Effect of storage temperatures and stresses on the survival of Salmonella spp. in halva.

The presence of Salmonella spp. in halva has been associated with foodborne illnesses and product recalls from the markets. This study investigated the effect of environmental stresses on the survival of Salmonella spp. in halva during storage for 12 months at 10 and 25°C (log (N0 /N) g-1 ). Halva samples were inoculated with a cocktail of four strains of unstressed, desiccation stressed or heat stressed Salmonella (106 -107  CFU per gram). In general, survival of Salmonella spp. in halva decreased significantly (P Ë‚ 0·05) as storage time and temperature increased. At the end of halva shelf life at 10°C, the initial populations of unstressed, desiccation stressed or heat stressed Salmonella spp. decreased by 2·7, 2·6 or 2·8 log CFU per gram (reduction rate c. 0·2 log CFU per month), respectively. While at 25°C, the populations decreased 5·2, 6·7 or 6·3 log CFU per gram, respectively (reduction rate c. 0·4-0·5 log CFU per month). The populations of stressed Salmonella spp. in halva samples were not significantly different (P ≥ 0·05) from populations of unstressed cells during storage at 10 and 25°C, except during the last 3 months of storage at 25°C when populations of unstressed cells were higher (P < 0·05). Exposing Salmonella spp. to desiccation or heat stress prior product contamination may play a role in Salmonella spp. survival in halva during storage. SIGNIFICANCE AND IMPACT OF THE STUDY: Contamination of halva (tahini halva) with Salmonella from raw materials or during production was documented. Halva and tahini have been involved in salmonellosis outbreaks in different countries. The study demonstrated enhanced survivability of stressed and unstressed Salmonella spp. in halva over a 12-month storage period at 10 and 25°C with lower log reductions than expected. Exposing Salmonella spp. to desiccation or heat stress prior product contamination may play a role in microbial survival in halva during storage. These findings serve as a model to halva producers to implement control measures to prevent Salmonella spp. contamination in halva.

Evaluation of a new enrichment broth for detection of Cronobacter spp. in powdered infant formula.

The aim of this study was to investigate the potential of using Al-Holy-Rasco (AR) medium, a novel broth for detection and isolation of Cronobacter spp. in infant formula milk (IFM). The new medium's composition is generic brain heart infusion broth with the addition of 1% NaCl, 15% sucrose, and 0.80 g/liter sodium deoxycholate as selective ingredients. AR broth outperformed Enterobacteriaceae enrichment broth (EE), Enterobacter sakazakii enrichment broth (ESE), modified lauryl sulfate broth, and milk as enrichment media to stimulate the growth of a cocktail of 10 strains of Cronobacter. Additionally, AR broth significantly suppressed the growth of competing non-Cronobacter Enterobacteriaceae as compared with EE, ESE, modified lauryl sulfate broth, and milk. The recovery of desiccated Cronobacter (1 to 5,000 CFU/100 g) from powdered IFM in the presence of competing non-Cronobacter Enterobacteriaceae was determined by EE, ESE, and AR broth with 10 and 15% sucrose. AR broth with 15% sucrose outperformed all other examined broths and recovered Cronobacter from all samples tested at all Cronobacter concentrations. AR broth must be validated before it can be used for rapid detection and isolation of Cronobacter from powdered IFM.

Heat resistance of Cronobacter species (Enterobacter sakazakii) in milk and special feeding formula.

AIM: To determine D- and z-values of Cronobacter species (Enterobacter sakazakii) in different reconstituted milk and special feeding formula and the effect of reconstitution of powdered milk and special feeding formula with hot water on the survival of the micro-organism. METHODS AND RESULTS: Five Cronobacter species (four C. sakazakii isolates and C. muytjensii) were heated in reconstituted milk or feeding formula pre-equilibrated at 52-58 degrees C for various times or mixed with powdered milk or feeding formula prior to reconstitution with water at 60-100 degrees C. The D-values of Cronobacter at 52-58 degrees C were significantly higher in whole milk (22.10-0.68 min) than in low fat (15.87-0.62 min) or skim milk (15.30-0.51 min) and significantly higher in lactose-free formula (19.57-0.66 min) than in soy protein formula (17.22-0.63 min). The z-values of Cronobacter in reconstituted milk or feeding formula ranged from 4.01 degrees C to 4.39 degrees C. Water heated to > or =70 degrees C and added to powdered milk and formula resulted in a > 4 log(10) reduction of Cronobacter. CONCLUSIONS: The heat resistance of Cronobacter should not allow the survival of the pathogen during normal pasteurization treatment. The use of hot water (> or =70 degrees C) during reconstitution appears to be an effective means to reduce the risk of Cronobacter in these products. SIGNIFICANCE AND IMPACT OF THE STUDY: This study supports existing data available to regulatory agencies and milk producers that recommended heat treatments are sufficient to substantially reduce risk from Cronobacter which may be present in these products.

Survival and growth of Cronobacter species (Enterobacter sakazakii) in wheat-based infant follow-on formulas.

