HK1096265A - Xylooligosaccharide composition with high purity - Google Patents

Abstract

A xylooligosaccharide composition having a high purity is produced while preventing the formation of UV-absorbing matters or coloring components. A method of producing a xylooligosaccharide composition having a high purity and containing little UV-absorbing matters or coloring components which comprises, in a method of purifying a crude sugar liquid containing residues obtained by treating a plant material (wood, corn cob, cotton seed husk, bagasse, rice straw or the like) with an alkali or by heating the material under elevated pressure and then conducting an enzymatic treatment, concentrating the above-described liquid optionally followed by a desalting treatment and an active carbon treatment. According to this method, a saccharification liquid is concentrated and then desalted/treated with active carbon to prevent the formation of UV-absorbing matters or coloring components and thus a xylooligosaccharide composition having a high purity can be produced.

Description

High purity xylo-oligosaccharide composition

Technical Field

The present invention relates to a process for producing high-purity xylo-oligosaccharides, which comprises subjecting a plant material selected from wood, corn cob, cottonseed hull, bagasse and straw to a pretreatment and then to a saccharification treatment to produce a xylo-oligosaccharide solution, wherein the crude sugar solution obtained by the saccharification treatment is subjected to a solid-liquid separation and a decolorization with high efficiency, thereby obtaining high-purity xylo-oligosaccharides with a small amount of UV-absorbing substances and coloring components.

Background

Application of xylo-oligosaccharide

Oligosaccharides are characterized by having not only low sweetness, low calorie, low corrosiveness and the like but also an action of promoting the proliferation activity of bifidobacteria (an effect of improving intestinal flora), and many specific health foods having an intestinal function have been marketed. Among these oligosaccharides, xylo-oligosaccharide is not easily decomposed by digestive enzymes such as acid and amylase, and after ingestion by a human body, it is not decomposed and absorbed and reaches the large intestine directly, and it is selectively utilized by bifidobacteria parasitizing in the large intestine, so that a small amount of xylo-oligosaccharide can selectively proliferate bifidobacteria, thereby having the effects of improving stool properties, promoting Ca absorption, etc., and having a wide range of applications in the fields of foods, etc.

Basic method for preparing xylo-oligosaccharide

With the progress and development of enzyme chemistry, many microbial-derived hydrolases, transferases, and the like have been discovered, and further intensive studies have made it possible to inexpensively mass-produce various oligosaccharides. Particularly, with the development of high-activity xylanase, hemicellulose-xylan contained in a large amount in plants with low utilization resources such as wood, corn cob, cottonseed hull, bagasse and straw can be used for producing xylo-oligosaccharide with good physical properties and functionality.

Heretofore, there have been technologies for producing xylooligosaccharides from plant materials, including:

(1) method for directly preparing xylo-oligosaccharide solution by saccharification treatment such as pressure heating, crushing or alkali treatment, and the like,

(2) Method for producing xylooligosaccharide containing xylotetraose as main component and having average degree of polymerization of up to 5.4 by acid treatment of lignocellulose from chemical pulp, and,

(3) Method for producing xylo-oligosaccharide solution by using xylan after pressure heating, alkali heating treatment or extraction and refining as initial raw material, and saccharifying the initial raw material by allowing enzyme to act on the initial raw material,

(4) A method for producing a xylo-oligosaccharide solution, which comprises pulverizing a plant material into fine pieces, subjecting the pieces to alkali heating treatment, directly subjecting the pieces to an enzyme action on the material to saccharification treatment, and then subjecting the resultant product to solid-liquid separation.

For example, the subnatal part of the day (journal of the society of agricultural and chemical sciences of Japan, volume 50, No. 5 p.209-215, 1976) uses corn cob as a raw material, and is pretreated with alkali, washed with water to remove alkali components until the pH becomes neutral, and hydrolyzed with an enzyme derived from Bacillus to produce xylo-oligosaccharides.

Necessity of high-purity xylooligosaccharide

When xylooligosaccharide is added to processed foods, beverages, and the like for use, colorless xylooligosaccharide is preferable for the purpose of increasing the degree of freedom in processing of processed foods, beverages, and the like. In addition, in the production of processed foods, beverages, and the like, high-temperature heat treatment is often performed in order to kill microorganisms. It is known that heating causes coloring of sugar, and xylo-oligosaccharide has a large tendency to be colored by heating. The coloring is noticeable in the low-polymerization degree xylooligosaccharide, and when the polymerization degree is high, the coloring tendency becomes small. However, when the polymerization degree is large, it is not easily metabolized and utilized by intestinal bacteria such as bifidobacterium and lactobacillus (Okazaki et al, Bifidobacterium microflavol.9, p77, 1990), so xylooligosaccharide containing xylobiose having a polymerization degree of 2 as a main component is preferable. Thus, it is preferable that the xylooligosaccharide is colorless and has a small tendency to be colored after heat treatment at high temperatures.

