Effects of Osmotic Pre-Drying Treatments, Duration and Drying Temperature on Some Nutritional Values of Tomato Fruit

Abstract

Tomato (Lycopersiconesculentum) is a highly perishable crop widely grown in most parts of the tropical region of the world. It is rich in vitamin A, C and E, soluble solids, ash and protein and also a good source of lycopene. Drying is one of the most widely used methods of preserving tomato for a longer period. This research was carried out to study the effect that osmotic pre-drying treatment has on the nutritional qualities of the processed tomato product. Fresh Roma tomato samples were sliced to a thickness of 5 mm and the seeds were removed. Weight of 300 g was measured for each of the three replicates and immersed in a hypertonic solution of sucrose of different concentrations 40 and 60 OBx each held for osmotic duration of 1 and 2 hr, drained for 10 min and then dried at 50, 60, and 70 OC in a mechanical dryer. Control samples were also weighed 300 g per replicate and dried at 50, 60, and 70 OC without pre- drying treatment. Moisture loss of each sample was monitored and recorded hourly until the product has reached the desired final moisture content (≤7%).Colour and nutritional content which include vitamin C, soluble solids, ash and crude protein were analysed for each sample. Statistical analysis was carried out to know the level of significance difference of individual treatment and their interaction at p≤0.05 using ANOVA, DNMRT and Independent samples T-Test. The results show that control samples have the highest content of vitamin C, ash and protein contents with average values of 37.97 mg/100 g, 4.941% and 20.39% respectively. Samples pre-treated with 60 OBxconcentrations have the highest value of soluble solids with an average value of 30.78% than those with 40 OBxconcentration and the control having 30.54% and 21.94% respectively. The best colour grade 3.5 was obtained for samples pre-treated with 60 OBxconcentrations at 2 hr osmotic duration and dried at 50°C. Therefore it was concluded that drying temperature of 50 OC, pre- drying concentration of 60 OBx and 2 hr osmotic duration have great influence on the colour of dried tomato fruit which is one of the most visible quality attributes used by consumers for accepting or rejecting processed vegetables.