Assessment of disinfestation ability of microwave against rice weevil and its effect on physicochemical and functional properties of two exotic rice varieties

Fumigation is a critical unit operation that preserves the quality and quantity of food grains during storage. However, due to its possible detrimental impact on the environment and human health, a collective effort could be seen to reduce the use of such chemical based grain preservation processes. This study investigates the effects of microwave treatment on rice weevil (Sitophilus oryzae) and native fungal flora, as well as different quality parameters of milled black rice (Oryza sativa L. indica) and soft rice (Oryza sativa). The milled rice grains were microwave-treated by well mixed microwave system at two microwave power levels (1600 W & 1800 W) and for four different time intervals (30, 60, 90 & 120 s). Results showed that the mortality percentage increased by increasing the microwave power and exposure time. It was observed that 120 s of microwave exposure was enough to achieve 100 % insect mortality for both rice varieties at an 1800 W power level. The lowest fungal load was recorded at 1800 W for 120 s exposure. As expected, moisture content and water activity decreased with the increase in microwave power and exposure time. At 1800 W with an exposure time of 120 s, the highest temperature was measured 58.5 ± 0.42 °C and 56.0 ± 0.82 °C for black rice and soft rice, respectively. Proximate composition, thermal properties, FTIR signature spectra, cooking properties, and sensory properties of untreated and microwave-treated milled rice did not show any significant difference in quality (power level 1800 W for 120 s). This research recommends that microwave as an effective method of disinfesting milled black rice and soft rice to extend their storage quality. Especially considering the hot and humid condition of North-East India where the two rice varieties are grown in organic condition the findings are having economic significance for the farmers.