Influence of air drying temperature on kinetics, physicochemical properties, total phenolic content and ascorbic acid of pears

This study was conducted to evaluate quality and structural changes in parallelepipedic pieces of pears during convective drying at different air temperatures (30-70 degrees C). Submitted to atmospheric O-2 conditions, ascorbic acid deterioration demonstrated first-order kinetic behaviour and was found to depend on air temperature and pear moisture content. Loss of ascorbic acid content increased with increasing air temperature. Possible explanation could be the irreversible oxidative reaction occurring during drying. Phenol content degradation fitted a pseudo first-order reaction and was significantly influenced by air temperature. Variations in bulk density, shrinkage and porosity essentially depended on changes in moisture content. Porosity exhibited a nonlinear variation with respect to moisture content. Volume change showed, as expected, a linear variation with moisture content. Drying temperature significantly induced the increase of a* and b* colorimetric parameters due to non-enzymatic browning reaction, which turned the samples more reddish and yellow when the temperature rose. (C) 2011 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.