Modeling of thin layer drying kinetics of grape juice concentrate and quality assessment of developed grape leather

Abstract

Abstract: Studies on modeling of thin layer drying kinetics of grape juice concentrate were conducted using pilot scale convective dryer.  Experiments were conducted in temperature range of 55-75⁰C and drying bed thickness of 3-7 mm, to attain desired moisture content (14±1% db).  Different thin layer drying models like newton, page, logarithmic, two term, two term exponential and midilli models were fitted to the experimental data of convective dehydration and their adequacy of fit was investigated.  All the samples witnessed falling rate period drying irrespective of the selected temperature and thickness.  The effective moisture diffusivity and activation energy were found in range of 7.18-2.56 m²/sec and 26.07-21.59 kJ/mole respectively for 3-7 mm drying bed thickness.  Among the various models investigated, two term exponential model was found to be best fitted model for depicting the drying kinetics of grape juice concentrate.  The quality properties such as total sugars, non enzymatic browning (NEB), protein, titrable acidity, texture (cutting force), color change, water activity and overall acceptability of dried grape leather were determined and data were analyzed as per ANOVA.  The grape leather developed at 55⁰C drying temperature witnessed maximum acceptability irrespective of the drying bed thickness.

Keywords: convective drying, drying kinetics, drying models, grapes, quality parameters