TOTAL PHENOLIC CONTENT AND ANTIOXIDANT ACTIVITY OF INFUSIONS FROM TWO BY-PRODUCTS: WALNUT (JUGLANS REGIA L.) SHELL AND ONION (ALLIUM CEPA L.)

Abstract

Total phenolic content and antioxidant activity of two by-products of onion (Allium cepa L.) and walnut (Juglans regia L.) processing were studied in order to establish the possibility of capitalization as antioxidant sources. The by-products analyzed were walnut shell and onion peel. From these by-products, infusions were prepared using water as solvent. Total phenolic content was determined using Folin-Ciocalteu method, while the radical scavenging ability of the infusions was monitored using the stable free radical DPPH (1,1-diphenyl-2-picrylhydrazyl). Walnut shell infusion had a relatively low content in phenolic compounds (32.08 mg GAE/g), below the level reported for other walnut by-products. Given the low phenolic content, walnut shell infusion exhibited a reduced radical scavenging capacity (7.82%). On the contrary, the onion peel infusion had both high phenolic content (280.32 mg GAE/g) and antioxidant activity (69.38%). Based on these two results it was confirmed that onion peels resulted from bulb processing are suitable for reuse in antioxidants’ extraction in both food and pharmaceutical industries.