Impact of Maturity Stage on Free Radical Scavenging and Antidiabetic Activities of Melinjo (Gnetum gnemon L.) Seed Proteins

Seed storage proteins are a major protein source due to their readily available bioactive peptides. Melinjo (Gnetum gnemon L) seeds have a promising potential for massive production in Indonesia because of their high protein content. The composition and protein content of these seeds depends on their stage of maturity. This study investigated the effect of melinjo seed proteins at green (GG), yellow (YG), and red (RG) stages of maturity on their antioxidant and antidiabetic activities. Also, this study aimed to determine seed maturity's impact and identify the seeds most active stage on free radical scavenging (antioxidant) and antidiabetic activity. This study analyzed the amino acid composition, protein profiles, free radical scavenging, and in vitro antidiabetic activities of GG, YG, and RG seed proteins. The concentration of amino acids in melinjo seed samples was 0.36-9.69 g/100 g protein, with the total amino acid content in GG seeds (59.92 g/100 g protein) being significantly higher than in YG (53.91 g/100 g protein) or RG (52.79 g/100 g protein) seeds. The protein from GG seeds also exhibited significantly (p<0.05) higher free radical scavenging and in vitro antidiabetic activities than YG or RG seeds. The free radical scavenging activities were measured using ABTS, hydroxyl radical, and superoxide radical assays. The antidiabetic activity was assessed based on α-amylase and α-glucosidase inhibitory activities. The results indicated that the maturity stage of the seed proteins significantly affected (p<0.05) free radical scavenging and in vitro antidiabetic activities. GG seed protein showed high potential as an antioxidant and antidiabetic agent, suggesting its possible use in future nutraceuticals and human health applications.