Ultrasound-assisted extraction (UAE) and characterization of citrus peel pectin: Comparison between pummelo (Citrus grandis L. Osbeck) and sweet lime (Citrus limetta Risso)

Abstract

Citrus peels are a commercial source for pectin extraction which is widely used in the food industry as a hydrocolloid, fat mimetic, and gelling agent. Acid extraction is an established method for extraction; however, environmental and consumer concerns are pushing processors to explore sustainable and green methods to provide clean solutions. The present study was designed to optimize pectin extraction from pummelo and sweet lime peels using ultrasound-assisted extraction (UAE). The optimized conditions of UAE obtained through response surface methodology (RSM) were: sonication time = 9.38 min, power = 44.01%, and liquid-solid ratio (L:S) of 46.8:1. These levels resulted in maximum pectin yield (26.35%) and high galacturonic acid content (69.11%; GalA) from pummelo peels as compared to sweet lime peels. The pectin extracted via UAE was food-grade with a low degree of methylation (<50%) and high functional quality. Characterization of pectin through Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and rheology confirmed its similarity to commercial pectin. Pummelo peel pectin demonstrated high biological activity in inhibiting lipid deposition in HepG2 cells and low cytotoxicity in 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay. Overall, based on rheological and functional properties, pummelo peels were found to be superior to sweet lime for commercial pectin extraction. The findings suggest that citrus peel pectin with low degree of esterification (DE<50%) is a valuable ingredient for formulating low glycemic functional foods. Overall UAE seems to be an efficient, economic, and sustainable method for extraction of high-quality pectin.