Proteolytic and antioxidant activity of protein fractions of seeds of Cucurbita moschata

A modified Osborne fractionation method was used to isolate the proteins such as albumins, globulins, prolamins and glutelins from Cucurbita moschata (pumpkin) seeds. Amino acid composition and molecular weight distribution of all protein fractions were determined in this study. Proteolytic activity of the fractionated proteins was analyzed using casein and milk-clotting activity was assessed using skim milk. The effect of temperature (30-90 °C) and pH (3-11) on enzymatic activities were also evaluated. Additionally, the antioxidant activities of the protein fractions were evaluated using DPPH radical scavenging, ABTS radical scavenging, hydrogen peroxide scavenging, nitric oxide radical scavenging, lipid peroxidation inhibition, phosphomolybdate and reducing power assays. Cucurbita moschata showed the highest milk-clotting activity over a broad temperature range (50-70 °C) and pH range (6-7). Among all the fractions, albumins showed the highest proteolytic and milk-clotting activity. Globulins showed strongest antioxidant capacity while glutelins obtained as the weakest antioxidant potential. The experimental findings of this study suggest that C. moschata may be a substitute for commercial animal rennet for cheese production and may serve as a natural antioxidant.