Dynamic Changes in Amino Acid Release Patterns of Different Plant Protein Sources During In Vitro Digestion and Their Nutritional Value Assessment

A gastric-intestinal two-step enzymatic hydrolysis in vitro digestion simulation system was used to systematically investigate the digestion kinetics and amino acid release characteristics of five plant protein sources: soybean meal, rapeseed meal, corn DDGS, corn gluten meal, and corn germ meal. The results showed that in the gastric digestion phase (120 min), the protein hydrolysis degree of soybean meal was the highest (61.8%, <i>p</i> < 0.001), which was 4.4 times that of corn gluten meal (14.0%). In the intestinal digestion phase (240 min), the low-molecular-weight peptide release of corn gluten meal (31.2 mg/g) was significantly higher than that of corn DDGS (17.4 mg/g), showing a "weak in the stomach but strong in the intestine" characteristic. The "nutritional value equivalence" model constructed with soybean meal as the reference showed that the gastric digestion phase equivalence of rapeseed meal was only 32.2% (significantly lower than other materials), and the intestinal digestion phase equivalence of corn gluten meal was 62.9%. This study clarified the differences in digestion characteristics and key related indicators of different plant protein sources, providing quantitative references and scientific support for the food and feed industries to precisely select protein sources according to digestion phases and optimize the formula design.