AIMS: To determine the survival and growth characteristics of Cronobacter species (Enterobacter sakazakii) in infant wheat-based formulas reconstituted with water, milk, grape juice or apple juice during storage. METHODS AND RESULTS: Infant wheat-based formulas were reconstituted with water, ultra high temperature milk, pasteurized grape or apple juices. The reconstituted formulas were inoculated with Cronobacter sakazakii and Cronobacter muytjensii and stored at 4, 25 or 37 degrees C for up to 24 h. At 25 and 37 degrees C, Cronobacter grew more (>5 log(10)) in formulas reconstituted with water or milk than those prepared with grape or apple juices (c. 2-3 log(10)). The organism persisted, but did not grow in any formulas stored at 4 degrees C. Formulas reconstituted with water and milk decreased from pH 6.0 to 4.8-5.0 after 24 h, whereas the pH of the formulas reconstituted with fruit juices remained at their initial pH values, c. pH 4.8-5.0. CONCLUSIONS: Cronobacter sakazakii and C. muytjensii can grow in reconstituted wheat-based formulas. If not immediately consumed, these formulas should be stored at refrigeration temperatures to reduce the risk of infant infection. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study will be of use to regulatory agencies and infant formula producers to recommend storage conditions that reduce the growth of Cronobacter in infant wheat-based formulas.

Effect of desiccation, starvation, heat, and cold stresses on the thermal resistance of Enterobacter sakazakii in rehydrated infant milk formula.

Enterobacter sakazakii is an opportunistic foodborne pathogen that has been isolated from powdered infant milk formula. This study determined the effect of desiccation, starvation, heat and cold stresses on the thermal inactivation of E. sakazakii in rehydrated infant milk formula (RIMF). Stressed cells were mixed with RIMF at 52, 54, 56, and 58 degrees C for various time periods. The D- and z-values were determined by using linear regression analysis. D-values for unstressed E. sakazakii at 52, 54, 56, and 58 degrees C were 15.33, 4.53, 2, and 0.53 min, respectively. Desiccation and heat stresses, but not starvation or cold stress, caused significant (P < 0.05) reduction in D-values. The z-values of desiccated, starved, heat stressed, and cold stressed E. sakazakii were not significantly different from unstressed cells (4.22 degrees C). Thermal resistance of E. sakazakii in RIMF is affected by the environmental stresses; that is, desiccation and heat stresses that may surround the bacterium prior to the contamination of infant formula. The results of this study may be of use to regulatory agencies, infant milk producers, and infant caregivers to design heating processes to eliminate E. sakazakii that may be present in infant milk formula.

Detergent and sanitizer stresses decrease the thermal resistance of Enterobacter sakazakii in infant milk formula.

This study determined the effect of acid, alkaline, chlorine, and ethanol stresses on the thermal inactivation of Enterobacter sakazakii in infant milk formula. Unstressed or stressed cells were mixed with reconstituted powdered infant milk formula (PIMF) at temperatures between 52 and 58 degrees C for various time periods or mixed with PIMF prior to reconstitution with hot water between 50 and 100 degrees C. D- and z-values were determined using liner regression analysis. In general, detergent and sanitizer stresses decreased the thermal resistance of E. sakazakii in infant milk formula. The results of this study may be of use to regulatory agencies, manufacturers, and infant caregivers to design heating processes to eliminate E. sakazakii.

Inactivation of Enterobacter sakazakii in infant milk formula by gamma irradiation: determination of D10-value.

Enterobacter sakazakii is an emerging foodborne pathogen that has caused several cases of meningitis and necrotizing enterocolitis in infants and has been associated with infant formulas. Five strains of E. sakazakii were inoculated individually into brain heart infusion broth and rehydrated or dehydrated infant milk formula and exposed to ionizing radiation. E. sakazakii strains in brain heart infusion broth and rehydrated infant milk formula (RIMF) were exposed to irradiation dose of up to 1 kGy while strains in dehydrated infant milk formula (DIMF) were exposed to irradiation dose of up to 9 kGy. The D(10)-values were determined by using a linear regression model. Average calculated D(10)-values ranged from 0.21 to 0.29 kGy, 0.24 to 0.37 kGy, and 1.06 to 1.71 kGy in brain heart infusion broth, RIMF, and DIMF, respectively. The results obtained from this study will be useful for powdered infant milk formula industries to reduce the risk associated with E. sakazakii.

Thermal inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in breaded pork patties.

Decimal reduction times (D-values) and thermal resistance constants (z-values) for 3 foodborne pathogenic bacteria in formulated ready-to-eat breaded pork patties were determined with thermal inactivation studies. Meat samples, inoculated with Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes cultures or uninoculated controls, were packaged in sterile bags, immersed in circulated water bath, and held at 55, 57.5, 60, 62.5, 65, 67.5, and 70 degrees C for different durations of time. The D- and z-values were determined by using a linear regression model. Average calculated D-values for E. coli O157:H7, Salmonella, and L. monocytogenes at a temperature range of 55 to 70 degrees C were 32.11 to 0.08 min, 69.48 to 0.29 min, and 150.46 to 0.43 min, respectively. Calculated z-values for E. coli O157:H7, Salmonella, and L. monocytogenes were 5.4, 6.2, and 5.9 degrees C, respectively. The results of this study will be useful to food processors to validate thermal lethality of the studied foodborne pathogens in ready-to-eat breaded pork patties.