Preservation of fruits and vegetables using solar drier: a comparative study of natural and solar drying, III; chemical analysis and sensory evaluation data of the dried samples (grapes, figs, tomatoes and onions)

Abstract

In spite of the detailed studies which have proved the superiority of the quality attributes for solar dried fruits and vegetable over that of naturally dried [1–5], we have chosen in our investigation some parameters to be used as a guide to test the changes occurring for some nutrients like sugars. Another indicator has been used which was the percent ash to test the extent of contamination with sand from the surroundings. Consequently we can compare the properties and qualities of natural and solar dried fruits and vegetables to arrive at the preferred drying method. From the project results obtained for the dried fruits and vegetables using natural and solar drying, we can conclude that the mixed and indirect modes of drying were more effective than natural drying, since the final moisture contents for grapes were 12.5, 20.05 and 68.45%, respectively. The figs moisture was reduced to 23.5% using mixed mode drying and 46.9% in case of natural drying for the same period. No significant difference was noted in the case of tomatoes, while there was little significant difference between the two drying methods for onions, but the drying was higher for slices than lobes. There was a highly significant difference for percent ash between the solar dried grapes and naturally dried samples (2.95 and 12.1%, respectively). In sugar determination, the solar drying was found to alter the sugars more than natural drying. This is not surprising because the temperature inside the drying chamber was far higher (80.5°C). This study included also the sensory evaluation of the quality attributes (color, flavor and texture) of the dried samples. The fruits were presented to untrained panelists (consisting of engineers, employees, Ph.D. holders and workers from the Center for Solar Studies) who were asked to evaluate the fruits by scoring the attributes with grades ranged from 2 to 12, where 2=weakly accepted and 12=excellent quality. The data represent the relative frequency distribution ×100 (for color, flavor and texture) reported by the panelists using a hedonic scale from (1–12). Lower scores indicate poor quality (unacceptable) while higher scores indicate much better quality or highly acceptable. These data clearly indicate that the solar drying technique is much better from the sensory quality viewpoint when compared with the natural sun drying technique. Such conclusions are completely true for all samples except tomatoes, and both direct methods of drying as well as mixed mode approach of solar drying. Since negative findings were reported using the indirect approach.