Total phenolic content and antioxidant capacity of agri-food waste and by-products

Agri-food waste (AFW) and by-products represent sources of phytochemicals, such as phenols and antioxidant compounds that can be used as functional ingredients in animal feed. In this study, a selection of AFW and by-products were collected and analysed for their nutrient composition. After chemical (with methanol) and physiological (in vitro digestion) extraction, total phenolic content and antioxidant capacity (AOC) were determined in AFW and by-product samples using Folin–Ciocalteu and 2,2′-azinobis(3-ethylbenzothiazoline 6-sulfonic acid)-ABTS methods, respectively. Sample digestibility was also assessed using a multi-step enzymatic technique. After chemical extraction, grape marc showed the highest total phenolic content (4480.5 ± 886.58 mg TAE/100g; p <.05). Fruit and vegetable waste (FVW), orange peel, strawberry, citrus pulp and Camelina sativa cake showed a total phenolic content ranging from 238.0 ± 4.24 to 1583.0 ± 154.35 mg TAE/100g. Grape marc also showed the highest AOC (15440.7 ± 2671.85 mg TE/100g). In all other samples, AOC ranged from 43.3 ± 3.17 to 1703.9 ± 391.07 mg TE/100g. After physiological extraction, total phenolic content values higher than 3000 mg TAE/100g were observed in FVW, grape marc and orange peel. Grape marc, C. sativa cake and orange peel had AOC values of over 5000 mg TE/100g. The digestibility of AFW and by-products ranged from 44.20 to 97.16%. The lowest digestibility value was observed in grape marc (44.2 ± 2.31%). In conclusion, the results obtained in this study indicate that AFW and by-products could be a source of bioaccessible phenols and antioxidant molecules as ingredients for monogastric compound feeds.Highlights Agri-food waste and by-products can be reused in feed industry. Agri-food waste and by-products are a source of valuable compounds as phenols and antioxidant molecules.