Influence of Raspberry and Its Dietary Fractions on the In vitro Activity of the Colonic Microbiota from Normal and Overweight Subjects

Raspberry is a source of dietary fibre and phenolic compounds, which are metabolised by the gut microbiota, resulting in the production of short chain fatty acids (SCFAs) and phenolic catabolites; but the formation of these compounds depends on the microbiota composition. The aim of this study was to investigate whether the raspberry and its fractions (phenolic extract, total and insoluble dietary fibre) affect the microbial activity depending on the body weight condition. For this, in vitro fermentations of raspberry fractions were carried out using faeces from normal-weight (NW) and overweight volunteers (OW) during 48 h, and phenolic catabolites and SCFAs were analysed at 0, 6, 24 and 48 h. The whole raspberry and the phenolic extract produced greater quantities of urolithins and total SCFAs when compared with fibre fractions, reaching the highest amount between 24 and 48 h. The body weight condition was an important factor, since faeces from NW led to greater production of urolithins from non-extractable phenolic compounds bound to fibre fractions, whereas in OW the urolithins production was higher from the fractions with more extractable polyphenols. In summary, the whole raspberry has been shown to have a prebiotic effect, mainly due to its phenolic compounds content rather than its fibre content.