Alicia Orta-Ramirez

Thermal inactivation kinetics for Salmonella Enteritidis PT30 on almonds subjected to moist-air convection heating.

A traditional thermal inactivation kinetic model (D- and z-value) was modified to account for the effect of process humidity on thermal inactivation of Salmonella Enteritidis PT30 on the surface of almonds subjected to moist-air heating. Raw almonds were surface inoculated to approximately 10(8) CFU/g and subjected to moist-air heating in a computer-controlled laboratory-scale convection oven. Time-temperature data were collected for 125 conditions (five dry bulb temperatures, 121 to 232 degrees C; five process humidity levels, 5 to 90% moisture by volume; and five process durations). Moisture status at the surface of the almond, rather than the humidity of the bulk air, was a primary factor controlling the rate of inactivation; therefore, the D-value could not be a simple function of process temperature. Instead, the traditional D- and z-value model was modified to account for the dynamic water status at the surface of the product under humid heating conditions. The modified model needs only the dew point temperature of the processing air and dynamic surface temperature history of the almonds during moist-air heating. The modified model was more robust and accurate than the traditional model. The accuracy of the modified model was improved by 32 to 44% (in terms of the root mean squared error [RMSE] for the model fit) when compared with the traditional model in all moist-air heating conditions. Also, the prediction error of the modified model (RMSE = 1.33 log reductions) against an independent validation data set was approximately one-half that of the traditional model (RMSE = 2.56 log reduction) in the humidity range of 5 to 90% moisture by volume.

Modeling the effect of prior sublethal thermal history on the thermal inactivation rate of Salmonella in ground Turkey

Traditional models for predicting the thermal inactivation rate of bacteria are state dependent, considering only the current state of the product. In this study, the potential for previous sublethal thermal history to increase the thermotolerance of Salmonella in ground turkey was determined, a path-dependent model for thermal inactivation was developed, and the path-dependent predictions were tested against independent data. Weibull-Arrhenius parameters for Salmonella inactivation in ground turkey thigh were determined via isothermal tests at 55, 58, 61, and 63 degrees C. Two sets of nonisothermal heating tests also were conducted. The first included five linear heating rates (0.4, 0.9, 1.7, 3.5, and 7.0 K/min) and three holding temperatures (55, 58, and 61 degrees C); the second also included sublethal holding periods at 40, 45, and 50 degrees C. When the standard Weibull-Arrhenius model was applied to the nonisothermal validation data sets, the root mean squared error of prediction was 2.5 log CFU/g, with fail-dangerous residuals as large as 4.7 log CFU/g when applied to the complete nonisothermal data set. However, by using a modified path-dependent model for inactivation, the prediction errors for independent data were reduced by 56%. Under actual thermal processing conditions, use of the path-dependant model would reduce error in thermal lethality predictions for slowly cooked products.

Identification of Core Competencies for an Undergraduate Food Safety Curriculum Using a Modified Delphi Approach.

Identification of core competencies for undergraduates in food safety is critical to assure courses and curricula are appropriate in maintaining a well-qualified food safety workforce. The purpose of this study was to identify and refine core competencies relevant to postsecondary food safety education using a modified Delphi method. Twenty-nine experts representing food safety professionals in academia, government, and industry were given 2 rounds of questionnaires that specified initial food safety competencies, core domains, and subdomains. Competencies were defined as a set of skills, knowledge, and abilities that correlate to success of a trainee. The framework for which competencies were classified consisted of (1) core domains, defined as broad food safety subjects; and (2) subdomains, or more specific food safety subjects. The expert panel used a 5-point Likert scale with an acceptance criterion, or consensus, of 75%, with a rating of “4” or greater. After 2 rounds of questionnaires and revisions from the expert panel, 5 core domains were established: (1) Food Production, Manufacturing, Retail, and Consumer; (2) Foodborne Hazards; (3) Public Health; (4) Legislation and Policy; and (5) Communication and Education. Specific responses from the experts highlighted areas in which further curriculum revision would be beneficial. This study provides a framework for the development of a vetted, standardized undergraduate food safety curriculum. The Delphi method, with its inclusion of professionals representing various sectors of food safety, provided relevant perspectives for curriculum design, and also allowed participants the opportunity to contribute to the education of future food safety professionals.

