Comparative optimization of microwave and ultrasound assisted extraction of pine nut skin bioactives and its application as a natural coating to prevent lipid oxidation in pine nuts

This research focused on enhancing the recovery of bioactive compounds from pine nut skin (PNS) through two green extraction approaches: Microwave-assisted (MAE) and ultrasonic-assisted (UAE) techniques. The results showed that UAE outperformed MAE in terms of both total phenolic content (TPC) and antioxidant activity (AOA). Under optimized UAE conditions (10% ultrasonic power, 8.56 g/100 mL solid-liquid ratio, and 60% ethanol concentration), the extract exhibited significantly higher phenolic content (835.15 ± 0.28 mg GAE/g) and antioxidant activity (76.27 ± 2.25%) compared to MAE. The optimized PNS extract was applied to postharvest pine nuts, and the effect of extract and glycerol content were evaluated through oxidation analyses (peroxide value, thiobarbituric acid reactive substances (TBARS), p-anisidine value, and Totox value) during accelarated storage. Among the nine coating formulations tested, the G20E10 coating solution (containing 10% extract and 20% glycerol) was the most effective one in preventing oxidation and quality loss in postharvest pine nuts. It reduced peroxide, TBARS, and Totox value increases during storage by approximately 86%, 82%, and 91%, respectively, compared to the uncoated samples, thereby demonstrating a protective effect against lipid oxidation. The G20E10 coating significantly reduced lipid oxidation under accelerated storage conditions, indicating its potential as a natural approach to improve oxidative stability and maintain quality parameters of pine nuts.