Effects of Natural and Artificial Drying Methods on the Nutritional Value and Functional Properties of Vegetables Grown in Sudan

Abstract

Background and Objective: The processing technique of drying or dehydration is probably the oldest method practiced by human kind for food preservation. The removal of water from food during this process has been found to prevent microbial growth and enzymatic and nonenzymatic reactions and therefore, the dried food materials can be easily stored under normal ambient temperature. The purpose of this research was to study the effects of natural and artificial drying methods on the nutritional value and functional properties of some locally grown vegetables in Sudan, namely, potatoes (Solanum tuberosum), tomatoes (Lycopersicon esculentum) and carrots (Daucus carota). Materials and Methods: The previously mentioned fresh vegetables were divided into two different groups. The first group of fresh vegetable samples was dried under natural convection air flow at room temperature (33-35°C) for three days, while the second group was put in a cabinet dryer for six hours at 75°C. Then, the vegetable samples before and after drying were investigated for their chemical composition and physico-chemical characteristics. Results: The natural drying method used in this study was found to decrease the moisture contents in fresh potatoes, tomatoes and carrots from 79.87, 94.17 and 88.27 to 7.12, 5.45 and 4.62%, respectively. Meanwhile, the artificial drying method decreased their moisture contents to 6.23, 5.04 and 3.43%, respectively. In general, the concentrations of dry matter and protein in vegetable raw materials that were dried with the artificial method were found to be higher than those of the same vegetables that were dried naturally at room temperature. In contrast, the naturally dried vegetables recorded higher percentages of reducing sugars in potatoes (0.32%), tomatoes (20.80%) and carrots (5.78%) on a wet basis. On the other hand, the vegetable samples that were dried by the cabinet dryer were found to have better functional properties in comparison with the naturally dried samples. All of the artificially dried vegetable samples were found to have higher bulk density (0.909, 0.619 and 0.781 g mL^–1) and water solubility (11.097, 13.484 and 19.071 g/100 g) values along with lower rehydration (24.53, 15.99 and 13.18%) and water absorption index (1.64, 3.32 and 5.56 g gel g^–1 DM) values in potatoes, tomatoes and carrots, respectively. Conclusion: This study found that the fresh potatoes, tomatoes and carrots could be easily dried naturally under convection air flow or by using a cabinet dryer at home or at industrial levels for the production of dried vegetable products with high nutritional values and acceptable functional properties.