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Does the protein increase after the soybean meal is fermented?


Fermentation is an "old" process. The earliest application of microorganisms in my country during the Shang and Zhou Dynasties-"brewing of wine". After thousands of years, microorganisms and their applications have been deeply integrated into people's lives, such as pickles, and Production of sauce, vinegar and soy sauce, etc. However, until the French scientist Pasteur in the 18th century created the basic research method of microorganisms, "fermentation" has always been a black "mysterious" field. With the rapid development of modern science, "fermentation" has become increasingly "scientific". In this paper, the material changes of soybean meal fermentation and the suggestion of its "nutrition parameters" are preliminary discussed.

1、 The carbohydrate composition of soybean meal
Table 1 Soybean meal carbohydrate composition and content (Choct et al., 2010)
Among them, the NSP of soybean meal includes: pectin, non-cellulose polymers and cellulose (Figure 1). Oligosaccharides include: sucrose (disaccharide, about 5%), stachyose (trisaccharide, about 4%), raffinose (tetrasaccharide, about 1%) and verbascose (pentasaccharide, about 0.3%) .
Figure 1 Classification and composition of non-starch polysaccharides

2、Material changes during the production and processing of soybean meal
2.1 Anaerobic fermentation of lactic acid bacteria
In the fermentation process: on the one hand, lactic acid bacteria secrete sucrase and galactosidase to degrade 8% oligosaccharide into "monosaccharide", and convert "monosaccharide" into the same amount of "lactic acid". However, the decomposition and utilization of NSP by lactic acid bacteria are very limited; On the other hand, the addition of exogenous protease can degrade "macromolecular protein" into "small molecular protein". Of course, because of the cost of exogenous enzyme and the technical ability of manufacturers, the antigen degradation of soybean meal products fermented by "bacteria enzyme synergy" is also different. In the drying process: on the one hand, lactic acid is heated and decomposed under normal pressure, and when it is concentrated to 50%, part of it becomes lactic anhydride (melting point of lactic acid is 18 ℃, boiling point is 122 ℃). The difference of drying process adopted by manufacturers is an important reason for the difference of lactic acid content in commercial fermented soybean meal. On the other hand, the product lost some water (5%).
Therefore, using the anaerobic fermentation process of lactic acid bacteria (as shown in Figure 2), the material changes of soybean meal are mainly reflected in the decrease of oligosaccharides and water (8% + 5%) and the increase of lactic acid (2 ~ 5%), the total material loss is about 8% and 11%, and the process yield is 89 ~ 92% (assuming the final water is 7%).
Figure 2 Changes in the substance of soybean meal fermented by lactic acid bacteria

2.2 Bacillus aerobic fermentation
During the fermentation process: On the one hand, a large amount of carbohydrate enzymes are secreted, and it is assumed that about 8% of the "oligosaccharides" are also degraded, but the difference is that the carbon conversion form during the fermentation process of Bacillus changes from "lactic acid" to "CO2". On the other hand, Bacillus uses protease, exopeptidase, and carboxypeptidase that are autogenously secreted to convert "large molecular proteins" into "debittered oligopeptides and small peptides." During the drying process: the product only loses part of the water (5%).
Therefore, using the Bacillus aerobic fermentation process (Figure 3), the material change of soybean meal is mainly reflected in the loss of soybean meal. The material change is mainly reflected in the reduction of oligosaccharides and moisture (8%+5%), and the total loss of materials About 13%, the process yield is 87% (assuming the finished product moisture content is 7%).
Figure 3 Changes in the substance of soybean meal fermented by Bacillus
2.3 Contribution of bacterial protein to total protein after fermentation
In the process of soybean meal fermentation by Bacillus, using the carbon source and nitrogen source of soybean meal, the bacteria proliferate to about 109 CFU/g. The pure bacillus powder produced by liquid fermentation is about 1011-12CFU/g. Based on this calculation, the bacillus fermented soybean meal product contains 1~10 kg/ton (0.1~1%) of pure bacillus cells (the content of cell proteins). The crude protein content is about 60%).
Therefore, the bacillus proliferated during fermentation can actually only increase the crude protein content of fermented soybean meal products by 0.06 to 0.6%, and the contribution is very limited.
2.4 The "material conservation" principle of fermented soybean meal protein
Through the analysis of the material changes of soybean meal and bacteria (Figure 2 and Figure 3), the crude protein, NSP (including crude fiber) and crude ash content of soybean meal before and after fermentation basically did not change in total. Only oligosaccharides are lost in different forms during the production process of fermented soybean meal (lactic acid bacteria are fermented in the form of lactic acid in the drying process, and Bacillus fermentation is in the form of CO2 in the fermentation process), so the crude protein, crude ash and crude fiber The relative content is correspondingly increased (positively correlated with protein content). The expected concentration rates of lactic acid bacteria and Bacillus fermented products are 10% and 11.5%, respectively.
Therefore, assuming the use of 46% soybean meal (7% of the finished product moisture), the final protein of the soybean meal fermented by lactic acid bacteria and Bacillus will reach 50.6% and 52.9% (Xijie soytide is fermented with 48% soybean meal, and the protein content of the finished product is guaranteed. ≥55%).

3、Conclusions and recommendations
3.1 The increase in the "protein content" of fermented soybean meal comes at the expense of the "concentration" of soybean meal components
3.2 When soybean meal components are concentrated, the content of crude ash and crude fiber will inevitably increase
3.3 Appropriate "relaxation" of the crude ash content will help further increase the protein content of fermented soybean meal

Translated by Carrie Guo
International business department
Huatai Group