Preparation Of Polypeptide-zinc Complexes And Investigation Of Their Biological Activities

Zinc is an extremely important trace metal element in the human body,which is involved in the synthesis of more than 200 enzymes,thus regulating the metabolism of the human body.Zinc deficiency can lead to a number of chronic diseases,including growth retardation and immune deficiency.At present,the zinc supplement on the market are mainly inorganic zinc salt and simple organic zinc,but the utilization rate of inorganic zinc salt in human body is very low,while the synthesis process of simple organic zinc is slow and the cost is high.It is found that food-derived proteolytic peptides can form soluble complexes with zinc,which has a high bioavailability in intestinal tract.Soybean meal and peanut meal have the advantages of high protein and low price,so they are suitable for the extraction of peptides.In this paper,the preparation process and binding mechanism of soybean peptide-zinc complex and peanut peptide-zinc complex were systematically studied using soybean meal and peanut meal as raw materials.In addition,the regulation of peptide-zinc complexes on the growth metabolism and fermentation performance of yeast,as well as the bioavailability of peptide-zinc complex in mice were investigated.The results are as follows:Studies on preparation optimization process and binding mechanism of peptide-zinc complex.The results showed that when the hydrolysis time of peptides were 6 h,the coordinate temperature was 65 ?,the p H was 5,the peptide-zinc ratio was 4:1,and the reaction time was 90 min,the maximum binding rate of the soybean peptide-zinc complex reached 12.55 ± 0.463%,and the binding rate of peanut peptide-zinc complex was 14.13 ±0.582%.The binding mechanism and morphologic characteristics of peptide-zinc were analyzed by UV,fluorescence spectrum,FTIR and SEM-EDS methods.The results showed that zinc ions mainly combined with peptides through Zn-O and Zn-N bonds to form peptide-zinc complexes.The complexes are compact and granular with a nano scale.Studies on physicochemical properties of peptide-zinc complexes.The thermogravimetric analysis showed that the peptide-zinc complex had better thermal stability than the peptides.The peptide-zinc complex has good solubility of acid and base.At intestinal p H 7.5,the zinc solubility rates of soybean peptide-zinc complex and peanut peptide-zinc complex were 60.4±1.34% and 52.7±1.98%,respectively,while the zinc sulfate was only 8.65±1.58%,indicating that the peptide-zinc complexes had better p H stability.The results of simulated gastrointestinal digestion showed that soybean peptide-zinc complex and peanut peptide-zinc complex had high zinc dialysis rate during digestion,and their free zinc ion contents were 81.53±0.80% and 78.91±0.61%,respectively.The cytotoxicity tests showed that the two peptide-zinc complexes had proliferation effect on Caco-2 cells in the range of zinc content of 25-100 ?mol/L,and no cytotoxic and side effects occurred in the range of experimental concentration.Regulation of peptide-zinc complexes on growth and metabolism of yeast.The soybean peptide and peanut peptide obtained after 6 h hydrolysis had the best effect on the proliferation of yeast cells,and their peptide-zinc complex at low dose(20 ?g/m L zinc)could increase the biomass,activity value and total protein content of yeast,and the effect was better than that of zinc sulfate and zinc gluconate.ELISA tests revealed that both peptides and their zinc complexes could improve the activities and contents of related enzymes(ethanol dehydrogenase,Cu-Zn SOD and carboxypeptidase)in yeast cells,and thus improved the fermentation performance of yeast cells,enhanced the utilization of sugar and free FAN.In addition,the results of stress experiments showed that the peptides and their zinc complexes could improve the heat,acid and ethanol tolerance of yeast to a certain extent.In summary,we conclude that peptides and peptide-zinc complexes can improve the fermentation performance and tolerance by increasing the biomass or enzyme activity of yeast.Bioavailability of peptide-zinc complexes in mice.The results of mice experiments showed that the peptide-zinc complexes helped to improve the growth quality of mice,and the effect was better than zinc sulfate and zinc gluconate.The body weight of low dose complex peptide zinc complex group was increased by 7.5% compared with the control group.In addition,peptide-zinc complex can significantly increase the zinc levels in serum and liver,as well as the contents of total protein and albumin in serum of mice,in a dose-dependent manner.Enzyme linked immunoassay indicated that the peptide-zinc complexes could significantly increase the activities of serum AKP,SOD and liver SOD in mice,while the activity of serum AKP increased in a dose-dependent manner.The q PCR results showed that the intake of peptide-zinc complexes could up-regulate the m RNA expression levels of Pep T1 and Zn T1 in the small intestine of mice.In summary,peptide-zinc complexes are mainly absorbed by small intestinal epithelial cells through Pep T1 and Zn T1 transporters.Intake of peptide-zinc complexes can supplement zinc and promote growth in mice,and can increase the activity of zinc-related enzymes in mice.