Physicochemical properties of silkworm larvae protein isolate and gastrointestinal hydrolysate bioactivities

The objectives of this study were to investigate the amino acid composition and thermal properties of silkworm larvae protein isolate (SLPI) and to evaluate the in vitro angiotensin-converting enzyme (ACE) inhibitory and antioxidant activities of its hydrolysate prepared with gastrointestinal enzymes. The results showed that, SLPI was a high quality protein source with a well-balanced composition of essential amino acids, which was especially rich in glutamic acid (13.79 g/100 g protein), aspartic acid (10.44 g/100 g protein), leucine (8.68 g/100 g protein), lysine (8.01 g/100 g protein) and arginine (6.59 g/100 g protein). In additon, three endothermic denaturation transitions were observed in DSC thermograms of SLPI. The maximum transition peak occurred in the third thermal transition, which denaturation temperature (Td), peak temperature of denaturation (Tp) and enthalpy change (ΔH) were 76.95°C, 80.42°C and 783.75 J/g, respectively. SLPI hydrolysate exhibited strong ACE-inhibitory activity (IC50=8.3 μg/ml) and relatively higher 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (IC50=57.91 μg/ml) and ferrous ions chelating capacity (IC50=2.03 mg/ml). Moreover, the hydrolysate showed notable reducing power. It was concluded that, SLPI might be considered as a multifunctional ingredients for functional foods with protein supplements, ACE-inhibitory and antioxidant activity.Key words: Silkworm larvae protein isolates (SLPI), amino acid composition, thermal properties, gastrointestinal enzymes, hydrolysis, ACE inhibition, antioxidant