Ultrasound-assisted extraction of pectin from citrus peel and its gelling properties

Abstract:

Pectin is a high-value hydrocolloid extracted commercially from citrus peel using hot acid hydrolysis, a process that consumes large volumes of mineral acid and generates effluent. Ultrasound-Assisted Extraction (UAE) may offer a cleaner alternative by disrupting cell walls through acoustic cavitation, improving yield while reducing acid use and processing time. This research compared UAE at 40 kHz for 20, 40, and 60 minutes with conventional acid extraction and enzyme-assisted extraction for pectin yield, Degree of Esterification (DE), galacturonic acid content, molecular weight, and gel strength from Mexican lime (Citrus aurantifolia Swingle) peel collected in Monterrey, Nuevo León, during March-August 2023. UAE at 40 minutes gave the highest yield (23.4 ± 1.6%), significantly above conventional acid extraction (14.2 ± 1.8%) and enzyme-assisted extraction (16.1 ± 1.9%). The UAE-40 pectin had a DE of 68.3%, galacturonic acid content of 72.6%, and formed gels with a rupture strength of 186.4 g comparable to commercial citrus pectin. Extending UAE to 60 minutes lowered yield slightly (21.8%) and reduced gel strength by 14%, likely due to partial depolymerisation. These findings position 40-minute UAE as an efficient, reduced-acid method for recovering high-methoxyl pectin from Mexican lime peel.