Effect of radio frequency energy combined with natamycin on Aspergillus niger survival and quality of dried shiitake mushroom with different moisture content

Effectively controlling molds in dried shiitake mushrooms is important for food industry to maintain the product quality. To improve the edible safety of shiitake mushrooms, this study applied radio frequency (RF) energy combined with natamycin to inactivate Aspergillus niger spores, and evaluate the quality changes after the treatment. The results showed that the population of A. niger spores in shiitake mushrooms with different moisture contents (MCs) could achieve a 5-log (CFU/g) reduction after the combined treatment at different temperatures. Weibull distribution (R² = 0.978 to 1.000) provided a better fit for the inactivation kinetics of A. niger spores than Linear model (R² = 0.954 to 0.990) and Logistic one (R² = 0.953 to 0.988). Meanwhile, the three-dimensional inactivation curves were constructed based on the sample MCs, RF heating time, and holding time. In addition, the MCs of treated shiitake mushrooms decreased by 4.12%–7.66% (w.b.) after natural cooling, achieving synchronous drying. There was no significant difference in textural properties of shiitake mushrooms after the combined treatment. The changes in color, structure, rehydration ratio, and total sugar content were affected by the treatment time and temperatures. As one of the main aroma substances, the content of sulfur-containing compounds in shiitake mushrooms after treatment increased compared to that of the control samples. This study indicates that the combination of RF energy and natamycin is feasible for inactivating pathogens in shiitake mushroom and ensuring the safety of their consumption.