Hydrolysis Of Whey Protein And ACEI Peptide Of Hydrolysate

Whey protein is a protein of high nutritive value and the important source for preparation of bioactive peptide. Angiotensin-I-converting enzyme inhibitory peptide is of more interest for research and development.Enzymatic hydrolysis of whey protein was investigated with whey protein concentrate in this paper. The main parameters included pH, hydrolysis temperature, enzyme-substrate ratio and hydrolysis time on hydrolysis reaction. The conditions of enzymatic hydrolysis with Alcalase was optimized by single-factor analysis and SAS software as follows: pH 8.5, hydrolysis temperature 55℃, enzyme concentration 0.05 per gram of substrate. The resulted hydrolysis degree was 19.34%。The molecular weight (MW) distribution of whey protein hydrolysate was determined by G-25 gel chromatography. The molecular weight (MW) distribution of whey protein hydrolysates ranged from 600Da to 1400Da. The MW distribution was confirmed by high performance liquid chromatography-electrospray ionization-mass Spectrometry, as 300～1400 Da, and most of whey peptide was under 1000Da.The Thermodynamics nature, Tg and melting point were accessed by DSC. The thermal denaturation temperatures shifted from 120℃ (whey protein) to 160℃ (whey protein hydrolysate). The temperature elevation indicated the thermal stability of the whey protein hydrolysate increased during the course of hydrolysis.The ACE-inhibition activity was observed, in vitro, with the reaction of Hippuryl-L-histidyl-L-leucine (HHL) and ACE. The research showed that whey peptides had a lowering the blood pressure activity as 0.51mg/mL.The hydrolysate was first ultrafiltered by using 6 kDa membrane, than was fractionated by using a G-25 gel chromatography. The IC₅₀ dropped to 0. 47mg/mL for ultrafiltered sample, while the IC₅₀ of fraction sample dropped to 0.12mg/mL. The fractioned sample was of the highest ACE-inhibition activity.