Comparative study of impingement and fixed-bed drying: Kinetics and quality aspects of pregerminated GI rice

The objective of this research was to investigate an effect of two different heat sources drying on drying kinetics and physical qualities of pre-germinated geographical indication (GI) Sangyod rice variety. The drying with hot air (HA) convection and with impingement (IP) was used for moisture removal of pre-germinated Sangyod paddy samples with high γ-amino butyric acid (GABA) content. The fresh soaked GABA rice with initial moisture content ranging of 47-51% dry-basis and dried until the final moisture content reached to 20-25 %dry-basis. The drying strategies among temperature ranging of 60-100°C were provided by tray drying and impingement drying. In addition, effect of drying strategies on drying kinetics and quality of dried rice samples. For determination of drying kinetics, the results concluded that the simulated values using the Page and Logarithmic model had a good agreement with the experimental values for air impingement drying and hot air drying, respectively. The effective diffusion coefficient (D_eff) relatively increased with increase of the drying temperature. The results showed that drying time of impingement was relatively shorter than those of hot air drying. For qualities evaluation, the conclusion stated that due to starch gelatinization during drying with high temperature and tempering stage, the HRY of dried GABA Sangyod rice was significantly higher than the control rice dried with ambient air ventilation. In addition, the brightness (L*), redness (a*) and yellowness (b*) value using both HA and IP drying techniques was slightly higher than control rice. For sensory evaluation, the total dried GABA Sangyod rice was acceptable.