Effect of low pressure cold plasma treatment on microbial decontamination and physicochemical properties of dried walnut kernels (Juglans regia L.)

In this study, dried walnut kernels were processed by radiofrequency low pressure cold plasma (LPCP) treatment using normal air. Dried walnut kernels were treated with LPCP at different powers (20, 30, 40, and 50 W) and at different times (10, 15, and 20 min), and finally compared with the untreated sample. The tests performed in this study included microbial load reduction, decimal reduction time (D-value), peroxide value, moisture content, texture firmness, and color parameters. The LPCP treated samples compared with the control sample significantly reduced the microbial load (p < 0.05). The highest microbial log reduction was observed in 50 W for 20 min. Total viable count, coliform, and mold log reduction were equal to 1.09, 0.97, and 0.89 log CFU/g, respectively. D-values were also calculated, with the maximum reduction observed at 50 W. The lowest D-values for the total count, coliform, and mold were 19.66, 18.25, and 18.18 min, respectively. There was no significant difference between the treated and untreated samples in terms of peroxide value and firmness (p > 0.05). However, the treated samples' moisture content diminished with increasing power and LPCP exposure time (p < 0 .05). The result indicated that the LPCP darkened the treated samples' color. Practical Applications This study demonstrates the potential of low pressure cold plasma applications for the decontamination of dried walnut kernels. It is an appropriate alternative for product disinfection such as nuts, spices, aromatic plants, and other sensitive foods to high-temperature processing, due to the lack of waste production, low energy consumption, low cost, and keeping the physicochemical properties of products intact.

Automated summary

The study demonstrates that radiofrequency low pressure cold plasma treatment can effectively reduce microbial load in dried walnut kernels, with D-values increasing with power. Treated samples showed no significant difference in peroxide value and firmness compared to untreated samples, but moisture content decreased with increasing power and exposure time.