The effect of the method of drying on the colour of dehydrated products

We tested the hypothesis that an optimum method of drying fruit could be de signed. The effect of the method used for drying on colour of apple, banana , potato and carrot was investigated for five different methods of drying: conventional, vacuum, microwave, freeze and osmotic drying. Colour characte ristics were studied by measuring lightness (L), redness (a) and yellowness (b) using a Hunter Lab chromatometer. The method used to dry the material was found to significantly affect the three colour parameters. The changes in redness (a) and yellowness (b) were found to follow a first order kineti c model. Air-, vacuum- and microwave-dried materials caused extensive brown ing in the fruits and vegetables, this was manifested by a significant drop of the L parameter and an increase of the a and b parameters. Osmotically pretreated samples did not brown as much as the untreated samples and the v alue for lightness (L) decreased only slightly while a and b increased slig htly. Freeze drying seems to prevent colour changes, resulting in products with improved colour characteristics.