Drying Tomatoes in a Small Tray Dryer

Abstract

Drying tomatoes with high initial moisture content have advantages such as: maintenance of mineral constituents, inhibition of the action of microorganisms, reduction of the cost of transportation, handling, and storage and is an alternative to the problems of waste disposal and pollution. Moreover, dried products, besides the more economical and affordable package, is an option for light and quick meals. Small and low cost tray dryers are hard to find in the Brazilian market. Producing your own dehydrated food is a practice used in many countries for domestic consumption, as a gift, for small-scale enterprises, because some people appreciate handmade products that are related to a healthier product, without additives. The present study aimed to dry tomatoes and evaluates the characteristics such as: loss of final mass, drying time, and cost of drying in a portable low cost tray dryer. The dryer was built in plastic body and trays. Two heating conical resistors with 600 W each, and a 26W-fan were used. Approximately 1.4 kg of tomatoes was used in this test. They were previously sliced, washed, and the endocarp and seeds were removed. The weight loss during the process was obtained ​​by successive weightings of tomatoes in the trays each hour. The final drying was determined when the tomatoes were around 25% of moisture content. The initial moisture content of the tomatoes was determined by oven drying using 10 g of chopped tomatoes, dried at 95°C for 24h. To evaluate the drying cost the yield of dried tomatoes, the losses during the preparation of the fresh tomatoes slices, the drying time, and the rate of product ready for the drying period were determined. The energy cost was R$ 4,72, plus R$ 0,30 of osmotic solution, additional R$ 7.80/kg of tomatoes (off season). The final cost was R$ 12,82 (U$S 5.35) to process 1 kg of fresh tomatoes. During the season, one can buy tomatoes at R$ 1,00/kg, which reduces the cost to R$ 6.02/kg (U$S 2.50). Whereas the process reduces weight by 10.83 times, the pound of dried tomatoes would cost R$ 65,20 (U$S 27.15) in crop condition. As this portable dryer holds 2 kg of tomatoes by drying, the cost could be reduced to R$ 3.66/kg (U$S 1.55) considering fresh tomatoes or R$ 39,60/kg (U$S 16.50) dried tomatoes. The dryer presented the ideal medium parameters for drying fruits (51.6°C and 1.2 m/s) in a drying process of 8 hours. The cost per hour of drying in this experiment, due to be in between tomato crop season was considered high. However, there are conditions to reduce this cost at the harvest time and by increasing the density of tomatoes in the dryer trays.