Sources and risk factors for contamination, survival, persistence, and heat resistance of Salmonella in low-moisture foods are reviewed. Processed products such as peanut butter, infant formula, chocolate, cereal products, and dried milk are characteristically low-water-activity foods and do not support growth of vegetative pathogens such as Salmonella. Significant food safety risk might occur when contamination takes place after a lethal processing step. Salmonella cross-contamination in low-moisture foods has been traced to factors such as poor sanitation practices, poor equipment design, and poor ingredient control. It is well recognized that Salmonella can survive for long periods in low-moisture food products. Although some die-off occurs in low-moisture foods during storage, the degree of reduction depends on factors such as storage temperature and product formulation. The heat resistance of Salmonella is affected by many factors, mostly by strain and serotypes tested, previous growth and storage conditions, the physical and chemical food composition, test media, and the media used to recover heat-damaged cells. Salmonella heat resistance generally increases with reducing moisture. Care must be taken when applying published D- and z-values to a specific food process. The product composition and heating medium and conditions should not be significantly different from the product and process parameters used by the processors.

In February 2008, the FDA released a draft Compliance Policy Guide (CPG) on Listeria monocytogenes and proposed that ready-to-eat (RTE) foods that do not support the growth of L. monocytogenes may contain up to 100 CFU/g of this pathogen. Frozen foods such as ice cream fall in that category since they are consumed in the frozen state. However, other frozen foods, such as vegetables and seafood that are thawed and served at salad and food bars, may support the growth of Listeria and would not be allowed to contain 100 CFU/g according to the draft CPG. In the current study, growth curves were generated for L. monocytogenes inoculated onto four thawed frozen foods -corn, green peas, crabmeat, and shrimp -stored at 4, 8, 12, and 20ºC.Growth parameters, lag phase duration (LPD), and exponential growth rate (EGR) were determined using a two-phase linear growth model and the Square Root Model. The results demonstrated that L. monocytogenes has a very short LPD on these thawed frozen foods during refrigerated storage and that there would be several orders of magnitude of growth (i.e., more than 1.7 log increase at 4 ºC) of the organism before the product is found to be organoleptically unacceptable. Although it would not be possible to take advantage of any extended lag phase duration caused by freeze injury to the organism, frozen foods containing less than 100 CFU/g of L. monocytogenes that are thawed, or thawed and cooked, and then consumed immediately, should not represent a public health hazard.iii

Long-term survival of heat-stressed Salmonella Tennessee, Salmonella Typhimurium DT104, and Enterococcus faecium was evaluated in four model peanut paste formulations with a combination of two water activity (aw) levels (0.3 and 0.6) and two fat levels (47 and 56%) over 12 months at 20 ± 1°C. Prior to storage, the inoculated peanut paste formulations were heat treated at 75°C for up to 50 min to obtain an approximately 1.0-log reduction of each organism. The cell population of each organism in each formulation was monitored with tryptic soy agar plate counts, immediately after heat treatment, at 2 weeks for the first month, and then monthly for up to 1 year. The log reductions (log CFU per gram) following 12 months of storage were between 1.3 and 2.4 for Salmonella Tennessee, 1.8 and 2.8 for Salmonella Typhimurium, and 1.1 and 2.1 for E. faecium in four types of model peanut paste formulations. Enhanced survivability was observed in pastes with lower aw for all organisms, compared with those with higher aw (P < 0.05). In contrast, the effect of fat level (47 and 56%) on survival of all organisms was not statistically significant (P > 0.05). Whereas survivability of Salmonella Tennessee and Typhimurium DT104 did not differ significantly (P > 0.05), E. faecium demonstrated higher survivability than Salmonella (P < 0.05). Salmonella survived in the model peanut pastes well over 12 months, which is longer than the expected shelf life for peanut butter products. The information from this study can be used to design safer food processing and food safety plans for peanut butter processing.

The purpose of the present study was to determine the heat resistance of six non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes in comparison to E. coli O157:H7 in single-strength apple juice without pulp. The thermal parameters for stationary-phase and acid-adapted cells of E. coli strains from serogroups O26, O45, O103, O111, O121, O145, and O157:H7 were determined by using an immersed coil apparatus. The most heat-sensitive serotype in the present study was O26. Stationary-phase cells for serotypes O145, O121, and O45 had the highest D(56°C)-value among the six non-O157 serotypes studied, although all were significantly lower (P < 0.05) than that of E. coli O157:H7. At 60°C E. coli O157:H7 and O103 demonstrated the highest D-values (1.37 ± 0.23 and 1.07 ± 0.03 min, respectively). The D(62°C) for the most heat-resistant strain belonging to the serotype O145 was similar (P > 0.05) to that for the most resistant O157:H7 strain (0.61 ± 0.17 and 0.60 ± 0.09 min, respectively). The heat resistance for stationary-phase cells was generally equal to or higher than that of acid-adapted counterparts. Although E. coli O157:H7 revealed D-values similar to or higher than the individual six non-O157 STEC serotypes in apple juice, the z-values for most non-O157 STEC tested strains were greater than those of E. coli O157:H7. When data were used to calculate heat resistance parameters at a temperature recommended in U.S. Food and Drug Administration guidance to industry, the D(71.1°C) for E. coli O157:H7 and non-O157 STEC serotypes were not significantly different (P > 0.05).

