Study On The Production Of Debittered Functional Soybean Peptide With Microbe

Soybean peptide, which can be a kind of potential function food, is produced by hydrolyzing soybean protein into peptide with 3-6 amino acid residues. However, some bitter components, affecting the flavour of products, will be produced after hydrolyzation of soy protein.The methods of debittering existing now are not only laborious but of high cost. It cuts down production cost, and accelerates the industrialzation of functional peptide to produce peptide which combines hydrolyzing soy protein and debittering in one step with food-grade Bacillus sub tills. Thus the production of debittered functional soybean peptide with Bacillus subtilis will have widely-use prospect. There are no relative internal and external reports so far. This thesis focused on the following four aspects: (1)Screening of strain producing debittered functional soybean peptide; (2)Optimizing its liquid fermentation conditions; (3)Study of the soybean peptide production by stabilization of Bacillus subtilis: (4)Processing properties of soybean peptide produced by Bacillus subtilis. The results were as follows: (1)According to two indexes, bitterness value and content of 10%TCA soluable peptide, a strain coded Bacillus subtilis Shi HeziIII which was fit for hydrolyzing defatted soybean was screened out from eight Bacillus subtilis strains stored in the lab. The results of determination during liquid fermentation showed that the production of protease was synchronous with the growth of strain in liquid fermentation. The amino acids analysis of 48hr fermented liquid showed that this strain secreted some kinds of exopeptidase, which can specially hydrolyze three hydroxy amino acids-Tyr. Phe, and His.(2) After the study of effect of inoculation volume on peptide yield, four factors(defatted sovbean concentration, initial pH of fermented culture, fermentationtemperature and time) affecting peptide yield were optimized through orthogonal experiment. The results showed that 5% of inoculation is fittest for this strain to produce peptide. The best fermentation conditions of this strain were: defatted soybean 3g, H2O 50ml, pH natural, temperature 30 , time 48hr. The acid-soluable peptide content of the peptide solution produced by this strain after optimization could be over 1000 g/ml.(3) The effects of factors, including chitin concentration, area, and pH value, on absorption of Bacillus subtilis Shi HeziIII was studied. Besides, three quality indexes (acid-soluable peptide content, the average length of peptide, bitter value) of different fermentation batches were determined. It showed that the best absorbent condition for chitin to absorb the strain was whole piece of chitin 0.2g, pH 6.0. The stability of various batches was ideal. Three indexes of every batch of 48hr fermentation culture were as follows: acid-soluble peptide content was over 1 000 g/ml, average length of peptide 3.5, and bitter value 2. It could be concluded that chitin could not only promote the growth of the strain but be an effective bioreactor.(4) The processing specific properties of soybean peptide, such as nitrogen soluable index(NSI), turbidity, emulsifying characteristics, were studied. The result showed that peptide solutions with various fermentation time had different processing properties. I . Degree of hydrolyzation increased with fermentation time. II. NSI was related to both fermentation time and pH value, the longer time was, the higher NSI was, NSI was relatively high in neutral pH. III. The lower pH was, the higher turbidity was. The turbidity of 36hr peptide solution was low from pH3.0 to 7.0. IV. All the peptide solutions had high emulsifying active index(EAI) but low emulsifying stability index(ESI).