Yield and structural composition of pomelo peel pectins extracted under acidic and alkaline conditions

Extraction of pectin from pomelo peel was performed using water, acid and alkaline solutions with a microwave power of 1100 W for 2 min, and yield and structural/chemical characteristics of the extracted pectins were investigated. Extraction of pectin with water gave the lowest yield (6.5%, dry weight basis). The water-extracted pectin contained the highest amount of neutral sugar (29.5%), while equivalent molecular weight (MWeq) and degree of methylation (DM) were 43 kDa and 29.7%, respectively. Extraction of pectin with HCl solutions at concentrations of 25, 50, 100 and 200 mM resulted in a significant increase of pectin yields (12.1–20.5%) and pectins with high amount of galacturonic acid (83.3–85.6%). The MWeq and DM of the acid-extracted pectins ranged from 171 to 368 kDa and 53.9–82.5%, respectively. Compared to the acid, extraction with NaOH solutions at the same concentrations provided higher yields (13.9–24.2%), smaller size (142–187 kDa) and lower DM (<1.7%) pectins, while amount of galacturonic acid was comparable. The highest yield of extraction was found at a concentration of 50 mM for both HCl and NaOH solutions. Extraction of pomelo peel with 50 mM NaOH solution by reduction of the microwave power to 550 W and extending the extraction time to 15 min resulted in an increase of pectin yield (29.2%) and pectin with smaller size (76 kDa).