This spontaneous oxidized odor also has a great influence on the flavor of the sterilized milk, and therefore quality control of the raw milk is very important.

On the other hand, typical off-flavors that cause problems in the quality and flavor of the sterilized milk include the generation of carbonyl compounds such as soybean odor and hexanal, and also heat odor.

The causative substance of the heating odor is considered to be a sulfide compound as a representative. The sulfide-based compound means a sulfur compound, and specific examples thereof include dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS).

In the quality control of raw milk, the raw milk is rejected when spontaneous oxidation and odor can be confirmed in a receiving stage of the raw milk after being extruded from the raw milk and sent to a milk processing plant for a certain period of time.

On the other hand, when spontaneous oxidation odor can be confirmed after sterilization treatment in a milk treatment plant, the product (sterilized milk or the like) is shipped out.

Products such as raw milk and sterilized milk which spontaneously oxidize and smell are confirmed, and any of them is commercially useless and cannot be used as food. This causes losses in agricultural resources. That is, if the odor of raw milk or sterilized milk can be prevented or suppressed and milk having good quality or flavor can be stably supplied, agricultural resources can be effectively used without waste.

It is an important research subject in the dairy industry to find a mechanism of generation of off-flavor in raw milk and sterilized milk and to find a solution to prevent generation of off-flavor.

However, no adequate measures have been taken against the unpleasant odor of the raw milk and the sterilized milk, specifically, the spontaneous oxidative odor referred to as the soybean odor and the heat odor. For example, there has been no adequate solution for the method of suppressing the generation of carbonyl compounds such as hexanal and sulfide compounds, which are causative substances such as soybean odor and heat odor.

By thoroughly managing the quality of raw milk and sterilized milk, it is considered that the consumer's desire to purchase cow milk can be promoted if raw milk and sterilized milk having high commercial value and free from soybean odor or heated odor are stably supplied.

Therefore, it is necessary to suppress the off-flavor in the raw milk and the sterilized milk, specifically, to suppress so-called spontaneous oxidation odor caused by spontaneous oxidation of the raw milk called soybean odor, suppress the generation of carbonyl compounds such as hexanal which are causative substances of the above-mentioned spontaneous oxidation odor, suppress the heat odor which is a problem of the quality or flavor of the sterilized milk, and suppress the generation of sulfides which are causative substances of the heat odor.

As to conventional techniques for cow milk having good quality and flavor and a method for producing the same, Japanese patent application laid-open No. H05-049395, Japanese patent application laid-open No. H10-295341, Japanese patent application laid-open No. 2001-078665, Japanese patent application laid-open No. 2003-144045 and the like have been proposed.

Japanese patent application laid-open No. H05-049395 discloses the following method: storing raw milk before sterilization in a storage tank, introducing (blowing) inert gas (nitrogen gas), and performing deoxidation treatment to maintain freshness and inhibit bacterial proliferation.

However, although the case of the cow milk being treated in a tank (storage tank) after it is received in a factory is described as a stage of the deoxidation treatment of cow milk, there is no description of the state of the cow milk in a pasture, after it is stored in a tank, or the like.

That is, the introduction of the concept of time during the sterilization process from the start of milking is not considered. The time process from milking of raw milk in the pasture to delivery to the factory is up to 2-3 days. In addition, raw milk is also transported over long distances from the milking parlour to the milk processing plant. For example, raw milk extruded from the north sea of Japan is transported over long distances to the sites of milk processing plants, for example, to the continents of Japan.

As described above, carbonyl compounds such as hexanal, which are typical causative substances of spontaneous oxidative odor, which is a typical off-flavor that causes problems in the quality and flavor of raw milk, are increased with the passage of time during cold storage even though raw milk is not deteriorated in quality by bacteria due to strict hygiene control.

Here, even if the deoxidation treatment or the like is performed after entering the factory, the effect of suppressing spontaneous oxidation odor is insufficient.

Therefore, in order to produce milk with good quality or flavor, it is important to thoroughly manage the quality at an early stage after milking.

Japanese patent laid-open publication Nos. H10-295341 and 2001-078665 describe the following methods: introducing inert gas (nitrogen) into raw milk, deoxidizing, and sterilizing to obtain milk with good flavor. However, the flavor of milk after sterilization is described, and the quality and flavor of raw milk before sterilization are not described.

Japanese patent laid-open publication No. 2003-1440345 describes the following method: cow milk stored after sterilization in an aseptic tank is filled in a coating material having oxygen barrier properties with an inert gas (nitrogen gas) as an atmosphere to produce cow milk having a good flavor. However, although the flavor of milk before filling into a container (after sterilization) is described, the quality and flavor of raw milk before sterilization are not described.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a method for suppressing an unpleasant odor in raw milk and sterilized milk, and sterilized milk treated by the method.

Specifically, the object of the present invention is to provide the following method: a method for suppressing the off-flavor in raw milk and sterilized milk by suppressing so-called spontaneous oxidized odor caused by spontaneous oxidation of raw milk called soybean odor, suppressing the generation and/or increase of carbonyl compounds such as hexanal which are causative substances of the spontaneous oxidized odor, suppressing heated odor which is a problem of the quality or flavor of sterilized milk, and suppressing the generation and/or increase of sulfides which are causative substances of the heated odor.

The purpose of the present invention is to provide a pasteurized milk treated by the method for suppressing off-flavor, which is used for producing milk having good quality or flavor.

Accordingly, an object of the present invention is to stably supply commercially available raw milk and sterilized milk with little spontaneous oxidized odor, and to stimulate the desire of consumers to purchase cow milk by reducing the rejection or non-shipment of raw milk and sterilized milk due to spontaneous oxidized odor, thereby making good use of agricultural resources without wasting them.

Means for solving the problems

The present inventors have made extensive studies in view of the above-mentioned problems, and as a result, have found that a factor for suppressing spontaneous oxidative odor and thermal odor of a sterilized milk in a process of sterilizing a raw milk after milking the milk is dissolved oxygen in the raw milk.

The present inventors have found that the control and management of this factor can suppress so-called spontaneous oxidation odor, which is called soybean odor and is caused by spontaneous oxidation of raw milk, the generation and/or increase of carbonyl compounds such as hexanal, which are causative substances of the spontaneous oxidation odor, the generation and/or increase of heated odor which is a problem in the quality or flavor of sterilized milk, and the generation and/or increase of sulfides which are causative substances of the heated odor, and have completed the present invention.

The present inventors have found a concept of inhibiting factors such as spontaneous oxidation odor caused by spontaneous oxidation of raw milk, which is called soybean odor of raw milk or pasteurized milk, generation and/or increase of carbonyl compounds such as hexanal which are causative substances of the spontaneous oxidation odor, heated odor which is a problem of quality or flavor of pasteurized milk, generation and/or increase of sulfides which are causative substances of the heated odor, and the like, and thus have introduced time for change in quality or flavor of raw milk or pasteurized milk.

Specifically, it has been investigated whether or not experiments are effective in controlling and managing the concentration of dissolved oxygen in raw milk and sterilized milk when a certain time has elapsed after milk expression, and in terms of suppressing the generation and/or increase of carbonyl compounds such as hexanal, which are causative substances of spontaneous oxidation odor, the generation and/or increase of heated odor, sulfide compounds which are causative substances of heated odor, and the like in the raw milk and sterilized milk.

According to this result, it is known that the time after the factory collection is set, for example, the concentration of dissolved oxygen is controlled and managed from the time after the milk expression to 72 hours, preferably from 48 hours to 72 hours, more preferably from 48 hours, particularly preferably from 24 hours, and that the effect of suppressing the formation and/or increase of carbonyl compounds such as hexanal, which are causative substances of spontaneous oxidation odor, spontaneous oxidation odor of raw milk and sterilized milk, the generation and/or increase of heat odor, the generation and/or increase of sulfides which are causative substances of heat odor, and the like is large.

That is, it is known that, in the case where the concentration of dissolved oxygen is controlled and managed immediately after milking of raw milk and in the early stage of the sterilization process, for example, immediately after milking in a pasture, it is most preferable from the viewpoint of suppressing the generation and/or increase of carbonyl compounds such as caproaldehyde, which are causative substances of spontaneous oxidized odor, the generation and/or increase of heated odor, sulfide compounds which are causative substances of heated odor, and the like in raw milk and sterilized milk.

In addition, according to this experiment, it was found that the range of the dissolved oxygen concentration in the raw milk or the sterilized milk can be effectively determined from the viewpoint of suppressing the generation and/or increase of carbonyl compounds such as hexanal, which are causative substances of spontaneous oxidized odor, generation and/or increase of heated odor, sulfide, which is causative substances of heated odor, and the like.

