Biotechnology of forages: fodder yeast
Fodder yeast. Yeast is grown on hydrolysates from waste wood and other cellulose-containing plant raw materials that, when hydrolyzed, form carbohydrate forms that are easily assimilated for microorganisms. As a raw material with this technology for the production of fodder protein, waste from the pulp and wood processing industry, straw, cotton husks, sunflower baskets, linen fire, corncobs, beet molasses, potato meats, grape squeezes, beer grains, peaty little decomposed peat, bard alcohol production, waste confectionery and dairy industry.
Crushed vegetable raw materials containing a large amount of cellulose, hemicelluloses, pentosans, is subjected to acid hydrolysis at elevated pressure and temperature, whereby 60-65% of the polysaccharides contained in them are hydrolyzed to monosaccharides. The resulting hydrolyzate is separated from lignin, the excess acid used for hydrolysis is neutralized with lime milk or ammonia water. After cooling and settling, mineral salts, vitamins and other substances necessary for the vital activity of microorganisms are added to the hydrolyzate. The nutrient medium thus obtained is fed to the fermenter shop where the yeast is grown.
For the cultivation of plant waste hydrolysates, the yeast of the genera Candida, Torulopsis, Saccharomyces, which are capable of using hexoses, pentoses and organic acids as the carbon source, are most effective. Under optimal conditions of 1 ton of softwood waste, 200 kg of fodder yeast can be obtained.
To produce fodder yeast, the technology of their deep cultivation is used in special apparatuses-fermenters, in which a regime of constant mixing of a suspension of microbial cells in a liquid nutrient medium and optimal aeration conditions is provided. The working cycle of cultivation of the yeast culture lasts about 20 hours. At the end of the working cycle, the culture liquid, together with the yeast cells suspended in it, is removed from the fermenter, and the nutrient substrate and yeast culture for growth are again fed into it.
The suspension of microbial cells withdrawn from the fermenter is then fed to the flotation unit, by means of which the yeast biomass is separated from the culture liquid. During the flotation process, foaming of the suspension takes place, while the microbial cells float to the surface together with the foam, which is separated from the liquid phase by decantation. After settling, the yeast mass is concentrated with a separator. To achieve better digestibility of yeast in the animals, special treatment of microbial cells (mechanical, ultrasonic, thermal, enzymatic) is carried out, which ensures the destruction of their cell membranes. Then the yeast mass is evaporated to the required concentration and dried, the moisture content of the finished product should not exceed 8-10%.
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The dry yeast contains 40-60% of crude protein, 25-30% of digestible carbohydrates, 3-5% of raw fat, 6-7% of fiber and ash substances, a large number of vitamins (up to 50 mg%). By treating yeast with ultraviolet rays, they are enriched with vitamin D2, which is formed from the ergosterol contained in them. To improve the physical properties of the finished product, fodder yeast is released in granular form.
In Russia and some other oil-producing countries, technologies have been developed for producing fodder yeast from n-paraffin oil. Yeast cells can use as a source of carbon for their growth unbranched hydrocarbons with a number of carbon atoms from ten to thirty. They are liquid fractions with boiling points of 200-320 ° C, which are recovered from oil by distillation. The select strains of yeast Candida guilliermondii are most effective for cultivation on n-paraffins of oil. Isolation and drying of yeast mass is carried out approximately according to the same technology as in hydrolysis production. The dried yeast mass is granulated and used as a protein-vitamin concentrate (BVK) for feeding agricultural animals, containing up to 50-60% proteinaceous substances.
The National Center for Biotechnology of the Republic of Kazakhstan has developed technologies for obtaining microbiological fodder protein for animals. Several variants of feed additives have been obtained: fodder yeast based on Saccharomyces cerevisis, Candida tropicalis pcs. SK-4, as well as microbiological L-lysine, based on the lysine producer Brevibacterium sp. pcs. 92. Experiments of deep cultivation of Candida tropicalis pcs. SK-4 in fed-batch mode in a 7-liter fermenter using glucose as a carbon substrate. The conditions for cultivation of the lysine producer in the batch regime have been developed. A pilot batch of a feed additive for animals based on yeast Saccharomyces cerevisis was obtained (SK Barbasova et al., 2011).
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