Pepsin

Micellar casein isolate (MCI) and modified MCI (plasmin-treated MCI [PMCI], and calcium-reduced MCI [CaMCI]) were characterized to assess their potential applications in infant formula. Structural traits (protein composition, solubility, turbidity, particle size) and functional properties (enzyme-induced coagulation, hydrolysis) were systematically assessed, providing critical insights into gastric clotting and digestion behavior. Firstly, the protein profiling result proved that the degradation fragment peaks appeared in PMCI. Then, six kinds of protein blends were prepared by using different types of MCI and whey protein concentrate (WPC) at both human (40:60 w/w casein:whey) and bovine (80:20 w/w casein:whey) milk-equivalent ratios, the bovine milk was used as reference. For the 40:60 ratios mixtures, PMCI: WPC and CaMCI:WPC had better solubilities than normal MCI:WPC. Furthermore, CaMCI:WPC blends showed the lowest turbidity of both ratios (40:60 and 20:80). After the pepsin and chymosin treatment, pepsin-induced coagulation of MCI:WPC (80:20) resulted in lower gel strength compared with chymosin but still presented higher gel strength than PMCI:WPC (80:20). There was no difference in coagulation performance of PMCI blends between pepsin and chymosin, while MCI:WPC at 40:60 and CaMCI:WPC (both 40:60 and 80:20) samples did not coagulate at all. Based on levels of free N-terminal, for the MCI:WPC (80:20) and PMCI:WPC (80:20), chymosin and pepsin showed similar hydrolysis efficiency, while in their 40:60 blends, pepsin induced greater hydrolysis than chymosin. CaMCI blends had the highest soluble protein content, but the lowest hydrolysis efficiency. Correlation analysis further demonstrated the relationship between physicochemical properties of ingredient blends with functional metrics.

Low water solubility strictly limits the potential applications of rice (Oryza sativa) protein isolate and glutinous rice (Oryz asatin L. var. glutinosa Matsu) protein. This study aimed to enhance the solubility of rice protein isolate (RPI) and glutinous rice protein (GRP) through enzymatic hydrolysis using pepsin and trypsin. It evaluated the impact of hydrolysis time (30, 60, and 120 min) and enzyme types (pepsin and trypsin) on their physicochemical characteristics and functional properties. The solubility of GRP hydrolyzed by pepsin for 60 min reached 46.86 %, whereas that of RPI hydrolyzed under the same conditions for 120 min stood at 35.16 %. Microstructural analysis indicated that enzymatic hydrolysis destroyed the dense protein structure, leading to the formation of loose small particles. Surface hydrophobicity significantly decreased, and the emulsifying activity index (EAI) of GRP hydrolysates reached a maximum of 0.28 m²/g. Antioxidant assays confirmed that the DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical scavenging rate of pepsin-hydrolyzed protein hydrolysate (60 min) reached 80 %, and the ABTS (2,2'-Azobis-3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging rate of pepsin-trypsin-hydrolyzed products (30 min) was 70 %. This study provides quantitative data supporting the application of RPI and GRP in functional foods.