Optimization of microwave drying process for rice milling and stabilization of rice bran
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Date
2023
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Punjab Agricultural University
Abstract
Investigations were carried out on optimization of microwave drying process for rice milling (PR121) and stabilization of rice bran. Experiments were planned with Box- Behnken design with five process variables viz. microwave power levels (180, 300, and 450 W), air velocity (3, 5, and 7 m/s), exposure time (4, 8 and 12s), bed thickness (3, 4.5, and 6 cm) and moisture content (12, 14 and 16%, wb). The response variables were milling recovery (MR), head rice yield (HRY), broken percentage (BP), degree of milling (DOM), free fatty acids (FFAs), peroxide value (PV) and saponification value (SV). Most of drying occurred in falling rate period and the peak value of drying rate varied between 1.718 - 4.702%, db/min. Paddy temperature during microwave reached a peak value of 56.73- 118.90oC. Average effective moisture diffusivity (Deff) ranged between 0.1415 - 0.6580 10-9 m2/s. Page model was found to be best among nine models tested describing the drying kinetics of paddy. Optimum values of process variables for drying of paddy were found to be microwave power level: 297.61 W, air velocity: 4.77 m/s, exposure time: 8.01s, bed thickness: 4.26 cm, and moisture content: 14.26%, wb with overall desirability of 0.819. The, optimum values of milling fractions and rice quality were MR: 72.06, HRY: 56.58, BP: 15.06, DOM: 7.71, FFA: 2.63%, PV: 3.44 meq/kg oil and SV: 181.39 mg KOH/g oil. At optimum conditions of microwave drying, MR and HRY increased by 3 and 6.73% respectively, DOM and lightness (L*) value of whitened rice reduced by 6 and 4% respectively; hardness (13%), cooking timing (4.41 min), water uptake ratio (19.24%), gruel solid loss (18%), cooked L/B ratio (4.2%), elongation ratio (3.44%) and overall colour difference (23.5%) were slightly higher than hot air drying. Further, thermal, and drying efficiency was higher by 67.43 and 92.95% respectively, but specific energy consumption decreased by 48.67% compared to hot air drying. Microstructure of starch granules treated with microwave showed more aggregated starch matrix and smooth surface structure than hot air drying. Further, the storage stability of rice bran from optimized microwave heating was extended to 60 days in vacuum packed refrigerated stored bran compared to 30 days in traditional (control).
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Ozukum, Merenungla (2023). Optimization of microwave drying process for rice milling and stabilization of rice bran (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.