Pasteurization of dried basil leaves using radio frequency heating: A microbial challenge study and quality analysis

Abstract

The current microbial reduction techniques have low consumer acceptance or may have an adverse effect on the quality of spices and herbs. This requires a need for an alternative decontamination method that can effectively reduce the microbial load and minimize the food quality losses. Radio frequency (RF) heating is a dielectric heating method that has been proven effective to pasteurize various low-moisture foods. The present research was designed to evaluate the efficacy of RF heating for the reduction of Salmonella in dried basil leaves, evaluate the suitability of Enterococcus faecium NRRL B-2354 as a surrogate for Salmonella, and assess the quality of dried basil leaves post RF treatment. Dried basil leaves inoculated with a Salmonella cocktail or E. faecium were conditioned to a higher moisture content such that the moisture content of the treated sample post RF treatment fall within the typical range. The inoculated samples were packaged in the teabag and placed in the identified cold spot (top center) of a laminated paper tray filled with uninoculated sample. Samples were subjected to RF heating for 45, 55, and 65 s during which the cold-spot temperature reached 65, 80, and 100 °C, respectively. The results showed that at 55 s, Salmonella and E. faecium population decreased by 4.8 and 2.7 log CFU/g, respectively. Both microorganisms reached below the detection limit (>6.5 log CFU/g reduction) at 65 s of RF heating. Therefore, the quality analysis of the dried basil leaves was performed with the samples treated with RF for 65 s. The results showed that the RF heating had no significant effect on the quality parameters (color, total volatiles, total phenolics, and antioxidant activity) of the dried basil leaves. Therefore, RF processing results in rapid heating of the dried basil leaves enhancing food safety with insignificant impact on quality. Furthermore, the food processing facility may use E. faecium as an appropriate surrogate for Salmonella when conducting an in-plant validation study.