SUN-DRYING AND DRYER: COMPARISON OF PRODUCT QUALITY

Tomatoes cut into two parts, added with salt and dried (desiccated) are an important element of the food tradition in Sicily. The drying process of tomatoes in Sicily is still carried out with a sundrying process, with an empiric method. The final product obtained through this process has a general high quality which it is not homogeneous. Today the product on the market, because of its increased costs of production, is imported from other countries of the Mediterranean basin, and it is produced in driers with too high flows of hot air (90-110 ºC), in order to reduce the kinetics of desiccation (around 3-5 h) and the plant hold-up. The final product has low quality because it does not correspond to the sensorial characteristics mentioned before. No further studies on the qualitative variations of dried tomatoes submitted to "low" temperatures (< of 75 ºC) have been found. At temperatures lower than 65 ºC, probably the is better from sensorial point of view, but close to the "degrading" reactions listed above, we must consider biochemical reactions and particularly heat-stable enzymatic activities, which could affect the final qualities of the product even if they are expounded in the first phases of the drying process. The drying process nevertheless, even if one of the most ancient techniques of preserving foods, continue to be one of the more complicated unit operations, whose optimization from the system point of view is made of approximations and attempts instead of calculations of a rigorous mathematical model. On the other hand, a quantification of the phenomenon and a model are necessary in order to orientate a dimensioning of the systems and an optimization of the process. This process will have to foresee the study of physical phenomena involved and it will be essential to evaluate the conditions, the costs and the study of the chemical and biological transformations which take place during the process itself. The quality of the dried products depends from these conditions, and as a consequence also their commercial value. Thanks to these brief considerations it is underlined not only the complexity of the process, but also how essential is to test the drying in a pilot plant, directly on the raw materials which has to be used in factories, to search for the optimal processing conditions and to obtain a useful model that can be used. The influence of different drying conditions was checked with different parameters. In particular, there was a significant difference in the antioxidant activity measured in the sun-drying tomato and in tomato dried with pilot plant dryer.