That is, the present invention provides a method for suppressing the off-flavor in raw milk and sterilized milk, characterized in that in the milk processing step, the dissolved oxygen concentration is reduced in the process from milk expression to sterilization.

Here, the treatment for lowering the dissolved oxygen concentration is performed from the time of milking to the time of 72 hours.

After the treatment for reducing the dissolved oxygen concentration is performed, the dissolved oxygen concentration is kept low until the sterilization treatment.

In the method for suppressing an unpleasant odor in raw milk or pasteurized milk of the present invention, the suppression of the unpleasant odor may be performed by using any one or more of the following:

(1) inhibition of spontaneous oxidative malodor of raw milk;

(2) suppression of the production and/or increase of hexanal;

(3) inhibition of heating odor;

(4) the formation and/or increased inhibition of sulfides.

The raw milk is inhibited from spontaneous oxidative odor, for example, soybean odor.

The sulfide compounds whose production and/or increase are inhibited are at least 1 or more of dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS).

Next, the sterilized milk of the present invention is treated by the method for suppressing the off-flavor in the raw milk and the sterilized milk of the present invention.

Effects of the invention

According to the present invention, the generation and/or increase of carbonyl compounds such as hexanal, which are substances causing spontaneous oxidation odor, the generation and/or increase of heated odor which is a problem in the quality or flavor of the sterilized milk, and the generation and/or increase of sulfides which are substances causing heated odor, can be suppressed, thereby suppressing the off-flavor in the raw milk and the sterilized milk.

Further, it is possible to provide a sterilized milk which is treated by the method for suppressing an offensive odor and which can be used for producing a milk having a good quality and flavor.

Thus, there is provided: raw milk and pasteurized milk, which are commercially available with little spontaneous oxidative odor and can be stably supplied, are reduced in rejection or factory stop due to spontaneous oxidative odor, thereby promoting the desire of consumers to purchase cow milk and effectively utilizing agricultural resources without waste.

Drawings

FIG. 1 is a graph showing the change with time of the dissolved oxygen concentration when the dissolved oxygen concentration of raw milk is not adjusted, the dissolved oxygen concentration is decreased immediately after milking, and when the raw milk is held in an open container, the raw milk is held in a closed container.

FIG. 2 is a graph showing the change with time of soybean odor when the dissolved oxygen concentration of raw milk is not adjusted, the dissolved oxygen concentration is decreased immediately after milking, and when the raw milk is held in an open container, the raw milk is held in a closed container.

FIG. 3 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration of the starting milk is not adjusted, the dissolved oxygen concentration is decreased immediately after milking, and when the starting milk is held in an open container and held in a closed container.

FIG. 4 is a graph showing the change with time of the dissolved oxygen concentration when the dissolved oxygen concentration is decreased immediately after milking, when the dissolved oxygen concentration is decreased after 24 hours from milking, and when the dissolved oxygen concentration is decreased after 48 hours from milking, in the case where the dissolved oxygen concentration of the raw material milk is not adjusted.

FIG. 5 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration is decreased immediately after milking, when the dissolved oxygen concentration is decreased after 24 hours from milking, and when the dissolved oxygen concentration is decreased after 48 hours from milking, in the case where the dissolved oxygen concentration of the raw material milk is not adjusted.

FIG. 6 is a graph showing the change with time of the dissolved oxygen concentration when the dissolved oxygen concentration immediately after milking is lowered to 0.8ppm without adjusting the dissolved oxygen concentration of the starting milk which is likely to undergo spontaneous oxidation.

FIG. 7 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration immediately after milking is lowered to 0.8ppm without adjusting the dissolved oxygen concentration of the starting milk which is liable to undergo spontaneous oxidation.

FIG. 8 is a graph showing the change with time of the dissolved oxygen concentration when the dissolved oxygen concentration of raw milk which is difficult to spontaneously oxidize is not adjusted, and when the dissolved oxygen concentration after 24 hours from milk expression is reduced to 2.0ppm, and when the dissolved oxygen concentration after 48 hours from milk expression is reduced to 5.0 ppm.

FIG. 9 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration of the raw material milk which is difficult to spontaneously oxidize was decreased to 2.0ppm after 24 hours from the milk expression and to 5.0ppm after 48 hours from the milk expression, when the dissolved oxygen concentration of the raw material milk which is difficult to spontaneously oxidize was not adjusted.

FIG. 10 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration of the starting milk which is liable to spontaneously oxidize is decreased to 2.1ppm after 24 hours from milk squeezing when the dissolved oxygen concentration of the starting milk is not adjusted.

FIG. 11 is a graph showing the change with time of the hexanal concentration when the dissolved oxygen concentration of the raw milk which is difficult to spontaneously oxidize is decreased to 2.1ppm after 24 hours from milk squeezing when the dissolved oxygen concentration of the raw milk is not adjusted.

FIG. 12 is a hexanal concentration chart in the case where the dissolved oxygen concentration of the raw material milk was not adjusted and the dissolved oxygen concentration after 24 hours from the milk expression was reduced to 2.1ppm and 5.0ppm in the case where the raw material milk was subjected to the heat treatment, the dissolved oxygen concentration after 24 hours from the milk expression was reduced to 2.0ppm and 5.0ppm in the case where the raw material milk was subjected to the heat treatment as it was, and the raw material milk was kept in a sealed state for 24 hours and then subjected to the heat treatment as it was.

FIG. 13 is a heating odor chart in the case where the dissolved oxygen concentration of the raw material milk is not adjusted and the dissolved oxygen concentration after 24 hours from milk expression is reduced to 2.1ppm and 5.0ppm when the raw material milk is subjected to the heat treatment, and the dissolved oxygen concentration after 24 hours from milk expression is reduced to 2.0ppm and 5.0ppm when the raw material milk is subjected to the heat treatment as it is, and the raw material milk is kept in a sealed state for 24 hours and then subjected to the heat treatment as it is.

FIG. 14 is a graph showing the area values of sulfides (area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) in raw milk, i.e., in heat-treated pasteurized milk, pasteurized milk having 2.0ppm hypoxia, pasteurized milk having 5.0ppm hypoxia, pasteurized milk having unadjusted pasteurized milk or pasteurized milk having 2.0ppm hypoxia, and pasteurized milk having 5.0ppm hypoxia, respectively.

FIG. 15 is a graph showing the area values of sulfides (area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) in a pasteurized milk obtained by heating a raw milk without adjusting the dissolved oxygen concentration, a pasteurized milk immediately after hypoxia milking, a pasteurized milk obtained by 24 hours after hypoxia milking, and a pasteurized milk obtained by 48 hours after hypoxia milking.

Fig. 16 is a graph showing the area values of sulfides (area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) in the heat-treated pasteurized milk and the low-oxygen (degassed) (2.1ppm) pasteurized milk without adjusting the dissolved oxygen concentration of the raw milk.

Detailed Description

According to the method for suppressing the unpleasant odor in raw milk and pasteurized milk of the present invention, the treatment for lowering the dissolved oxygen concentration is performed in the process from milk expression to pasteurization in the step of treating milk.

Here, the treatment for reducing the dissolved oxygen concentration is preferably performed from milking to 72 hours.

In addition, it is preferable to keep the dissolved oxygen concentration low between the treatment of lowering the dissolved oxygen concentration and the sterilization treatment.

The above-mentioned odor can be suppressed by using any one or more of the following:

(1) inhibition of spontaneous oxidative malodor of raw milk;

(2) suppression of the production and/or increase of hexanal;

(3) inhibition of heating odor;

(4) the formation and/or increased inhibition of sulfides.

The suppression of spontaneous oxidative odor of the raw milk, for example, soybean odor, and the sulfide to be suppressed in the production and/or increase, respectively, means at least 1 or more of dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS).

According to the experiment of the present inventors, in the raw milk subjected to the treatment of reducing the dissolved oxygen concentration, any one of spontaneous oxidation odor of the raw milk, production and/or increase of hexanal, and production and/or increase of sulfides is suppressed.

Here, in order to suppress the off-flavor in the raw milk and the sterilized milk by the treatment of reducing the dissolved oxygen concentration of the raw milk, any of the suppression of spontaneous oxidation odor, the suppression of the generation and/or increase of hexanal, the suppression of heat odor, and the suppression of the generation and/or increase of sulfides of the raw milk can be employed.

