GB2151635A - Production of single cell protein and sucrose - Google Patents

Abstract

Production of single cell protein from a sucrose-containing raw material, in particular cane sugar in a plant which can produce single cell protein and sucrose. The single cell protein is produced by treating the raw material in the presence of a base, the product is clarified, then addition of organic nutrients to lower the pH, finally fermentation and extraction. The plant may be operated to produce either single cell protein or sugar separately or to produce both commodities together.

Description

SPECIFICATION Production of single cell protein and sucrose The invention relates to a process and apparatus for producing single cell protein or for producing single cell protein and sucrose and in particular to a process and apparatus using sugar cane as a raw material.

During the past twenty years a number of processes for the production of single cell protein by cultivation of microorganisms have been proposed using various materials, including hydrocarbons, alcohols and carbohydrates, as carbon sources for growth of the microorganisms. The single cell protein produced can be used as a component of human or animal foods particularly as a component of poultry feeds. In the production of single cell protein it is an advantage if a process can use a material which is readily available locally as a carbon source.

In the production of sucrose from sugar cane, the sugar cane is harvested and the harvested cane is treated in a raw sugar factory to produce raw sugar, comprising mainly sucrose, and molasses. Generally the sugar cane is first fired to remove trash, i.e.

tops, leaf and straw, and is then cut and hauled to a mill where it is further cut into billets which are passed to the cane reception stage of the raw sugar factory. Occasionally sugar cane tops are collected for feeding to animals. In the factory cane billets are supplied from the reception to presses or tandems and the pressed juice produced is further treated by clarification and evaporation to yield a saturated syrup, from which sucrose can be crystallised, and molasses. Sugar cane can contain sucrose and invert sugar in differing proportions. In this process, if the cane is fired, it is necessary to harvest it rapidly in order to avoid inversion of its sucrose to produce invert sugar.Moreover it is necessary to harvest the cane and treat it in the plant at the time of maximum sucrose content period of three to four months in the yearand not throughout the year. This results in inefficient use of the plant.

According to the present invention we provide a process for the production of single cell protein or of single cell protein and sucrose from a sucrose-containing raw material which comprises the steps of treating the sucrosecontaining raw material to produce a sucrosecontaining juice, clarifying the juice in apparatus adapted to supply clarified juice to a fermentation process and/or to a sucrose production process, supplying all or part of the clarified juice to a culture of microorganisms, capable of utilizing sucrose as a carbon source for growth, in a fermenter, culturing the microorganisms in the fermenter, removing culture from the fermenter and separating single cell protein from the removed culture.

Further according to the invention we provide a process for the production of single cell protein from a sucrose-containing raw material which comprises the steps of treating the sucrose-containing raw material to produce a sucrose-containing juice, heating the juice and treating it with a base (the heating and basetreatment steps being carried out in either order or simultaneously), clarifying the heated and base-treated juice, treating the clarified juice by adding thereto one or more inorganic nutrients for a culture medium thereby reducing the pH of said clarified juice, supplying the treated clarified juice to a culture of microorganisms, capable of utilizing sucrose as a carbon source for growth, in a fermenter, culturing the microorganisms in the fermenter, removing culture from the fermenter and separating single cell protein from the removed culture.

The process of the invention however carried out for the production of single cell protein, is preferably operated in apparatus adapted to produce single cell protein and sucrose simultaneously or either commodity alone and such apparatus is included within the scope of the invention. Any sucrose-containing raw material may be used including sugar beet and sugar cane but sugar cane or material derived from it is preferred. Preferably the process of the invention is operated continuously.

The microorganisms which are cultured to provide single cell protein may be any yeasts or bacteria capable of utilizing sucrose as a carbon source for growth. However yeasts are preferred, particularly strains which can also utilize any invert sugar present with the sucrose. Suitable yeasts include strains of the genus Saccharomyces. Examples of suitable strains are Saccharomyces cerevisiae strains NCYC 479, NCYC 1406 and NCYC 994, cultures of which are deposited at and are available from the National Collection of Yeast Cultures (NCYC), Colney Lane, Norwich, NR4 7AU, England, UK.Another suitable strain of Saccharomyces cerevisiae is deposited at the National Collection of Yeast Cultures as NCYC 1514 and is also deposited elsewhere as CBS 431, ATCC 10611 and NRRLY-1555. CBS is the Centraal Bureau voor Schimmelcultures, Oosterstraat 1, 3740 A 9, Baarn, The Netherlands. ATCC is the American Type Culture Collection, 1 2301 Parklawn Drive, Rockville, Maryland 20852, USA. NRRL is the collection maintained by the US Department of Agriculture at 181 5 North University Street, Peoria, Illinois 61604, USA.

