Optimum Conditions For Preparation Of Soybean Peptides By Liquid State Fermentation

The preliminary study shows that, using Bacillus subtilis 1389, Aspergillus niger AS3.350, Aspergillus oryzae A-9005 to ferment soybean meal can obtained large peptide products ,because various proteases can cut the appropriate sites of soybean meal protein then modify and rearrange some peptides and hydrophobic amino acid groups. The conversion rate of soy peptides can up to 89%. The absorption rate of low molecular weight peptides (molecular weight less than 1000Da) can up to 90% on human body. Low molecular weight peptides can accelerate protein synthesis, enhance the absorption of mineral elements utilization, improve animal immunity, also they can hinder the absorption of fat, and promote lipid metabolism, therefore, it is necessary to survey the distribution of soybean peptide's molecular weight.By the optimization of fermentation conditions we can obtain much soybean peptide products of low molecular weight. This thesis focused on the following aspect: Mensurating molecular weight distribution of soybean peptides, conversion rate of peptides and the distribution of the enzyme systems of fermentation process on five different conditions: fermented by Bacillus subtilis1389, Aspergillus niger AS 3.350, Aspergillus oryzae A-9005, and Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350 and Aspergillus oryzae A-9005.Analyzing the correlation of each index and then to determine the optimal process conditions by the indicator of soybean peptide's conversion,and evaluated the bitterness of soybean peptides. The results were as follows:(1)Through the research we known that using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350 and Aspergillus oryzae A-9005 to fermented soybean can get more low molecular weight peptide than using Bacillus subtilis 1389, Aspergillus niger AS 3.350 and Aspergillus oryzae A-9005. Using Bacillus subtilis 1389 mixed with Aspergillus oryzae A-9005 to fermented soybean, the conversion rate of low molecular weight peptide can up to 56%,and the conversion rate of peptide can up to 61.54% on 48h,while the conversion rate of low molecular weight peptide can up to 51.3%,and the conversion rate of peptide can up to 77.59% using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350.(2)By the research of changes of conversion in fermentation liquid with time,we can known that the conversion of low molecular weight peptides using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350 to fermented soybean was highest (55.9%),and it reached the maximum at first.(3)By researching the correlation between the distribution of molecular weight and enzyme in different time and natural pH,we found that the rate of low molecular weight peptides and protease activity were higher using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350 and Aspergillus oryzae A-9005 to fermented soybean. The protease activity reached max. at 48h and the rate of low molecular weight peptides reached 91.9% using Bacillus subtilis 1389 mixed with Aspergillus oryzae A-9005. The protease activity reached max. at 36h and the ratio of low molecular weight peptides changed little using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350. Because the types of protease was much in mixed microbial fermentation process and the sites of cleavage was also much, there was some correlation between the distribution of molecular weight and enzyme.(4)By researching the correlation between the distribution of molecular weight and DH in different time and natural pH,we found that there was no correlation between the distribution of molecular weight and DH. So it was not doable to control the rate of low molecular weight peptides by controling the degree of hydrolysis of proteins.(5)The fermentation liquid's bitterness and odor was not obvious using Bacillus subtilis 1389 mixed with Aspergillus niger AS 3.350 and Aspergillus oryzae A-9005 to fermented soybean. Soybean peptide which molecular weight was more than 6000Da can not be feeling bitter. When the molecular weight of soybean peptide was 500Da ~ 1000Da the bitterness was serious .