Effect of High-Power Short-Time Microwave Heating on Inactivation of Microbes on Rough Rice

Abstract

<b><sc>Abstract. </sc></b>Maintaining the safety of rice has become a priority in the food industry, especially due to rice‘s gluten-free label and increasing utilization as flour or ingredient for formulating various products. The objective of this study was to investigate the effectiveness of using high-power, short-time treatment of rough rice with microwaves propagated at 915 MHz frequency to inactive microbes on rice without compromising its quality attributes. Freshly-harvested, high moisture content (MC) rough rice at 21% (wet basis) and 20 mm bed thickness was exposed to microwave at powers of 16, 18, and 20 kW, for various durations (1, 2, and 3 minutes). Standard procedures were used to determine microbial load on treated and untreated samples. Serial dilutions of both treated and control samples were carried out and transf  erred to 3M petrifilms for the total aerobic count (TAC) and total fungal count (TFC) enumeration. The 3M petrifilms were incubated at 30°C for 2 days and 25°C for 5 days for TAC and TFC, respectively. The comparison of the enumeration showed that samples treated with the highest microwave power (20 kW) over the longest exposure durations (3 minutes) had the highest reductions in TAC and TFC - up to 1.21 cfu/g and 5.01 cfu/g log reductions in TAC and TFC, respectively. A separate study reports the impact of these treatments on quality characteristics of rice. Meanwhile, the results from this study suggest that there is potential for using high microwave powers with exposure duration of only 3 min to achieve significant inactivation of microorganism on rough rice.