In the method for suppressing the unpleasant odor in the raw milk or the pasteurized milk of the present invention, the treatment for lowering the dissolved oxygen concentration may be performed at a time substantially in the course of the pasteurization treatment after the milk is squeezed.

For example, the following steps are generally performed after milking and before sterilization treatment: (1) milking from cows; (2) storing in a milk collecting trough (a trough arranged in the pasture) in the pasture; (3) transport from a trough in a pasture to a truck (vehicle, ship, airplane, etc.); (4) transporting by a truck; (5) transport from truck to milk processing plant, etc.

Some of the above-described steps from the milking to the reception in the factory may be omitted, but the treatment for lowering the dissolved oxygen concentration may be basically performed in any of these steps.

Here, for example, it is considered that the treatment for lowering the dissolved oxygen concentration is performed in any of the following devices, instruments, apparatuses, and the like:

(A) in a hose or conduit for milking from a cow;

(B) a trough (milk collecting trough) arranged in a pasture for collecting milk;

(C) a hose or conduit for transporting raw milk from the milk collection trough to a truck for transporting raw milk;

(D) in the tank of the truck;

(E) in a hose or conduit carrying raw milk from a truck to a milk processing plant.

However, from the viewpoint of stably securing a sterilized milk having good quality and flavor, it is preferable to perform a treatment for lowering the dissolved oxygen concentration of the raw milk in a short time after milking.

When the dissolved oxygen concentration of the raw milk is decreased in a short time after milking, the effect of suppressing deterioration in the quality or flavor of the raw milk is increased, and the quality or flavor of the sterilized milk obtained by sterilizing the raw milk is also improved, which is advantageous.

Here, when the treatment for lowering the dissolved oxygen concentration of the raw milk is performed immediately after milk expression in a pasture, any of spontaneous oxidation odor of the raw milk, production and/or increase of hexanal, heat odor, and production and/or increase of sulfides is suppressed, and the effect of suppressing the off-flavor in the raw milk and the sterilized milk is exhibited optimally.

The above-mentioned effects can be exhibited by the treatment of lowering the dissolved oxygen concentration of the raw milk at the time of 72 hours after the milk expression or during the time before the milk expression, which is about 72 hours after the milk expression until the storage in the factory.

However, it is preferable to perform a treatment for lowering the dissolved oxygen concentration of the raw milk in a short time after milking because any of spontaneous oxidation odor of the raw milk, production and/or increase of hexanal, heating odor, and production and/or increase of sulfides is suppressed, and the effect of suppressing the odor in the raw milk and the sterilized milk is exhibited. Here, it is desirable that the treatment for lowering the dissolved oxygen concentration of the raw milk is performed within 72 hours, preferably within 48 hours, more preferably within 24 hours, and most preferably immediately after milking.

The method for reducing the dissolved oxygen concentration of the raw milk is not particularly limited. For example, a method of degassing in a vacuum atmosphere, a method of replacing oxygen with an inert gas, or the like can be used. In the method of replacing oxygen with inert gas, when aeration (bubbling) with inert gas is employed, no complicated apparatus is required. When the oxygen gas is replaced with an inert gas, nitrogen gas may be used as the inert gas. The nitrogen is easy to operate and low in price.

The numerical range of the dissolved oxygen concentration in the above-mentioned treatment of reducing the dissolved oxygen concentration of the raw milk is not particularly limited, but a low dissolved oxygen concentration of the raw milk is preferable from the viewpoint of a large effect of suppressing deterioration in quality or flavor of the raw milk.

According to experiments conducted by the present inventors, it is empirically thought that as conditions for suppressing spontaneous oxidation odor and hexanal production in arbitrary raw milk which is liable to spontaneous oxidation (deterioration in quality), the dissolved oxygen concentration of the raw milk needs to be 2ppm or less.

On the other hand, it is empirically thought that as conditions for suppressing the spontaneous oxidized odor and the production of hexanal in any raw milk which is difficult to oxidize spontaneously (has good quality), the dissolved oxygen concentration of the raw milk is sufficient to be 5ppm or less, and the same effect of suppressing the production of hexanal as 2ppm or less can be obtained.

That is, the numerical range of the dissolved oxygen concentration when the treatment for lowering the dissolved oxygen concentration of the raw milk is performed is influenced by the quality of the raw milk which is less susceptible to spontaneous oxidation (good quality) and more susceptible to spontaneous oxidation (poor quality).

The feeding conditions (feed, land, etc.) and seasonal changes of dairy cattle have an influence on the quality of raw milk.

Generally, the quality of raw milk is controlled in a good state (state in which spontaneous oxidation is difficult). Here, although the numerical range of the dissolved oxygen concentration when the treatment of reducing the dissolved oxygen concentration of the raw milk is performed is 5ppm, any of the spontaneous oxidized odor of the raw milk, the generation and/or increase of hexanal, the heated odor, and the generation and/or increase of sulfides is suppressed, and the effect of suppressing the off-flavor in the raw milk and the sterilized milk can be exhibited.

However, even if the raw milk is in an environment where the odor is relatively likely to be generated, if the dissolved oxygen concentration is lower when the raw milk dissolved oxygen concentration is reduced, the raw milk is inhibited from undergoing spontaneous oxidation odor, the generation and/or increase of hexanal, the heat odor, and the generation and/or increase of sulfides, and the odor-suppressing effect in the raw milk and the sterilized milk can be more effectively exhibited.

The dissolved oxygen concentration in the case of performing the treatment for reducing the dissolved oxygen concentration of the raw milk is preferably 4ppm or less, more preferably 3ppm or less, and particularly preferably 2ppm or less.

In the method for suppressing the unpleasant odor in the raw milk and the pasteurized milk of the present invention, it is preferable that the dissolved oxygen concentration is kept low between the time of the sterilization treatment and the time after the treatment for reducing the dissolved oxygen concentration. Here, as a method of keeping the dissolved oxygen concentration low, for example, a method of avoiding contact with oxygen may be employed.

When the dissolved oxygen concentration of the raw milk is reduced, the dissolved oxygen concentration of the raw milk is kept low, whereby the effect of suppressing deterioration in the quality or flavor of the raw milk is increased, and the quality or flavor of the sterilized milk obtained by sterilizing the raw milk is also improved. Further, when the dissolved oxygen concentration of the raw milk is kept low after the dissolved oxygen concentration of the raw milk is reduced, the raw milk having good quality and flavor can be stably secured.

As described above, the treatment for reducing the dissolved oxygen concentration of the raw milk can be performed in any of, for example, a hose or a pipe for milking cows, a tank (milk collection tank) provided in a pasture for collecting milk, a hose or a pipe for transporting raw milk from the milk collection tank to a truck for transporting raw milk, a tank of a truck, a hose or a pipe for transporting raw milk from a truck to a milk processing plant, and the like.

Here, in order to maintain the dissolved oxygen concentration in the raw milk after the treatment for lowering the dissolved oxygen concentration of the raw milk low, it is preferable to manage all the devices, apparatuses and apparatuses listed above, which are used for the treatment for lowering the dissolved oxygen concentration, and which are provided between the sterilization treatment steps in the factory after the apparatus, and to maintain the dissolved oxygen concentration of the raw milk low in the step.

In this case, it is important to control and manage the dissolved oxygen concentration of the raw milk in the tank or the pump. Here, it is necessary to provide a method of introducing nitrogen atmosphere into the tank, or a method of providing a liquid feed pump in a somewhat airtight container and introducing nitrogen atmosphere into the container.

As described above, the method for suppressing the unpleasant odor in raw milk and sterilized milk according to the present invention is characterized in that immediately after the milk is squeezed or when a predetermined time has elapsed after the milk is squeezed, the dissolved oxygen concentration is reduced, and if necessary, the dissolved oxygen concentration is kept low in the subsequent process.

In the present invention, sensory evaluation of spontaneous oxidized odor (soybean odor) or heated odor of raw milk was performed by using the concentrations of hexanal and sulfides as indicators, and it was confirmed that the raw milk and sterilized milk had an effect of suppressing the odor thereof.

The method according to the present invention has the effects of not only improving the flavor of the sterilized milk, preventing the generation of an off-flavor, and preventing the loss of commercial value, but also including an industrially novel viewpoint. That is, the flavor is improved, and the quality can be prevented from being deteriorated, which is different from the conventional art. The introduction of the concept of time from the milking to the sterilization treatment is also different from the conventional techniques.

The present invention will be described below with reference to examples, but the present invention is not limited thereto.

