Foam-Mat Drying of Tomatoes: Quality Evaluation and Kinetic Modelling

Abstract

Tomato is a seasonal annual crop with high moisture content and perishability. Consequently, it needs to be dried immediately after ripening to be affordable all year round. Therefore, this study was aimed to dry tomato through the use of the foam-mat drying method. Experiments were carried out at three different concentrations of foaming agent; egg albumen (EA): 20, 25 and 30% and whipping time: 6, 9 and 12 mins, to generate foams from tomato puree. Foamed tomato purees were dried at temperatures of 60, 65 and 70 ?C, using hot air oven. Kinetic modelling of the drying process was carried out using different existing models. Quality analyses (colour, vitamins, minerals, carotene and lycopene) of the foam-mat dried tomato were carried out. The corresponding foam expansion and densities for whipping time of 6, 9 and 12 mins are (1.22 – 9.09), (2.44 – 29.87) and (7.32 – 32.47) %; and (0.77 – 0.83), (0.70 – 0.76) and (0.69 – 0.73) g/ cm3, respectively. Foamed tomato at 30% EA concentration had the lowest drying time (570, 540 and, 450) at every drying temperature compared to those with 25 (660, 630 and 450) and 20% (660, 660 and 540) EA concentrations. The average time for foam mat drying of the foamed tomato puree was 630, 620 and 480 mins at 60, 65 and 70 °C respectively. The Wang and Singh model best fitted the experimental data with R2 of 0.9912, 0.9927 and 0.9982 at 60, 65 and 70 ?C and lowest SSE value (0.0029). The L* value ranged from (37.90 – 42.97). The a* value ranged from (24.93 – 29.49). The carotene and lycopene contents of foam-mat dried tomato ranged from (4.9805 – 9.9813) and (5.3737 – 5.4673), respectively. The highest protein content and fat content of the foam mat dried tomato are 29.2880 and 9.0640, respectively. The combination of high foaming agent and low drying temperature gave better colour, carotenoid and lycopene contents for the foam-mat dried tomato. The foam-mat drying technique satisfactorily dried the tomato puree

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