Glass transitions and shrinkage during drying and storage of osmosed apple pieces

The relationship between shrinkage during drying and 'glass'-'rubber' transitions of apple tissue was studied. Our results did not indicate that structural collapse of apple pieces can be reduced by diminishing the difference Delta T between drying temperature and glass transition temperature (T-g) of the fruit matrix. Apple shrinkage was not consistently depressed by reducing drying temperature, infusing larger amounts of T-g-depressing agents (sucrose, maltose, lactose) or infusing similar amounts of solutes with higher anhydrous T(g)s. However, sugars added during osmotic dehydration pretreatments help decreasing structural collapse during subsequent air drying, which was reflected by a 20-65% increase in final volume of samples treated with 50% sucrose and maltose solutions as compared to an air-dried, control sample. Dried samples remained in the "rubbery" state after drying and shrunk during subsequent storage. (C) 1999 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology. All rights reserved.