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

Abstract

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.

Keywords: Gas production; Human inoculum; In vitro fermentation; Porcine model; Undigested protein.

Figure 1.

Measured 48 h in vitro cumulative gas production (GP) of ileal digesta from pigs fed four different human foods, whey protein isolate (WPI) and WPI hydrolysates (WPIH) using human (I) and porcine (II) faecal inoculum (blank). All samples contained 10 mg of nitrogen and mean values from three incubation runs were used.

Figure 2.

Overview of in vitro fermentation parameters of porcine ileal digesta (containing 10 mg nitrogen) originating from thirty-one different human foods incubated with human faecal inoculum. Data distribution, mean and coefficient of variation (CV) are shown for lag time (T_lag, h), maximum gas production rate (R_max, ml/h), time when maximum rate occurred (T_Rmax, h), cumulative gas production of protein substrate determined by the model (GP_s, ml/10 mg nitrogen), time when GP_s occurred (T_GPs, h) and slope of the linear line of the model (slope, ml/h). Average value from three independent runs was used for each food. The shape of the violin plots illustrates the distribution of data points across the range of values. Symmetry or asymmetry in the plot shape indicates skewness or uniformity of the data distribution, while wider or narrower sections highlight regions of higher or lower data density, aiding in visual interpretation of variability.

Figure 3.

In vitro fermentation parameters of porcine ileal digesta samples containing 10 mg nitrogen, incubated with human faecal inoculum. Ileal digesta originated from previous studies investigating the digestibility of thirty-one different human foods. Values are means (se) of lag time (T_lag), maximum gas production rate (R_max), time when maximum rate occurred (T_Rmax), cumulative gas production of protein substrate determined by the model (GP_s), time when GP_s occurred (T_GPs) and slope of the linear line of the model (Slope) of three incubation runs.

Figure 4.

In vitro fermentation parameters of porcine ileal digesta samples (containing 10 mg nitrogen) incubated with human faecal inoculum in three independent runs. Ileal digesta originated from previous studies investigating the digestibility of thirty-one different human foods were grouped into animal proteins (AP), grains, legumes, fungi, algae and microorganisms (FAM) and others. Values are means (se) of lag time (T_lag), maximum gas production rate (R_max), time when maximum rate occurred (T_Rmax), cumulative gas production of protein substrate determined by the model (GP_s), time when GP_s occurred (T_GPs) and slope of the linear line of the model (Slope) for each food category.

Figure 5.

Scatter plot and linear regression coefficients (mean (sd)) of in vitro fermentation parameters of porcine ileal digesta incubated with human and porcine faecal inoculum. Parameters include the maximum gas production rate (R_max) and the time at which the cumulative gas production of the protein substrate, as determined by the model, occurred (T_GPs). Ileal digesta samples were obtained from growing pigs fed a wide range of human foods (n 30 for R_max and n 31 for T_GPs). The average values from three incubation runs for each food were used.