Structural changes and mass transfer during glucose infusion of apples as affected by blanching and process variables

The effect of process variables and blanching on the rate of dewatering of apple slices through immersion in glucose solutions was analyzed. The adequ acy of the Hawkes and Flink's and Peleg's models for fitting the rate data was evaluated as well as the structural changes produced in the tissue subj ected to osmotic process. High concentration values (33-42% (w/w)) of the s oaking solution favored significantly water loss (WL) but only slightly aff ected solid gain (SG). Increasing system temperature over the range 20-50 d egrees C generally provided an increase in WL and in SG. The increase in th ickness decreased significantly both mass transfer rates. The use of sucros e instead of glucose lead to a greater SG while blanched samples showed hig her rates of WL and SG. Microscopic studies revealed that, when applying sh ort treatments, cells appeared slightly shrinked and cells walls folded. Af ter long treatments, although an extensive plasmolysis of cellular membrane s was observed, cells looked very similar to the control. Thermal treatment produced the rupture of cellular membranes, modifying in a great extension the initial resistance of structure to WL and SG. Somehow, original arrang ements of cells were rather well maintained and cells looked more rounded.