The Valorization of Rapeseed Meal as Hydrolyzed and Lyophilized Extract to Improve the Antioxidant Properties of Refined Rapeseed Oil During Frying and Fried French Fries

In the present study, methanolic extracts from rapeseed meal, an oil industry by-product, were treated with alkaline hydrolysis, acid hydrolysis, and lyophilization to enhance their antioxidant features. Antioxidant activity (AA) of the prepared rapeseed meal extracts was determined using three modified spectrophotometric methods: 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing antioxidant power (FRAP) methods. The effect of acid-hydrolyzed and lyophilized rapeseed meal extract (HLRME) at 200 ppm on the antioxidant properties of refined rapeseed oil heating at 180 °C for 24 h and French fries fried in it was estimated. Moreover, the total phenolic content (TPC) in rapeseed meal extracts, enriched rapeseed oils before and after the thermo-degradation processes, and fried French fries was analyzed. The addition of HLRME affected the oxidation stability of refined rapeseed oil heated for 8 h daily for 3 days at 180 °C by preventing an increase in the peroxide values (PV), anisidine values (<i>p</i>-AnV), TOTOX and INTOX indexes, conjugated dienes (K₂₃₂), and total polar material (TPM). However, thermal degradation generated similar amounts of conjugated trienes (K₂₆₈) in non-supplemented and supplemented rapeseed oils. Fortified rapeseed oils after each heating cycle and French fries fried in them revealed higher antioxidant properties than those prepared in refined rapeseed oils without HLRME. Results from the present study suggest that HLRME, as a potential source of natural antioxidants from oil industry by-products, can prevent the degradation of refined rapeseed oil and help improve the quality of French fries.