Vegetables are often overproduced and discarded, generating large amounts of waste (vegetable surpluses that are not used for distribution and marketing). Vegetables have high moisture content and deteriorate over a short period. One possibility to take advantage of these products is through the drying process. The final vegetable quality is highly dependent upon the drying method, as well as their composition and physical properties. The aim of this study was to produce dehydrated vegetables from the Northern Portugal, tomato (Solanum lycopersicum), Turnip (Brassica rapa L.), Courgette (Cucurbita pepo L.) and Cucumber (Cucumis sativus L.), using two different drying methods: convective air-drying (T=60°C; 8h-tomato; 4h-turnip and cucumber, 6h-courgette) and freeze-drying (P/t=0.7Pa/48h).
In this work moisture, ash, protein, carbohydrates and fibre content, water activity (aw), texture and color were determined. The analysis of variance (ANOVA) and the Tukey test were used to determine statistically different values at a significant level of p<0.05. Results showed that carbohydrate content was higher in CD than in FD vegetables ?(except for cucumber). On the contrary, it was found a slight decrease on protein content between fresh and dried vegetables. It was also found that FD scored higher protein content compared to CD, for all vegetables, with the exception of cucumber. Concerning the crude fibre and ash contents there were no differences between CD and FD vegetables.
In conclusion it was demonstrated that both dehydration methods are efficient in relation to the maintenance of nutritional properties, being a useful alternative to extend the vegetables shelf-life and consequently to reduce food waste in the primary sector, fresh vegetable industry. However, the freeze-drying process showed to be a better process because it provides vegetables that are more similar to the fresh product in terms of colour and texture.