| This study adopted comparative analysis method to evaluate the effect of solid state fermentation on the total quantity of substrate, nutrient composition, the molecular size of protein and protein characteristics in soybean meals before and after fermentation. Meanwhile, the amount of fungal protein and the anti-oxidative activity of fermented substrate have been studied. Two experiments were carried out.Firstly, soybean meals which contained 35% moisture were fermented by Aspergillus oryzae SICC 3.302 for 48 hours.After fermentation, the dry matter (DM), the composition of crude protein, protein nutritional properties, antioxidant activity, the content of total phenol and isoflavones, etc.,were measured, and to investigate the transformation of nutrient level and biological activity after fermentation. The results showed that:1.The amount of DM and gross energy (GE) of soybean meals decreased respectively 5.14% and 3.86% after fermentation.2.The absolute amount of nitrogen was un-changed, the crude protein content significantly increased (P<0.05) but its composition varied that the absolute content of true protein (TP) reduced 19.08%(P<0.05),and the absolute level of non-protein nitrogen (NPN),small peptide, free amino acid(FAA) and ammonia nitrogen(NH3-N) significantly increased 369.08%,260.23%,634.62%and 544.44%(P<0.05)before and after fermentation. Fermentation increased the amount of small-size peptides (<30kDa) (P<0.05) compared with un-fermentation soybean meals, while significantly decreasing large-size peptides (>60kDa) (P<0.05)and medium-size peptides (30kDa-60kDa) (P<0.05) and eliminated most of soybean antigens and anti-nutritional factors.3.Fermentation significantly degraded the absolute level of NDF, ADF and NFE respectively by 16.62%(P<0.05),12.32%(P<0.05) and 22.14%(P<0.05),while the absolute content of crude fat increased 179.25%(P<0.05).4.Fermentation with A.oryzae significantly increased the reducing power, metal chelating ability of soybean meals and had a stronger scavenging activity against DPPH., O2-·and·OH radicals.The content of isoflavones and the total phenol respectively increased 491.91% and 244.12% after fermenting with A.oryzae.Secondly, quantification of fungal protein produced during soybean meal fermentation was carried out, through the correlation between the amount of glucosamine and fungal protein level of A. oryzae.Influencing factor of the correlation of between glucosamine amount and fungal protein contained incubation time, culture conditions (liquid or solid medium), carbon and nitrogen source have been measured and the correlation between glucosamine and fungal protein content in solid-state fermented soybean meals was corrected with soymilk agar which had the same nitrogen source as soybean meals.The results showed that:The correlation between the glucosamine level and fungal protein content remained constant independent of incubation time, culture conditions and carbon source.The linear equation (y=3.5966x+0.3305, r=0.9904, P<0.05) about the glucosamine and fungal protein content in solid-state fermented soybean meals was obtained after correcting with soymilk agar which had the same nitrogen source with soybean meals. And it was indirectly measured that 21.30mg fungal protein per 1 gram soybean meals fermented 48hours by A. oryzae.These works indicate that fermentation with A. oryzae could significantly transform the nutrient of soybean meals,and significantly degradate the macromolecule of protein. The macromolecular proteins are degraded into small polypeptides and amino acids, and the antioxidant activity is enhanced with mainly consumpting some carbohydrates as energy in fermentataion process.But the amount of fungal protein has a limited contribution to the protein content of fermented soybean meals.
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