Effects Of Ultrasound-ionic Liquid Treatment On Physicochemical Properties And Activities Of Hydrolysates Of Whey Protein

Whey protein accounts for about 20% of total protein in milk.Whey protein has high nutritional value and easy digestion and absorption characteristics,contains a variety of active ingredients.Whey protein,as a function factor,has become one of the hottest topics in food research field.In this paper,the effects of ultrasound-ionic liquid?UIL?treatment on physicochemical properties of whey protein were studied by the methods of infrared spectrometry,raman spectrometry,polyacrylamide gel electrophoresis and fluorescence spectrometry.Characteristics changes of enzymatic hydrolysis for whey protein after UIL treatment were studied by thermodynamics parameters and hydrolysis kinetic model.Moreover,the effects of UIL treatment on biological activities of hydrolysate from whey protein were studied by antioxidant activity analysis,ACE-inhibitory activity analysis and immune activity analysis.The results showed that compared with untreated whey protein,free sulfhydryl content of UIL treated whey protein was increased by 46.8%,while its disulfide bond content was decreased by 29.6%.After UIL treatment,contents of ?-helix and ?-turn for whey protein were decreased by 27.7% and 62.9%,respectively,while its contents of ?-sheet and random coli were increased by 97.0% and 46.2%,respectively.In addition,UIL treatment caused a 68.3% increase in hydrophobicity for whey protein.The secondary structure of whey protein has changed significantly while its primary structure is not changed after UIL treatment.Compared with untreated whey protein,UIL treatment caused a 39.1% decrease in Ea,a 41.3% decrease in ?H,a 39.9% decrease in ?S and a 1.4% decrease in ?G.The initial rate of enzymatic hydrolysis of whey protein was increased by 37.3%.The kinetic equations of enzymatic hydrolysis for untreated and treated whey protein were established.The kinetic equation of untreated whey protein was DH=7.25ln[1+?18.45E0/S0-0.0105?t].The kinetic equation of treated whey protein was DH=7.40ln[1+?22.53E0/S0-0.0073?t].UIL treatment changed the kinetic model for enzymatic hydrolysis and the critical enzyme concentration?e0?required for enzymatic reaction of whey protein was decreased by 43.1%.In addition,UIL treatment significantly increased the ?5ku fraction content of whey protein hydrolysate?P<0.05?.The hydrolysate of UIL treated whey protein had a 12.2% increase in ?5ku fraction content.The results of thermodynamics parameters and kinetic model of enzymatic hydrolysis reaction reveal that whey protein hydrolysis is more easily to occur after UIL treatment.Compared with the untreated whey protein hydrolysate,UIL treatment caused a 14.4% increase in scavenging DPPH radical activity and a 28.4% increase in chelating Fe²⁺ capacity for whey protein hydrolysate.Moreover,its reducing power activity was improved evidently.After UIL treatment,in vitro ACE-inhibitory activity of whey protein hydrolysate was 57.19% higher than untreated whey protein.The immune activity of whey protein hydrolysate was also significantly enhanced after UIL treatment.In conclusion,this study reveals that UIL treatment can change physicochemical properties and enzymatic hydrolysis characteristics of whey protein.Moreover,the UIL treatment could promote the hydrolysis of whey protein and increase the antioxidant activity,ACE inhibitory activity and immunological activity of its hydrolysates.