Mass Transfer in Mixed Solute Osmotic Dehydration of Apple Rings

Abstract

Development and verification of a model for mass transfer in osmotic dehydration of apple rings in mixed solute osmotic media is described. ‘Red Delicious’ apple rings were osmotically dehydrated in sucrose-sodium chloride solutions of 50% total solids-50% water. The sodium chloride concentration was varied at 0, 2.5, 5 and 10% by weight. The temperatures used were 20, 30, and 50° C, and contact times were 0, 1, 2, 3, and 4 h. Moisture loss (Y) was calculated as a fraction of original moisture in apple rings, and the combined solute-gain was expressed as an “equivalent molality”, C, of sucrose and sodium chloride in the liquid phase of apple rings. Both Y and C were modeled as functions of osmotic solution composition, temperature and time of contact. An empirical equation was developed to establish a relationship between the instantaneous mass fractions of sucrose and sodium chloride in apple rings. The above three equations and a fourth equation derived from mass balance on total solids originally present in apple rings, were solved simultaneously to give the ratio of instantaneous to original total mass of apple rings (mq/m0) and instantaneous mass fractions of sucrose (w2), sodium chloride (w1), and water (w4) in the apple rings. Knowing mq/m0, w1, w2, and w4, and from the knowledge of total solids originally present in the material, one can calculate the moisture loss and individual solutes-gain during osmotic contacting.