Unravelling the effects of extrusion and drying temperatures on the radical scavenging capacity of aquafeeds supplemented with mango and pineapple by-products

Antioxidant supplementation of aquafeeds with natural sources is a current research trend within the context of a circular economy. However, natural antioxidants are highly vulnerable to thermal conditions during feed manufacturing, particularly during extrusion and drying. This study examines the impact of extrusion and drying temperatures on the antioxidant properties of aquafeeds supplemented with natural antioxidants from mango and pineapple peels. A control dietary mixture and two dietary mixtures with 2 % inclusion of either mango (M) or pineapple (P) peel flour were subjected to different combinations of extrusion temperatures (110 °C, -H vs 25 °C - C) and drying temperatures (60 °C vs 35 °C). Ingredients, manufacturing process intermediate stages, and final diets were analysed for their natural antioxidant composition (vitamins, carotenoids, free and fibre-bound phenolic compounds) and antioxidant capacity via the DPPH⁺, ABTS^•+ and ORAC assays, the latter of which is the most representative for biological models. Results show that incorporating 2 % of either pineapple or mango peel flour increases the antioxidant content and capacity of aquafeeds compared to a control diet subjected to the same manufacturing conditions. Phenolic compounds were more abundant and resistant to the feed manufacturing process than vitamins and carotenoids. Specifically, ORAC results for free and fibre-bound extracts in diet PH-60 (1674.3 and 1216.2 mg TE 100 g DM⁻¹, respectively) were significantly higher (P < 0.001) than the control CH-60 (694.8 and 422.8, respectively). Moreover, free extracts from diet PC-60 (1312.0 mg TE 100 g DM⁻¹) and fibre-bound extracts from diets MH-60 and PH-35 (719.2 and 871.1 mg TE 100 g DM⁻¹, respectively) were also significantly higher than the control (P < 0.001). A PCA analysis showed that pineapple diets with hot extrusion, as well as the mango diet with hot extrusion and hot drying, are more closely associated with higher antioxidant capacity in both free and bound extracts. Overall, fruit peel flours show promise as antioxidant supplements for mitigating oxidation in aquafeeds.