| Abstract | In this study, the effect of processing parameters on the quality of germinated brown rice (GBR) and parboiled germinated brown rice (PGBR) were inve stigated. Initially, hydration kinetics and dimensional changes of brown ri ce kernels during soaking at the temperatures of 30 − 60 ° C were studied. The changes in length, width, perimeter, and projected area of the kernels as a function of soaking time were determined by an image analysis. To determine the optimum conditions for producing GBR and PGBR with high GABA content, factors affecting GABA accumulati on in rice grains during the germination process were investigated, including soaking pH (5.0 − 6.5), soaking temperature (30 − 45 ° C), soaking time, and incubation time. In the parboiling process, GBR was parboiled by a steam temperature of 97 − 99 ° C and the effect of steaming time on GABA content, white belly, and microorganism were determined. GBR and PGBR were dried by hot air drying (40 − 80 ° C) and hot-air flui dized-bed drying (110 − 150 ° C). A laboratory-scale superheated-steam fluidized-bed dryer was designed and fabricated to simultaneously parboil and dry rice grains at steam temperatures of 110 − 150 ° C for PGBR preparation. The effects of drying methods and conditions (temperature and time) on quality of the GBR and PGBR, including GABA content, yello wness, internal fissuring, white belly, pasting properties, cooking time, water absorption, total solids loss, hardness, microstructure, and sensory evaluation, were examined. The results indicated that water absorption and dimensional change s of the brown rice kernels increased with soaking temperature and time. Water absorption was described by the Fick’s second law of diffusion. Th e effective diffusivity varied from 5.30 × 10 -11 to 1.56 × 10 -10 m/s 2 . The soaking temperature dependence of the effective diffusivity was described by an Arrhenius-type relationship. The activation energy for moisture diffusion was 30.46 kJ/mol. The dimensional changes follo wed first-order kinetics and the activation energy values for the changes in kernel leng th, width, perimeter, a nd projected area were 25.27, 23.01, 26.39, and 31.05 kJ/mol, respectively. The Page model presented the best fit and represented an excellent tool for estimating moisture content in brown rice. On the other hand, the Midilli model was superior to the others for describing the changes in kernel dimensions during soaking. During the germination process, pH and temperature of soaking water significantly affected the GABA accumulation in the grains. The optimum pH and temperature for maximizing GABA accumulation were 6.0 and 35 °C, respectively. GABA content also increased significantly with soaking time. The highest GABA content (23.31 ± 0.61 mg/100 g, 11 times of the un-germinated brown rice) was obtained from brown rice soaked at the optimum pH and temperature for 4 h and then incubated in the moist condition (relative humidity of 90%) at the same temperature for 20 h. In the parboiling process, the suitable condition for producing PGBR with complete starch gelatinization was a steam temperature of 97−99 °C and the processing time of 10 min. The results also revealed that the germination caused significant changes in the properties of brown rice due to the starch hydrolysis. Parboiling also altered the properties of GBR owing to the starch gelatinization. During the drying process, PGBR required longer drying time to achieve the same final moisture content than GBR for all the drying methods. Increased drying temperature and time altered the properties of the GBR and PGBR similarly for all the hot air drying methods but the range was different. In case of GBR, drying conditions had a greater effect on the properties of GBR whereas, the influence of starch gelatinization on the properties of PGBR was more pronounced than the influence of drying conditions. In a hot-air fluidized-bed drying, internal fissured kernels were considerably higher when final moisture contents were lower than 27.37−28.70% d.b. for GBR and lower than 25−28.18% d.b. for PGBR at the temperature range of 110−150 °C. In a superheated-steam fluidized-bed drying, superheated steam drying represents a good practice in the production of PGBR. Steaming and drying were combined into a single stage that can reduce the number of operating steps and also minimize the effect of heating time on GABA content in grains. Increasing steam temperature and time significantly affected the properties of PGBR as well. Two-stage drying is recommended in superheated-steam fluidized-bed technique to protect the kernel from internal fissuring through heat stress or moisture gradient. The optimum final moisture content of PGBR subjected to steam drying are 19.19−22.00% d.b. at the steam temperatures of 110−150 °C. Under all drying methods, moisture transfer from GBR and PGBR was described by applying the Fick’s second law of diffusion. The effective diffusivity was 2.41×10-11 to 7.93×10-10 m/s2 . The activation energy for moisture diffusion ranged from 12.97 to 27.27kJ/mol. The Midilli model was found to be the best model for describing the drying behavior of the GBR and PGBR under all drying methods. Therefore, Understanding the effect of processing parameters on the quality of GBR and PGBR is important to design, control, and optimize processes for better quality of the products. |