Nutritionally enhanced oat-based cookies through the sustainable valorisation of berry surpluses

• BIDF ingredient was obtained from berry surpluses via green extraction. • BIDF cookies have increased dietary fibre, (poly)phenol and antioxidant capacity. • Enriched cookies reduced glucose release during in vitro digestion. • The addition of BIDF enhanced butyric acid production during in vitro fermentation. • 5% BIDF cookies were well accepted, supporting a circular, health-focused approach. Berries are a good source of dietary fibre, and their surpluses represent a valuable circular ingredient due to their richness in non-starch polysaccharides and (poly)phenols. This study aimed to develop oat-based functional cookies by incorporating 5% and 10% of a berry insoluble dietary fibre-rich ingredient (BIDF) obtained from berry surpluses through green extraction processes. The cookies were evaluated for proximate composition, dietary fibre (DF) and non-starch polysaccharides, in vitro starch digestibility, extractable and non-extractable (poly)phenols using HPLC-DAD, antioxidant capacity, potential prebiotic effect by in vitro faecal fermentation, colour, texture, and sensory acceptance. Enriched cookies were compared with a control, showing that BIDF incorporation significantly increased DF (∼1.5-fold) —particularly pectin—and reduced glucose release by ∼12%, suggesting a potential glycaemic-lowering effect. Moreover, the enrichment led to higher levels of (poly)phenols (2.2-fold in CF-5 and 3.6-fold in CF-10), especially anthocyanins and ellagic acid derivatives, enhancing antioxidant capacity. Colour parameters were affected by the addition of the ingredient, while textural properties remained unchanged. Sensory analysis showed that cookies with 5% of BIDF ingredient were well accepted, with minimal impact on taste compared to the control. Additionally, in vitro fermentation assays revealed an increased production of short-chain fatty acids, particularly butyric acid (∼23% increase), supporting the prebiotic potential of the ingredient. 5% inclusion achieved functional benefits and consumer acceptance. These results demonstrate the feasibility of incorporating a circular fibre rich ingredient from berry surpluses into bakery products as a strategy to enhance nutritional quality, promote gut health, and contribute to sustainable, circular food systems.