Salmonella enteriditis and Staphylococcus aureus were separately inoculated onto fresh chicken thighs prior to dipping in 0, 1.0,2.5, or 5.0% potassium sorbate solutions adjusted to pH 6.0. Treated samples were packaged in Nylon/Plexar/Surlyn bags under air, vacuum, 20%, 60%, or 100% CO2 atmospheres and stored at 10°C ? l.O"C for 10 days. Changes in gaseous headspace composition, sorbate concentrations, surface pH, and microbial numbers were monitored during the storage period. S. enteriditis was more sensitive to potassium sorbate than S. aureus; growth on poultry of the latter organism was more effectively inhibited by exposure to high levels of CO2. Increased concentrations of sorbate dip solutions in combination with higher concentrations of CO2 in the package environment provided a more effective inhibitory system against growth of both pathogens on fresh poultry.

Survival of a five-strain mixture of stationary phase (nonadapted) and acid-adapted Escherichia coli O157:H7 in single-strength lemon and lime juices was evaluated at room temperature (22 degrees C). The juices were reconstituted from concentrates that contained no preservatives and intrinsic pH values of 2.5 to 2.6 and titratable acidities of 4.51 to 4.53% (wt/vol, citric acid). A greater than 5-log reduction of stationary-phase cells was achieved in both lemon and lime juices after 72 h of incubation. Similar log reductions were obtained when the reconstituted juices were adjusted to pH 2.7, which is above the highest value normally observed in juice processing plants during the reconstitution of single-strength lemon or lime juice from concentrates. Lemon juice had a significantly higher inhibitory effect (P < 0.05) on E. coli O157:H7 than did lime juice. Validation tests with commercially produced shelf-stable lemon and lime juices confirmed that storage of the juices at room temperature (22 degrees C) for 3 days may be an alternative to heat treatment to ensure the 5-log reduction of vegetative pathogens of concern required for the products under the U.S. Food and Drug Administration juice hazard analysis and critical control point regulations.

A study was conducted to determine the effects of three commercially available disinfectants on the reduction of Alicyclobacillus acidoterrestris spores in single-strength apple juice applied to stainless steel surfaces. Apple juice was inoculated with A. acidoterrestris spores, spread onto the surface of stainless steel chips (SSC), dried to obtain spore concentrations of approximately 10(4) CFU/cm2, and treated with disinfectants at temperatures ranging from 40 to 90 degrees C. The concentrations of disinfectants were 200, 500, 1,000, and 2,000 ppm of total chlorine for Clorox (CL) (sodium hypochlorite); 50, 100, and 200 ppm of total chlorine for Carnebon 200 (stabilized chlorine dioxide); and 1,500, 2,000, and 2,600 ppm for Vortexx (VOR) (hydrogen peroxide, peroxyacetic acid, and octanoic acid). For all temperatures tested, VOR at 2,600 ppm (90 degrees C) and CL at 2,000 ppm (90 degrees C) were the most inhibitory against A. acidoterrestris spores, resulting in 2.55- and 2.32-log CFU/cm2 reductions, respectively, after 2 min. All disinfectants and conditions tested resulted in the inactivation of A. acidoterrestris spores, with a maximum reduction of > 2 log CFU/cm2. Results from this study indicate that A. acidoterrestris spores, in single-strength apple juice, may be effectively reduced on stainless steel surface by VOR and CL, which may have practical applications in the juice industry.

While both predictive microbiology and hazard analysis critical control point (HACCP) programs are still in the developmental stages as food-safety tools, predictive models are available that are potentially useful in the development and maintenance of HACCP systems. When conducting a HACCP study, models can be used to assess the risk (probability) and determine the consequence of a microbiological hazard in food. The risk of a hazard is reduced and controlled within the HACCP framework by assigning critical control points (CCPs) to the food process. By using predictive models, ranges and combinations of process parameters can be established as critical limits for CCPs. This has the advantage of providing more processing options while maintaining a degree of safety equivalent to that of a single set of critical limits. Validation testing of individual CCPs can be reduced if the CCP models were developed with a similar food type. Microbiological as well as mechanical and human reliability models may be used to establish sets of rules for rule-based expert computer systems in an effort to automate the development of HACCP plans and evaluate the status of process deviations. Models can also be used in combination with sensors and microprocessors for real-time process control. Since HACCP is a risk-reduction tool, then predictive microbiological models are tools used to aid in the decision-making processes of risk assessment and in describing process parameters necessary to achieve an acceptable level of risk.