A Thesis Submitted to Sudan University of Science and Technology in Partial Fulfillment for the Requirements of Master Degree in Food Science and Technology

Abstract

The main goal of this research was to study the suitability of natural and artificial cabinet drying methods for production of ready-to-serve dried vegetable soup with high nutritional value and functional properties from locally grown vegetables in Sudan. Therefore, the chemical and the physical characteristics of fresh potatoes, tomatoes and carrots before and after natural and artificial cabinet drying were investigated. The results indicated that the natural drying method used in this study was found to decrease the moisture content in fresh potatoes, tomatoes and carrots from 79.87%, 94.17% and 88.27% to about 7.12%,5.45% and 4.62% in the dried vegetables, respectively. Whereas, the artificial drying by using the cabinet dryer decreased their moisture contents to about 6.23%, 5.04% and 3.43%, respectively. In general, the vegetables raw materials that dried with the cabinet dryer at 75°C were found more better than the same samples which are dried naturally at room temperature, with respect to their dry matter and protein contents, but the naturally dried vegetables recorded the higher values of reducing sugars which were 0.32%, 20.80% and 5.78% in potatoes, tomatoes and carrots, respectively, on wet basis. Also, the dried vegetables raw materials produced by the cabinet dryer were found with higher functional properties in comparison with those of the naturally dried samples. All the artificially dried vegetable samples had the higher values of bulk density (0.909,0.619 and 0.781 g/ml), water solubility (11.097,13.484 and 19.071g/100g) and the lower values of rehydration (24.53, 15.99 and 13.18%) and water absorption index (1.64, 3.32 and 5.56 g.gel/gDM), for potatoes, tomatoes and carrots, respectively. However, after formulation and preparation of the ready –to-serve dried mixed vegetable soups, the products were also, evaluated for their nutritional values, physical and organoleptic properties. The results showed the naturally dried vegetables soup to have the higher levels of moisture (11.90), total carbohydrates (62.21%), total sugars (8.33%) and reducing sugars (4.0%), while, the dried mixed vegetable soup which produced by the cabinet dryer had the higher levels of protein (14.0%), fibre (12.76%) and non-reducing sugars (4.50%). No marked differences were existed between the two soups in regard to their minerals and vitamin-C contents. Also, both of the products appeared to be of good functional properties, but the dried vegetable soup which produced by the cabinet dryer recorded the higher values of bulk density (0.77g/ml), water solubility (5.78%) and the lower value of water absorption index (2.63 g.gel/gD). Finally, the sensory evaluations for the two products revealed insignificant differences (P<0.05) between the naturally and artificially produced dried vegetable soups with respect to their taste, consistency and overall – quality, but, the colour of the latter soup was found to be better than that of the former soup which had the better flavour in comparison with the artificially produced dried vegetables soup.