In examples 1 to 3 and 7 to 9, any raw milk (raw milk) which is easily spontaneously oxidized was used. On the other hand, in examples 4 and 6, any raw milk (raw milk) which is difficult to spontaneously oxidize was used. In examples 1 to 4 and 7 to 8, the method of replacing oxygen with inert gas was used to reduce the dissolved oxygen concentration. On the other hand, in examples 5, 6 and 9, the method of decreasing the dissolved oxygen concentration was a method of degassing in a vacuum atmosphere.

Example 1

(the concentration of dissolved oxygen immediately after milking is reduced, and the concentration of soybean odor and hexanal changes with time when the milk is held in an open container or in a closed container)

The changes with time of the concentrations of soybean odor and hexanal when the milk was held in an open container and a closed container by lowering the dissolved oxygen concentration immediately after milking were examined.

About 30 minutes after milking, the raw milk is cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 9.6ppm (temperature 8 ℃ C.). The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

Immediately after milking, nitrogen gas was introduced into the unadjusted raw milk to reduce the dissolved oxygen concentration to 0.8ppm (temperature 7 ℃ C.).

The raw milk with the adjusted dissolved oxygen concentration was filled into 2 kinds of containers. Each container is a plastic box (a container made of polyethylene, which is referred to as an "open container") having poor gas barrier properties and a stainless steel can container (which is referred to as a "closed container") having good gas barrier properties. These are referred to as "raw milk in a low-oxygen open state" and "raw milk in a low-oxygen closed state", respectively.

The results of comparison of the dissolved oxygen concentration, soybean odor, and hexanal concentration of the unadjusted raw milk, the raw milk in a low-oxygen open state, and the raw milk in a low-oxygen closed state are shown in fig. 1 to 3.

At this time, the raw milk was stored for several days under conditions of a temperature of 2 ℃ in a dark place. In the following examples, the raw milk was stored for several days under conditions of 2 ℃ in the dark.

Fig. 1 shows the change with time of the dissolved oxygen concentration of raw milk in an unadjusted state, raw milk in a hypoxic/open state, and raw milk in a hypoxic/closed state.

The dissolved oxygen concentration was measured by a portable DO meter, namely DO-21P (manufactured by DKK Co., Ltd.).

The dissolved oxygen concentration is measured by the following method because the measurement value is slightly unstable depending on the measurement conditions. Namely, (1) stirring the measured fluid (raw milk) by a stirrer, wherein the flow rate is more than 10 cm/s; (2) to the stirred starting milk, an electrode of a DO meter was inserted, and after about 3 minutes, a stable value was read. According to this method, a measurement value with good reproducibility can be obtained.

The dissolved oxygen concentration of the raw milk without adjustment shifts at a high value.

The dissolved oxygen concentration of the starting milk in the low-oxygen/open state reached a value equivalent to that of the starting milk without adjustment after 24 hours from the start of milking.

The dissolved oxygen concentration of the raw milk in a low-oxygen and closed state was kept as low as immediately after the adjustment.

From the above analysis, it was confirmed that it is effective to keep the dissolved oxygen concentration of the raw milk low in the sealed state after the dissolved oxygen concentration is adjusted to a low value.

As a method for keeping the dissolved oxygen concentration at a low value, it is conceivable to store the raw milk in an inert gas (nitrogen gas or the like) atmosphere in addition to the sealed state.

Fig. 2 shows changes with time in beany odor of raw milk in an unadjusted state, raw milk in a hypoxic/open state, and raw milk in a hypoxic/closed state.

Sensory evaluation of Bean odor: the 7-grade evaluation was performed by 5 members of the professional evaluator: the conditional average values were compared for 0 point (no feeling), 0.5 point (slight feeling), 1 point (slight feeling), 1.5 point (slight feeling), 2 point (feeling), 2.5 point (obvious feeling), and 3 point (strong feeling).

The soybean odor of the unadjusted raw milk was evaluated as 0 immediately after milking, and all the panelists did not have any feeling of soybean odor, but had some feeling after 12 hours from milking to 0.4. Thereafter, the soybean odor increased to 3 after 72 hours, and all panelists had a strong feeling of soybean odor.

The soybean odor of the raw milk in the low-oxygen/open state was 0 after 12 hours from milk expression, and all panelists did not have any feeling of soybean odor, but had a subtle feeling of 0.9 after 24 hours from milk expression. Thereafter, the soybean odor increased and reached a value equivalent to that of the raw milk without adjustment after 72 hours.

The starting time of soybean odor of the raw milk in the low-oxygen open state was delayed compared to that of the untreated raw milk.

The soybean odor of the raw milk in the low-oxygen and closed state was 0 after 12 hours from milk expression, and all panelists had no feeling of soybean odor, but had a little feeling of 0.4 after 24 hours from milk expression. Thereafter, the soybean odor slightly increased, and even after 72 hours, it reached 1.0 with only a subtle feeling.

As described above, the odor of the raw material milk beans in the low-oxygen and sealed state is low. The formation of a closed state after the dissolved oxygen concentration is adjusted to a low value is effective for preventing and suppressing the soybean odor of the raw milk.

Even if the container is left open after the dissolved oxygen concentration is adjusted to a low value, the container has a soybean odor-suppressing effect after 24 hours from the adjustment. However, after 48 hours had passed from the adjustment, the soybean milk had a value equivalent to that of the raw milk without adjustment, and the soybean odor was not suppressed.

Fig. 3 shows the change with time of the hexanal concentration in the raw milk without adjustment, the raw milk in the low-oxygen open state, and the raw milk in the low-oxygen closed state.

The hexanal concentration was measured by the following solid phase microextraction method (SPME method). That is, (1) a sample (volume 10mL (mL)) was collected in a glass vial (volume 20mL), and Methylisobutylketone (MIBK) was added as an internal standard substance and sealed; (2) heating the small glass bottle at the temperature of 60 ℃ for 40 minutes; (3) the "malodorous components" present in the headspace of the vial were extracted with solid phase micro-fibers (85 μm Stable FlexCarboxen/PDMS); (4) analysis was performed by GC/MS (column: CP-WAX); (5) to quantify the hexanal concentration, hexanal standards were added to the milk and internal standards were used to generate a standardized standard curve.

The solid phase micro extraction method (SPME method) can rapidly analyze volatile "odor components" with high sensitivity, but its quantitative nature is considered problematic. However, quantitative analysis can be rapidly performed by the present method.

The hexanal concentration of the unadjusted raw milk was 1. mu.g/L (microgram/liter) immediately after milking, but reached 5. mu.g/L after 12 hours from milking and 10. mu.g/L or more after 24 hours. Then, the hexanal concentration increased and reached more than 20. mu.g/L after 48 hours.

The hexanal concentration of the starting milk in the low-oxygen and open state was 3. mu.g/L after 12 hours from milk expression and 10. mu.g/L or less after 24 hours. Then, the hexanal concentration increased and reached the same value as the unadjusted starting milk after 48 hours.

However, the hexanal concentration of the starting milk in the low-oxygen open state is delayed from the hexanal concentration of the starting milk to increase in feeling compared with the starting milk without adjustment.

The hexanal concentration of the starting milk in a low-oxygen and closed state was 1. mu.g/L after 12 hours from milk expression, which was the same as that immediately after milk expression. Further, even when the amount of the hexanal contained in the starting milk was 2. mu.g/L from the time of milking to the time of 72 hours, the hexanal concentration of the starting milk in a low-oxygen and closed state was almost unchanged and was changed at a low value.

When the dissolved oxygen concentration was adjusted to a low value and then kept in a sealed state, it was confirmed that it was effective for keeping the hexanal concentration of the raw milk low.

Even if the dissolved oxygen concentration is in an open state after being adjusted to a low value, the increase of the hexanal concentration is effectively inhibited after 24 hours from the adjustment. However, after 48 hours had passed from the adjustment, the value reached the same value as that of the raw milk without adjustment, and the increase in the hexanal concentration could not be effectively suppressed.

In addition, the correlation between the soybean odor and the hexanal concentration was confirmed again by comparing fig. 2 with fig. 3.

In the following examples, only hexanal concentration was evaluated and the evaluation of soybean odor was omitted.

Example 2

(Change with time of hexanal concentration immediately after milking, when dissolved oxygen concentration decreased after 24 hours from milking and after 48 hours)

The chronological change in the hexanal concentration immediately after milking, 24 hours after milking, and 48 hours after milking was examined with respect to the decrease in the dissolved oxygen concentration.

