Radio-Frequency Processing for Inactivation of Salmonella enterica and Enterococcus faecium NRRL B-2354 in Black Peppercorn

Abstract

Several Salmonella outbreaks linked to black pepper call for effective inactivation processes, because current decontamination methods result in quality deterioration. Radio-frequency (RF) heating provides a rapid heating rate and volumetric heating, resulting in a shorter come-up time. This allows for choosing a high-temperature and short-time combination to achieve the desired inactivation with minimal quality deterioration. The objectives of this study were to evaluate RF heating for inactivation of Salmonella enterica and Enterococcus faecium in black peppercorn and evaluate quality changes of RF-treated black peppercorn. Black peppercorns were inoculated with a five-strain cocktail of Salmonella or E. faecium to attain initial population levels of 6.8 and 7.3 log CFU/g, respectively, and were then adjusted to a moisture content of 12.7% (wet basis) and a water activity of 0.60 at room temperature. A stability test was performed to quantify the microbial reduction during inoculation and equilibration before RF heating inactivation. During RF heating, the cold spot was determined to be at the center on the top surface of the treated sample. In addition to inoculating the entire sample, an inoculated packed sample was placed at the cold spot of the tray. An RF heating time of 2.5 min provided a 5.31- and 5.26-log CFU/g reduction in the entire sample contained in the tray for Salmonella and E. faecium, respectively. Color parameters (L*, a*, b*), piperine content, total phenolics, scavenging activity, and most of the volatile compounds of 2.5-min RF-treated samples were not significantly different from those of the control samples. These data suggest that RF heating is a promising thermal inactivation treatment for Salmonella without significant quality deterioration, and E. faecium seems to be a suitable surrogate for Salmonella to validate the efficacy of RF heating of black peppercorn.

Evaluation of Enterococcus faecium NRRL B-2354 as a surrogate for Salmonella enterica in milk powders at different storage times and temperatures

“…The results in this study showed that Salmonella in milk powder experienced a rapid death rate in the first few weeks of storage followed by a slower death rate are in agreement with several published studies (LiCari and Potter, 1970;Lian et al, 2015). A similar reduction in Salmonella population has been observed during the postinoculation process of low water activity foods, such as black pepper (Wei et al, 2018(Wei et al, , 2019, cumin seeds (Chen et al, 2019), egg white powder (Wei et al, 2020b), almond (Abd et al, 2012), wheat flour (Forghani et al, 2019), and walnut kernel (Blessington et al, 2012). Salmonella cells need time to adapt to a low water activity environment.…”

“…Also, due to the difficulty of directly introducing the target pathogen into the processing plant, the use of a surrogate to replace the pathogen is recommended by FDA (2013) to conduct the validation study in the industrial processing plant. Several studies (Bianchini et al, 2014;Liu et al, 2018;Verma et al, 2018;Wei et al, 2018) have previously demonstrated that Enterococcus faecium NRRL B-2354 is a suitable surrogate for Salmonella during thermal processing of low water activity foods.…”

Radiofrequency heating for powder pasteurization of barley grass: antioxidant substances, sensory quality, microbial load and energy consumption

“…More applied RF cases have been developed in depth, although other authors asserted that a limitation of applied RF is undesirable non‐uniform heating . For all the reports of pasteurization using RF in a number of products, the study of RF sterilization of powder products is still scarce . And no work on pasteurizing barley grass powder has been reported, but more drying was conducted in other materials …”

Induction of the Viable-but-Nonculturable State in Salmonella Contaminating Dried Fruit

“…The Salmonella enterica strains used in this study are shown in Table 2 and were kindly provided by Nathan Anderson (U.S. Food and Drug Administration, Institute for Food Safety and Health, Bedford Park, Illinois). The strains were selected because of their involvement in LMF-associated outbreaks and also because they have been employed in storage and thermal resistance studies ( 46 ). Media and conditions routinely used for growth include Trypticase soy broth (TSB) (Becton, Dickinson & Co., Sparks, MD) containing 0.6% yeast extract (TSB-YE) (Becton, Dickinson & Co.) and TSB-YE supplemented with 1.2% agar (TSA-YE) (Becton, Dickinson & Co.) incubated statically at 37°C for 24 h. Bacterial culture stocks were preserved in TSB containing 20% glycerol (Fisher Scientific, Fair Lawn, NJ) at −80°C.…”