Microwave drying of corn seeds: Effect of Temperature on Drying Time, Energy Consuption and Germination Rate

Abstract

Previous studies on the microwave drying of corn seeds have shown that the process parameters employed play a very important role in determining the properties and quality of this grain (Gürsoy et al, 2013). Among these parameters, the drying temperature has a fundamental role (Nair et al, 2011). The main objective of this work is to evaluate the effect of temperature on drying time, energy consumption and germination rate of corn seeds after they have been dried with microwave energy. To achieve the proposed objective, the drying process of these seeds was carried out in a rotating turntable domestic microwave oven (LACOR Model 69330), with a capacity of 30 liters and a total output power of 900 W, fitted with a PID temperature controller Eurotherm 3216 L. In this oven, 100 g of corn seeds, with an initial humidity of approximately 20%, was heated up to 3 drying temperatures (35, 55 and 75 °C). The seeds were weighed every 30 minutes and the drying process was considered completed when a humidity of 12 % was obtained. For each drying temperature studied, the experiments were carried out in duplicate. In each experiment, the electrical energy consumption was measured using a FLUKE 1735 energy analyzer. A sample of the dried seeds was subject to germination tests in a petri dish using filter paper and a volume of distillate water of 20mL to achieve sufficient humidity for them to sprout. Table 1 shows the average values obtained from the variables evaluated for each drying temperature.   Table 1. Results of the microwave drying experiments of the corn seeds at different temperatures and their germination tests. Drying temperature (ºC) Drying time to reach a humidity of 12% (min) Energy consumption (Wh) Germination rate (%) 35 345,0 880,3 90,0 55 118,5 330,0 81,3 75 73,5 183,9 12,0   As can be seen in Table 1, the temperature exerts a significant influence on the drying process and the germination rate of the corn seeds. An increase in the drying temperature causes a simultaneous decrease in drying time (∿ 78%) and in energy consumption (∿ 79%), which are very positive aspects. However, there is also an unacceptable decrease (∿ 87%) in the germination rate of the corn seeds.   References Gürsoy, S., Choudhary, R., Watson, D.G. Int. J Agric. & Biol. Eng., 2013, 6, 1, 90–99.Nair, G.R., Li, Z., Gariepy, Y., Raghavan, V. Drying Technology, 2011, 29, 11, 1291-1296.