From extraction to the synergistic effects of spent red and white grape pomaces on the oil's oxidative stability

This study investigates the potential of post-distillation grape pomaces, as a natural source of antioxidants, to inhibit lipid oxidation in vegetable oils. Extracts from both white and red spent grape pomaces (WGP and RGP, respectively) were obtained using conventional extraction, ultrasound-assisted extraction (UAE), and a combination of both methods. The most efficient extraction process was determined based on the total phenolic content and ferric-reducing antioxidant power (FRAP) of each extract. UAE emerged as the optimal method, owing to its lower energy consumption and the higher FRAP values (i.e., 88.61 ± 12.00 mg Trolox equivalent (TE).g-1 dry weight (DW) for WGP and 45.75 ± 4.94 mg TE.g-1 DW for RGP) of the extracts obtained. Incorporating individual and mixed extracts at 30% v/v into various oils resulted in enhanced oxidative stability, as demonstrated by the Rancimat test. The natural extracts performed similarly to butylated hydroxytoluene, a synthetic antioxidant. The mixed extracts exhibited a synergistic effect, further increasing the induction period of oil oxidation, likely due to the mixed phenolic profile of the extracts and the regeneration of one antioxidant by another after neutralizing free radicals. These findings underscore the significant antioxidant potential of spent grape pomace phenolic extracts as natural additives for oilbased food systems, providing reliable data for further research and application in the food industry.