Keywords :yeast; nutrition; feed; production 1 Nutritional characteristics of feed yeast Feed yeast is generally composed of yeast and its culture, and is a protein feed produced by yeast fermentation using agricultural by-product waste or food industry waste. There are three kinds of technological routes for the bioconversion of starchy waste residue into high-protein feed by microorganisms at home and abroad: (1) chemically or enzymatically degrading the substrate to culture non-starch hydrolyzed yeast; (2) using yeast with strong assimilation starch ability The strain is fermented; (3) the starch assimilation yeast is mixed with the cellulose-degrading Trichoderma reesei or Trichoderma viride. These three production processes essentially convert the starch and cellulose degradation in the substrate into a yeast high protein feed. China's slag resources are very rich, and about 60 million tons of slag can be produced each year (Zhao Jianguo, 2001). Table 1 shows the chemical composition of common dry slag dry powder feed. This kind of slag resource can be transformed into yeast protein feed with high nutritional value through biotechnology. It is important to meet the needs of society and reduce the use of conventional protein feed such as soybean meal and fish meal. significance. After the fermented slag products are fermented by yeast cells, the protein content is significantly increased. Bai Yuyun et al (2008) reported that after fermentation, the protein of yeast feed is 43% to 58%, mainly bacterial protein, 6% to 12% of nucleic acid, high lysine content, about 4.1%, and rich. B vitamins, fermented products have a strong aroma, also contains unknown growth factors, high nutritional value. Bai Xiaoting (2005) reported that VB1 15~18mg/kg, VB2 54～68mg/kg, niacin 500～600mg/kg, pantothenic acid 130～160mg/kg, choline 600mg/kg, biotin 1.6～ in feed yeast powder. 3.0 mg/kg, folic acid 3.4 mg/kg. Zhao Jianguo (2006) used saccharified yeast, Trichoderma viride and Aspergillus oryzae as strains. After fermentation of unconventional raw materials, the B vitamins of the fermentation products were significantly increased, VB1 was 34.6 times that of fish meal; VB2 was 1.7 to 3.3 times that of fish meal. It is 4.7 times that of soybean meal; VB3 is 2.2 times of fish meal and soybean meal; VB6 is 5 times of fish meal, 3.3 to 4 times of soybean meal; VB11 is 13.75 times of fish meal, 3.1 to 8.5 times of soybean meal. 2 Mechanism of action of yeast The role of yeast products in monogastric animals is mainly concentrated in the stomach, duodenum and small intestine. The current research suggests that yeast can play a role mainly through the following ways: (1) Yeast regulates gastrointestinal environment and flora structure, regulates gastrointestinal fermentation, reduces lactate production, improves pH stability, and promotes Lactic acid bacteria and cellulose bacteria are the main beneficial bacteria breeding and vitality, and enhance the concentration of beneficial bacteria. (2) Yeast can be used as a living bacterial precursor. After entering the gastrointestinal tract, it will increase its vitality, inhibit the reproduction of harmful pathogenic microorganisms, participate in the survival competition of pathogenic microbial flora, and repel the adhesion of pathogenic bacteria in the gastrointestinal mucosa to assist the body. Eliminate toxins and their metabolites, prevent the absorption of toxins, enhance the body's immunity and disease resistance, and play a health care role in the prevention and treatment of animal digestive diseases. (3) Yeast cells can be produced in the digestive tract of the animal or released after cell lysis, and these enzymes can effectively help the animal to digest the nutrients in the intestine. (4) Immunomodulatory effects. Yeast polysaccharides such as mannan and β-glucan remaining in the yeast cell wall have obvious immunomodulatory effects, which can improve the resistance of animals to external adverse factors and reduce the loss caused by stress. [NextPage] 3 applications 3.1 Chicken Wang Xiaoming et al. (2002) studied the nutritional value comparison between feed yeast and soybean meal and fish meal. Through the broiler metabolism test, the true digestibility of lysine, methionine and essential amino acids in feed yeast were 87%, 83.4% and 85%, respectively; The true digestibility of lysine, methionine and essential amino acids of soybean meal were 83.5%, 93.7% and 88.9%, respectively; the digestibility of lysine, methionine and essential amino acids of fish meal were 89.8%, 91% and 93.2%, respectively; yeast The overall essential amino acid digestibility was 3.9% lower than that of soybean meal and 8.2% lower than that of fish meal; the true digestibility of feed yeast crude protein was 66.6%, which was higher than the true protein digestibility of 42%. This indicates that the digestibility and protein quality of the yeast's overall amino acid are basically the same as those of soybean meal, which is close to the level of fishmeal, which can replace some soybean meal and fish meal in production. Shen Aihua et al. (2003) replaced 5% soybean meal with 5% feed yeast in laying hens. After 30 days of feeding experiment, the results showed that compared with the control group, the egg production rate of the yeast group increased by 3.28%, and the egg breaking rate decreased. 