Development of a radio frequency pasteurisation process for Acidovorax citrulli control in watermelon seeds

It is challenging to control pathogens in contaminated seeds without damaging seed vigour by using heat treatments. In this study, a treatment process for pasteurising watermelon seeds was developed using the emerging technology of radio frequency (RF) energy. To reduce the temperature difference between the layers, the polypropylene frame (covering 40% of the sample surface area) with the inside medium of air was added to the centre of the first layer. The length, width, height, and thickness of the polypropylene frame were 134, 94, 17, and 2 mm, respectively. The optimised process involved that seeds with stacked four layers were heated by RF energy for 6.5 min followed by holding in the hot air oven at 64.5 ± 0.5 °C for 50 min. After that, samples with separated four layers were dried in the hot air oven for 30 min followed by cooling for 6 min in forced ambient air (6.0 ± 0.1 m s⁻¹). This treatment produced in excess of a 4-log reductions of Acidovorax citrulli while differences in germination rate, germination energy, vigour index, germination index, and leachate electrical conductivity were insignificant (P > 0.05) between control and the optimised process treated seeds. Meanwhile, the average moisture content of seeds was reduced to 8.05% wet basis after pasteurising. These findings can further be expanded to develop potential industrial applications of RF pasteurisation for maintaining quality in agriculture products.