Comparison Of Hot Air Drying Versus Combined Radio Frequency & Hot Air Drying Of Corn Seed

Corn seeds were dried by using combined radio frequency(RF)and hot air drying during which parallel electrodes RF heating system taken as the main source of heat and hot air assisted to improve the cross-ventilation coefficient.Drying characteristics and seeds quality were investigated at different RF heating rates(electrode gap of 140,150 and 160mm)and different initial moisture contents(IMC)of corn seeds(29.21%,25.80%and 23.35%).In order to better illustrate the feasibility of application of combined RF and hot air drying on corn seeds,tempering-intermittent hot air drying of corn seeds was studied and its drying dynamics and seeds quality were analyzed.Main conclusions are as following.(1)Hot air drying rate could be improved after tempering,and drying time decreased with shortened tempering intervals and elevated air temperature.Cracking rate increased,germination rate decreased and the comprehensive quality score was reduced with extended tempering intervals and elevated air temperature,while germination percentage and dehydrogenase activity(DHA)with a tempering interval of 10 min were worse than those of 20 min,indicating that shortened tempering intervals may contribute a lot in accelerating drying rate while harmful for protecting the embryo of corn seeds.In consideration of overall quality indexes and drying rate,the optimal drying performance was obtained at drying temperature of 40℃ and tempering intervals of 20 min.(2)Combined RF and hot air drying could increase the drying rate of corn seeds obviously.At fixed IMC of corn seeds,the drying rate increased but comprehensive quality score decreased with accelerated RF heating rate.At fixed electrode gap,a higher IMC of corn seeds would be beneficial for the comprehensive quality.A lower IMC would contribute to a higher drying rate at the early drying stage,but due to the more severe destroy to the microstructure by RF heating which ultimately hindered the moisture migration,a lower drying rate was obtained at the final drying stage.The optimal drying performance was obtained at IMC of 29.21%and electrode gap of 160mm in consideration of comprehensive quality and drying rate.(3)With a capacity of three times that of hot air drying,combined RF and hot air drying rate was improved obviously,drying time of which accounting for only one third that of hot air drying.Quality indexes related to stress damage and seed vigor after combined RF and hot air drying were better than those of hot air drying,while nutrient contents,which were closely related to temperature,were poorer than those of hot air drying due to its higher inner temperature.A higher DHA while lower germination rate was obtained for samples by combined RF and hot air drying as compared with those by hot air drying,the reason might be because combined RF and hot air drying urged corn seeds dormancy which was proved by germination performance after dormancy breaking experiments.