Grinding levels of raspberry pomace affect intestinal microbial activity, lipid and glucose metabolism in Wistar rats

This study presents the effect of raspberry pomace and its grinding level on microbial activity in the gastrointestinal tract as well as on the parameters involved in the regulation of lipid and glucose metabolism in Wistar rats. The nutritional experiment was performed using 24 male Wistar rats, which were divided into 3 groups of 8 animals each. The animals were fed a standard diet (C) or a modified diet containing 7% raspberry pomace subjected to standard (SG) or fine (FG) grinding. Finer grinding increased the concentration of polyphenols and altered the composition of the dietary fibre, thereby affecting the intestinal microbial activity and related mechanisms that regulate systemic parameters. The FG diet considerably increased the level of total ellagitannin metabolites in the colon (23.56 mu g/g for SG and 79.54 mu g/g for FG) and plasma (0.029 mu g/mL for SG and 0.041 mu g/mL for FG) and reduced beta-glucuronidase and alpha-glucosidase activity (19.2 and 19.7 for SG and 13.3 and 8.7 mu mol/h/g for FG, respectively) and short-chain fatty acid production (55.84 mu mol/g for SG and 48.60 mu mol/g for FG) in the caecum. Compared to the SG, the FG diet improved the antioxidant capacity of water-soluble substances in plasma (4.34 mu g/mL for SG and 4.92 mu g/mL for FG). Both diets with raspberry pomaces increased the plasma HDL cholesterol (0.48 mmol/L for C, 0.56 mmol/L for SG, 0.57 mmol/L for FG) and decreased the atherogenic index (AI = (TC-HDL)/HDL: 2.57 for C, 1.98 for SG, 2.00 for FG). The FG diet resulted in the lowest plasma glucose level (10.8 mmol/L for C, 8.2 mmol/L for SG, 7.3 mmol/L for FG). In conclusion, both diets with raspberry pomaces modulated intestinal microbial activity and related systemic parameters; however, FG pomace exhibited greater inhibitory effects than SG pomace in the lower gut environment and glucose metabolism.