Mass and color kinetics of foamed and non foamed grape concentrate during convective drying process: A comparative study

Experiments were conducted on drying of grape concentrate to form leather by using convective and foam mat drying process. Mass and color degradation kinetics of both non foamed and foamed grape concentrate were studied at selected temperatures (55, 65 and 75°C) at constant drying bed thickness of 5 mm. The results indicated that the drying took place in falling rate period where as higher drying rate was observed for foamed grape concentrate when compared with non foamed grape concentrate. The Ea values for foamed and non foamed grape concentrate for 5 mm was 36.35 and 29.10 kJ/mole, respectively. Two term exponential model was found to be the best fitted for drying data of foamed and non foamed grape concentrate. In order to explain the color degradation kinetics for various color parameters, the zero order was adjudged as the best fitted models  for ‘a’, ΔE, ‘hue angle’ and first order model for ‘L’, ‘b’ ‘Chroma’. Hue and b values, based on activation energy, were the most sensitive measures of color change for the temperature range of 55 to 75°C.   Key words: Grapes, thermal degradation kinetics, color degradation kinetics.