Optimization of Hydrolysis Conditions and Bio-functional Properties of Whey Protein Hydrolysate Obtained from Ash Gourd (Benincasa hispida) Protease

Background: Enzymatic hydrolysis alters the bio-functionality of whey proteins by generating bioactive peptides. Plant serine proteases as an alternative to animal and microbial proteases, recently considered useful for whey protein hydrolysate preparation to enhance nutritional and bio-functional properties. Objectives: The present study thus aims at optimization of whey protein hydrolyzing conditions employing ash gourd protease (AGP) and evaluation of 2, 2 diphenyl -1-picrylhydrazyl (DPPH) radical scavenging (antioxidant) and angiotensin I- converting enzyme (ACE) inhibition activities and potency of the generated hydrolysate. Methods: Optimization was accomplished using response surface methodology and generating treatment combinations applying central composite design in two steps: first temperature (50-90°C) and pH (6-9) was optimized adding same concentration of AGP (0.3% v/v) at reconstituted WPC (0.6% protein) and then E/S ratio (2-6 %v/v) and hydrolysis time (1-6h) was optimized at reconstituted WPC (4% protein). The effect of hydrolysis time at optimized condition was also evaluated with response to degree of hydrolysis, antioxidant and ACE inhibition activities of the generated hydrolysate and its ultra-centrifuged fractions ≤3kDa and >3kDa. The AGP (Adjusted to activity 2U/mL) obtained after partially purification by three phase partitioning method was used for hydrolysis experiments. Results: The optimum conditions for enzymatic hydrolysis of whey protein to achieve maximum degree of hydrolysis (13.99%) and DPPH radical scavenging activity (23.05%) were observed at 7.48 and 66.40°C. Similarly, the enzyme performed optimally at enzyme by substrate ratio of 5.85% (v/v) for 6 hours of hydrolysis, providing 19.31 % of degree of hydrolysis and 47.71 % of DPPH radical scavenging activity. AGP hydrolyzed whey protein compared to un-hydrolysed whey protein had significantly higher degree of hydrolysis, DPPH radical scavenging and ACE inhibition activity. The lower molecular weight peptides fractions ≤3kDa was found to be more effective (1.45 times) than the peptide fractions >3kDa however was less effective (1.19 times) than the whole hydrolysate regarding antioxidant activity. Similarly, ≤3kDa fraction of hydrolysate had 1.9 times higher ACE inhibition potential as compared to its whole hydrolysate. Conclusion: Overall, the study showed that the AGP employed whey protein hydrolysate has potential for use as a natural antioxidant and ACE inhibition agent.