Combination of fiber-degrading enzymatic hydrolysis and lactobacilli fermentation enhances utilization of fiber and protein in rapeseed meal as revealed in simulated pig digestion and fermentation in vitro

Abstract

As the increased rapeseed meal (RSM) production in last decades, improving the utilization of RSM is considered a major target in agricultural biotechnology. A series of in vitro studies were conducted to determine the effects of fiber-degrading enzymes and lactobacilli fermentation on the nutritional value of RSM. In experiment 1, the mixture of three strains of lactobacillus (L. reuteri L45, L. plantarum L47, and L. johnsonii L63) were applied to ferment RSM for 48 h after fiber-degrading enzymatic hydrolysis (a mixture of 10 FPU/g cellulase and 10 U/g pectinase) for 28 h. Four treatment groups were assigned: i) RSM without lactobacilli and enzymes (CON); ii) RSM with lactobacilli (LA); iii) RSM with enzymes (EN); and iv) RSM with enzymes and lactobacilli (EN + LA). Each group had 4 replicates. Lactobacilli growth characteristics were detected after the experiment. All RSM samples were dried and used for experiment 2. In experiment 2, samples of 4 groups were digested by pepsin and pancreatin to simulated small intestine digestion. Digestibility of dry matter and crude protein (CP) in vitro was measured. In experiment 3, undigested residues from each group were incubated with fresh pig rectum digesta as inoculums for 48 h to simulated the porcine large intestine fermentation in vitro. Accumulative gas production was recorded and modeled to estimate kinetics of gas production. Short-chain fatty acid (SCFA) concentration was measured at the end of fermentation. In experiment 1, the results demonstrated that reducing sugar concentration in EN was higher than that in CON. Compared with LA, lactic acid concentration and count of viable Lactobacillus were higher, and pH was lower in EN + LA. Rapeseed meal treated with EN + LA presented the lowest value of glucosinolate and the highest value of CP as well. In experiment 2, in vitro dry matter and CP digestibility of RSM was increased by 23 % and 20 %, respectively, by the addition of EN regardless of LA addition through a simulated small intestine digestion in vitro. The findings in experiment 3 showed that EN + LA reduced the accumulative gas production and SCFA compared with CON, indicating an improvement in utilization of carbohydrates and protein in both enzymatic hydrolysis and lactobacilli fermentation and in vitro digestion. Overall, fiber-degrading enzymes promoted the growth of lactobacilli on RSM, and the combination of fiber-degrading enzymatic hydrolysis and lactobacilli fermentation enhanced nutritional value and utilization of fiber and protein in RSM.