Abstract:
The purpose of this reserch is to study the effect of fluidization drying technique with superheated steam on the physicochemical properties of Thai Native rice, namely Sung Yod Phatthalung and Nauykaur, for making instant rice product. The drying temperature was set at 170 ˚C at different drying time i.e. 2.5, 3 and 4 min, respectively. The shade dried rice was employed as control sample. The crystallinity testing shows that %V-type crystallinity of both dried rice was increased when the drying time is longer. The result of pasting properties showed that the pasting temperature of both dried rice was significantly increased when compared to the control sample, while peak viscosity, breakdown, final viscosity and setback were lower than those of the control sample. The SEM images depicted that the starch granule of control samples was in normal shape but those of dried samples were changed with the increased drying time in such the ways that the starch granules were partially gelatinized and/or melted. For amylose analysis, the amylose contents of both dried rice were not different from all drying conditions. The EC50 analysis was conducted to investigate the total optimum extraction time for EC50 as well as for phenolic. It was found that optimum extraction time for EC50 and total for phenolic content of Sung Yod Phatthalung rice were the same at 30 min, and for Nauykaur rice were 4 h and 24 h respectively. Effect of boiling time to obtain desied viscosity for both rice were investigated. The result showed that suitable boiling time of Sung Yod Phatthalung was 45 min and it took 55 min for Nauykaur. Rehydration capacity of both instant rice i.e. control and dried samples showed that the control sample had rehydration capacity more than those of dried samples. Moreover, when drying time under superheated steam was longer, this capacity was decreased. As the rehydration capacity of Sung Yod Phatthalung rice was better than Nauykaur. Therefore, Sung Yod Phatthalung in both control and after drying for 2.5 min sample were selected for product development of instant rice. The instant rice product from control and dried Sung Yod Phatthalung rice under superheated steam for 2.5 min can be stored in sealed laminated aluminium bag for more than 2 months.