Microbially Fermentative Production Of Corn Oligopeptides At High Fisher’s Ratio

High Fisher’s-ratio oligopeptides are a kind of mixed oligopeptides with high molar-ratio of branched-chain amino acids to aromatic amino acids in its amino acid composition.These oligopep-tides have been used widely in functional food and pharmaceutical industry.Production of high Fisher’s-ratio oligopeptides by using corn yellow meal is of great current interest.However,current high Fisher’s-ratio oligopeptides are mainly prepared by protease hydrolysis,and few studies have focused on the production of high Fisher’s ratio oligopeptides by direct microbial fermentation.Ac-cordingly,based on two-stage enzymatic hydrolysis approach of producing high Fisher’s ratio oligo-peptides constructed in our laboratory,in this thesis,a production process of high Fisher’s ratio oli-gopeptides and by-product recovery process was established by using microbial fermentation method with maize yellow powder as raw material.The contents of the study are as follows:To obtain a strain of Bacillus natto with high production of alkaline protease,a wild-type strain stored in our lab was mutagenized by DES（diethyl sulfate）and ARTP（room temperature plasma at atmospheric pressure）.The plate with skim milk powder was used as the screening plate,and the absolute diameter of the proteolysis transparent circle and the relative diameter of the transparent circle diameter were selected as the primary screening index.Combined with shake-flask repeat screening,a strain capable of high alkaline protease activity was obtained.Results showed that the alkaline protease activity was 116 U·m L^-1,which is 45%higher than that before mutagenesis.Fer-mentation was further optimized by single-factor and orthogonal optimization experiments at shake-flask level.The alkaline protease activity reached 129 U·m L^-1,which is more than 10%higher than that before optimization.Then,the fermentation process of high Fisher’s ratio oligopeptides was established.The enzy-matic hydrolysis process of alkaline protease was optimized,and the effect of alkaline protease hy-drolysis was improved.The process of preparing high Fisher’s ratio oligopeptides by Aspergillus oryzae was optimized.The fermentation conditions were as follows:fermentation temperature 28℃,liquid volume 70 m L/250 m L,inoculum 6%,fermentation time 68 h,rotational speed 180 r·min^-1.Under this selected condition,the concentration of oligopeptide was 20 g·L^-1,the content of oligo-peptide was about 10 g·L^-1,the ratio of oligopeptides was 80%of the total peptides,and the F value was 21.8,which has met the standard of high F-value.This production process,including key enzyme production,enzymatic degradation,Aspergillus oryzae fermentation and adsorption,was further mag-nified at 5L level,showing that high Fisher’s ratio oligopeptides with Fisher’s ratio of 20.99 was prepared.Additionally,an excellent antioxidant activity in vitro was found.Finally,the process of activated carbon desorption from above peptide adsorption and by-prod-uct recovery was explored.The variety ofsolvents in accordance with the national food safety stand-ard was selected for the desorption.The parameter of desorption process was obtained as follows:cyclic desorption of ethanol and ethyl acetate,desorption water bath temperature 90℃,solid-liquid ratio 1:40,63 cycles.Under selected condition,90%of the adsorbed peptides and aromatic amino acids was recovered by desorption,and the activated carbon could be reused after desorption.