In the process of the invention, when sugar cane is used as the sucrose-containing raw material, it is treated to produce sucrosecontaining juice by being supplied in billet form to cane presses. Typically these are combined in pairs known as "tandems" and the juice leaving the presses passes through screens to remove solid material. Juice leaving the presses is typically at a pH in the range 4 to 7, most frequently at pH 5.5.

The pressed juice from the "tandems" passes to a clarifier and, in a preferred embodiment of the process, is subjected to heating and base treatment steps before it enters the clarifier. The heating and base treatment steps may be performed in either order or simultaneously but preferably the juice is heated before being treated with base. Preferably the heat treatment step raises the temperature of the juice to a value within the range 50"C to 100"C, especially within the range 70"C to 90"C. Treatment with base preferably raises the pH of the juice to a value within the range 6 to 9, especially within the range pH 7 to pH 8.Any suitable base may be added to the juice to raise the pH but calcium oxide or hydroxide are preferred since upon addition to the juice they assist in the removal of organic contaminants. During clarification, sediment is removed from the juice as sludge. Clarification takes place in a tank, sediment being removed from the lower part of this tank. Typically the residence time of juice here averages between 1 5 mins and 90 mins. The raising of the pH in the base treatment step together with subsequent residence in the clarification tank serves not only to produce clarification of the Ijuice but also to kill any yeast cells therein which could otherwise contaminate the culture during the later fermentation stage of the process.

After clarification juice intended to be used for production of sucrose passes to a multieffect evaporation system and from there as a concentrated syrup to later stages of a conventional raw sugar/molasses production process. Juice intended to be used in the production of single cell protein is preferably passed into a nutrient mixing tank in which there is added to it one or more of the inorganic nutrients required in the subsequent fermentation step for example phosphoric acid, and sources of potassium, magnesium and trace elements. These additions preferably reduce the pH of the clarified juice to a value within the range 2 to 4.It is preferred that in the nutrient mixing tank the temperature is maintained at a value within the range 60'C to 95"C. Typically the residence time for the clarified juice in the nutrient mixing tank averages between 0.5 and 3 hours. The period of residence at a reduced pH in the nutrient mixing tank serves to kill any thermotolerant, neutral-growing bacteria such as strains of Bacillus stereothermophilus which have survived previous treatments and which could otherwise contaminate the culture when the treated clarified juice is supplied to the fermenter. To improve the energetic efficiency of the process it is preferred that the treated clarified juice is cooled to a temperature within the range 20 to 40"C as it passes from the nutrient mixing tank to the fermenter.

Fermentation of microorganisms to produce single cell protein can take place in any suitable fermenter. However a "pressure-cycle" fermenter, in which culture is circulated continuously around a system comprising a riser and a downcomer, connected at their upper and lower ends, by compressed air blown into culture in the lower part of the riser, is preferred. It is convenient to add nitrogen as ammonia in the compressed air stream. Such fermenters are described in our UK Patents Nos. 1353008, 1417486 and 1417487. Depending upon the strain of microorganism employed in the fermentation, the fermentation temperature will generally be between 30"C and 40"C. In order to control the temperature of culture within the fermenter to a value within this range a cooler is necessary.

In hot climates it may be desirable to equip the fermenter with a refrigeration system.

Culture produced during the fermentation step is removed from the fermenter and is subjected to a post-fermentation treatment including such steps as product thickening and evaporative drying to give as a product dried single cell protein. In the evaporative drying step the process described in UK Patent 1477039 may usefully be used.

The single cell protein product may be used as a component of human or animal feed compositions for instance as a protein supplement in poultry feed in partial replacement of the vegetable protein normally used for this purpose. Poultry feeds are formulated to achieve a required nutritional specification at minimum cost. Principle items in such a specification are total metabolisable energy, total protein content and amounts of essential amino acids. It is found that part of the vegetable protein supplement usually used in the formulation of a diet may be replaced with a lesser weight of single cell protein while maintaining the same nutritional specification, thus giving the single cell protein a value exceeding that of the vegetable protein source on a weightbasis.

The process of the invention is particularly advantageous when cane juice is the raw material. Since the fermentation process takes place in an aqueous medium, it is not necessary to remove water from the juice before its introduction to the process. It is an advantage of the process that both sucrose and invert sugar are converted to single cell protein. This introduces the possibility of harvesting cane throughout the year and not, as in current practice, only at the time of maximum sucrose content. If the cane is fired to remove trash, it becomes no longer necessary to harvest the cane rapidly to forestall inversion.

If cane harvesting takes place for only part of the year, then it is possible to continue to operate the process using stored raw sugar and molasses, or concentrated sugar syrup.

