Optimized microwave pretreatment and ultrasound-assisted deep eutectic solvent extraction for efficient valorization of Citrus paradisi peel bioactives

Abstract

Abstract This study presents a sustainable approach for recovering bioactive compounds from grapefruit ( Citrus paradisi ) peel using a glycerol–glucose-based deep eutectic solvent as a green extraction medium. Spectroscopic characterization confirmed the formation of stable hydrogen-bonded eutectic networks within the solvent systems. Response surface methodology (RSM) based on a Box–Behnken design was employed to systematically investigate the effects of solvent concentration, solvent-to-solid ratio, and extraction time on phytochemical recovery and antioxidant activity. The extraction process was successfully optimized using RSM, with the optimum conditions identified as 74% water-content Aq-DES, 20 min sonication time, and a solvent-to-solid ratio of 35 mL/g. Under these conditions, the optimized extract exhibited total phenolic and flavonoid contents of 86.33 mg gallic acid equivalents (GAE)/g DW and 5.93 mg rutin equivalents (RE)/g DW, respectively, along with strong antioxidant activities, achieving 87.40% scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and 55.09% scavenging of 2,2′-azino-bis(3-ethylbenzothiazoline−6-sulfonic acid) (ABTS) radicals. The developed RSM models demonstrated strong statistical adequacy and reliable predictive performance. Furthermore, the optimized extracts exhibited notable antibacterial activity against Staphylococcus aureus and Salmonella typhi , producing inhibition zones of 21 and 20 mm, respectively, in the undiluted extract. Overall, the findings demonstrate that glycerol–glucose deep eutectic solvent based microwave pretreated ultrasound-assisted extraction provides an efficient, rapid, and environmental friendly strategy for valorizing grapefruit peel waste into high-value antioxidant and antimicrobial products, with promising potential for applications in the food and pharmaceutical industries.