Comparative analysis of microwave and ultrasound extraction techniques for valorizing almond milk byproducts

This study explores the sustainable valorization of almond okara, a nutrient-rich by-product of almond milk production, through advanced green extraction technologies. Although conventional solid-liquid extraction (CSLE) has previously shown the potential of almond okara due to its high content of bioactive compounds, this research focuses on assessing and optimizing ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) to enhance the recovery of polyphenols and related phytochemicals. While UAE demonstrated significantly higher polyphenol yields than CSLE under comparable conditions, indicating superior extraction efficiency, MAE ultimately outperformed both methods, emerging as the most effective technique overall. Systematic optimization of MAE parameters, such as microwave power, extraction time, and solid-to-solvent ratio, resulted in significantly increased recoveries of total polyphenols (800 mg GAE/100 g dry okara), phenolic acids (770 mg CAE/100 g), tannins (670 mg GAE/100 g), and flavonoids (480 mg CE/100 g). Additionally, antioxidant activity peaked at 1280 mg AAE/100 g under optimal MAE conditions (400 W, 1:50 g/mL, 90 min). Moreover, UHPLC-UV analysis revealed a more diverse and abundant polyphenol profile in MAE extracts. These results highlight MAE as a powerful, efficient, and eco-friendly extraction method, endorsing the sustainable use of almond okara in functional foods, nutraceuticals, and cosmetics, aligned with green chemistry principles and the circular economy. • Compared MAE, UAE, and CSLE for extracting bioactives from almond okara. •MAE showed highest yields of polyphenols, tannins, flavonoids, and phenolic acids. •Optimized MAE parameters to enhance extraction efficiency and antioxidant yield. •UHPLC-UV-MS confirmed superior catechin and epicatechin in MAE extracts. •Findings support okara valorization via green, efficient extraction approaches.