Enzymatic hydrolysis for functionalisation of watermelon seed protein from ultrasound-assisted extraction in comparison to soy protein isolate

The functional characteristics of a watermelon seed protein isolate (UA-WSPI), which resulted from an underutilised protein source by ultrasound-assisted extraction and freeze-drying, and a commercial spray-dried soy protein isolate were compared. Both were enzymatically treated with pepsin plus trypsin (PT) or additionally with PT plus Alcalase (PAT) for functionalisation by obtaining different partial hydrolysates. Composition, DPPH scavenging activity, digestibility and technological functionality (such as dispersibility, water-/oil-holding capacity, and zeta potential) were analysed for each protein isolate and the hydrolysates. UA-WSPI had advantages such as higher protein solubility. Enzymatic digestion of UA-WSPI resulted in the highest peptide yields and degrees of hydrolysis. Hydrolysis by the PT treatment even increased the antioxidant activity and emulsifying properties of the hydrolysate compared to UA-WSPI, whereas the soy protein isolates yielded hydrolysates of lowered antioxidant activity. Watermelon seeds proved to yield protein isolates as new functional food components, especially when applying appropriate enzyme combinations.