Functional cookies are a popular snack owing to their affordability and convenience. Recently, the incorporation of fruits and by-products into functional cookies has gained attention due to its potential for boosting their health benefits, increasing their fiber and mineral contents, and enhancing their nutraceutical potential by incorporating phenolic compounds with effective antioxidant properties [1, 2]. In this study, an antioxidant-rich chestnut (Castanea sativa) shell (CS) extract prepared by Subcritical Water Extraction and previously validated by in vitro and in vivo studies was incorporated into fortified cookies (1.77%). The cookies were characterized regarding their nutritional composition, phenolic profile, biological effects, and sensory analysis performed by a trained panel (n=20) using a nine-point scale. The bioaccessibility of the cookies were assessed through in vitro gastrointestinal digestion.

The cookies' nutritional composition unveiled high contents of carbohydrates (54%) and fat (33%), followed by fiber (5%) and minerals (2%). The remarkable antioxidant/antiradical effects attested by ferric reduction (FRAP) and scavenging of synthetic (ABTS^•+ and DPPH^•) and biological radicals (reactive oxygen and nitrogen species) were positively correlated to the cookies' phenolic composition, represented by 60.8% hydroxybenzoic acids, 7.5% hydroxycinnamic acids, 26.4% hydrolyzable tannins, and 5.3% flavonoids. The total phenolic concentration was 152 mg/100 g cookies; caffeine was also detected (2.71 mg/100 g). In sensory analysis, the cookies achieved an overall acceptance of 84%, with all attributes scoring above 5 (appearance, color, texture, taste, flavor, sweetness, crunchiness, and hardness). Using an in vitro model, the phenolic concentrations and antioxidant properties of the cookies increased during digestion, reaching 153 mg/100 g after the intestinal phase (versus 164 mg/100 g for undigested cookies). Chromatographic analysis underlined the distinct phenolic profiling of undigested and digested cookies, with higher concentrations of phenolic acids upon digestion.

Overall, these findings sustain the efficacy of antioxidant-rich CS extract as a functional ingredient for cookies, offering a novel strategy to repurpose this agro-waste.