Detection of Biologically Active Compounds and Antioxidants in Some Agricultural Waste Used for Industrial Purposes

Abstract

Agro-industrial by-products such as rice bran, onion peels, and pomegranate peels are rich sources of bioactive compounds with strong antioxidant potential. Their valorisation offers a sustainable alternative to synthetic additives for food preservation and nutraceutical applications. Therefore, the present study aimed to evaluate the nutritional composition, bioactive compounds, and antioxidant potential of selected agro-industrial by-products, namely rice bran (Oryza sativa L.), onion peels (Allium cepa L.), and pomegranate peels (Punica granatum), and to investigate their potential utilisation as natural antioxidants in edible oils. The results revealed significant differences among the investigated by-products in their chemical composition and antioxidant properties. Rice bran exhibited the highest contents of crude protein (15.75%), ether extract (19.50%), phosphorus (1129 mg/100 g), potassium (730.20 mg/100 g), and zinc (4.12 mg/100 g). Pomegranate peels recorded the highest crude fibre content (13.50%), total phenolic content (13.60 mg GAE/g), total flavonoid content (3.50 mg rutin equivalent/g), and antioxidant activity (92.0% DPPH inhibition). Onion peels were characterised by elevated levels of calcium (425.50 mg/100 g), magnesium (145.20 mg/100 g), iron (39.30 mg/100 g), α-tocopherol (11.61 μg/g), and vitamin K (12.85 μg/g). HPLC analysis demonstrated the presence of several important phenolic acids, including protocatechuic, ferulic, chlorogenic, caffeic, gallic, and p-coumaric acids, with marked variation among the tested samples. Antioxidant activity assays showed that all phenolic extracts significantly reduced peroxide formation in blended oil during accelerated storage compared with the untreated control. Among the tested extracts, pomegranate peel extract at 400 ppm exhibited the strongest antioxidative effect, followed by rice bran and onion peel extracts, producing peroxide values comparable to those of the synthetic antioxidant TBHQ after 120 h of storage. These findings indicate that the investigated agro-industrial by-products are promising natural sources of nutrients, antioxidants, and bioactive compounds with potential applications in food preservation and the development of functional foods.