Effects of blanching and calcium infiltration on PPO activity, texture, microstructure and kinetics of osmotic dehydration of apple tissue

HTST blanching of apple pieces caused PPO inactivation and sample softening. PPO inactivation was minimal during immersion in water at 40 degrees C, but it increased with temperature after 15 min exposure at 55 to 65 degrees C. Associated softening decreased when adding 0.6% CaCl2 to the blanching medium. Samples blanched at 40 degrees C were softer than those heated at 55 degrees C in calcium solution, thus suggesting PME activation after 15 min at 55 degrees C. Vacuum infiltration of apple pieces caused cellular damage that increased as the applied pressure increased from 59.9 to 9.3 kPa, and was unaffected by the speed of restoration of ambient pressure. Texture improved when using aqueous CaCl2 solutions instead of distilled water, but no positive effect was observed for HTST blanched apples by vacuum infiltration of calcium. As a result of osmotic dehydration (OD) with aqueous sucrose solutions apple pieces lost water and texture and gained sucrose. HTST-blanched apple pieces suffered extensive material losses during OD and had poor final textures. Untreated apples and samples treated with 0.6% CaCl2 at 40 degrees C (Ih) behaved similarly. Samples treated with 0.6% CaCl2 at 55 degrees C (15 min) and vacuum (9.3 kPa) infiltrated with 2% CaCl2 had the largest sucrose gains and best final textures. Improved texture was generally associated with improved maintenance of sample microstructure. (C) 1999 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology. All rights reserved.