Effects of radio frequency heating on microbial populations and physicochemical properties of buckwheat

Microbial contamination is a persistent problem for grain industry. Many studies have shown that radio frequency (RF) heating can effectively reduce pathogens populations in low moisture foods, but there is a lack on the efficacy to decontaminate natural microbiome. The main objectives of this study were to investigate the effects of different RF heating conditions on natural microbial populations and physicochemical properties of buckwheat. In this study, 30 buckwheat samples collected from 10 different Provinces in China were analyzed for their microbial loads, and the samples with the highest microbial populations were used for further study to select the suitable RF heating conditions. The results showed that microbial loads in tested buckwheat kernels were in the range of 3.4-6.2 log CFU/g. Samples from Shanxi (SX-3) had significantly higher microbial counts than other samples. The selected four temperature-time combinations: 75 degrees C-20 min, 80 degrees C-10 min, 85 degrees C-5 min, and 90 degrees C-0 min of RF heating could reduce microbial counts to <3.0 log CFU/g in buckwheat kernels at 16.5% w.b. moisture content. Furthermore, the reduction populations of the inoculated pathogens (Salmonella Typhimurium, Escherichia coli, Cronobacter sakazakii, and Bacillus cereus) reached 4.0 log CFU/g under the above conditions, and almost 5.0 log CFU/g especially at high temperature-short holding time combinations (85 degrees C-5 min and 90 degrees C-0 min). Besides, physicochemical properties evaluation also showed the insignificant color changes and nutrients loss after RF treatment at 90 degrees C-0 min. Therefore, the RF heating at 90 degrees C-0 min holds greater potential than the other lower temperature-longer holding time combinations for applications in buckwheat pasteurization.

Automated summary

Microbial contamination is a persistent problem in the grain industry. This study investigated the effects of radio frequency (RF) heating on the natural microbial populations and physicochemical properties of buckwheat. The results showed that RF heating at 90 degrees Celsius for 0 minutes was the most effective condition for reducing microbial counts and pathogen populations in buckwheat kernels, while maintaining insignificant changes in color and nutrient loss.