Effect of different soluble dietary fibres on the phenolic profile of blackberry puree subjected to in vitro gastrointestinal digestion and large intestine fermentation

The aim of this study was to investigate the modulation of polyphenols profile of blackberry purees by soluble dietary fibres (inulin or pectin), during a simulated in vitro gastrointestinal digestion and large intestine fermentation process. Untargeted profiling evidenced that the free phenolic fraction of blackberry puree was characterized mainly by flavonoids, followed by phenolic acids, lignans and other low molecular weight polyphenols, showing clear differences from the bound phenolic fraction detected. This trend could be related to the interactions of dietary fibre and polyphenols, showing synergistic and/or antagonist effect on the bioactivity of polyphenols. On the other hand, in vitro large intestine fermentation of blackberry purees following in vitro gastrointestinal digestion revealed that the highest inclusion level (10% w/w) of soluble dietary fibres was effective in modulating the bioaccessibility of some phenolic classes (mainly phenolic acids, lignans and flavones) characterizing the blackberry puree. In addition, multivariate statistics following metabolomics-based profiling showed that the interaction between fibres and blackberry purees determined a marked modification of both anthocyanins and flavonols during in vitro large intestine fermentation, thus leading to the formation of low-molecular-weight compounds (such as tyrosol, followed by gallic and benzoic acids).