About 30 minutes after milking, the raw milk is cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 9.6ppm (temperature 8 ℃ C.). The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

The time after milking to lower the dissolved oxygen concentration was set to 3 different elapsed times immediately after milking, 24 hours after milking, and 48 hours after milking.

Immediately after milking, 24 hours after milking, and 48 hours after milking, the unadjusted raw milk was purged with nitrogen gas to reduce the dissolved oxygen concentration to 0.8ppm (temperature 7 ℃) and filled into a stainless steel can having a good gas barrier property (referred to as a "closed container"). These are referred to as "raw milk immediately after the milking under hypoxia", "raw milk after 24 hours of the milking under hypoxia", "raw milk after 48 hours of the milking under hypoxia", respectively.

Fig. 4 shows the results of comparison of the dissolved oxygen concentrations of the unadjusted raw milk, the raw milk immediately after the hypoxia milking, the raw milk after 24 hours of the hypoxia milking, and the raw milk after 48 hours of the hypoxia milking.

The dissolved oxygen concentration of the unadjusted raw milk, the raw milk immediately after hypoxia milking, the raw milk after 24 hours of hypoxia milking, and the raw milk after 48 hours of hypoxia milking was measured with time by the method described in example 1.

The dissolved oxygen concentration of the raw milk without adjustment shifts at a high value.

The dissolved oxygen concentration of the starting milk immediately after the low oxygen milking is shifted to a value as low as the value of the starting milk immediately after the adjustment.

The dissolved oxygen concentration of the raw milk after 24 hours and 48 hours after the hypoxia milking was high, which was the same as that of the raw milk before the adjustment, but was shifted to a low value after the adjustment.

From the above analysis, it was confirmed again that the raw milk is effective in keeping the dissolved oxygen concentration of the raw milk low in the sealed state after the dissolved oxygen concentration was adjusted to a low value.

As described above, as a method for keeping the dissolved oxygen concentration at a low value, a method of keeping raw milk in an atmosphere of an inert gas (nitrogen gas or the like) may be considered in addition to the sealed state.

Fig. 5 shows the chronological changes in the hexanal concentration of the unadjusted raw milk, the raw milk immediately after hypoxia milking, the raw milk after 24 hours of hypoxia milking, and the raw milk after 48 hours of hypoxia milking.

The hexanal concentration was measured by the same method as described in example 1.

The hexanal concentration of the unadjusted raw milk was 1. mu.g/L immediately after milking, but reached 5. mu.g/L after 12 hours from milking and 10. mu.g/L or more after 24 hours. Then, the hexanal concentration increased to 20. mu.g/L or more after 48 hours.

The hexanal concentration of the starting milk immediately after milking, which is low in oxygen, was 1. mu.g/L after 12 hours from milking, which was the same value as immediately after milking. Even if the concentration of hexanal in the starting milk immediately after the milking was 2. mu.g/L after 72 hours from the milking, the hexanal concentration in the starting milk was almost unchanged and changed at a low value.

The hexanal concentrations of the starting milk after 24 hours from the start of the hypoxia/milk expression and 48 hours from the start of the hypoxia/milk expression were as high as those of the starting milk before the adjustment, but the adjusted values were unchanged or slightly decreased.

The increase in the hexanal concentration was stopped not only immediately after milking but also when the dissolved oxygen concentration was adjusted to a low value after 24 hours or 48 hours from milking. That is, when the dissolved oxygen concentration is adjusted to a low value, spontaneous oxidation is stopped.

The earlier the dissolved oxygen concentration of the raw milk is decreased, the greater the effect of suppressing spontaneous oxidized odor is, and it can be confirmed that the dissolved oxygen concentration is decreased to some extent before the spontaneous oxidation reaction reaches a saturated state.

After the dissolved oxygen concentration was decreased, the raw milk was kept in a sealed state, and it was confirmed that the raw milk was effective in keeping the hexanal concentration low again.

Example 3

(Change of hexanal concentration with time when changing dissolved oxygen concentration of raw milk liable to spontaneous oxidation by substitution of oxygen with inert gas)

The change with time of the hexanal concentration when the dissolved oxygen concentration was changed immediately after milking of the starting milk susceptible to spontaneous oxidation was examined.

As a method for reducing the dissolved oxygen concentration, a method of replacing oxygen with an inert gas can be used.

About 30 minutes after milking, the raw milk was cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 9.6ppm (temperature 8 ℃ C.).

The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

The dissolved oxygen concentration after milking was set at two levels of 0.8ppm and 4.8ppm (temperature 7 ℃).

That is, immediately after milking, the raw milk without adjustment is filled into a stainless steel can container (referred to as "closed container") having a good gas barrier property by introducing nitrogen gas into the raw milk to reduce the dissolved oxygen concentration to the above value. These are called "raw milk of hypoxia 0.8 ppm" and "raw milk of hypoxia 4.8 ppm", respectively.

The results of comparison of the dissolved oxygen concentration of the unadjusted raw milk, low oxygen 0.8ppm, and the hexanal concentration are shown in fig. 6 and 7.

Fig. 6 shows the change with time of the dissolved oxygen concentration of the raw milk without adjustment and the raw milk with hypoxia 0.8 ppm.

The dissolved oxygen concentration was measured by the method described in example 1.

The dissolved oxygen concentration of the raw milk without adjustment shifts at a high value.

Since the dissolved oxygen concentration of 4.8ppm low-oxygen raw milk is the same as that immediately after adjustment, the explanation is omitted.

The dissolved oxygen concentration of the raw milk containing low oxygen 0.8ppm was changed at a low value equivalent to that immediately after the adjustment.

When the dissolved oxygen concentration was lowered to about 1ppm and then the resulting mixture was sealed, it was confirmed that the dissolved oxygen concentration was kept low and the spontaneous oxidation reaction of the starting milk could be stopped.

Fig. 7 shows the change with time of the hexanal concentration of the unadjusted raw milk and the raw milk containing 0.8ppm of hypoxia.

The hexanal concentration was measured by the method described in example 1.

The hexanal concentration of the unadjusted raw milk was 1. mu.g/L immediately after milking, 5. mu.g/L after 12 hours from milking, 10. mu.g/L or more after 24 hours, and thereafter, the hexanal concentration increased to 20. mu.g/L or more after 48 hours.

The hexanal concentration of the raw milk containing 4.8ppm of hypoxia reached the same value as that of the raw milk without adjustment after 24 hours from the milk expression, and thereafter increased to the same value as that of the raw milk without adjustment, so that the explanation thereof is omitted.

The hexanal concentration of the raw milk containing hypoxia 0.8ppm was 2. mu.g/L after 72 hours from milk expression, and was shifted to a low level without much difference from the level immediately after milk expression.

If the dissolved oxygen concentration is reduced to 1ppm, the increase in the hexanal concentration is stopped. That is, the concentration of dissolved oxygen is reduced to 1ppm or less, and spontaneous oxidation is stopped.

The lower the dissolved oxygen concentration of the raw milk is, the greater the effect of suppressing spontaneous oxidized odor is.

In this example, since raw milk which is liable to spontaneous oxidation is used, the dissolved oxygen concentration of the raw milk needs to be 1ppm or less as a condition for suppressing the generation of spontaneous oxidized odor or hexanal.

However, in example 4, as described below, when an experiment was performed using raw milk that is less likely to undergo spontaneous oxidation, it was sufficient that the dissolved oxygen concentration of the raw milk was 5ppm as a condition for suppressing the formation of spontaneous oxidized odor or hexanal, and when raw milk that is less likely to undergo spontaneous oxidation was used, if the dissolved oxygen concentration of the raw milk was 5ppm or less, the hexanal formation suppression effect was comparable to that obtained when the dissolved oxygen concentration of the raw milk was 2 ppm.

That is, the requirement for the dissolved oxygen concentration and the like is influenced by the quality of the raw milk.

The quality of raw milk is affected by the feeding conditions (feed, land, etc.) of dairy cows, seasonal variations, etc. It is considered that the quality of the raw milk is difficult to spontaneously oxidize due to the good state management, and therefore, the effect of suppressing spontaneous oxidation odor is exhibited even when the dissolved oxygen concentration is 5ppm or less.

Example 4

(Change of hexanal concentration with time when changing dissolved oxygen concentration of raw milk which is difficult to spontaneously oxidize by replacing oxygen with inert gas)

The change with time of the hexanal concentration of the raw milk which was difficult to spontaneously oxidize was examined from milk expression to when the dissolved oxygen concentration was changed after 24 hours.

As a method for reducing the dissolved oxygen concentration, a method of replacing oxygen with an inert gas can be used.

