Microbial Prevalence on Freshly-Harvested Long-Grain Pureline, Hybrid, andMedium-Grain Rice Cultivars

Abstract. The prevalence of microorganisms on freshly-harvested long-grain hybrid, long-grain pureline, and medium-grain rice has not been elucidated. The objective of this study was to determine the relative prevalence of microbes on freshly-harvested, high moisture content rice of different types and cultivars. Long-grain hybrid (XL723 and XL753), long-grain pureline (CL152 and RoyJ), and medium-grain (Caffey and Jupiter) rice were grown at four different Arkansas locations (Stuttgart, Rohwer, Colt, and Keiser) for the study. The total and surface aerobic plate counts (APC) and mold counts in terms of log colony forming units per gram (log CFU/g) of rice were determined. The study was conducted in the 2013 and 2014 harvest seasons. In 2013, harvested samples of all the studied rice cultivars, the long-grain hybrid cultivars had the lowest APC levels (M = 8.10, SD = 0.09) (M and SD symbolize mean and standard deviation, respectively). Similarly, in 2014 harvested samples, of all the studied rice cultivars, the long-grain hybrid cultivars had the lowest mold count levels (M = 5.97, SD =0.27). For the 2013 samples, within medium-grain and long-grain hybrid and long-grain pureline rice types, the studied cultivars had no significant difference in APCs or mold counts (p>0.05). The geographic location where rice was grown also influenced the level of microbial contamination of the rice at harvest and the observed trends varied from year to year. Understanding the relative prevalence of mold on different rice cultivars at harvest may help producers prioritize drying schedules to minimize rice deterioration caused by discoloration and mycotoxin development.