20.44%, feed costs decreased by 2.5%. Xie Aizhen et al (2006) added 30% red yeast protein feed to the laying hen diet. The results showed that the carotenoids in the egg yolk were as high as 37.72 μg/g, which was 2.15 times that of the control group; the average egg production rate was 90.83%, The difference in the control group was not significant. Sun Yanan et al. (2008) used yeast to replace 25%, 50%, 75% and 100% of fishmeal in broiler diets. After 42d feeding trials, the results showed that the 42d body weight gain and feed-to-weight ratio of the 25% fish meal group were compared with the control. The difference was not significant, and the consumption was reduced by 2.93%. In the replacement of 75% fish meal group, the body weight gain and feed-to-weight ratio were 3.12% and 3.5% lower than the control group, respectively, and the difference was not significant. The above tests showed that the feed yeast and the soybean meal have considerable nutritional value, and the production performance is even due to the pure soybean meal group. Feed yeast can partially replace the fish meal in the diet, but has little effect on the performance of the chicken and can reduce production costs. 3.2 Pig Nutritional studies on pigs have shown that yeast or yeast cultures can increase pig feed intake, increase production speed, reduce diarrhea rates in weaned piglets, and promote feed digestibility in growing season pigs. Wang Xuebing et al (2008) replaced 25%, 50%, 75% and 100% of imported fishmeal in the diet of weaned piglets with yeast powder. After 28d feeding trial, the weight gain of 25% and 50% yeast group was 10.88kg and 10.65kg. The control group was 10.63 kg; the ratio of 25% to 50% of the material was 1.36 and 1.39, which was lower than 1.48 of the control group; compared with the fishmeal group, the feed cost was reduced by 9.06%. From the perspective of production performance and feed cost, feed yeast can replace 25% to 50% of fishmeal in the diet. Lu Jirong et al. (2006) studied the effects of adding 2.5% fish meal and 2.5% yeast feed on the performance of weaned piglets. After 28 days of feeding experiment, the daily weight gain of weaned piglets in yeast group was increased by 9.08%. The daily feed intake increased by 5.39%, and the feed-to-meat ratio decreased by 5.96%. Zou Youjing et al. (2006) replaced 3% fish meal and 2% soybean meal in growing pig diet with 5% yeast feed. After 28 days of feeding experiment, the daily weight gain of pigs in yeast group was 768g/d, the weight-to-weight ratio was 2.36; The weight is 793g/d, and the material-to-weight ratio is 2.35, which is basically equivalent. The test showed that yeast can replace fishmeal and soybean meal in the diet in an appropriate amount without affecting the performance of growing pigs. The above test results show that the yeast feed as a fermentation product can replace part of the fish meal in the pig feed, because the content of vitamins, proteins and beneficial bacteria is obviously increased after the feed is fermented by yeast cells. 3.3 Aquatic products Fishmeal is a major protein source for aquatic animals due to its comprehensive nutrition, balanced nutrition and good palatability. Feed yeast is rich in various nutrients such as protein, B vitamins, fat, sugar, enzymes and some unknown growth factors. Studies have shown that feed yeast can replace some of the fishmeal in aquatic feed as a protein source for aquafeeds. Li Zijin et al. (2009) studied the effects of 3% fish meal group and 3% yeast group on the performance of grass carp. The test results showed that the weight gain rate of fishmeal group was 317%, the feed coefficient was 1.55, and the fish feed cost was 3.83 yuan/kg. The weight gain rate of the yeast group was 324%, the feed coefficient was 1.48, and the fish feed cost was 3.4 yuan/kg. This indicates that the use of fishmeal in grass carp feed does not affect its production performance, and it can also reduce production costs. Zhou Guitan (2003) studied the effect of replacing some fishmeal with beer yeast on the performance of juveniles. The addition ratio of yeast in juveniles was 1.7%~34.4%. The results showed that the proportion of yeast in juvenile feed was 5.3%. When growing, the best results. Zhang Liang et al. (2003) studied the effect of feed yeast replacing some fish meal on the growth of freshwater white peony. Considering the production performance, cost and other factors, the amount of yeast in freshwater white peony can be increased to 17%, and the amount of fishmeal can be reduced to 10%. . 4 Quality control of feed yeast Feed yeast has played a huge role in saving the use of conventional protein feeds, improving animal performance and reducing feed costs. However, due to the uneven quality of feed yeast powder products on the market, the feed mills should consider the following aspects when purchasing feed yeast powder: 4.1 Cell count One of the most important indicators for evaluating feed yeast is the determination of the total number of cells and the number of viable cells. The more the total number of feed yeast cells, the more complete the fermentation; the more the number of living cells, the greater the cell activity. The simple method for measuring the total number of yeast cells and living cells is to weigh 5 g of feed yeast in a 100 mL beaker, add 50 mL of distilled water, soak for 30 min, filter with double-layer gauze, stir the filtrate, and pipette 1 mL into a graduated cylinder. 