Concentrating Fruit Juices by Reverse Osmosis

Abstract

The difference between reverse osmosis and ultrafiltration lies principally in the retention characteristics of the membranes. With respect to food processing, ultrafiltration membranes are able to retain protein-sized molecules, whereas reverse osmosis membranes retain lower molecular weight solutes such as sodium chloride or sucrose. In order to concentrate fruit juice, it is necessary to retain sugars, e.g., disaccharides such as sucrose (molecular weight 342, typically present in fruit juices as 5% of the total weight), and monosaccharides such as glucose and fructose (MW 180, also present in fruit juices at about 5% total weight). It is also necessary to retain organic acids such as citric acid (MW 192) or malic acid (134), typically present in fruit juices at the 1 to 2% level, and various salts present at less than half a percent. In addition, it is desirable to retain trace amounts of low molecular weight (<150) aroma compounds such as alcohols, esters, aldehydes, etc.; typically there might be 100 such compounds in a fruit juice with a total concentration of less than 400 parts per million.