Preparation Of Peptides With Differential Hydrophobicity And Charge And Their Zinc Complexes And Their Application In The Growth And Fermentation Of Lactic Acid Bacteria

As a structural ion,regulatory ion or catalytic ion,zinc is involved in the biosynthesis of various enzymes and cellular metabolic activities.Zinc supplementation can alleviate a variety of diseases caused by zinc deficiency,while inorganic zinc has low utilization rate and strong side effects in the human body,so seeking safe,high absorption and utilization of zinc preparations has become a research focus.The results show that Zn-peptide complex is an excellent zinc supplement preparation with high bioavailability in vitro and in vivo,and has a variety of biological activities and functional properties.Therefore,the study on the application of Zn-peptide complex in lactic acid bacteria is of great significance to expand the application field of Zn-peptide complex.In this study,soybean protein isolates were used as raw materials to prepare soybean peptides by enzymatic hydrolysis.To obtain peptides with different hydrophobicity and charge,soybean peptides were purified by ultrafiltration technology,macroporous adsorption resin and ion exchange chromatography.The zinc complexes with different hydrophobicity and charge properties were prepared,and their structures were characterized.The application of peptide-zinc complex in the growth and fermentation of lactic acid bacteria can broaden its application field.This can lay a foundation for the development and utilization of polypeptide-zinc complexes.The main research contents and results of this paper are as follows:1.Preparation and structural characterization of hydrophobic and chargability differential peptides and their Zinc complexes:Low molecular peptide(LMWP),weak hydrophobic peptide(WHP),medium hydrophobic peptide(MHP),strong hydrophobic peptide(SHP),positive charge peptide(PCP)and negative charge peptide(NCP)were obtained by Alcalase hydrolysis and DEAE anion exchange column using ultrafiltration technique.Different peptides interact with zinc ions to form different Zn-peptide complexes,among which,the NCP has the highest zinc coordination rate(129.11±3.01?g/mg).The structure of the polypeptide-zinc complex was characterized by precipitation qualitative analysis,UV and FTRI.The conclusion that zinc and the active groups(-COOH,NH)of the polypeptide took place was obtained.2.Effects of Zn-peptide complex on the growth and reproduction of Lactic acid bacteria:The results showed that zinc could promote the growth of lactobacillus delbrueckii subsp bulgaricus at low concentration,and zinc concentration was200?g/m L.Both hydrophobic and charge differential peptides and their zinc complexes can promote the growth and reproduction of lactobacillus delbrueckii subsp bulgaricus,and the Zn-MHP can promote the cell proliferation,cell activity,sugar consumption and acidity of lactobacillus delbrueckii subsp bulgaricus,which is higher than other components.3.Enhanced effect of Zn-MHP on the resistance of lactobacillus delbrueckii subsp bulgaricus to acid stress:Under acid stress,the survival rate of Zn-MHP group was higher than that of Zn-MHP group,and the intracellular ATP content and H~+-ATPase activity of Zn-MHP group were always higher than that of Zn-MHP group.The active enzyme activities of 3-phosphoglyceraldehyde dehydrogenase(GAPDH),lactate dehydrogenase(LDH)and pyruvate dehydrogenase(PDH)in the Zn-MHP group were higher than those in the Zn-MHP group.SEM and TEM showed that the damage of lactobacillus delbrueckii subsp bulgaricus in Zn-MHP treatment group was less than that in Zn-MHP treatment group,indicating that Zn-MHP has a protective effect on lactobacillus delbrueckii subsp bulgaricus under acid stress and improves their ability to resist acid stress.4.Effects of Zn-MHP on the fermentation process and quality of yoghurt:With the increase of fermentation time,the p H and acidity of yoghurt gradually decreased and solidified into gelatinous yoghurt.The results showed that the p H value of lactobacillus delbrueckii subsp bulgaricus in Zn-MHP group was lower than that in the group without Zn-MHP,and the p H decrease rate and acidity value were higher than that in the blank control group,indicating that Zn-MHP can promote the acid production of lactobacillus delbrueckii subsp bulgaricus.According to the fluidity and texture observation,the yoghurt was coagulated at 5h,while the zn-mhp was coagulated at 4h,indicating that zn-mhp could accelerate the gel properties of yoghurt.Rheological property tests showed that the storage modulus and loss modulus of yoghurt in the Zn-MHP group at 4h and 6h were higher than those in the blank control group,indicating higher gel strength and better viscoelastic properties.