Studies On The Biological Activity Of Soybean Flour Processed By Lactic Acid Fermentation And Enzymatic Hydrolysis

Soybean is an important plant protein source for human nutrition.Lactic acid fermentation can highly improve the nutritive value of soybean products.However,most of studies until now have been investigated the effects of lactic acid fermentation on the components and flavor of soybean products.Little study has been done about the beneficial physiological effects of lactic acid fermented soybean products,such as antioxidant activity and ACE inhibition activity.In the present study,firstly,we selected a strain of lactic acid bacteria which is suitable for the solid fermentation of soybean flour.Second,we investigated the parameters of solid-state fermentation,the changes of components in soybean flour during the fermentation,the effect of lactic acid fermentation on the antioxidant and ACE inhibitory activity of soybean flour,the isolation and purification of bioactive peptides from the fermented soybean flour.Furthermore,the effect of lactic acid fermented soybean flour on the weaning transition of newly weaned piglets and its mechanism were investigated.1.Selection of lactic acid bacteria strains for the fermentation of soybean flour and study of the parameters for fermentationFirstly,in the present study,we compared the growth performance,titratabale acidity and the degree of protein hydrolysis of different strains of lactic acid bacteria in soybean flour. After that,we selected the Lactobacillus plantarum Lp6 as the best strain for the solid-state fermentation of soybean flour.After one factor and orthogonal design experiment,we obtained the best parameters of fermentation are 0.2%inoculum volume,55%of moisture contents,0.5%acid protease addition and natural pH.The mixture was then fermented at 37℃for 72 h.2.Changes of components in soybean flour during the lactic acid fermentation and enzyme hydrolysisSoybean flour was fermented by L.plantarum Lp6 and the changes of some components in soybean flour were investigated during the fermentation.Lactic acid fermentation can improve the in vitro digestibility of protein in soybean flour.The high molecule weight protein in soybean flour was degraded into small peptides.Lactic acid fermentation can also decrease the content of total sugars,increase the content of reductive sugars,at the same time, the content of stachyose and raffinose were also decreased.Furthermore,the content of antinutritive factors,such as trypsin inhibitor,phytate and urease were also degraded.3.Extraction of bioactive peptides from soybean flour processed by lactic acid fermentation and enzyme hydrolysisLactic acid fermentation can improve the antioxidant and ACE inhibitory activity of soybean flour.The ACE inhibitory and·OH scavenging activities of the extract from fermented soybean flour was increased after sugars and salt removal by macroporous resinby and hollow fibre ultrafiltration with molecular weight cut-off 6000 Da,the molecule weight of 90%of peptides in the water extract after ultrafiltration was less than 1500 Da suggesting ultrafiltration is an effective technique to enrich for food protein-derived bioactive peptides. The 6000 Da permeates have higher contents of aromatic amino acid than the corresponding protein in soybean flour.The impact of digestive proteases on ACE inhibitory activity of the ACE inhibitory peptides was evaluated under simulated gastrointestinal digestion.Little change has been observed after simulated gastrointestinal digestion,indicated that the ACE inhibitory peptides may exert their ACE inhibitory activity in human body after administration.4.Antioxidant activity of bioactive peptides from soybean flour processed by lactic acid fermentation and enzyme hydrolysisThe oxidative models of thymocytes induced by H₂O₂ was established and to study the protective effects of bioactive peptides from fermented soybean flour on thymocytes.The peptides could enhance the cell viability and activities of GSH-Px,SOD,A-SAC,and T-AOC in cells.The concentration of GSH and the ratio of GSH/GSSG were increased by peptide from fermented soybean flour.The peptides decreased the concentration of ROS and MDA in cells,it also raised the expression of p53 gene in cells.The peptides from fermented soybean flour could block the oxidative damage of thymocytes induced by H202.5.Purification and identification of peptides from soybean flour processed by lactic acid fermentation and enzyme hydrolysisIn the present study,isolation and characterization of ACE inhibitory and antioxidant peptides derived from the fermented soybean flour was done in order to realize the relationship between the bioactive activity of peptides and its structure.A peptide 7-â…¡-f-R2 was isolated from fermented soybean flour by Sephadex G-15 column,SP-Sephadex c-15 column, two-step reverse-phase high performance liquid chromatography(RP-HPLC) and identified by matrix assisted-laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF- MS/MS) and amino acid composition analysis.The amino acid sequence of peptide 7-â…¡-f-R2 is VPDALR,and its IC₅₀ of ACE inhibitory and·OH scanvenging activity is 29.3μg/mL,83.2μg/mL,respectively. 6.Effect of fermented soybean flour on the weaning transition of newly weaned animalsThe effect of lactic acid fermented soybean flour on the weaning transition of newly weaned piglets and its mechanism was investigated in the present study.Seventy-two piglets were allotted to three dietary treatments for 28 days.Aider the feeding trial,the piglets were slaughtered and samples of digesta and intestinal tissue were collected for analysis.The results showed the addition of fermented soybean flour in the diet of piglets improved the growth performance,decreased the diarrhea rate,increased the activity of antioxidant enzyme in the blood,increased the numbers of intestinal lactobacilli,decreased the numbers of intestinal enterobacteria and increased villus height and the villus height to crypt depth ratio at the small intestinal mucosa compared to the control group.In conclusion,lactic acid fermented soybean flour can be used as an excellent protein source for newly weaned animals.