Comparisons between conventional, microwave- and ultrasound-assisted methods for extraction of pectin from grapefruit

Microwave-assisted Extraction (MAE) and Ultrasound-assisted extraction (UAE) techniques have been employed as complementary methods to extract carbohydrates, polysaccharides and other functional compounds from vegetable sources. In this work, the effect of microwave power and heating time on the yield and quality of extracted pectin from grapefruit was investigated. The highest total amount of pectin yield was found to be 27.81% (w/w) for 6 min of extraction at 900 W. It was observed that yield, the galacturonic acid content (GalA), and degree of esterification (DE) increased with an increase in microwave power and heating time. Besides, the molecular weight decreased with an increase in heating time; however, the effects of power on the molecular weight were dramatically more than heating time. In addition, laboratory studies on the extraction of pectin treated with high-intensity ultrasound were carried out. The effects of temperature and time on quality and quantity of extracted pectin were investigated. The highest yield was for sonication time of 25 min (17.92%) in a constant bath temperature of 70 degrees C. Furthermore, a preliminary ultrasonic heating of grapefruit solution, as a pretreatment for MAE, was found to provide a higher yield. Intermittent sonication gave better results in comparison to the continuous sonication. (C) 2011 Elsevier B.V. All rights reserved.