Protein hydrolysates from silkworm (Bombyx mori) pupae protein treated with a novel neutral protease

Abstract

Edible insects, regarded as a potential contributor to food security are currently given wide consideration due to their rich protein and other micronutrients contents. In this study, protease-assisted hydrolysis proposes an economically effective approach to hydrolyse proteins from silkworm (Bombyx mori) pupae to improve its functional properties. The proteolytic activity of a novel neutral protease (265.14 U/ml) with appreciable thermal activities, was identified using 16S rDNA as Stenotrophomonas maltophilia JW20 (SmNP20). The neutral protease with an apparent molecular weight of 28 kDa emerged active at pH 7 and maintained stability in pH range 6.0-8.0. The optimum temperature was 60 °C and stable at 55-60 °C, maintaining over 80% of its initial activity, with a half-life of 78.75, 89, 66.8 and 44 min at 50, 60, 70 and 80 °C. It was purified to 9.98-fold with a specific activity of 455.06 U/mg and 63.73% yield. The Km and Vmax values were 0.70 mg/ml and 9.48 μmol/min/mg, respectively. Enzymolysis with neutral protease enhanced the degree of hydrolysis (97.46±4.87%), increased water solubility over 50%, and a significant protein solubility of 63.44±0.65%. The Km and Vmax of the protein yield were 0.24 mg/ml and 165.63 μmol/min/mg respectively. A total of 17 amino acids have been detected in the hydrolysates obtained from the silkworm pupae protein. In comparison with neutrase and flavorzyme®, the enzyme possesses an elevated hydrolytic and catalytic efficiency. Emulsion activity and foam capacity ranged from 8-48 m2/g and 6-25% respectively. Hence, this study confirms the unique and efficient characteristics of an insect-enzyme correlation that is practically significant with potential improvement in nutritional composition and functional quality of insect proteins.