The invention is illustrated by the accompanying drawings wherein: Figure 1 is a schematic diagram showing the basic features of a plant for carrying out the process of the invention using sugar cane as the raw sugar source.

Figure 2 is a schematic diagram showing in greater detail a plant for carrying out a preferred embodiment of the process of the invention using sugar cane as the raw sugar source.

In the plant shown in Fig. 1, sugar cane billets are supplied to cane reception stage 1 from which they pass to cane presses 2, which work in pairs or "tandems" and are supplied with imbibition water through pipe 3. From cane presses 2, pressed juice flows to clarifier 4 whilst bagasse is transported to bagasse furnace 5. In clarifier 4 juice is separated from waste sludge which leaves along pipe 6. The clarified juice leaving clarifier 4 can be separated into two streams, one of which passes to fermenter 7 to be converted into single cell protein whilst the other passes to a multi-effect evaporation stage 8 for the production of sucrose and molasses using the further treatment steps of a conventional sugar process. In Fig. 1 these further treatment steps of a conventional process are contained schematically within boundary 9.The plant is so designed that clarified juice may pass simultaneously to fermenter 7 and evaporation stage 8 or it may be directed only to either one of these dependent upon operational requirements at any time.

In fermenter 7, the sugar content of the clarified juice forms the carbon source in an aqueous culture medium for microorganisms which are continuously cultivated and harvested to produce single cell protein. Generally the clarified juice will be mixed with water and some or all of the other nutrients in the culture medium before being supplied to fermenter 7. Compressed air is supplied to fermenter 7 from compresser 10 and the temperature of the culture medium in fermenter 7 is controlled using refrigeration system 11. A culture of microorganisms is continuously withdrawn from fermenter 7 and subjected to a further treatment which includes evaporative drying stage 1 2 from which a dried single cell protein product leaves the plant along pipe 1 3.

In the sugar production aspect of the plant the clarified juice entering multi-effect evaporation stage 8 is concentrated to produce a saturated syrup (meladura) which passes to crystallisation/centrifugation stages 1 4. Condensate produced in evaporation stage 8 leaves the plant along pipe 1 5. From crystallisation/centrifugation stage 1 4 two product streams 1 6 and 1 7 leave the plant. Product stream 1 6 carries raw sugar, typically comprising approximately 97% by weight sucrose.

Product stream 1 7 carries blackstrap molasses, an aqueous mixture typically comprising approximately 34% by weight sucrose and 18% by weight invert sugar. Typically the process will produce raw sugar and blackstrap molasses in approximately the relative proportions 73% and 27% by weight.

Bagasse furnace 5 supplies steam to multieffect evaporation stage 8 and to evaporative drying stage 12 along pipe 18.

The plant shown in Fig. 2 contains the same basic features as that shown in Fig. 1 and has a cane reception stage 1, cane presses 2 fed with imbibation water along a pipe 3, a clarifier 4, a bagasse furnace 5, a fermenter 7 having a refrigeration system 11 and supplied with compressed air from a compresser 10 and a multi-effect evaporation stage 8 and an evaporative drying stage 12, both supplied with steam from bagasse furnace 5 along a pipe 18, all of which are shown in Fig. 2. Single cell protein product leaves the plant along pipe 1 3 and waste sludge from clarifier 4 leaves along pipe 6 to be spread on land as a soil conditioner. Fig. 2 does not show the later further treatment steps of the conventional sugar process, i.e.

crystallisation/centrifugation stages 1 4 and raw sugar and blackstrap molasses streams 1 6 and 1 7 respectively. It will be appreciated that the saturated syrup leaving multi-effect evaporation stage 8 in the plant of Fig. 2 will be treated in the same way as is syrup produced in the equivalent stage in the plant of Fig. 1.

Fermenter 7 in the plant of Fig. 2 is a "pressure-cycle" fermenter of the type described in e.g. our UK Patent No. 1 353008.

Fig. 2 illustrates in detail the manner in which the pressed juice leaving presses 2 is treated before it is supplied to fermenter 7 and/or to multi-effect evaporation stage 8.

Pressed juice leaving presses 2 passes first through screens 19, to remove residual solid material, and is then heated in heater 20 to a temperature in the range e.g. 60 to 95"C.

The heated juice then passes to base treatment tank 21 in which a base is added to it to increase its pH. The pressed juice leaving screens 1 9 can be for example at approximately pH 5.5 which pH can be raised to e.g.

