An innovative process for extraction of fruit juice using microwave heating

The objectives of this study were to evaluate the possibility of extracting juice from selected fruits (plum, apricot, grape) using microwaves and gravity, and to characterize this process. The process uses microwaves for hydrodiffusion of juice from the inside to the exterior of fruit material and earth gravity to collect the fruit juice outside the microwave cavity. The extraction kinetics were fitted by a descriptive model and the corresponding parameters were correlated to the operating conditions. Best yields were obtained at optimized microwave power and from frozen fruits respectively 480 ml kg(-1) for plums, 620 ml kg(-1) for grapes, and 550 ml kg(-1) for apricots. The obtained juices were brightly colored, as this method allows inactivation of endogenous enzymes such as polyphenol oxidase prior to fruit grinding. They were perceived as fairly acidic and for plum and grape presented detectable astringency. The present apparatus permitted fast and efficient extraction even from "hard to press" fruits such as plums and apricots, yielding an original, brightly coloured product. (C) 2010 Elsevier Ltd. All rights reserved.