Preparation And Charaterization Of Whey Protein Peptide-zinc Chelate

Zinc is known as the "life element",which plays an important role in maintaining the normal physiological state and life activity of human body.Zinc deficiency is a worldwide nutritional deficiency disease,it can cause a series of pathological changes in the body,for example,growth retardation,the decline of the body gonad skills,human immune and neurological dysfunction.It was found that the peptide could promote the absorption of zinc and react with zinc to form stable and soluble polypeptide-zinc chelate.The chelate can make zinc not be affected by various substancesin the gastrointestinal tract like phytic acid,and the chelatecan beabsorbed by the body in the way of peptides which provide a new way to fill the body with zinc.The purpose of this study was to improve the bioavailability of zinc and to prepare peptide-zinc chelate by using the peptide obtained from natural protein hydrolysis,and the structure characteristics,biological activity and bioavailability of chelate were studied.The protein of whey protein,mung bean protein isolate and soy protein isolate were used as raw protein.Two indexes,including zinc-binding ability and precipitation rate during the Zn-binding reaction,were used to screen the optimal peptides.The WPH(whey protein hydrolysates)obtained using trypsin hydrolysis of 6 h possessed the highest zinc-binding ability and the least precipitation rate,so the WPH was used asreaction substrate.Optimize the orthogonal test of zinc-binding ability,the optimum reaction condition is reactant mass ratio 3:1,pH 5.0,reaction temperature 60?,reaction time 60 min.After the verification experiment,the zinc-binding ability was 82.61%.UV,FTIR,TG and XRD were used to characterize the structure of the peptide-zinc chelate and peptide.The results showed that the polypeptide reacted with zinc.Moreover,the intermolecular and intramolecular action of peptides exert more after chelation with zinc,and the crystallinity was increased significantly.At the same time,using EDX to carry on the quantitative analysis of the elements,the content of zinc in peptide-zinc chelate was 16.58%.The results of molecular weight distribution and amino acid composition of peptide-zinc chelate showed that the amino acid involved in reaction were mainly acidic amino acid,the average molecular weight of peptide-zinc chelate was 770 Da,the molecular weight of small peptides in 180-480 Da accounted for 52.99%.The zinc dissolution rate of peptide-zinc chelate under different pH values was measured,the results showed that compared with inorganic zinc salt,zinc dissolution rate of peptide-zinc chelate was higher in the intestinal pH environment.The in vitro simulated gastrointestinal digestion-dialysis method was used to study thebioavailability of zinc in chelate.The results showed that the dialysis rate of zinc in chelate(42.95%)was significantly higher than those in the inorganic zinc salts(22.81%),the bioavailability of chelate was higher.After gastrointestinal digestion,peptide still binded with zinc,andthe average molecular weight of digestion products were 367 Da.The antioxidant activity of peptide-zinc chelate was evaluated by measuring the scavenging ability of hydroxyl,total reducing power and ABTS radical scavenging capacity.Peptide-zinc chelate had a certain antioxidant activity,and in the experimental concentration range,the hydroxyl radical scavenging capacity,total reducing power and free radical scavenging ability of ABTS were positively correlated with the concentration of chelate and its antioxidant activity was not inactivation by digestion.The effects of peptide-zinc chelate on the growth and viability of lactic acid bacteria were analyzed.When the peptide-zinc chelate completely replaced the organic nitrogen source in the MRS medium,it could inhibit the growth and the acid producing ability of lactic acid bacteria.However,when chelate replaced the organic nitrogen source partly,it could promote the growth of lactic acid bacteria to some extent.In the medium of skim milk,the growth acid production ability of lactic acid bacteria increased with the increase of the amount of chelate.