Effect of Beef Product Physical Structure on Salmonella Thermal Inactivation

Numerous studies have assessed thermal inactivation of Salmonella in beef. However, the impact of muscle structure has been considered only recently, with several studies reporting enhanced thermal resistance in whole-muscle as compared to ground meat. The functional relationship between meat product physical structure and Salmonella thermal resistance has not been reported; therefore, it is not known whether thermal resistance is affected by the degree of grinding (that is, size of resulting particles). The objective of this study was to evaluate the relationship between thermal resistance of Salmonella and degree of grinding (whole-muscle, coarsely ground, finely ground, and beef puree). Each of the 4 product types was irradiated to sterility and inoculated with a marinade containing an 8-serovar Salmonella cocktail to achieve approximately 10(7.8) CFU/g. Samples (5 g each) were packed into sterile brass tubes, which were sealed, held at 60 degrees C in a water bath, and removed at 30 s intervals. Samples were then serially diluted and plated on Petrifilm aerobic count plates to enumerate surviving salmonellae. All samples had the same composition, thermal history, and initial Salmonella counts; therefore, differences in thermal resistance were due entirely to the degree of grinding. Overall, thermal resistance of Salmonella was highest (P < 0.0001) in whole-muscle (D = 2.7 min), but there were no differences among the 3 ground products (D(mean)= 1.2 min). Therefore, it would be prudent for Salmonella thermal inactivation models to consider whether a product is whole-muscle or ground, but not necessarily the degree of grinding. Practical Application: The results of this study suggest that thermal process validations for ready-to-eat meat products should also consider the structure of the product (which in this study was changed by the physical act of grinding). Salmonella was more resistant to heat in whole-muscle beef than in ground products; however, the degree of grinding did not affect the resistance.

Single directional migration of Salmonella into marinated whole muscle turkey breast

Irradiated, whole muscle turkey breasts were cut into blocks measuring 10 by 10 by 6 cm and exposed on one side to a marinade inoculated to contain a cocktail of eight Salmonella serovars at 10(8) CFU/ml. After exposure for 5, 10, or 20 min with or without vacuum (101.3 kPa), cylindrical cores perpendicular to the exposed surface were removed from the blocks with a hand-coring device and subdivided into 1-cm segments. Each segment was macerated, serially diluted in sterile peptone water, and plated to quantify Salmonella. Bacterial migration was greater under vacuum, compared with nonvacuum marination, at 20 min (P < 0.05). When all time levels were pooled within the vacuum and nonvacuum treatments, vacuum processing during marination increased bacterial migration into turkey breast (P < 0.05). This study provides evidence that if bacteria are present on the surface of the muscle, they could migrate into the intact muscle with or without the aid of vacuum.

Thermal inactivation of pathogens and verification of adequate cooking in meat and poultry products.

Publisher Summary This chapter discusses thermal inactivation of pathogens and verification of adequate cooking in meat and poultry products. The chapter reviews thermal processing as a means to eliminate microbial pathogens in meat and poultry. Besides discussing the evolution of thermal processing regulations in the US and listing official and alternative tests to verify compliance with the cooking requirements, an effort has been made to evaluate the advantages and disadvantages for each of the verification methods as well as the challenges to determine the thermal inactivation kinetics of microbial pathogens. The chapter reviews the thermal processing requirements currently implemented in the US; thermal inactivation of most common microbial pathogens found in meat and poultry products, and the use of thermometers, color determination, endpoint temperature indicators, and time-temperature integrators as means of verifying thermal processing adequacy.

Enhanced thermal resistance of salmonella in marinated whole muscle compared with ground pork.