8 by treatment in tank 21. Very suitably the base added in tank 21 is calcium oxide or calcium hydroxide which remove organic contaminants. From base treatment tank 21 pressed juice passes to clarifier 4. Waste sludge leaving clarifier 4 along pipe 6 passes through filter 22, the filtrate from which is returned to the clarified juice stream. Clarified juice leaving clarifier 4 and intended for conversion to raw sugar and molasses passes to multi-effect evaporation stage 8, for further treatment as in a conventional sugar process, whilst that intended for use as a carbon source in the production of single cell protein passes to nutrient mixing tank 23. Here other culture medium nutrients and antifoam are added to it, entering tank 23 along supply lines 24 and 25 respectively. From tank 23, clarified juice with added nutrients passes to fermenter 7 through juice cooler 26.In the fermentation to produce single cell protein the preferred nitrogen source for the culture medium is gaseous ammonia. This nutrient is added separately from those added to the clarified juice in mixing tank 23. It is supplied along pipe 27 to be admixed with the compressed air supplied to fermenter 7 from compresser 10. Culture comprising microorganisms is continuously withdrawn from fermenter 7 and passes first to product thickener stage 28 and then to evaporative drying stage 12, from which the dried microorganism cells which form the single cell protein product leave the plant along pipe 1 3. Recycle medium from product thickener stage 28 is returned to fermenter 7 along pipe 29. Evaporative drying stage 1 2 is supplied with steam from bagasse furnace 5 along pipe 1 8 and with oil (see GB 1477039) and power along pipe 30 and line 31 respectively. Clean condensate leaves evaporative drying stage 1 2 along pipe 32.

The plant shown in Fig. 2 can be used, like that shown in Fig. 1, to produce raw sugar/ blackstrap molasses or to produce single cell protein or to produce both these products simultaneously depending upon operational requirements.

When the plants of Figs. 1 and 2 are operated to produce only raw sugar and blackstrap molasses they function similarly to conventional raw sugar factories.

Claims (10)

1. A process for the production of single cell protein or of single cell protein and sucrose from a sucrose-containing raw material which comprises the steps of treating the sucrose-containing raw material to produce a sucrose-containing juice, clarifying the juice in apparatus adapted to supply clarified juice to a fermentation process and/or to a sucrose production process, supplying all or part of the clarified juice to a culture of microorganisms, capable of utilizing sucrose as a carbon source for growth, in a fermenter, culturing the microorganisms in the fermenter, removing culture from the fermenter and separating single cell protein from the removed culture.

2. A process for the production of single cell protein from a sucrose-containing raw material which comprises the steps of treating the sucrose-containing raw material to produce a sucrose-containing juice, heating the juice and treating it with a base (the heating and base-treatment steps being carried out in either order or simultaneously), clarifying the heated and base-treated juice, treating the clarified juice by adding thereto one or more inorganic nutrients for a culture medium thereby reducing the pH of said clarified juice, supplying the treated clarified juice to a culture of microorganisms, capable of utilizing sucrose as a carbon source for growth, in a fermenter, culturing the microorganisms in the fermenter, removing culture from the fermenter and separating single cell protein from the removed culture.

3. A process according to claim 1 or claim 2 wherein the sucrose-containing raw material is sugar cane.

4. A process according to any one of the preceding claims wherein the microorganism which is cultured in the fermenter is a yeast.

5. A process according to claim 5 wherein the yeast is a strain of the species Saccharomyces cerevisiae.

6. A process according to any one of claims 2 to 5 wherein the heating step raises the temperature of the juice to a value within the range 50"C to 100"C.

7. A process according to any one of claims 2 to 6 wherein the base treatment step raises the pH of the juice to a value within the range pH 6 to pH 9.

8. A process according to any one of the preceding claims wherein clarification takes place in a tank and the residence time of juice in the tank averages between 1 5 minutes and 90 minutes.

9. A process according to any one of the preceding claims wherein, after clarification, inorganic nutrients are added to the juice to be supplied to the fermenter to reduce its pH to a value within the range pH 2 to pH 4 and it is maintained at that pH in a residence tank for a period between 30 minutes to 3 hours.

10. An apparatus for the production of single cell protein and sucrose which comprises in combination the following features: (i) treatment means for treating a sucrosecontaining raw material to produce a sucrosecontaining juice; (ii) transport means for transporting sucrose-containing juice to a clarifier; (iii) a clarifier for the clarification of sucrosecontaining juice; (iv) supply means for supplying clarified sucrose-containing juice from the clarifier separately to a fermenter and to the evaporation stage of a sucrose production apparatus; (v) a fermenter for the aerobic cultivation of a culture of microorganisms with removal means for removing culture from the fermenter and separation means for separating single cell protein from the removed culture; and (vi) sucrose production apparatus for producing sucrose from the clarified sucrose-containing juice from the clarifier; wherein the supply means can supply clarified juice to the fermenter alone or to the sucrose production apparatus alone or to both the fermenter and the sucrose production apparatus simulataneously.