However, in any of the above-mentioned methods (1) to (4), the crude sugar solution obtained by the saccharification contains various impurities and residues. Therefore, in order to remove these impurities and residues, the crude sugar solution has been conventionally purified by filtration or an adsorbent such as an ion exchange resin, a synthetic adsorbent, or activated carbon. In particular, sugar solutions hydrolyzed with enzymes or the like contain a large amount of impurities extracted from plant materials such as lignin, which cannot be removed by ordinary filtration. In addition to the methods for removing the coloring matter components and the like by using activated carbon and ion exchange resin, other various methods have been proposed.

Refining method using activated carbon and ion exchange resin

In japanese patent No. 3229944, japan living and eastern harmony, the following method is disclosed: although there is no disclosure of a method for suppressing the generation of UV absorbing substances such as furfural, although cottonseed hulls are subjected to a cooking treatment and then to an enzymatic hydrolysis to obtain a crude sugar solution containing xylo-oligosaccharide, which is subjected to an activated carbon treatment and a deionization treatment. This method is a method for cooking cotton seed hulls, and is not a method for purifying a crude sugar solution derived from a raw material containing a large amount of a polymer pigment component.

In Japanese patent application laid-open No. 2001-2264090 of the paper-making by prince, high polymerization degree xylo-oligosaccharides containing xylotetraose (X4) and pentaose (X5) as main components and having no absorption at 280nm and 250nm and low ash content are obtained by treating enzyme delignified pulp obtained from broad-leaved tree wood chips with xylanase, decomposing with sulfuric acid to obtain a crude xylo-oligosaccharide solution having a high polymerization degree, concentrating the crude solution, and then treating with ion exchange resin and activated carbon. In this method, the saccharified solution contains little lignin, and the saccharified solution is subjected to ion exchange resin treatment and activated carbon treatment to obtain a liquid having no absorption at 280nm and 250 nm. The oligosaccharide produced was xylo-oligosaccharide with high degree of polymerization containing X4 and X5 as main components, and the proportion of xylose monosaccharide in the total sugar was as low as 8.37%, and furfural having absorption at 280nm was less likely to be produced than xylo-oligosaccharide with low degree of polymerization.

Other refining methods

When xylo-oligosaccharides are obtained by subjecting corn cob, cottonseed hull, bagasse, straw and the like to an enzymatic reaction, the enzymatic reaction cannot efficiently produce xylo-oligosaccharides unless the raw materials are subjected to pretreatment such as alkali treatment and high-temperature high-pressure treatment. However, when corncobs are used as a raw material, impurities such as water-soluble impurities of a polymer remain in a liquid after pretreatment and saccharification in the above-described manner.

The method for removing the water-soluble impurities of the polymer includes: a method of using a UF film (Kakoku Kokai: Japanese unexamined patent publication No. 61-285999), a method of oxidizing impurities into organic acids by ozone treatment and then adsorbing the organic acids by an ion exchange resin (Kakoku Kokai: Japanese unexamined patent publication No. 62-281890), and the like. However, in the purification method using the UF membrane, the UF membrane is clogged with the residue contained in the crude sugar solution, and therefore, it is necessary to filter the solution to be clear. Further, the method of ozone treatment has a problem that it takes much time and labor and a satisfactory removing effect cannot be obtained. Then, Suntory et al (Japanese patent laid-open No. 5-253000) have found that: as a result of the present inventors found that a very good filtration effect can be obtained by subjecting plant materials such as corncobs, which have been finely ground, to an alkali treatment, washing with water, then subjecting the resulting material to an enzymatic saccharification reaction, then adding lime and carbon dioxide without separating the residue to form insoluble calcium carbonate, and then subjecting the resulting material to filtration, whereby the yield can be improved, impurities such as water-soluble polymers can be sufficiently removed, and the pure sugar content can be improved. Then, in a purification process for preparing the purified liquid into a finished product, the purified liquid is decolorized with activated carbon or an ion exchange resin, desalted with an ion exchange resin, passed through a sterilizing filter if necessary, and concentrated.

Necessity of high concentration of xylooligosaccharide

On the other hand, it is preferable that the xylose oligosaccharide solution has a sugar concentration as high as possible in order to prevent the proliferation of microorganisms during storage of the xylose oligosaccharide solution, to prevent the original composition of foods from being impaired when added to foods and the like for use, and to reduce transportation costs. In addition, in the production of xylo-oligosaccharide powder, it is preferable to spray-dry the concentrated liquid.