The internal muscle environment may enhance thermal resistance of bacterial pathogens. Based on the migration of pathogens into whole muscle products during marination, the validity of current thermal inactivation models for whole muscle versus ground products has been questioned. Consequently, the objective of this work was to compare thermal resistance of Salmonella in whole muscle versus ground pork. Irradiated samples of whole and ground pork loin (5.5 to 7.5 g) were exposed to a Salmonella-inoculated (10(8) CFU/ml) marinade (eight serovar cocktail) for 20 min, placed in sterile brass tubes (12.7 mm diameter), sealed, and heated isothermally at 55, 58, 60, 62, or 63 degrees C, and surviving salmonellae were enumerated on Petrifilm aerobic count plates. The thermal lag times and initial bacterial counts were similar for both whole muscle and ground samples (P > 0.05), with all samples having equivalent compositions, inocula, and thermal histories. Heating temperature and physical state of the meat (whole versus ground muscle) affected Salmonella inactivation, with greater thermal resistance observed in whole than in ground muscle (P < 0.05). Assuming log-linear inactivation kinetics, Salmonella was 0.64 to 2.96 times more heat resistant in whole muscle than in ground pork. Therefore, thermal process validations for pork products should also account for the physical state of the product to ensure microbial safety.

Thermal inactivation of Salmonella in whole muscle and ground turkey breast.

The effect of the physical structure of turkey meat (ground and whole muscle) on the thermal resistance of Salmonella was evaluated. Irradiated whole and ground turkey breasts were exposed to a marinade containing eight serovars of Salmonella at approximately 10(8) CFU/ml for 20 min. Inoculated samples then were subjected to isothermal heating at 55, 60, or 62.5 degrees C, for varying times. Salmonella counts before and after the thermal lag time (time to reach the target temperature) were not significantly different (alpha = 0.05). The first-order inactivation rate constants in whole muscle were approximately 50% lower than those in ground muscle of the same composition, at each temperature, indicating that the Salmonella inactivation rate was greater (P < 0.05) in ground samples than in whole-muscle samples. These results suggest that internalization of Salmonella in whole-muscle product leads to enhanced thermal resistance.

R-phycoerythrin as a time-temperature integrator to verify the thermal processing adequacy of beef patties.

The objective of this study was to relate R-phycoerythrin (PE) fluorescence decay to the inactivation of Salmonella in beef patties cooked using adequate and inadequate thermal processes as defined by the U.S. Department of Agriculture (USDA) safe harbor requirements and lethality standards. Ground beef containing 4.8 or 19.1% fat was inoculated with an eight-strain cocktail of Salmonella and formed into 113-g patties. Capillary tubes containing PE in borate buffer at pH 9.0 were attached to a thermocouple and inserted horizontally into the patties. Patties (n = 43) were cooked on a grill maintained at 177 degrees C for 6 to 13 min and reached internal temperatures ranging from 57 to 77 degrees C. Patties were analyzed for Salmonella survivors and for fluorescence decay of PE. The thermal lethality of each process was calculated at a reference temperature of 65 degrees C. Twenty-four of the 43 high-fat patties met the USDA safe harbor regulations, with thermal lethalities of >66 s, whereas only 20 of these patties met the proposed 5-log10 lethality standard. Three of the 20 low-fat patties that met USDA regulations did not meet the proposed lethality standard. A normalized PE fluorescence value of about 0.3 (confidence interval = 99%) indicated that patties had been processed sufficiently to reduce Salmonella by 5 log10 cycles. PE has the potential for use as a marker to verify processing adequacy in food-processing plants and in other settings in which the use of the target pathogen is inappropriate.

Sucrose, sodium dodecyl sulfate, urea, and 2-mercaptoethanol affect the thermal inactivation of R-phycoerythrin

Thermal inactivation kinetics (D- and z-values) of the algal protein, R-phycoerythrin (R-PE), were studied under different buffer conditions (pH 4.0, 7.0, and 10.0) and concentrations of sucrose, sodium dodecyl sulfate (SDS), urea, and 2-mercaptoethanol (ME). R-PE solutions were heated in capillary tubes at temperatures between 40 and 90 degrees C depending on buffer conditions. Thermal inactivation parameters for R-PE, calculated on the basis of fluorescence loss, were modified by addition of chemicals. Overall, sucrose and ME had a thermostabilizing effect, while SDS and urea decreased thermal stability of R-PE. The z-values ranged from 5.9 degrees C in 50 mM NaCl, 20 mM glycine buffer, pH 10.0, to 37.8 degrees C in 60% sucrose, 50 mM NaCl, 20 mM phosphate buffer, pH 7.0. The z-values obtained for R-PE closely matched the z-values of some target microorganisms in food processes, suggesting R-PE might be used as a time-temperature integrator to verify thermal processing adequacy.