Study On Microwave Drying Characteristics And Technologies Of Germinated Brown Rice

Germinated brown rice, rich in active ingredients like γ-aminobutyric acid(GABA), has high nutritional value and important physiological function. Germinated brown rice(GBR) in high moisture content is easy to mildew and hard to storage. Improper drying method may cause the loss of nutrients and quality degradation for germinated brown rice. Therefore, it is necessary to choose the suitable drying technology to retain the quality of germinated brown rice for safety storage. In view of the existing problems between efficiency and quality during the drying process of germinated brown rice, a combination drying method was developed as microwave heating and tempering and drying again process. The microwave drying characteristics and the effects of microwave drying parameters on dried quality were investigated to determine the optimal parameters of microwave drying. A microwave drying dynamics model was established based on the drying characteristics. The changes of moisture content were analyzed during the drying process. The similarity criterions of microwave drying process were established and the optimal parameters were obtained. Under the premise of drying efficiency, the research results may improve the drying quality of dried germinated brown rice.A single-factor experimental design was employed to study the microwave drying characteristics and the influences of various process parameters on dried quality, as well as determine the effect of microwave conditions, in terms of the microwave intensity, drying time per cycle, surface velocity and tempering ratio, on moisture content, drying rate, fissure rate,γ-aminobutyric acid content and chrominance. The results showed that microwave drying characteristics have significantly negative correlation with the microwave intensity, drying time per cycle, surface velocity and tempering ratio. Based on the drying rate, microwave drying process consist of three obvious stages as pre-drying, steady drying and falling rate drying stages,and temperature changes had two obvious stages as sharp rising and steady stages. The drying time per cycle had the most significant effect, while surface velocity had the least effect on the fissure rate and γ-aminobutyric acid content. The increasing tempering ratio may significantly reduce the fissure rate, and microwave intensity and drying time per cycle had the significant effect on the chrominance.The effects of processing parameters on the quality index including fissure rate,γ-aminobutyric acid content and chrominance were researched by using Central Composite Design method. The results showed that the effect order of the different factors on fissure rate from high tolow were microwave intensity, drying time per cycle, tempering ratio and surface velocity. The influences degree on the γ-aminobutyric acid content from high to low were microwave intensity,tempering ratio, drying time per cycle and surface velocity. The effect sequence on chrominance L* were drying time per cycle, microwave intensity, tempering ratio and surface velocity. The importance on chrominance a* were microwave intensity, tempering ratio, drying time per cycle and surface velocity. The order on chrominance b* were the same as that of chrominance L*. Microwave intensity and drying time per cycle were the important factors in dried qualities. The optimal parameters were obtained as microwave intensity of 2.6 W/g, drying time per cycle of 3.5 min, surface velocity of 1.6 m/s and tempering ratio of 1:4. According to this condition, high qulaity germinated brown rice was obtained with fissure rate of 24.3%,γ-aminobutyric acid content of 17.5 mg/100 g and chrominance L* of 60.4, chrominance a* of 4.4and chrominance b* of 23.9.In order to accurately predict the change of moisture content of germinated brown rice during the microwave drying process, a microwave drying dynamics model was established. The results suggested that Page equation was better suitable for microwave drying dynamics model(p<0.05), and the fitting value was accordance with the verifying result. Based on physical dimension analysis method, an experiment formula was obtained combining drying kinetics constants K with microwave power p, mass m, drying time t, tempering ratio n, surface velocity v,and this formula could accurately analyse and evaluate the drying characteristics of germinated brown rice under microwave drying conditions. According to the physical dimension homogeneity and the second law of physical dimension, similarity criterions were established which extend optimal results to the large-scale microwave equipment.Tempering stage during microwave drying process was proposed to guarante the drying quality of germinated brown rice. The optimal parameters of microwave drying were obtained, and it is helpful to provide theoretical basis of microwave drying for germinated brown rice industrialization.