Influence of Air Temperature on the Drying Kinetics and Quality of Tomato Slices

Abstract

The influence of different drying temperatures on the drying kinetics and quality of tomato slices was studied. In particular, the effect of hot air temperature on the lycopene content, non-enzymatic browning, colour and flavour changes during drying at various temperatures in the range of 50-80 o C was investigated. Drying time reduced from 1140 mins to 540 mins as the air temperature increased from 50 to 80 o C. The non-enzymatic browning increased with temperature from 0.485 to 1.40. The lycopene levels of the fresh tomatoes significantly (p=0.05) increased from an initial value of 2.96 mg/100g to 61.23 mg/100g, 59.10 mg/100g, 60.88 mg/100g, and 65.28 mg/100g when dried at 50, 60, 70, and 80 o C respectively. Eleven out of the twelve sensors used in the electronic nose system indicated flavour degradation of all dried samples compared with the fresh tomatoes. The values of the hue angles recorded for the dried tomatoes ranged between 51.81 o and 61.95 o , revealing that the dried tomatoes were yellow hued, thus indicating less browning. The drying characteristics curves were evaluated against the Page, Henderson and Pabis, and the Logarithmic mathematical models but the Page model best described the drying of tomato slices. The effective moisture diffusivity coefficient increased with increasing drying temperature and was found to be 5.13×10 -10 m 2 s -1 , 6.45×10 -10 m 2 s -1 , 8.44×10 -10 m 2 s -1 , and 10.26 ×10 -10 m 2 s -1 at respective hot air temperatures of 50, 60, 70, and 80 o C with activation energy for moisture removal of 22.28 KJ/mol.