Ultrasound-assisted extraction of pectin from Citrus limetta peels: Optimization, characterization, and its comparison with commercial pectin

With an aim of complete reuse and recycling of citrus by-products, this study investigated the pectin extraction from Citrus limetta peels employing the ultrasound-assisted extraction (UAE) technique. The extraction process was optimized using Box-Behnken Design and a maximum pectin yield of 28.82% was obtained under the optimal conditions of 40 °C temperature, 37% amplitude, and 1.9 pH after 24 min sonication time, which was validated by the experimental results (28.73 ± 0.12%). The pectin extracted under optimum conditions was characterized for its physicochemical, antioxidant, functional, structural, thermal, apparent viscosity and was compared with commercial pectin. Both commercial (CP) and ultrasound extracted pectin (UAEP) were highly esterified with degree of esterification of 59.71 ± 0.12% and 55.29 ± 0.51%, respectively and methoxyl content of 7.06 ± 0.10% and 7.19 ± 0.15%, respectively. In addition, UAEP exhibited high antioxidant and similar water/oil holding capacities and emulsifying properties as compared to CP. XRD patterns of pectin samples suggested high crystallinity of UAEP than CP, SEM exhibited smoother surface of UAEP as compared to CP, and FT-IR spectra proved the presence of GalA units in both samples. The thermal analysis by DSC and TGA showed high thermal stability of UAEP than CP. A detailed comparative study on properties of ultrasound extracted pectin from C. limetta peels and commercial pectin confirmed that the extracted pectin was of good quality as can be potentially utilized as food ingredient in food sector.