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Several Salmonellaoutbreaks 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 entericaand Enterococcus faeciumin black peppercorn and evaluate quality changes of RF-treated black peppercorn. Black peppercorns were inoculated with a five-strain cocktail of Salmonellaor E. faeciumto 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 Salmonellaand 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 Salmonellawithout significant quality deterioration, and E. faeciumseems to be a suitable surrogate for Salmonellato validate the efficacy of RF heating of black peppercorn.

An increase in the number of foodborne outbreaks and recalls due to Salmonellain low-moisture foods has resulted in the need for the development and validation of process controls to ensure their microbiological safety. Furthermore, the Food Safety Modernization Act Preventive Controls for Human Food final rule requires food processors to validate their process controls to ensure food safety. The objective of this study was to develop a response surface model to predict Salmonellainactivation in oat flour, as affected by moisture, fat content, screw speed, and temperature. Oat flour was adjusted to different moisture (14 to 26% wet basis) and fat (5 to 15% [w/w]) contents and was then inoculated with a five-strain cocktail of Salmonella. Inoculated material was extruded through a single-screw extruder running at different screw speeds (75 to 225 rpm) and temperatures (65 to 85°C), without a die. Once steady-state conditions were attained, extruded samples were collected, cooled, and stored under refrigeration, and Salmonellasurvivors were enumerated. A split-plot central composite second-order response surface design was used, with the central point replicated six times. Temperature showed a significant (P< 0.0005) positive effect on microbial reduction. Moisture content showed significant linear (P= 0.0014) and quadratic (P= 0.0005) effects, whereas higher fat content showed a significant (P< 0.0001) protective effect on Salmonelladestruction. The screw speed did not play a major role in inactivating Salmonella,but it had a significant (P= 0.0004) interactive effect with temperature. Results indicated that a >5.5-log reduction was achieved in oat flour extruded at a temperature above 85°C at all moisture and fat contents evaluated at a screw speed of 150 rpm. The developed response surface model can be used to identify the extrusion process conditions to achieve a desired reduction of Salmonellabased on the moisture and fat contents of the product.

Escherichia coliO157:H7 is a human pathogen that can cause bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. E. coliO157:H7 illnesses are mainly associated with undercooked beef; however, in recent years, outbreaks have been linked to fresh produce, such as spinach, lettuce, and sprouts. In 2009, flour was implicated as the contamination source in an outbreak involving consumption of raw cookie dough that resulted in 77 illnesses. The objectives of this research were to determine (i) whether E. coliO157:H7 could be translocated into the internal tissues of wheat (Triticum aestivum)seedlings from contaminated seed, soil, or irrigation water and (ii) whether the bacterium could survive on flowering wheat heads. The levels of contamination of kanamycin-resistant E. coliO157:H7 strains in seed, soil, and irrigation water were 6.88 log CFU/g, 6.60 log CFU/g, and 6.76 log CFU/ml, respectively. One hundred plants per treatment were sown in pot trays with 50 g of autoclaved soil or purposely contaminated soil, watered every day with 5 ml of water, and harvested 9 days postinoculation. In a fourth experiment, flowering wheat heads were spray inoculated with water containing 4.19 log CFU/ml E. coliO157:H7 and analyzed for survival after 15 days, near the harvest period. To detect low levels of internalization, enrichment procedures were performed and Biotecon real-time PCR detection assays were used to determine the presence of E. coliO157:H7 in the wheat, using a Roche Applied Science LightCycler 2.0 instrument. The results showed that internalization was possible using contaminated seed, soil, and irrigation water in wheat seedlings, with internalization rates of 2, 5, and 10%, respectively. Even though the rates were low, to our knowledge this is the first study to demonstrate the ability of this strain to reach the phylloplane in wheat. In the head contamination experiment, all samples tested positive, showing the ability of E. coliO157:H7 to survive on the wheat head.

Multiple outbreaks of salmonellosis have been associated with the consumption of low-moisture products, including extruded products. Therefore, there is a need for a nonpathogenic, surrogate microorganism that can be used to validate extrusion processes for Salmonella. The objective of this research was to determine if Enterococcus faeciumNRRL B-2354 is an adequate surrogate organism for Salmonelladuring extrusion. Extrusions at different temperatures were done in material contaminated with both organisms. Results indicated that the minimum temperature needed to achieve a 5-log reduction of E. faeciumwas 73.7°C. Above 80.3°C, the enumeration of E. faeciumshowed counts below the detectable levels (<10 CFU g-1). Salmonellawas reduced by 5 log at 60.6° C, and above 68.0°C the levels of this organism in the product were below the detection limit of the method. The data show that E. faeciumis inactivated at higher temperatures than Salmonella, indicating that its use as a surrogate would provide an appropriate margin of error in extrusion processes designed to eliminate this pathogen. Attempting to minimize risk, the industry could validate different formulations, in combination with thermal treatments, using E. faeciumas a safer alternative for those validation studies.

Outbreaks of salmonellosis and recalls of low-moisture foods including extruded products highlight the need for the food and feed industries to validate their extrusion processes to ensure the destruction of pathogenic microorganisms. Response surface methodology was employed to study the effect of moisture and temperature on inactivation by extrusion of Enterococcus faeciumNRRL B-2354 in a carbohydrate-protein mix. A balanced carbohydrate-protein mix was formulated to different combinations of moisture contents, ranging from 24.9 to 31.1%, and each was inoculated with a pure culture of E. faeciumto a final level of 5 log CFU/g. Each mix of various moistures was then extruded in a pilot scale extruder at different temperatures (ranging from 67.5 to 85°;C). After the extruder was allowed to equilibrate for 10 min, samples were collected in sterile bags, cooled in dry ice, and stored at 4°;C prior to analysis. E. faeciumwas enumerated with tryptic soy agar and membrane Enterococcusmedia, followed by incubation at 35°;C for 48 h. Each extrusion was repeated twice, with the central point of the design being repeated four times. From each extrusion, three subsamples were collected for microbial counts and moisture determination. Based on the results, the response surface model was y=185.04 - 3.11X12 4.23X2+ 0.02X12-0.004X1X2+ 0.08X22, with a good fit (R2= 0.92), which demonstrated the effects of moisture and temperature on the inactivation of E. faeciumduring extrusion. According to the response surface analysis, the greatest reduction of E. faeciumfor the inoculation levels studied here (about 5 log) in a carbohydrate-protein meal would occur at the temperature of 81.1°;C and moisture content of 28.1%. Other temperature and moisture combinations needed to achieve specific log reductions were plotted in a three-dimensional response surface graph.