1 mL of sulfuric acid, diluted with distilled water to 10 mL, aspirate the diluent a little in the hemocytometer, and observe the total number of cells under the microscope. For the determination of the number of viable cells, a drop of the filtrate was taken with a clean glass rod, placed on a glass slide, and a drop of the methylene blue stain was added dropwise, stained for 3 min, and observed under a microscope, the stained person was a dead cell, and the faded person was a living cell. China's national standards stipulate that the number of feed yeast cells is at least 15 billion/g, but there is no clear regulation on the number of live yeast cells. 4.2 warm water mixing Dissolving and stirring by warm water is one of the sensory indicators for judging the quality of the feed yeast. The fermented feed yeast is stirred in water and easily suspended and has a large amount of white bubbles. The foam disappears slowly, while the inferior feed yeast powder is stirred in warm water to form little foam, and the foam disappears quickly, or no foam. . At the same time, the inferior yeast has more sediment or floating objects in the water. 4.3 Iodine reaction The iodine solution reacts blue with the starch in the sample to determine whether the sample contains starch. China's national standards stipulate that the iodine reaction should not be blue. The true pure feed yeast, the color of the iodine reaction is colorless. If the iodine reaction is blue, it indicates that the feed yeast may be a non-fermented feed yeast powder, and it is possible to use a pseudo-yeast powder having a similar appearance and a similar smell produced by corn protein powder plus sawdust, rice bran plus flavoring agent. At the same time, it can be further determined by detecting the content of crude fiber. The national standard stipulates that the crude fiber content of the feed yeast is 1.5%. If the crude fiber content is obviously high, this proves that the feed yeast is mixed with plant matter. 4.4 Urea mixed Most of the feed yeasts are produced by solid fermentation. Urea and other bacteria can be used by yeast to synthesize non-protein nitrogen sources of bacterial proteins. Appropriate addition is beneficial to the fermentation, but manufacturers often add a large amount for the purpose of improving crude protein. The product contains a large amount of non-protein nitrogen substances that are not converted by yeast, and such products are harmful to the health of monogastric animals. Weigh 2~3g of the tested yeast into a 250mL flask, add 100mL of distilled water, 20mL of soybean powder filtrate (5g soy bean powder soaked in 100mL water for 1h, filter), shake it and place it in a water bath of 40~45°C. Warm for 30min (the temperature should not exceed 45 °C, otherwise urease is inactivated), and finally use a pair of red litmus paper to dip into the solution, if the test paper turns blue; indicating that the test yeast is mixed with urea. 4.5 True Proteins and Amino Acids The crude protein of the feed yeast is 40% to 60%, and the presence of inorganic nitrogen in the feed. The simple detection of the crude protein does not determine the nutritional value of the feed, and the true protein of the feed should also be detected. The true protein of the feed yeast is more than 26%. If the content of the true protein is too low, it indicates that the feed yeast may be mixed with non-protein nitrogen such as urea, and the quality of the feed yeast can be directly determined by measuring the amino acid. 4.6 Salmonella detection If the fermentation technology is not enough for the feed yeast, the base material is not completely sterilized before fermentation, and it is easy to cause pathogen contamination. This is not allowed by the national feed hygiene standards. If the feed is used, it will cause losses to the aquaculture industry. In order to ensure safe production, This health indicator must be taken seriously. Wang Ling et al. (2001) used biochemical reaction medium to detect the presence of Salmonella in several feed yeast samples. The results showed that there was a feed yeast sample with the presence of Salmonella. 5 prospects In short, high-quality feed yeast has played a huge role in improving animal intestinal health, reducing feed costs, and increasing feed conversion ratio. When using feed yeast, not only the crude protein index, but also the total number of cells, living cells, true protein, vitamins and other indicators, to determine the quality of feed yeast. With the maturity and improvement of the production process, feed yeast will play a greater role in aquaculture production. Seals For Agitators & Reactors Mechanical seals under [SEALMANN" trademark, apply the advanced design concepts and the latest Seals For Agitators & Reactors,Rubber Bellow Mechanical Seal,Dry Running Agitators Seals,Single Balance Liquid Agitators Ningbo FLK Technology Co., Ltd. , https://www.flk-global.com
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