Study And Development Of Yeast Extract And The Research Of Replacing Spary-Dried Plasma Protein With The Yeast Extract And Fermented Soybean Meal

In this research, the optimum route of preparing yeast extract from active dry yeast was explored by the autolysis-enzymolysis method. At the same time, we defined the optimum conditions of fermented soybean meal through the technology comparison and amplification experiment. Finally, the composite products, by mixing the yeast extract and fermented soybean meal, are used to replace imported plasma protein by feeding experiment. The following main results we have achieved:We prepared yeast extract from active dry yeast by the autolysis-enzymolysis method, Through the single factor experiments and orthogonal test, the optimum conditions was determined:the concentration of yeast suspension is 12.5%, then added 2% white granulated sugar to activate (40℃15min,30℃15min), and added 3% ethyl acetate and 2% flavourzyme. Under the condition of pH 6.0,50℃, autolyzed at closed environment for 54 hours in the constant temperature water bath, then centrifuged twice. Finally, the yields of amino nitrogen and yeast extract of the product was 2.73% and 50.82% respectively. When this technology was used at the fresh Pichia pastoris, the yields of amino nitrogen and yeast extract of the product reached at 3.86% and 56.32% respectively. Compared with active dry yeast, as the raw material, fresh Pichia pastoris is more suitable for preparing yeast extract.Yeast extract is not suitable for adding before the soybean meal fermentation, and is difficult in the process of soybean meal fermentation, so the yeast extract could only mixed with fermented soybean meal according to a certain ratio after the soybean meal fermentation.The results demonstrate that,when the yeast extract is added before soybean meal fermention,it has a higher loss ratio,and it is more difficult to operate.So,it is the best way to remix them according to a certain ratio after soybean meal fermention.The research of substitution composite products for plasma protein in the feed of weaned piglets showed that,compared with adding 5% of plasma protein, adding 5% of composite products to the feed of weaned piglets have made the feed conversion ratio reduced 15%, and economic benefits increased more than 15%, but the content of lysine and tryptophan in the serum not only have no significant difference, and also the structure of intestinal microvilli. So the composite products can replace imported plasma protein flour completely in the fodder of weaned piglets.