Effect of Combined Pretreatments on Yield and Quality of Cold-Pressed Pomegranate Seed Oil

Abstract

In this study, the effects of combined thermal and biochemical pretreatments on the yield and quality of cold-pressed pomegranate seed oil (PSO) were systematically investigated. Convective and microwave roasting were applied individually and in combination with acid or with a commercial pectolytic–cellulolytic enzyme preparation, allowing a comparative evaluation of their synergistic effects under identical cold-pressing conditions. Microwave and convective roasting reduced the seed moisture content from 6.06% to 3–4%, whereas acid pretreatment significantly decreased the seed pH from 4.63 to 3.25–3.33. Lipase activity ranged from 0.061 to 0.191 U/g, with the highest activity in untreated seeds and the lowest in microwave-treated seeds, indicating pretreatment-induced enzyme inactivation. Among all treatments, microwave–acid pretreatment achieved the highest oil yield (11.20%) and the lowest free fatty acid content, whereas microwave–enzyme pretreatment resulted in the lowest peroxide value and the longest oxidative induction period, indicating superior oxidative stability. All pretreatments reduced peroxide value, p-anisidine value, and free fatty acidity compared with the control. Microwave-treated oils exhibited the highest carotenoid content (67.85 mg/kg), while enzyme-treated oils exhibited the lowest carotenoid content (12.05 mg/kg). Total phenolic content was highest in the control oils and decreased following pretreatment. Correlation analysis revealed that oil yield was negatively correlated with seed pH and lipase activity, demonstrating that acid-induced matrix modification and lipase suppression are key mechanisms governing oil recovery. Overall, this study provides new mechanistic insight into the structure enzyme quality relationships in PSO extraction and demonstrates that pretreatment selection should be guided by the intended end use. Microwave–acid pretreatment is most suitable for yield-driven applications (e.g., cosmetic or technical applications), whereas microwave–enzyme pretreatment offers an optimal balance between oxidative stability and quality preservation for food and nutraceutical applications.