However, the xylose oligosaccharide solution obtained by the enzymatic decomposition and the digestion treatment has a low sugar concentration, and for example, in the method of the above-mentioned Japanese patent application laid-open No. 5-253000, the Brix of a pure sugar solution obtained by completely removing impurities such as a water-soluble polymer is as low as 2.61. Further, the salt concentration is high, and low-molecular-weight dye components remain. Therefore, it is necessary to further decolor, refine, concentrate, and produce the final product.

Therefore, the above pure sugar solution needs to be concentrated, but when the sugar solution is concentrated after decolorization with activated carbon or ion exchange resin and desalting with ion exchange resin, xylose contained in xylooligosaccharide is more easily colored than other hexoses such as glucose and sucrose, and UV-absorbing substances such as furfural are generated and further colored, and impurities are increased. In particular, when concentration is performed under an alkaline condition, high-temperature operation causes decomposition of xylooligosaccharide, formation of coloring matter, and reduction of concentration efficiency, and in addition, when concentration is performed under an acidic condition, scale caused by calcium adheres to the concentration tank to significantly reduce heat transfer efficiency, thereby reducing concentration efficiency. In order to prevent this, a large amount of alkali and acid is required to keep the pH neutral, and after concentration, in order to remove these alkali and acid, desalting with a large amount of ion exchange resin is required, which not only increases the cost, but also results in a decrease in recovery of xylooligosaccharide in the desalting process.

In addition, the raw material for producing the food oligosaccharide is preferably hemicellulose of a plant which has been once eaten, and the raw material can be easily obtained, and the like. From the above-mentioned viewpoint, xylooligosaccharide using corncob, which is a core of corn, as a raw material is superior to xylooligosaccharide using cotton seed hulls, wood chips, and the like as a raw material. However, no method for producing xylooligosaccharide has been known in the past: xylo-oligosaccharide containing xylobiose as main component and having low polymerization degree and containing little UV-absorbing substance and coloring substance is prepared from saccharified solution containing polymer pigment and UV-absorbing substance such as corn cob.

[ patent document 1] Japanese patent No. 3229944

[ patent document 2] Japanese patent application laid-open No. 2001-

[ patent document 3] Japanese patent application laid-open No. S61-285999

[ patent document 4] Japanese patent application laid-open No. S62-281890

[ patent document 5] Japanese patent application laid-open No. 5-253000

[ non-patent document 1] journal of the Japanese society for agricultural and chemical industries, Vol.50, No. 5 p.209-215, 1976

[ non-patent document 2] Bifidobacterium microfara, Okazaki et al, vol.9, p77, 1990

Disclosure of Invention

The present invention provides a method for producing high-purity xylo-oligosaccharides, which comprises subjecting a plant material such as corncob, cottonseed hull, bagasse or straw to pretreatment such as alkali treatment or high-temperature high-pressure treatment, and then efficiently removing water-soluble impurities of high molecules remaining in a saccharified crude sugar solution, thereby producing high-purity xylo-oligosaccharides with less inclusion of UV-absorbing substances and coloring substances.

The invention also provides a method for producing high-purity xylo-oligosaccharide, which is used for producing high-purity xylo-oligosaccharide with less UV absorption substance and coloring substance inclusion and high xylo-oligosaccharide content with the polymerization degree of 2-3.

The present invention further provides a method for producing high-purity xylooligosaccharide, which is capable of producing high-purity xylooligosaccharide with little contamination by UV-absorbing substances and coloring substances and with little formation of UV-absorbing substances and coloring substances even when the solid content is concentrated to 30 to 75% by boiling.

The present invention further provides a method for producing high-purity xylooligosaccharide, which is capable of producing high-purity xylooligosaccharide with less UV-absorbing substance and coloring matter inclusion, a high content of xylooligosaccharide with a polymerization degree of 2 to 3, and less generation of UV-absorbing substance and coloring matter even when the solid content is concentrated to 30 to 75% by boiling.

The present invention also provides high-purity xylooligosaccharide produced by the method of the present invention, which has a low content of UV-absorbing substances and coloring substances.

The present inventors have made intensive studies to solve the above problems, and as a result, have found that: the more highly UV-absorbing substances (referred to as UV-absorbing substances) are included in xylooligosaccharide, the more intense the coloration thereof by the high-temperature heat treatment. Then, the present inventors have studied a method for improving the removal efficiency of the UV absorbing substance, and as a result, have found that: a process for producing xylooligosaccharide, which comprises subjecting a plant material selected from wood, corncob, cottonseed hull, bagasse and straw, preferably after pulverizing into fine pieces, to alkali treatment or pressure treatment, then subjecting the resultant to enzyme treatment, filtering the obtained crude sugar solution to remove solids, further concentrating the filtrate, and then subjecting the filtrate to desalination and/or activated carbon treatment.

