Effect of Sun‐Dried Raisins ( Vitis vinifera L.) on the In Vitro Composition of Gut Microbiota

Our aim was to investigate the effect of sun‐dried raisins on the colonic microbiota using an in vitro batch culture seeded with representative human gut bacteria. A model of gastric and small intestinal digestion was used to simulate the upper gastrointestinal digestion. Samples collected during a time course at 0, 4, 8 and 24h were analyzed for microbial composition and organic acid concentrations by 16S V4 rDNA analysis and high‐performance liquid chromatography (HPLC), respectively. The most abundant phylum identified across all samples was Firmicutes. Significant differences (P<0.05) in the proportional abundance of Proteobacteria and Bacteroidetes were observed after 8 and 24h fermentation. The shift in the whole microbioma suggested that raisins selectively modulated gut bacteria differently from fructo‐oligosaccharides (FOS). Growth of Bifidobacterium spp. was higher (P<0.05) with raisins and FOS after 4h compared to the negative control. Amongst Clostridiales, the numbers of Blautia producta increased after 24h with raisins compared to the negative control. The highest concentration of acetate, propionate, butyrate and lactic acid in the raisin samples was detected after 24h. These findings indicate that sun‐dried raisins could beneficially alter the composition of the human gut microbiota, thus improving gastrointestinal health.