Watermelon rind pectin structure influences digestibility and impacts on gut microbiota: a comparative in vitro study

Pectin is one of the most complex families of carbohydrate structures and one of the main sources of soluble fibre, with positive health effects when included in the diet. Additionally, food and agricultural waste are vast potential sources of further pectin ingredients. In this study, two watermelon rind pectin samples with less branched (LB) or branched (HB) structures were compared with standard citrus pectin (CP) and galactan (PG). The distinct pectin samples with well-defined structural features were subjected to in vitro human gastrointestinal digestion followed by a colonic static fermentation in order to study the impact of digestion on pectin composition, molecular weight, and also impact on gut microbiota composition and metabolic activity through 16S rRNA amplicon sequencing and short chain fatty acid (SCFA) profile, respectively. In the case of the lower molecular weight LB, no significant increase in SCFA production was observed despite maintaining higher alpha diversity of the gut microbiota composition compared to control. On the contrary, the natively highly branched pectin from watermelon (HB) displayed highest SCFA production, especially propionic acid (12-17 mM), compared to PG or CP references, despite a higher molecular weight (∼400kDa) hampering accessibility and reducing overall bacterial survival. The results put forward the potential of watermelon pectin sources as novel alternative prebiotic ingredients.