After milking for about 30 minutes, the temperature of the raw milk is cooled to 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 9.2ppm (temperature 8 ℃ C.).

The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

From the milk expression to the point after the lapse of 24 hours, the dissolved oxygen concentration was set at 2 levels of 2.0ppm and 5.0ppm (temperature 7 ℃).

That is, nitrogen gas was introduced into the unadjusted raw milk at the point of 24 hours after the milk expression to lower the dissolved oxygen concentration to the above-mentioned value, and the raw milk was filled into a stainless steel can container (referred to as "closed container") having a good gas barrier property. These are called "raw milk of 2.0ppm hypoxia", "raw milk of 5.0ppm hypoxia", respectively.

The results of comparing the dissolved oxygen concentration of the unadjusted raw milk, the raw milk with 2.0ppm hypoxia, and the raw milk with 5.0ppm hypoxia with the hexanal concentration are shown in fig. 8 and 9.

Fig. 8 shows the change with time in the dissolved oxygen concentration of raw milk that was not adjusted, raw milk that was low in oxygen 2.0ppm, and raw milk that was low in oxygen 5.0 ppm.

The dissolved oxygen concentration was measured by the method described in example 1.

The dissolved oxygen concentration of the raw milk without adjustment shifts at a high value.

The dissolved oxygen concentrations of the raw milk having 2.0ppm of hypoxia and the raw milk having 5.0ppm of hypoxia were shifted to values as low as those immediately after the adjustment.

When the dissolved oxygen concentration was adjusted to 5ppm and the milk was sealed, it was confirmed that the dissolved oxygen concentration was kept low and the spontaneous oxidation reaction of the raw milk was likely to stop.

Fig. 9 shows the change with time of the hexanal concentration of the unadjusted raw milk, the raw milk having 2.0ppm hypoxia, and the raw milk having 5.0ppm hypoxia.

The hexanal concentration was determined using the method described in example 1.

The hexanal concentration of the unadjusted starting milk was 4. mu.g/L at the beginning of the experiment, 10. mu.g/L after 72 hours and 12. mu.g/L after 96 hours. Thereafter, the hexanal concentration increased and reached 20. mu.g/L or more after 168 hours.

Hexanal concentrations of raw milk at 2.0ppm hypoxia and 5.0ppm hypoxia were reduced to 6 or 8. mu.g/L after 72 hours.

If the dissolved oxygen concentration is reduced to 5.0ppm, the increase in hexanal concentration is slowed.

That is, when the dissolved oxygen concentration is reduced to 5.0ppm or less, spontaneous oxidation is suppressed.

The lower the dissolved oxygen concentration of the raw milk is, the greater the effect of suppressing spontaneous oxidized odor is. When raw milk which is difficult to spontaneously oxidize is used, it is confirmed that the raw milk has an inhibitory effect on the formation or increase of hexanal even when the dissolved oxygen concentration of the raw milk is 5 ppm.

Example 5

(the hexanal concentration was changed with time by degassing in a vacuum atmosphere to change the dissolved oxygen concentration of the starting milk which was liable to undergo spontaneous oxidation)

The change with time of the hexanal concentration from milking of the starting material susceptible to spontaneous oxidation to the change in the dissolved oxygen concentration after the elapse of 24 hours was examined.

In this example, copper ions were added to the starting milk so that the final concentration was 1ppm, thereby preparing starting milk that was susceptible to spontaneous oxidation.

As a method for reducing the dissolved oxygen concentration, a method of degassing in a vacuum atmosphere can be used.

About 30 minutes after milking, the raw milk is cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 11.2ppm (temperature 8 ℃ C.).

The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

The method of degassing in a vacuum atmosphere was carried out as follows. About 500mL (milliliter) of the raw material milk was put into a pear-shaped flask (capacity 1L) and mounted on an evaporator. While cooling the pear-shaped flask with ice, a vacuum atmosphere (pressure 30mmHg) was introduced into the flask, and the flask was kept for 15 minutes. Thereafter, the flask was raised to atmospheric pressure with a nitrogen atmosphere in order to avoid sudden air inclusion.

As a result of these treatments, the dissolved oxygen concentration was set at 2.1ppm (temperature 7 ℃ C.) for a period of 24 hours from the milking.

This was filled into a stainless steel can container (referred to as "closed container") having a good gas barrier property (referred to as low-oxygen 2.1ppm raw milk).

The results of comparison of the hexanal concentrations of the raw milk without adjustment and the raw milk with hypoxia (degassing) · 2.1ppm are shown in fig. 10.

Fig. 10 shows the change with time of the hexanal concentration of the raw milk without adjustment and the raw milk with low oxygen (deoxygenation) · 2.1 ppm.

The hexanal concentration was determined using the method described in example 1.

The hexanal concentration of the unadjusted starting milk was 3. mu.g/L at the start of the experiment and 14. mu.g/L after 24 hours.

Hexanaldehyde concentration of raw milk of 2.1ppm, hypoxia (degassing), was low at 5. mu.g/L after 24 hours.

If the dissolved oxygen concentration is reduced to 2.1ppm or less, the increase in the hexanal concentration is slowed.

That is, when the dissolved oxygen concentration is reduced to 2.1ppm or less, spontaneous oxidation is suppressed.

When the results of the above examples were considered in combination, it was confirmed that spontaneous oxidation could be suppressed by lowering the dissolved oxygen concentration of the raw milk irrespective of the method of lowering the dissolved oxygen concentration, such as the method of degassing in a vacuum atmosphere or the method of replacing oxygen with an inert gas.

In this example, since the experiment was performed using raw milk which is easily oxidized spontaneously, the dissolved oxygen concentration of the raw milk must be 2.1ppm or less as a condition for suppressing the generation of the spontaneous oxidized odor or hexanal.

However, in example 4, as described below, it is sufficient that the dissolved oxygen concentration of the raw material milk is 5ppm as the condition for suppressing the generation of the spontaneous oxidized odor or the hexanal when the raw material milk which is difficult to oxidize spontaneously is used, and the effect of suppressing the generation of the hexanal equivalent to the dissolved oxygen concentration of the raw material milk of 2ppm can be obtained when the dissolved oxygen concentration of the raw material milk is 5ppm or less when the raw material milk which is difficult to oxidize spontaneously is used.

That is, the requirement for the dissolved oxygen concentration and the like is influenced by the quality of the raw milk.

The quality of raw milk is affected by the feeding conditions (feed, land, etc.) of dairy cows, seasonal variations, etc. It is considered that the quality of the raw milk is controlled in a good state, and spontaneous oxidation is difficult, and therefore, the effect of suppressing spontaneous oxidation odor is exhibited even when the dissolved oxygen concentration is 5ppm or less.

Example 6

(the hexanal concentration was changed with time by degassing in a vacuum atmosphere to change the dissolved oxygen concentration of the starting milk which was difficult to spontaneously oxidize)

The change with time of the hexanal concentration from milking of the starting material milk which is less likely to spontaneously oxidize to the change in the dissolved oxygen concentration after the elapse of 24 hours was examined.

As a method for reducing the dissolved oxygen concentration, a method of degassing in a vacuum atmosphere can be used.

About 30 minutes after milking, the raw milk is cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 11.2ppm (temperature 8 ℃ C.).

The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

In the method of degassing in a vacuum atmosphere described in example 5, the dissolved oxygen concentration was set at 2.1ppm (temperature 7 ℃ C.) for a period of 24 hours from the milking.

This was filled into a stainless steel tank container (referred to as "closed container") having a good gas barrier property (referred to as low-oxygen (degassed) · 2.1ppm raw milk).

The results of comparison of the hexanal concentrations of the raw milk without adjustment and the raw milk with hypoxia (degassing) · 2.1ppm are shown in fig. 11.

Fig. 11 shows the change with time of the hexanal concentration of the raw milk without adjustment, low oxygen (degassing) · 2.1 ppm.

The hexanal concentration was determined using the method described in example 1.

The hexanal concentration of the unadjusted starting milk was 3. mu.g/L at the start of the experiment and 7. mu.g/L after 72 hours.

Hexanaldehyde concentration of raw milk of 2.1ppm, hypoxia (degassing), was low at 4. mu.g/L after 72 hours.

If the dissolved oxygen concentration is reduced to 2.1ppm or less, the increase in the hexanal concentration is slowed. That is, when the dissolved oxygen concentration is reduced to 2.1ppm or less, spontaneous oxidation is suppressed.