Preparation of crude sugar solution

The plant material used in the method of the present invention may be 1, 2 or more than 2 kinds of wood, corn cob, cottonseed hull, bagasse, straw, etc. Particularly, when the corncob which is difficult to decolor the crude sugar solution is used as the raw material, the method has obvious effect.

The pretreatment of the raw material may be carried out by immersing in an alkali solution at a high temperature, or by a high-temperature high-pressure treatment, or by a lignin-degrading enzyme treatment. For example, the alkali treatment may be performed with caustic soda, ammonia, or the like. When the pretreatment is carried out with a ligninolytic enzyme, the pretreatment can be carried out under the optimum conditions for the enzyme.

The enzyme used for the enzyme treatment of the pretreated raw material is an enzyme capable of producing mainly oligosaccharides having a low degree of polymerization, such as xylobiose and xylotriose. Typical enzymes are xylanases, for example, enzymes produced by the bacteria Bacillus subtilis (Bacillus subtilis), Streptomyces (Streptomyces sp.), Aspergillus (Aspergillus), Trichoderma (Trichoderma), Penicillium (Penicillium), and Cladosporium (Cladosporium), and these enzymes are used according to the purpose. The enzyme treatment is carried out under conditions that allow the production of the target xylooligosaccharide containing xylobiose as a main component (20% by weight or more of the total sugars). Under the above conditions, a crude sugar solution containing xylobiose as a main component and/or containing monosaccharides in a ratio of 30 wt% or less, 5 wt% or less, based on the total sugar content, can be obtained. It is easy for those skilled in the art to modify and optimize these conditions.

It is preferable that the solid content contained in the crude sugar solution after the enzyme treatment is not necessarily removed by filtration. Filtration through celite is possible. Particularly preferred filtration methods are: lime is added to the crude sugar solution containing the residue obtained after the enzyme treatment, carbon dioxide is added to produce an insoluble lime salt, and then filtration is performed. Any acid that reacts with lime to form an insoluble lime salt may be used in place of carbon dioxide, for example, oxalic acid, phosphoric acid. By the formation of lime salt, the clogging of the filter membrane can be prevented and the filtration can be performed efficiently.

Concentration of crude sugar solution and purification after concentration

The method of the invention is characterized in that: the crude sugar solution from which solid components have been removed by filtration is purified by optimizing the combination of (1) desalting treatment, (2) concentrating treatment, and (3) activated carbon treatment, thereby obtaining a high-purity xylooligosaccharide composition.

When the concentration is to be performed, if salting-out is to be prevented, the salt concentration is first lowered by desalting, and then the pH is adjusted to about neutral, followed by concentration. Desalting can be carried out by a cation exchange resin and/or an anion exchange resin according to a conventional method.

After concentration to a predetermined concentration or a final concentration, desalting and/or activated carbon treatment are performed to suppress coloring and increase of UV-absorbing substances associated with heat concentration, and activated carbon treatment is performed on a sugar solution having a high sugar concentration obtained by concentration to improve decoloring and UV-absorbing substance removal efficiency. That is, by concentrating and purifying the crude sugar solution, rather than concentrating the purified sugar solution to a target sugar concentration, not only the formation of UV-absorbing substances during concentration, particularly during boiling concentration, can be suppressed, but also the efficiency of removing UV-absorbing substances and the efficiency of decoloring can be improved. The above fact is specifically shown in example 3.

The concentration is preferably carried out until the sugar concentration (solid concentration) is as close as possible to the final concentration, but if the concentration is too high, the viscosity increases significantly, and the workability in the subsequent activated carbon treatment or the like is deteriorated. Further, when the concentration is insufficient, it causes a decrease in the treatment efficiency of the activated carbon and the treatment efficiency of the ion exchange resin, and causes an increase in the coloring and UV absorbing substances caused by the concentration by heating thereafter. Therefore, the crude sugar solution is concentrated to a solid concentration of 40 to 75%, preferably 45 to 65%, before decolorization with activated carbon or ion exchange resin, and lignin is removed by the next purification operation, and high-purity xylooligosaccharide with little coloration and UV-absorbing substances produced in the concentration process can be obtained. The concentration of the solid content can be easily measured after drying the water, and the concentration of the solid content can be conveniently measured by a Brix saccharimeter.

The method for concentrating the crude sugar solution may be a method generally used for concentrating a sugar solution, and for example, the concentration may be carried out by boiling at a temperature around the boiling point under normal pressure or reduced pressure. The concentration device can adopt a multi-effect concentration evaporator and the like. More preferably, the concentration is carried out under reduced pressure.

