In vitro fermentation potential of diet-derived fermentable proteins of thirty-one human foods

Protein fermentation in the human gut is often associated with adverse health effects. Hence, understanding the fermentation characteristics of dietary undigested proteins is important for a comprehensive nutritional value of foods. This study investigated the protein fermentation kinetics of diet-derived proteins from thirty-one different foods using an in vitro model and human faecal inoculum. The undigested diet-derived protein substrate originated from porcine ileal digesta obtained from assessment of the digestible indispensable amino acid score (DIAAS) of the foods. Significant variations in fermentation kinetic parameters, particularly in maximum gas production rate (R_max) and time to reach cumulative gas production (GP) from the substrate (T_GPs), were observed. The R_max ranged from 15·5 (se 0·7) ml/h for wheat bran-derived to 24·5 (se 0·9) ml/h for oatmeal-derived proteins. Egg-derived proteins had the shortest T_GPs (14·7 (se 0·7) h), while mushroom-derived proteins had the longest (27·6 (se 7·1) h). When foods were categorised into five groups ('animal protein', 'grains', 'legumes', 'fungi, algae and microorganisms' and 'others'), no significant differences were found in fermentation kinetics parameters. Samples were additionally incubated with porcine inoculum to assess potential donor-species effects. Human inoculum showed significantly lower R_max, cumulative GP and microbiota turnover than porcine inoculum, indicating reduced fermentative activity. Linear regression analysis revealed correlations between human and porcine-derived inoculum only for R_max (R² = 0·78, P < 0·01) and T_GPs (R² = 0·17, P < 0·05). These findings underscore the importance of using human inoculum in in vitro studies to better predict health implications of foods with DIAAS values.