When the results of the above examples are considered in combination, spontaneous oxidation can be suppressed by suppressing the dissolved oxygen concentration of the raw milk irrespective of the method of decreasing the dissolved oxygen concentration and irrespective of the quality of the raw milk.

Example 7

(in the case of heat treatment by replacing oxygen with inert gas, the dissolved oxygen concentration after 24 hours from milk expression is reduced, and the hexanal concentration, the thermal odor, and the sulfide concentration in the case of heat treatment after 24 hours from milk expression are maintained in a sealed state)

Adopting a method of replacing oxygen by inert gas to reduce the dissolved oxygen concentration after 24 hours from milk squeezing, and heating the milk as it is; the dissolved oxygen concentration after 24 hours from milk expression was decreased, and the hexanal concentration, the heating odor, and the sulfide concentration at the time of heating treatment were examined after keeping the vessel in a sealed state for 24 hours.

As a method for reducing the dissolved oxygen concentration, a method of replacing oxygen with an inert gas can be used.

About 30 minutes after milking, the raw milk is cooled to a temperature of 8 ℃. The dissolved oxygen concentration of the raw milk at this time was 9.2ppm (temperature 8 ℃ C.).

The raw milk without the adjusted dissolved oxygen concentration was referred to as "raw milk without adjustment" as a control sample (control).

After 24 hours had elapsed from the milk expression, 4 different raw milk were prepared, in which the dissolved oxygen concentration was reduced to 2.0 and 5.0ppm (temperature 7 ℃ C.) by introducing nitrogen gas into the raw milk without adjustment, and the raw milk was kept in a closed state for 24 hours.

Then, the raw milk was extruded to an unadjusted raw milk after 24 hours and 48 hours, and the raw milk was subjected to heat treatment in an autoclave (temperature 110 ℃ C., holding time 1 minute). These are referred to as: "unadjusted pasteurized milk", "pasteurized milk containing 2.0ppm of hypoxia", "pasteurized milk containing 5.0ppm of hypoxia", "pasteurized milk containing unadjusted state and maintained state", "pasteurized milk containing 2.0ppm of hypoxia", "pasteurized milk containing 5.0ppm of hypoxia".

In the autoclave, the raw milk was filled in a stainless steel can (referred to as "closed container") having a good gas barrier property.

The results of comparison of the dissolved oxygen concentration, the hexanal concentration, the heat odor and the sulfide concentration of the unadjusted pasteurized milk, the 2.0ppm pasteurized milk, the 5.0ppm pasteurized milk, the unadjusted pasteurized milk, the 2.0ppm pasteurized milk, and the 5.0ppm pasteurized milk are shown in FIGS. 12 to 14.

The change with time of the dissolved oxygen concentration of the unadjusted pasteurized milk, 2.0ppm low-oxygen pasteurized milk, 5.0ppm low-oxygen pasteurized milk, unadjusted and maintained pasteurized milk, 2.0ppm low-oxygen pasteurized milk, and 5.0ppm low-oxygen pasteurized milk was measured by the method described in example 1.

FIG. 12 shows the change with time of the hexanal concentration in the non-modified pasteurized milk, the pasteurized milk having 2.0ppm of hypoxia, the pasteurized milk having 5.0ppm of hypoxia, the pasteurized milk having non-modified and maintained hypoxia, the pasteurized milk having 2.0ppm of hypoxia and maintained hypoxia, and the pasteurized milk having 5.0ppm of hypoxia and maintained hypoxia.

The hexanal concentration was determined using the method described in example 1.

The raw milk was not adjusted to have a hexanal concentration of 9. mu.g/L, and after 24 hours of storage as it was (sterilized milk without adjustment/storage), it was 9. mu.g/L, and the hexanal concentration was high.

On the other hand, although the hexanal concentrations of the pasteurized milks containing 2.0ppm of hypoxia and 5.0ppm of hypoxia were 6. mu.g/L, the hexanal concentrations were 7. mu.g/L and slightly increased but remained low after 24 hours of storage (pasteurized milks containing 2.0ppm of hypoxia and 5.0ppm of hypoxia).

If the dissolved oxygen concentration is reduced to 5.0ppm or less, the hexanal concentration is still low.

That is, if the dissolved oxygen concentration is reduced to 5.0ppm or less, spontaneous oxidation is suppressed.

The lower the dissolved oxygen concentration of the raw milk is, the greater the inhibitory effect of the bactericidal milk on spontaneous oxidized odor. In this example, raw milk which is easily oxidized spontaneously is used, and even if the dissolved oxygen concentration of the raw milk reaches 5ppm, the effect of suppressing the production or increase of hexanal in the pasteurized milk can be confirmed.

FIG. 13 shows the results of evaluation of the heat smell of unadjusted pasteurized milk, pasteurized milk having 2.0ppm of hypoxia, pasteurized milk having 5.0ppm of hypoxia, pasteurized milk having unadjusted holding state, pasteurized milk having 2.0ppm of hypoxia and pasteurized milk having 5.0ppm of hypoxia.

Sensory evaluation of heated malodor, 5-grade evaluations were performed by 5 panelists: the conditional average values were compared for 0 point (no feeling), 2 points (slight feeling), 3 points (slight feeling), 4 points (feeling), and 5 points (strong feeling).

The amounts of the non-conditioned and non-maintained sterilized milks were 4.4 and 4.2, respectively, and almost all panelists felt the hot smell.

The amounts of 2.0ppm of pasteurized milk, 5.0ppm of pasteurized milk, 2.0ppm of pasteurized milk with low oxygen, and 5.0ppm of pasteurized milk with low oxygen were 3.6, 3.4, and 3.2, respectively, and the panelists felt a little bad smell due to heating.

The dissolved oxygen concentration is low, and any of the sterilized milks subjected to heat treatment is less likely to be smelly when heated than the unmodified sterilized milks.

Even if the dissolved oxygen concentration of the raw milk is lowered for a certain period of time, the effect of suppressing the hot smell is obtained.

Therefore, as described above, the earlier the dissolved oxygen concentration of the raw milk is reduced, the greater the effect of suppressing the formation of hexanal concentration as an indicator of spontaneous oxidation odor is. From these viewpoints, it has been comprehensively judged that controlling and managing the dissolved oxygen concentration of the raw milk from an early stage after milking is effective for obtaining a sterilized milk having good quality and flavor.

In this example, after the dissolved oxygen concentration of the raw milk was reduced, the raw milk was sealed and kept in a low dissolved oxygen concentration state.

When the dissolved oxygen concentration of the raw milk is reduced, if the raw milk is in an open state, the heating odor suppression effect of the sterilized milk is slightly reduced due to the increase in the dissolved oxygen concentration. However, if the sterilization treatment is performed before the dissolved oxygen concentration is increased to 5ppm or more, the same effect of suppressing the hot smell can be obtained.

In this case, as described above, the effect of suppressing the formation of hexanal concentration, which is an index of spontaneous oxidation odor, is also obtained.

Fig. 14 shows the area values of sulfides (area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) in unadjusted pasteurized milk, 2.0ppm pasteurized milk, 5.0ppm pasteurized milk, unadjusted pasteurized milk, 2.0ppm pasteurized milk, and 5.0ppm pasteurized milk.

The area value of the sulfide was measured by the following solid phase microextraction method (SPME method), and the peak area value was evaluated as the concentration.

That is, (1) a sample (volume 10mL) was collected and sealed in a glass vial (volume 20 mL); (2) heating the small glass bottle at the temperature of 60 ℃ for 40 minutes; (3) the "malodorous components" present in the headspace of the vial were extracted with solid phase micro-fibers (85 μm Stable Flex Carboxen/PDMS); (4) analysis was performed by GC/MS (column: CP-WAX); the area value of the sulfide was determined.

The results of comparing the area values of sulfides in the pasteurized milk at 2.0ppm low oxygen, 5.0ppm low oxygen, 2.0ppm low oxygen, and 5.0ppm low oxygen with the area values of sulfides in the pasteurized milk at the state of being unadjusted and retained are as follows.

The sterilized milks containing 2.0ppm of hypoxia, 5.0ppm of hypoxia, 2.0ppm of hypoxia, and 5.0ppm of hypoxia in the area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) tend to be lower than those containing neither the control nor the control.

The area values of the sulfides in the pasteurized milk with hypoxia 2.0ppm, hypoxia 5.0ppm, hypoxia 2.0ppm and hypoxia 5.0ppm were all lower than the area values of the sulfides in the pasteurized milk without adjustment and holding.

Even if the dissolved oxygen concentration is adjusted to 5.0ppm or less for a certain period of time, the formation or increase of sulfides is effectively suppressed.