The concentrated crude sugar solution is subjected to purification by activated carbon treatment, cation exchange resin treatment and anion exchange resin treatment in any order. The activated carbon may be any activated carbon that can be used for purification of food. In this specification, the term activated carbon is synonymous with adsorbent, and the activated carbon may be replaced with adsorbent such as synthetic adsorbent including graphite carbon and styrene divinylbenzene polymer. The ion exchange resin used may be a strong acid cation exchange resin, a weak base anion exchange resin, or a mixed bed type ion exchange resin in which a cation exchange resin and an anion exchange resin are mixed.

Purification of the concentrated crude sugar solution can efficiently remove the UV-absorbing substance and the coloring substance. The removal of the UV-absorbing substance can be evaluated by measuring the absorbance at 280nm and 230nm of the substance and the absorbance at 420nm of the coloring substance, and by decreasing the absorbance as compared with that before the purification operation.

Detailed Description

Specific modes of the method of the present invention can be shown as follows.

(1) After enzyme saccharification, carrying out carbonation treatment, membrane separation, ion exchange resin treatment, activated carbon treatment and the like to remove impurities such as pigments and the like, reducing the salt concentration, then adjusting the pH to be about neutral, concentrating to a determined concentration, and then carrying out desalination and activated carbon treatment to finally obtain the xylo-oligosaccharide syrup with the sugar concentration of 75%. Diluting the syrup to a sugar concentration of 37.5%, measuring absorbance with a 5cm cuvette, the absorbance at 420nm being 0.2, preferably 0.06; further, as measured with a 1cm cuvette, the absorbance at 280nm and 230nm was 1.28 or less, 3.7 or less than 3.7, and a sugar solution showing little impurity in ultraviolet absorption was obtained. (the concentration of 50% in the treatment of example 3 in which 1% of activated carbon was added was converted to 37.5%)

(2) After enzymatic saccharification, carbonation treatment, membrane separation, activated carbon treatment or desalination are carried out to reduce the salt concentration and impurities such as pigments to a certain extent, then the pH is adjusted to be about neutral, and after concentration to a certain concentration, desalination is carried out, then monosaccharide is removed by ion exchange resin chromatography, activated carbon treatment is carried out, and then spray drying is carried out to obtain xylo-oligosaccharide powder with the water content of 6% or less than 6% and the monosaccharide of 5% or less than 5%. This powder was dissolved in water to prepare a 20% solution, and the hue of the solution was measured with a 5cm cuvette and the absorbance at 420nm was 0.1, preferably 0.05. Further, as measured with a 1cm cuvette, absorbances at 280nm and 230nm were 1 or less, 1, 2 or less, respectively, to obtain a sugar solution with less impurities showing ultraviolet absorption.

According to the present invention, since desalting and concentrating to a predetermined concentration are performed before decoloring the crude sugar solution with activated carbon and an ion exchange resin, and generation of impurities and coloring matter having UV absorption can be suppressed, the crude sugar solution such as xylooligosaccharide can be efficiently purified, and a purified product of xylooligosaccharide with less impurities and high purity can be obtained. Thereby inhibiting the coloring of the product using xylooligosaccharide.

The xylooligosaccharide produced by the method of the present invention is less colored, and therefore can be added to processed foods, beverages, health foods, nutritional supplements, foods for specified health use, cosmetics, pet foods, etc. to produce high-quality products.

The present invention will be described specifically with reference to examples, but the present invention is not limited to the examples, and methods of production based on the assumption thereof are also included in the present invention.

EXAMPLE 1 production of high-purity xylooligosaccharide solution

(1) Soaking the fine pieces of corn cob in warm water containing caustic soda dissolved therein, stirring at 90 deg.C for 90 min, filtering, washing with warm water, and removing alkali until pH is reduced to 11 or below 11.

(2) Water was added to the pretreated solid matter, the pH was adjusted to 5.6 with sulfuric acid or sodium hydroxide, and xylanase was added to the mixture to conduct an enzymatic reaction at 46 ℃ for 12 hours.

(3) Lime cream (CaO) in an amount of 40 wt% or more than 40 wt% based on the corn cob material was continuously added to the saccharification reaction solution while maintaining the liquid temperature of the enzyme reaction solution at 46 ℃, and then carbon dioxide was blown into the solution to control the pH to about 8.5, followed by immediate filtration to obtain a clarified sugar solution.

(4) The clarified filtrate WAs passed successively through a cation exchange resin (Mitsubishi Diaion PK-216) and an anion exchange resin (Mitsubishi Diaion WA-30). The desalted solution had a sugar concentration of 2.2% Brix. The pH of the desalting solution is preferably 4-7, and when the desalting solution is alkaline, sulfuric acid is added to adjust the pH to 4-7.

(5) And concentrating the desalted liquid with the pH value of 4-7 by using a multi-effect concentration evaporator until the sugar concentration is 20% Brix.

