Evaluation of polyphenolic content and antioxidant activity in agri-food wastes and by-products using chemical and physiological extraction

EU-28 produces about 100 Mtonnes/year of food waste, of which 40% is generated from agri-food industries. Agri-food waste (AFW) and by-products may contain components that could be valorised for their bioactivity. However, the bioaccessibility of these products is highly variable and dependent on a wide range of factors, including food matrix characteristics. Thus, the aim of this study was to determine the total phenolic content and the antioxidant capacity of some by-products and AFW using two different extraction methods. Twelve samples of by products (grape marc, Camelina sativa cake, olive pomace and whey) and 12 samples of AFW (fruits and vegetables waste FVW, citrus pulp, strawberry and orange dried) were processed using: methanol extraction (chemical procedure) and in vitro physiological extraction simulating pig gastro-intestinal tract adapted from Regmi et al., 2009. Soy and wheat were included as controls. Afterwards, the polyphenolic content was assessed by Folin–Ciocalteu assay while antioxidant capacity was determined by 2,2-Azino-bis-3-ethylbenzothiazoline-6-sulfonic Acid (ABTS) assay. Results obtained showed that the chemical extracts of by-products and AFW contain different amount of polyphenols; in particular, as expected, the grape marc showed the highest significant (4.5% w/w; p<.05) polyphenolic content compared to all samples considered. Of note, Camilina sativa cake, olive pomace, FVW, orange and strawberry dried showed a polyphenolic content of 1.3, 0.7, 1.3, 1.6 and 1.3% w/w, respectively. The antioxidant capacity of grape marc exhibited a higher (p<.05) value of 573.6 mmol Trolox equivalent (TE)/g compared to the other samples considered. Camilina sativa cake, olive pomace, FVW, orange and strawberry dried showed an antioxidant capacity of 29.2, 11.0, 28.4, 16.3 and 31.0mmol TE/g. The physiological extraction of grape marcs, Camilina sativa cake, olive pomace, FVW, orange, strawberry dried yielded a polyphenolic content of 3.6, 1.8, 3.2, 3.6 and 2.3% w/w, respectively. The antioxidant capacity showed a similar trend to polyphenolic content after physiological extraction. The results obtained in this study indicate that AFW and by-products could be considered a promising bioaccessible source of antioxidants and phenolic compounds with industrial applications for the production of ingredients to functionalize feedstuffs for monogastric animal.