Therefore, as described above, the lower the dissolved oxygen concentration of the raw material milk is, the greater the effect of suppressing the generation or increase of the hexanal concentration as an index of the spontaneous oxidation odor is.

From the viewpoint that the effect of suppressing deterioration in the quality or flavor of raw milk is increased in an environment where an off-flavor is slightly likely to be generated as the dissolved oxygen concentration of raw milk is lower, the dissolved oxygen concentration of raw milk is controlled or controlled to a low value, and thereby a sterilized milk having good quality or flavor can be effectively obtained.

As described above, even when the starting milk is in an open state and the sterilization treatment is performed before the dissolved oxygen concentration is increased to 5.0ppm, the same effect of suppressing the hot smell can be obtained.

In this example, the area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) were examined. As sulfide compounds, which are typical causative substances of the heat odor, dimethyl sulfide (DMS) is also mentioned in addition to the above. From the tendency of the area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) shown in the experimental results shown in fig. 13 and fig. 14, the effect of suppressing the formation or increase of dimethyl sulfide (DMS) can be exhibited by adjusting the dissolved oxygen concentration to 5.0ppm or less.

Example 8

(method of substituting oxygen with inert gas, in which dissolved oxygen concentration immediately after milking, after 24 hours and 48 hours from milking, sulfide concentration at the time of heat treatment)

The dissolved oxygen concentration immediately after milking, 24 hours after milking, and 48 hours after milking was examined for the sulfide concentration at the time of heat treatment.

As a method for reducing the dissolved oxygen concentration, a method of replacing oxygen with an inert gas can be used.

Immediately after milking, 24 hours after milking, and 48 hours after milking, 3 different raw milks were prepared by introducing nitrogen gas into the unadjusted raw milks to lower the dissolved oxygen concentration to 0.8ppm (temperature 7 ℃ C.), respectively.

Then, the raw milk was squeezed to an unadjusted raw milk over 72 hours, and the raw milk was subjected to a heat treatment in an autoclave (temperature 110 ℃ C., holding time 1 minute). These are referred to as: "unadjusted pasteurized milk", "pasteurized milk from low oxygen and freshly squeezed milk", "pasteurized milk from low oxygen and squeezed milk to 24 hours later", "pasteurized milk from low oxygen and squeezed milk to 48 hours later"

In the autoclave, the raw milk was filled in a stainless steel can (referred to as "closed container") having a good gas barrier property.

Fig. 15 shows the results of comparison of the area values of the non-modified pasteurized milk, the pasteurized milk immediately after the low-oxygen milking, the pasteurized milk after 24 hours from the low-oxygen milking, and the pasteurized milk after 48 hours from the low-oxygen milking.

Fig. 15 shows the area values of sulfides (the area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) in the unadjusted pasteurized milk, pasteurized milk immediately after the hypoxia milking, pasteurized milk after 24 hours from the hypoxia milking, and pasteurized milk after 48 hours from the hypoxia milking.

The area value of the sulfide species was measured by the method described above.

The area values of the low-oxygen and the pasteurized milk immediately after milking, the low-oxygen and the pasteurized milk after 24 hours of milking, and the low-oxygen and the pasteurized milk after 48 hours of milking were compared as follows.

Among the area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), the value of the sterilized milk immediately after the low oxygen and milking, after 24 hours, and after 48 hours was lower than that of the non-adjusted sterilized milk.

The area values of the pasteurized milk immediately after the milk expression under low oxygen, the pasteurized milk after 24 hours from the milk expression under low oxygen, and the pasteurized milk after 48 hours from the milk expression under low oxygen were all lower than the area values of the sulfides in the pasteurized milk without adjustment.

Even if the dissolved oxygen concentration is lowered for a certain time, the effect of suppressing the generation or increase of sulfides is exhibited.

Therefore, as described above, the earlier the dissolved oxygen concentration of the raw milk is reduced, the greater the effect of suppressing the generation or increase of the hexanal concentration as an index of the spontaneous oxidized odor is.

In view of the fact that the effect of suppressing deterioration in the quality or flavor of raw milk is increased in an environment where an off-flavor is slightly likely to be generated as the dissolved oxygen concentration of raw milk is lower, the dissolved oxygen concentration of raw milk is controlled and managed from the early stage after milking, and sterilized milk having good quality or flavor can be effectively obtained.

As described above, even when the starting milk is in an open state, the same effect of suppressing the hot smell can be obtained by sterilizing the starting milk before the dissolved oxygen concentration is increased to 5.0 ppm.

Example 9

(by degassing in vacuum atmosphere, the dissolved oxygen concentration is lowered after 24 hours from the milking of the starting milk, and the sulfide concentration in the heat treatment)

The sulfide concentration in the heating treatment was examined by decreasing the dissolved oxygen concentration after 24 hours from the milking of the raw material milk.

As a method for reducing the dissolved oxygen concentration, a method of degassing in a vacuum atmosphere can be used.

The raw material milk which had been squeezed to an unadjusted state after the lapse of 24 hours was degassed by the vacuum atmosphere shown in example 5 to lower the dissolved oxygen concentration from 11.2ppm (temperature 8 ℃ C.) to 2.1ppm (temperature 7 ℃ C.).

Then, these raw milk were subjected to heat treatment (referred to as "unadjusted sterilized milk", low-oxygen (degassed) · 2.1ppm sterilized milk, respectively) in an autoclave (temperature 10 ℃ C., holding time 1 minute).

In the autoclave, the raw milk was filled in a stainless steel can (referred to as "closed container") having a good gas barrier property.

The results of comparing the area values of the sulfides in the raw milk, the low oxygen (degassed) · 2.1ppm pasteurized milk, which were not adjusted, are shown in fig. 16.

Fig. 16 shows the area values of sulfides (area values of dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS)) of raw milk, low oxygen (degassed), 2.1ppm sterilized milk, which were not adjusted.

The area value of the sulfide compound was measured by the method described above.

The area value of sulfides in the low-oxygen (degassed) & 2.1ppm pasteurized milk was compared with the area value of sulfides in the raw milk without adjustment as follows.

Among the area values of dimethyl disulfide (DMDS), the low oxygen (degassed) (2.1ppm) sterilized milk was low compared to the unmodified sterilized milk.

Among the area values of dimethyl trisulfide (DMTS), the low-oxygen (degassed) (2.1ppm) sterilized milk was the same value as the unmodified sterilized milk.

The area value of sulfides in the low-oxygen (degassed) (2.1ppm) pasteurized milk was lower than that of sulfides in the unadjusted pasteurized milk.

When the results of the above examples are considered in combination, the dissolved oxygen concentration can be reduced independently of the method of reducing the dissolved oxygen concentration by degassing in a vacuum atmosphere, the method of replacing oxygen with an inert gas, or the like, and the generation of sulfides can be suppressed by reducing the dissolved oxygen concentration of the raw milk.

Even if the raw milk is in an open state, the same effect of suppressing the hot smell can be obtained by sterilizing the raw milk before the dissolved oxygen concentration is increased to 5ppm or more.

Claims (7)

1. A method for suppressing the odor of raw milk or sterilized milk, characterized in that in the step of treating milk, the treatment for lowering the dissolved oxygen concentration is performed in the process from milk expression to sterilization.

2. The method for suppressing the unpleasant odor of raw milk or pasteurized milk according to claim 1, wherein the treatment for lowering the dissolved oxygen concentration is carried out between the time of milking and the time of 72 hours.

3. The method for suppressing the off-flavor in raw milk and pasteurized milk according to claim 1 or 2, characterized in that the dissolved oxygen concentration is kept low between the time of sterilization treatment and the time after the treatment for lowering the dissolved oxygen concentration.

4. A method for suppressing an offensive odor in raw milk or pasteurized milk according to any one of claims 1 to 3, wherein the suppression of the offensive odor is carried out by using any one or more of:

(1) inhibition of spontaneous oxidative malodor of raw milk;

(2) suppression of the production and/or increase of hexanal;

(3) inhibition of heating odor;

(4) the formation and/or increased inhibition of sulfides.

5. The method for suppressing the off-flavor in raw milk and pasteurized milk according to claim 4, wherein the spontaneous oxidative odor is soybean odor.

6. The method for suppressing the off-flavor in raw milk and pasteurized milk according to claim 4, wherein the sulfide is at least 1 or more of dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl trisulfide (DMTS).

7. Sterilized milk, which is treated by the method for suppressing the off-flavor in raw milk or sterilized milk according to any one of claims 1 to 6.