Paddy (var. Sworn Masuri) was dried by hot air (50 °C), infrared hot air (4,185 W m−2 radiation intensity and 40 °C) and microwave rotary drum (0.37, 0.78, and 1.23 kW kg−1 power density) to evaluate the most suitable method of drying. Before drying, the paddy grains were soaked in water (60 °C, 6 h) followed by steaming (200 kPa, 10 min) to gelatinize the starch. The drying rate constants, apparent moisture diffusivity (Da), convective mass transfer coefficient (hm), head rice yield (HRY) and the broken percentage were estimated. The X‐ray diffraction analysis and scanning electron microscopy (SEM) of starch granules and outer husk of the dried paddy were carried out. Microwave rotary drum drying (MWD) was found to be faster as compared to hot air drying (HAD) and infrared hot air drying (IRHD). The hm in MWD was found to be 90.76–97.01% higher than HAD and 33.33–78.44% higher than IRHD. The HRY and specific energy consumption in MWD were, respectively, 5.87% and 89.16% lower than HAD. The microwave dried rice showed the lowest crystallinity percentage. The SEM of rice starch obtained by MWD showed cracks and fissures whereas IRHD induced microstructural changes only in paddy husk.
Practical applications
Rice is a staple food of 90% Asian population. The parboiled paddy is dried in the open sun (2–3 days) and by hot air (6–9 h) on farms and in the rice industry. These are highly laborious and time‐consuming methods. Therefore, the study was undertaken from industry suggestion to develop a cost‐effective microwave‐assisted drying method for parboiled paddy. The microwave rotary drum drying was found to give similar quality rice compared to hot air with a 90% reduction in specific energy consumption. Therefore, traditional open sun and hot air drying can be replaced by microwave rotary drum to save expenses towards the capital costs, energy, labor, and grain handling.
The commercially available dry turmeric powder at 10.34% d.b. moisture content was decontaminated using microwaves at high power density for short time. To avoid the loss of moisture from turmeric due to high microwave power, the drying kinetics were modelled and considered during optimization of microwave decontamination process. The effect of microwave power density (10, 33.5 and 57 W g), exposure time (10, 20 and 30 s) and thickness of turmeric layer (1, 2 and 3 mm) on total plate, total yeast and mold (YMC) counts, color change (∆E), average final temperature of the product (T), water activity (a), Page model rate constant (k) and total moisture loss (ML) was studied. The perturbation analysis was carried out for all variables. It was found that to achieve more than one log reduction in yeast and mold count, a substantial reduction in moisture content takes place leading to the reduced output. The microwave power density significantly affected the YMC, T and a of turmeric powder. But the thickness of sample and microwave exposure time showed effect only on T, a and ML. The colour of turmeric and Page model rate constant were not significantly changed during the process as anticipated. The numerical optimization was done at 57.00 W g power density, 1.64 mm thickness of sample layer and 30 s exposure time. It resulted into 1.6 × 10 CFU g YMC, 82.71 °C T, 0.383 a and 8.41% (d.b.) final moisture content.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.