Tree Leaves as Environmentally Friendly Preservatives: Evaluation of Antioxidant Activity

Oxidative spoilage of fresh food products results in significant economic losses in the food industry. Active packaging with natural antioxidants is a promising alternative to synthetic preservatives: it extends shelf life and provides consumer safety. The growing regulatory restrictions on synthetic antioxidants necessitate the development of natural analogs with GRAS status, i.e., generally recognized as safe. This study compared the antioxidant activities of different leaf extracts from Armenian tree species for active packaging prospects. Leaves of Quercus robur, Quercus iberica, Salix alba, and Lycium barbarum were collected during the full growing season in the Republic of Armenia. Their antioxidant properties were assessed using the kinetic method of cumene oxidation, which involved total antioxidant content (f [InH]) and the reaction rate constant with peroxide radicals (k7). This method provided a comprehensive description of the antioxidant mechanisms. The extract yields ranged from 3.4 ± 0.3% (S. alba) to 6.8 ± 0.3% (Q. iberica). The highest antioxidant content belonged to Q. iberica (1.34×10–4 mol/L) while the highest reactivity belonged to the S. alba extract (k7 = 1.01×105 L/mol·s). In DPPH equivalents, the antioxidant activity was 3.5–13.4 μg/mL, which was similar to that of green tea (8–20 μg/mL) and superior to rosemary fractions. The lack of correlation between the antioxidant content and the activity was due to the structural differences in the ph enolic components and their reaction mechanisms. The ethyl acetate extracts of Armenian wood species demonstrated high antioxidant activity at a low cost of raw materials ($5–10/kg vs. $15–50/kg of commercial antioxidants), which makes them a cost-effective and environmentally sustainable alternative to imported antioxidants.