Developing Peptide From Fermentation With Low Economic Value Soybean Protein

As we know, soybean peptide with special physical activity and excellent characteristics of processing is hydrolysis from soy protein. The production of soybean peptide is an important part of soy food processing. Compared with acid hydrolysis and enzymatic production, soybean peptide from fermentation has many advantages. While this research mainly focus on the selection of microbial strain, optimization of fermentation factors, separation and purification of the peptide.The results are summarized respectively as follows.Laboratory preserved Aspergillus oryzae 3.042 was chosen as original strain to select protease traits. In Aspergillus oryzae selecting, we used nuclear irradiation in Zhejiang Academy of Agricultural Sciences to mutate original strain. And during the repeated screening, The transparent circle size of colony was considered as selecting mark, finally 17 mutants were selected that had bigger transparent circle size than original strain, which shows the protease secretion of changes, even growth traits of some strains had also changed. In further rescreening, we found the protease activity of 4 day fermentation and peptide content of 8 day fermentation were better than original strain in the same condition. Among all these mutants, the strain A-9 produced the highest peptide content.In solid state fermentation, bean dregs were used to produce Aspergillus oryzae spore. The medium composition such as the ratio of bean dregs and bran, content of water, KH2PO4 and MgSO4 was selected by single factors. Under optimum condition, the medium was composite with 8g bean dregs,2g bran,20g water,5.5g sugar,0.3g KH2PO4,0.05g MgSO4. And after fermentation spore density was got to 298750000/ml. And Aspergillus oryzae grow better on the optimum medium, when fermented for 24h hypha grew quickly on solid medium and after 2-3 day the color of hypha turned from white to yellow green, spores were also produced. Generally solid medium were covered with green spores after 4 day fermentation.Collect the Aspergillus oryzae spores from solid medium and diluted the density to 0.5×108 per milliliter. Inoculate spores into soy milk remained from the soy film production and ferment to produce soybean peptide. Response surface methodology was used to optimize medium composition of soybean milk remained from the soy film production. Based on the study of single factor tests identified by initial screening method of Plackett-Burman., the KH2PO4, sucrose and wheat bran.were screened as the important influencing factors. Then the path of steepest ascent was undertaken to approach the optimal region. Box-Behnken design and response surface analysis were adopted to ascertain the optimum conditions as follows:KH2PO41.18%, sucrose 0.24%, wheat bran 1.81%, MgSO40.2%, NaCl0.2%, CaCO30.02%, Tween 0.05% and initial pH 7. Under these conditions, the radio of peptide reached to 63.31% after fermentation, four times higher than before.Under the optimal condition, we measured the total antioxidant capacity of samples pick-up with different fermentation time. The result showed antioxidant capacity grown with fermentation time which illuminated soybean peptide hydrolyzed from soy protein can improve antioxidant capacity.After centrifuged the fermentation sample, ultrafiltration separation was used to separate the sample into four pieces which molecular size are less than 1000Da 1000-5000Da,5001-10000Da and more than 10000Da. In antioxidant ability study we found that the piece of molecular more than 10000Da has weak antioxidant ability and antioxidant capacity was much better in the pieces of 1000-5000Da and 5001-10000Da. The antioxidant ability of piece which molecular was less than 1000Da became weaker. because there are more amino acids or some small peptide, Compared with 1000-5000Da and 5001-10000Da sample pieces, the 1000-5000Da pieces had better stability while the solution was light yellow and clarify. Separate 1000-5000Da piece with gel filtration, the analysis result showed that three main components were contained. And fragment 1 and 3 had strong antioxidant ability.