(6) The concentrate was desalted by using a mixed bed type ion exchange resin (Mitsubishi Diaion PK216, PA 412).

(7) Then concentrated until the sugar concentration is 50% Brix. The pH of the solution was 6.5.

(8) The concentrated solution was further passed through a mixed bed type ion exchange resin (Mitsubishi Diaion PK216, PA 412), then activated carbon was added thereto in an amount of 2 wt% based on the total sugar solids, and after 1 hour of treatment, diatomaceous earth was added thereto, and the activated carbon was removed by filtration.

(9) Then, concentration was carried out until Brix became 74.5, to obtain a high-purity xylooligosaccharide solution.

The sugar composition of the obtained xylo-oligosaccharide solution is as follows: 23.4% of xylose, 4.5% of glucose, 34.4% of xylobiose, 3.0% of cellobiose, 8.51% of xylotriose and 25.7% of oligosaccharide with the polymerization degree equal to or greater than that of xylotetraose.

The sugar solutions were diluted to sugar solutions having sugar concentrations of 50% and 37.5%, and color tones were measured with a 5cm cuvette, and as a result, absorbances at 420nm were 0.07 and 0.06, respectively, and almost colorless. Further, as a result of measurement with a 1cm cuvette, the absorbance at 280nm was 1.1 and 0.85, respectively, and the absorbance at 230nm was 3.2 and 2.5, respectively, and the sugar solution showed less impurities in ultraviolet absorption. In a sugar solution having a sugar concentration of 50%, furfural was 5 ppm.

[ Table 1]

	420nm (5cm cuvette)	280nm (1cm cuvette)	230nm (1cm cuvette)
				Absorbance of sugar solution having sugar concentration of 50%	0.07	1.1	3.2
Absorbance of sugar solution having a sugar concentration of 37.5%	0.06	0.85	2.5

EXAMPLE 2 production of high-purity xylooligosaccharide powder

The first mixed bed type ion exchange resin treatment in example 1 was performed, and then the resulting solution was concentrated to a sugar solution having a sugar concentration of 50% Brix, and the mixed bed type ion exchange resin treatment was performed again, and then monosaccharide such as xylose was removed by ion chromatography, thereby producing a xylose oligosaccharide solution having a monosaccharide of 5% or less than 5%. The solution was treated with activated carbon in the same manner as in example 1, and then celite was added to remove the activated carbon by filtration. By spray drying, high-purity xylo-oligosaccharide powder with 6% or less of water can be produced.

The sugar composition ratio of the powder is as follows: 0.67% of xylose, 33.2% of xylobiose, 13.78% of xylotriose, 46.29% of oligosaccharide with the polymerization degree equal to or greater than that of xylotetraose, 4.4% of cellobiose and 1.59% of monosaccharide such as glucose.

The above powder was dissolved in purified water to prepare a sugar solution having a sugar concentration of 20g/100ml, and the color tone was measured with a 5cm cuvette, whereby the absorbance at 420nm was 0.03 and almost colorless. Further, the absorbance at 280nm and 230nm as measured with a 1cm cuvette was 0.20 and 1.30, respectively, and the sugar solution showed less impurities in the UV absorption. In a sugar solution having a sugar concentration of 20%, furfural was 3 ppm.

[ Table 2]]

	420nm (5cm cuvette)	280nm (1cm cuvette)	230nm (1cm cuvette)
				Absorbance of sugar solution having sugar concentration of 20%	0.03	0.2	1.3

EXAMPLE 3 Effect of treating high-concentration sugar solution with activated carbon

The sugar solution obtained in example 1 was desalted and concentrated to a sugar concentration of 50% in solid content by the first mixed bed ion exchange resin (mitsubishi Diaion PK216, PA 412) and was diluted 10 times by weight to prepare a sugar solution of 5% in solid content. Adding 2%, 4%, and 8% by weight of activated carbon to a sugar solution containing 50% by weight of a solid component (1%, 2%, and 4% by weight of the solution), respectively; to a sugar solution containing 5% of a solid content, 2%, 4%, and 8% by weight of activated carbon (0.1%, 0.2%, and 0.4% by weight of the solution) was added, and the mixture was stirred at 50 ℃ for 60 minutes, followed by filtration.

As a result, it was found that when the weight ratio of the added activated carbon to the solid matter was the same, the removal rate of absorbance at 420nm, 280nm and 230nm of a sugar solution containing 50% of the solid matter treated with activated carbon was higher. That is, the removal efficiency of the UV absorbing substance and the coloring substance can be improved by subjecting the high concentration sugar solution to the activated carbon treatment.

The activated carbon-treated liquid containing 5% sugar solution as a solid content obtained above was heated at 100 ℃ for 30 minutes, and then the absorbances at 420nm, 280nm, and 230nm were increased.

