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 1100W 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 200mM 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 50mM for both HCl and NaOH solutions. Extraction of pomelo peel with 50mM NaOH solution by reduction of the microwave power to 550W and extending the extraction time to 15 min resulted in an increase of pectin yield (29.2%) and pectin with smaller size (76 kDa).