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.

明胶蛋白质水解物（GPH）是通过使用从黄花鱼（Johnius sp。）的皮肤中提取的明胶，并应用从两种淡水鱼类rohu（Labeo rohita）和catla（Catla（Catla）的胃肠道（GI）中提取的蛋白水解酶）制备的卡特拉）。所得的水解物称为明胶蛋白水解物-rohu蛋白酶（GPH-RP）和明胶蛋白水解物-catla蛋白酶（GPH-CP）。使用超滤（UF）膜将两种明胶水解物分馏成分子量分别为<1 kDa，1-3 kDa，3-5 kDa，5-10 kDa和> 10 kDa的不同范围。GPH-RP水解产物的1–3 kDa部分和<1 kDa GPH-CP水解产物的部分显示出最有效的血管紧张素I转换酶抑制（ACE）活性，并经过液相色谱-质谱（LC-MS / MS）进行肽测序，傅立叶变换红外（FT-IR）光谱，扫描电子显微镜（SEM）和氨基酸分析。GPH-RP（1-3 kDa）和GPH-CP（<1 kDa）的明胶水解产物级分的肽序列，⁺）值分别为1310.67 Da和662.32 Da。两个部分的FT-IR光谱均显示出无规卷曲结构和β-折叠。GPH馏分的微观结构具有结晶，碎玻璃状结构，薄片状和起皱的结构。