That is, the method of treating a sugar solution containing 50% of a solid content with activated carbon greatly reduced the absorbance at 420nm, 280nm, and 230nm, as compared with the method of treating a sugar solution containing 5% of a solid content with activated carbon and then concentrating the sugar solution to 50% by heating.

[ Table 3]

Absorbance of solid content 50% sugar solution treated with activated carbon (1cm cuvette)

	420nm		280nm		230nm
								Absorbance of the solution	Removal Rate (%)	Absorbance of the solution	Removal Rate (%)	Absorbance of the solution	Removal Rate (%)
Before treatment with activated carbon	0.142	--	6.13	--	12.15	--
							After adding 1% of activated carbon	0.05	64.8	1.7	72.3	4.99	58.9
After the treatment of adding 2 percent of activated carbon	0.027	81.0	1.03	83.2	3.42	71.9
							After adding 4% of activated carbon	0.007	95.1	0.58	90.5	2.28	81.2

Absorbance of 5% sugar solution of solid content after treatment with activated carbon (1cm cuvette)

	420nm		280nm		230nm
								Absorbance of the solution	Removal Rate (%)	Absorbance of the solution	Removal Rate (%)	Absorbance of the solution	Removal Rate (%)
Before treatment with activated carbon	0.012	--	0.613	--	1.215	--
							After adding 0.1% of activated carbon	0.007	41.7	0.262	57.3	0.652	46.3
After adding 0.2% of activated carbon	0.004	66.7	0.182	70.3	0.516	57.5
							After adding 0.4 percent of activated carbon for treatment	0.001	91.7	0.104	83.0	0.373	69.3
Adding 0.1% active carbon, treating, heating at 100 deg.C for 30 min	0.007	41.7	0.397	35.2	0.778	36.0
							(10 times concentration value)	0.07	--	3.97	--	7.78	--

Adding 0.2% active carbon, treating, heating at 100 deg.C for 30 min	0.005	58.3	0.318	48.1	0.638	47.5
							(10 times concentration value)	0.05	--	3.18	--	6.38	--
Adding 0.4% active carbon, treating, heating at 100 deg.C for 30 min	0.004	66.7	0.239	61.0	0.515	57.6
							(10 times concentration value)	0.04	--	2.39	--	5.15	--

Example 4 increase in coloring upon heating at a high UV absorption

The xylo-oligosaccharide syrup obtained in example 1 was diluted with purified water to a sugar solution having a sugar concentration of 2%, and as sample 1, the absorbance at 280nm, 230nm, and 420nm of sample 1 was 0.043, 0.142, and 0.000. Sample 1 was heated at 121 ℃ for 3 hours to give sample 2, and the absorbance at 280nm, 230nm, and 420nm of sample 2 was 7.72, 2.67, and 0.006, which was a nearly colorless solution.

The sample 2 was heated at 121 ℃ for 3 hours, and the absorbance was measured, and the absorbance at 280nm, 230nm and 420nm were 15.62, 4.63 and 0.021, showing a light brown color.

From this, it was found that when the absorbance at 280nm and 230nm exceeded 7.7 and 2.6, the solution was visible to the naked eye after further treatment at 121 ℃ for 3 hours.

[ Table 4]]

	420nm	280nm	230nm
				Before heating	0.000	0.043	0.142
Heating at 121 deg.C for 3 hr	0.006	7.72	2.67
				Heating at 121 deg.C for 6 hr	0.021	15.62	4.63
Heating at 121 deg.C for 9 hr	0.038	20.56	58.8

EXAMPLE 5 production of beverage

A beverage was prepared by adding 4g of the xylooligosaccharide syrup obtained in example 1 and 5g of citric acid to 200ml of water. The beverage has slight sweet taste.

[ reference example 1] the higher the polymerization degree of xylooligosaccharide, the less coloring

Dissolving xylose, xylobiose and xylotriose with purity of 95% or higher in purified water to obtain 2 wt% of sugar solution, and heating at 100 deg.C for 2 hr. The absorbance of the sugar solution at 280nm was measured using a 1cm cuvette, and as a result: 0.257 percent of xylose, 0.200 percent of xylobiose and 0.065 percent of xylotriose; absorbance at 230 nm: xylose was 0.791, xylobiose was 0.510, and xylotriose was 0.321, and the increase in UV absorption was smaller as the degree of polymerization was larger. After heating at 121 ℃ for 6 hours, the absorbance at 420nm was measured to observe coloration, and as a result, it was found that: xylose was 0.031, xylobiose was 0.023, and xylotriose was 0.012, and the increase in coloration was smaller as the degree of polymerization was larger.

