Influence of Drying Method on the Composition, Physicochemical Properties, and Prebiotic Potential of Dietary Fibre Concentrates from Fruit Peels

Dietary fibre concentrates (DFC) obtained from fruit and vegetable by-products are powders, mainly obtained by dehydration, used in food formulations to increase nutritional value and to improve functional properties. The modifications of insoluble, soluble, and total dietary fibres (IDF, SDF, and TDF), physicochemical properties (solubility, swelling capacity, water/oil retention capacity, pH, and tapping density), and prebiotic potential of DFC from orange, mango, and prickly pear peels obtained by freeze-drying (FD) and convective hot air-drying (HA) were studied. In vitro faecal fermentation was used to evaluate the short-chain fatty acid (SCFA) production as a prebiotic indicator. TDF in FD orange was 5.5 g·100 g−1 higher than that in the HA sample, whereas HA increased TDF in prickly pear (9.5 g·100 g−1). No differences in fibre composition were observed in mango DFC. The physicochemical properties mostly affected by dehydration treatment were solubility and swelling capacity. HA increased SCFA production in orange peel (48 mmol·g−1 higher) but decreased it in mango and prickly pear (15 and 19 mmol·g−1 lower). Butyrate production of HA orange DFC was comparable to that obtained with the positive control (4.5 mmol·g−1). No production of propionate or butyrate was observed after 6 h fermentation in mango samples, despite the high SDF content (≈20 g·100 g−1). A decrease of the SDF : TDF ratio produced by the drying method improved the SCFA production.