Valorizzazione degli estratti di vinacce d'uva come antiossidanti naturali per migliorare la stabilità ossidativa degli oli commestibili

Grape pomace is the main by-product of the winemaking process. This study aimed at recovering natural antioxidants from white and red grape pomace (WGP and RGP, respectively) to inhibit lipid oxidation in different vegetable oils, compared to butylated hydroxytoluene (BHT), a synthetic antioxidant. To obtain ethanolic extracts of the pomace samples, water bath (WB) and ultrasonic extraction (US) methods and a combination of them (WBUS) were used. After the extraction, three mixtures with different WGP:RGP ratios, including 50:50, 70:30, and 30:70 %, were prepared and, along with pure WGP and RGP, were subjected to total phenolic content (TPC) and antioxidant activity (AOA) evaluations, aiming at finding the optimal extraction method and extract concentration. The TPC and FRAP tests revealed that there is a significant difference among the yield of the methods (p≤0.05). Although WBUS showed the highest TPC values in TPC evaluation, the US method was chosen as optimal due to its sustainability and the RGP50+WGP50 mixture with the highest value was selected as the optimum sample. The same in FRAP, where the US method was selected as it is a sustainable method; nevertheless, instead of RGP30+WGP70 mixture, RGP50+WGP50 mixture was selected, highlighting the importance of the symmetric ratio in the sample. To determine the optimum concentration to be added to the oil sample, a preliminary test was done by applying RGP at 5, 10, and 30% on soybean oil, followed by subjecting the extract-added oil to the Rancimat test. The results revealed that for both Induction Time (IT) and Antioxidant Activity Index (AAI), according to the obtained significance levels (0.05), there is a significant difference between 30%RGP extract with other lower concentrations of RGP extract (p≤0.05). Determining the 50RGP+50WGP mixture at 30% concentration derived through the US as the optimum extraction, it was applied to the four edible oils, namely sunflower oil, soybean oil, corn oil, and grape seed oil, and the results were compared to BHT antioxidant. In addition, pure forms of RGP and WGP extracts at the same concentration were derived, and the same extraction method was used in the experiment to evaluate the performance of the mixture with pure forms, control, and BHT samples. Taking the value of AAI and IT into consideration, mixed grape pomace extracts significantly improve the oxidative stability of different edible oils more effectively than either individual grape pomace extracts or BHT at 200 ppm, suggesting a synergistic effect when red and white grape pomace are combined. The results of this study highlight the point that grape pomace-derived phenolic compounds possess considerable antioxidant potential, which can function as natural additives and produce functional foods.