From this result, it was found that the coloration of xylooligosaccharide mainly composed of xylobiose was larger than that of xylooligosaccharide mainly composed of xylooligosaccharide having a higher polymerization degree than that of xylobiose with heating.

[ Table 5]

Absorbance of 2 wt% sugar solution dissolved in purified water after heating

	420nm (121 ℃, 6 hours)	280nm (100 ℃, 2 hours)	230nm (100 ℃, 2 hours)
				Xylose	0.031	0.257	0.791
Xylobiose	0.023	0.200	0.510
				Xylotriose	0.012	0.065	0.321

Claims (13)

1. A process for producing high-purity xylooligosaccharide, which comprises subjecting a plant material selected from corn cob, cotton seed hull, bagasse and straw to alkali treatment or pressure-heating treatment, further subjecting the plant material to enzyme treatment, concentrating the obtained crude sugar solution, desalting and/or treating with activated carbon, and drying and powdering the obtained sugar solution if necessary, thereby producing high-purity xylooligosaccharide with little UV absorption and/or little coloration.

2. A process for producing high-purity xylooligosaccharide, which comprises subjecting a plant material selected from the group consisting of cob of maize, hull of cottonseed, bagasse and straw to alkali treatment or pressure-heating treatment, further subjecting to enzyme treatment, subjecting the obtained crude sugar solution to desalting and/or activated carbon treatment, concentrating, further subjecting to desalting and/or activated carbon treatment, and optionally drying and powdering the obtained sugar solution, thereby producing high-purity xylooligosaccharide with little UV absorption and/or little coloring.

3. A process for producing high-purity xylooligosaccharide, which comprises subjecting a plant material selected from corn cob, cottonseed hull, bagasse and straw to alkali treatment or pressure-heating treatment, further subjecting to enzyme treatment, reacting lime with carbon dioxide to produce an insoluble lime salt in the resulting residue-containing crude sugar solution, filtering the insoluble matter, concentrating the resulting crude sugar solution, subjecting the concentrated sugar solution to desalting and/or activated carbon treatment, and optionally drying and powdering the resulting sugar solution.

4. A process for producing high-purity xylooligosaccharide, which comprises subjecting a plant material selected from corn cob, cottonseed hull, bagasse and straw to alkali treatment or pressure-heating treatment, further subjecting to enzyme treatment, reacting lime with carbon dioxide to produce an insoluble lime salt in the obtained residue-containing crude sugar solution, filtering the insoluble matter, subjecting the obtained crude sugar solution to desalting and/or activated carbon treatment, concentrating, further subjecting to desalting and/or activated carbon treatment, and optionally drying and powdering the obtained sugar solution.

5. The method according to any one of claims 1 to 4, wherein the raw material is corncob.

6. The method according to any one of claims 1 to 5, wherein xylooligosaccharide having a monosaccharide ratio of 30% or less in the sugar composition is produced.

7. The production method according to claim 6, which provides the following xylo-oligosaccharide solution or xylo-oligosaccharide powder: at a sugar concentration of 37.5%, the absorbance measured at 280nm with a 1cm cuvette was 2 or less than 2, and/or the absorbance measured at 420nm with a 5cm cuvette was 0.2 or less than 0.2.

8. The method according to any one of claims 1 to 5, wherein xylooligosaccharide having a monosaccharide ratio of 5% or less than 5% in the sugar composition is produced.

9. The manufacturing method according to claim 8, which provides the following xylo-oligosaccharide solution or xylo-oligosaccharide powder: at a sugar concentration of 20%, the absorbance measured at 280nm with a 1cm cuvette is 1 or less than 1, and/or the absorbance measured at 420nm with a 5cm cuvette is 0.1 or less than 0.1.

10. The method according to any one of claims 1 to 9, wherein xylooligosaccharide mainly comprising xylobiose is produced.

11. Xylo-oligosaccharide solution or powder obtained by the process according to any one of claims 1 to 10, wherein the ratio of the monosaccharides in the sugar composition is 30% or less than 30%, and the absorbance at 280nm measured with a 1cm cuvette is 2 or less than 2 and/or the absorbance at 420nm measured with a 5cm cuvette is 0.2 or less than 0.2, at a sugar concentration of 37.5%.

12. Xylo-oligosaccharide solution or powder obtained by the method according to any one of claims 1 to 10, wherein the ratio of the monosaccharides in the sugar composition is 5% or less than 5%, and the absorbance at 280nm measured with a 1cm cuvette is 1 or less than 1 and/or the absorbance at 420nm measured with a 5cm cuvette is 0.1 or less than 0.1 at a sugar concentration of 20%.

13. Processed food, beverage, health food, nutritional supplement, specific health food, cosmetic, pet food, pharmaceutical, which contains xylooligosaccharide prepared by the method according to any one of claims 1 to 10.