Effect of Ultrasound Pretreatment and Cold Pressing on the Concentration of Bioactive Compounds and Antioxidant Characteristics of Grape Seed Oil

This study investigated ultrasound pretreatment of grape pomace seeds as a potential approach to improve cold-pressed grape seed oil yield, concentrations of bioactive compounds and antioxidant characteristics compared with oil obtained from untreated control seeds. Ultrasound frequency (37 and 80 kHz) and treatment duration (30 and 90 min) were evaluated. Oil yield was primarily influenced by treatment duration, increasing by 11.7% and 12.7% after 90 min at 80 and 37 kHz, respectively. In contrast, the response of bioactive compounds strongly depended on ultrasound frequency: tocochromanols responded more strongly at 37 kHz, with the highest increase of 8.1% after 30 min, whereas sterols showed greater response to 80 kHz and prolonged treatment, reaching a 7.2% increase after 90 min. The fatty acid profile remained largely unaffected. The most pronounced effect was observed for phenolic compounds, particularly at 37 kHz for 90 min, when nonflavonoids and flavonoids increased by 63.9% and 34.2%, respectively. H-ORAC also reached its highest value under these conditions (25.5% increase), whereas L-ORAC increased significantly at 37 kHz after both 30 and 90 min (12.1–13.8%). Very strong positive correlations were found between phenolic compounds and H-ORAC (r = 0.924) and between tocochromanols and L-ORAC (r = 0.986).