Optimizing conditions for the recovery of lignans from sesame cake using three green extraction methods: Microwave-, ultrasound- and accelerated-assisted solvent extraction

Lignans, a group of polyphenolic low molecular weight bioactive compounds with health benefits, are major constituents of sesame cake (SC), a by-product derived from sesame oil processing. The utilization of this by-product in the food or nutraceutical industries could explore its valorization route in compliance with sustainability and circular economy principles. This study aimed to investigate the impact of different environmental-friendly processing approaches such as ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) for lignans extraction from SC using central composite design (CCD) with response surface methodology (RSM). Sesaminol triglucoside (SETRI) and sesaminol diglucoside (SEDI) were identified and quantified as the major lignan glucosides in SC. Ethanol/water mixture was selected as 'green' solvent for all extraction methods. The influence of ethanol concentration (X-1), extraction time (X-2), temperature (X-3) and solid-to-solvent (SS) ratio or solid weight (X-4) on extraction yield (EY), SETRI and SEDI contents for each technique was examined. The developed models exhibited a high degree of desirability (> 0.72) with determined optimal levels of extraction parameters as follows: X-1 = 71%, X-2 = 10 min, X-3 = 50 degrees C, X-4 = 1.50 g/20 mL for UAE; X-1 = 80%, X-2 = 5 min, X-3 = 50 degrees C, X-4 = 0.85 g/20 mL for MAE; X-1 = 80%, X-2 = 20 min, X-3 = 65 degrees C, X-4 = 2 g for ASE. Under these optimal conditions, the experimental values for EY, SETRI and SEDI contents in SC extracts were: 8.28%, 105.98 mg/g and 16.93 mg/g, respectively for UAE; 8.75%, 105.41 mg/g and 18.76 mg/g, respectively for MAE; 9.34%, 108.00 mg/g and 18.34 mg/g, respectively for ASE. The ANOVA analysis from the RSM were fitted with quadratic models yielding acceptable R-2 (> 0.87), adjusted R-2 (> 0.77), predicted R-2 (> 0.74), and nonsignificant lack-of-fit (p > 0.05) values. Ethanol concentration and solid-to-solvent ratio were the most influencing factors affecting lignans extraction. Although ASE was found as the most suitable method for extracting lignans from SC, from an industrial viewpoint, UAE could be a more affordable technique due to advances in ultrasonic processing devices for large scale applications.