Improved Utilization of Croaker Skin Waste and Freshwater Carps Visceral Waste: Conversion of Waste to Health Benefitting Peptides

Gelatin protein hydrolysates (GPH) was prepared by using gelatin extracted from the skin of croaker ( Johnius sp.), by the application of proteolytic enzymes extracted from gastrointestinal (GI) tract of two freshwater fish species rohu ( Labeo rohita ) and catla ( Catla catla ). The resultant hydrolysates were designated as gelatin protein hydrolysate-rohu protease (GPH-RP) and gelatin protein hydrolysate-catla protease (GPH-CP). Both the gelatin hydrolysates were fractionated into different ranges of molecular weight < 1 kDa, 1–3 kDa, 3–5 kDa, 5–10 kDa and > 10 kDa using ultrafiltration (UF) membranes. The fraction 1–3 kDa of GPH-RP hydrolysate and the fraction < 1 kDa GPH-CP hydrolysate were showed most potent angiotensin I-converting enzyme inhibitory (ACE) activity, and were subjected to liquid chromatography–mass spectroscopy (LC–MS/MS) for peptide sequencing, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and amino acid analysis. The peptide sequence of gelatin hydrolysate fractions of GPH-RP (1–3 kDa) and GPH-CP (< 1 kDa), were identified as GLTGRPGDAGPQGK and GFPGER with relative molecular mass (M+H + ) values of 1310.67 Da and 662.32 Da, respectively. FT-IR spectra in both fractions revealed random coil-structure and β-sheet. Microstructure of GPH fractions had crystalline, broken glass like structure, flake-like and wrinkled structure.