Protein identification and potential bioactive peptides from pumpkin (Cucurbita maxima) seeds

Pumpkin is an economically important crop all over the world. Approximately, 18%-21% of pumpkins, consisting of peels and seeds by-products, are wasted during processing. In addition, the seeds are rich in protein and have the potency of bioactive peptide production. This study aims to recognize the proteins and investigate the potential bioactive peptides from pumpkin (Cucurbita maxima) seeds. Pumpkin seeds were subjected to hot air drying (HAD) at 55°C for 12 h and freeze-drying (FD) at -80°C for 54 h before they were powdered, analyzed, and precipitated by isoelectric point to obtain pumpkin seed protein isolates (PSPI). PSPI comprised 11S globulin subunit beta, 2S seed storage albumin, and chaperonin CPN60-1. To generate hydrolysate peptides, PSPI was hydrolyzed using papain, pepsin, and bromelain. FD group pepsin hydrolysates had the highest peptide content of 420.83 mg/g. ACE inhibition and DPP-IV inhibition activity were analyzed for each enzymatic hydrolysate. The pepsin hydrolyzed sample exhibited the highest ACE inhibition of 70.26%, and the papain hydrolyzed sample exhibited the highest DPP-IV inhibition of 30.51%. The simulated gastrointestinal digestion (SGID) conducted by pepsin and pancreatin increased ACE inhibitory activity from 76.93% to 78.34%, and DPP-IV inhibited activity increased from 58.62% to 77.13%. Pepsin and papain hydrolysates were fractionated using ultrafiltration to measure ACE and DPP-IV inhibition activity. The highest free radical scavenging abilities were exhibited by the <1 kDa hydrolysate fractions with 78.34% ACE inhibitory activities and 79.55% DPP-IV inhibitory activities. This research revealed that pumpkin seeds had the potency to produce bioactive peptides.