Effect of nisin, EDTA, and abuse temperature on the growth of Salmonella Typhimurium in liquid whole egg during refrigerated storage.

Salmonella spp. can be present in pasteurized liquid egg products because of its heat resistance or post-processing contamination, thereby representing a food safety risk. The effect of 1000 IU nisin/ml plus 20 mM disodium ethylenediaminetetraacetic acid (EDTA), two refrigerated temperatures (7 °C and 10 °C), and two inoculation levels (103 and 105 cfu/ml) were studied in the growth of S. Typhimurium in pasteurized liquid whole egg (LWE). Two mathematical models were used to fit the microbial curves. Physicochemical characteristics of LWE, such as pH and color, were assessed for 31 days at the two storage temperatures, and no significant changes (p < 0.05) were observed for most of the samples. Results showed the significant impact of temperature on microbial growth. Samples kept at 7 °C showed the decay of microbial cells during storage; meanwhile, the effect at 10 °C was shown as fast growth. The combination of nisin plus EDTA and 7 °C accelerated the decay of microbial cells during the storage showing a synergistic effect. The Weibull model described the decline of cells during the shelf-life. Meanwhile, the logistic model fitted the growth of Salmonella in LWE at 10 °C. Adding these additives to LWE, combined with the correct temperature during pasteurization and adequate conditions during the cold chain, can minimize the food safety risk related to Salmonella.

Evaluation of 405-nm monochromatic light for inactivation of Tulane virus on blueberry surfaces.

AIM: The study aim was to evaluate the potential of 405-nm light as a virus intervention for blueberries. METHODS AND RESULTS: Tulane virus (TV)-inoculated blueberries were treated with 4·2 mW cm-2 of 405-nm light for 5-30 min. To mitigate thermal heating due to the intense light, a dry ice-chilled, nitrogen-based cooling system was utilized. Blueberries were rotated to ensure exposure of all surfaces to 405-nm light. Five-, 15- and 30-min treatments resulted in little or no inactivation of TV on blueberries (average log reductions of -0·18; -0·02; and +0·06 respectively). Since 405-nm light's inactivation mechanism may involve singlet oxygen, two singlet oxygen enhancers, riboflavin and rose bengal, were used to coat the blueberries prior to 405-nm light treatment. When 0·1% riboflavin or rose bengal was added, resulting in an average PFU reduction of -0·51 and -1·01 logs respectively. However, it was noted that the addition of riboflavin and rose bengal in the absence of 405-nm light treatment produced some inactivation. Average untreated log reductions for riboflavin and rose bengal were -0·13 and -0·66 respectively. Also, 60-30-s 405-nm light pulses with 2-min ambient cooling periods without the dry ice nitrogen cooling system did not inactivate TV, suggesting that oxygen limitation by the nitrogen CO2 mixture was not the cause of limited inactivation. CONCLUSIONS: Overall results indicate that 405-nm light has some potential to inactivate viruses if singlet oxygen enhancers are present. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential of visible monochromatic violet/blue light (405 nm) as a nonthermal intervention for viruses on foods, such as berries that are prone to norovirus contamination, had not been previously evaluated. Use of food-grade singlet oxygen enhancer compounds in combination with visible spectra light may offer a means to inactivate foodborne viruses.

Localization, growth, and inactivation of Salmonella Saintpaul on jalapeño peppers.

Consumption of Salmonella-contaminated jalapeño peppers has been implicated in one of the largest foodborne illness outbreaks in the summer of 2008. The objective of this study was to investigate representative groups of native microflora and the distribution, growth, and inactivation of experimentally-inoculated Salmonella Saintpaul on jalapeño peppers. Two genetically modified strains of Salm. Saintpaul producing either green- or red-fluorescent protein were constructed and used in the study. Microbiological analyses showed that jalapeño peppers contained an average of 5.6 log units of total aerobic count and 3.5, 1.8, and 1.9 log units, respectively, of enterobacteriaceae, lactic acid bacteria, and yeast/mold per gram of tissue. Strains typical of Pseudomonas accounted for 8.3% of total aerobic count, and 0.2% of which exhibited pectolytic activity. On inoculated peppers, a vast majority (>90%) of Salm. Saintpaul was recovered from stem/calyx and only a small proportion recovered from fleshy pods. Growth of Salm. Saintpaul on peppers was indicated by an increase in the population of 3 log units after incubation of samples at 20 degrees C for 48 h. Fluorescent Salm. Saintpaul aggregates could be readily detected on stem/calyx using stereofluorescence imaging microscopy and scanning electron microscopy. Data presented showed that Salm. Saintpaul could survive for at least 8 wk on peppers stored at 4 degrees C. Immersion of inoculated peppers in 200 ppm of sodium hypochlorite, acidified sodium chlorite, or peroxy acetic acid for 10 min could reduce the number of Salm. Saintpaul on stem/calyx by 1.5 to 1.7 and that on flesh by 2.1 to 2.4 log units. Practical Application: Consumption of Salmonella-contaminated jalapeño peppers has been implicated in foodborne illness outbreaks. The vast majority of Salmonella Saintpaul recovered from inoculated jalapeño peppers (>90%) was from stem/calyx. Salmonella increased by 3 log units during storage at 68 degrees F (20 degrees C) for 48 h. Salmonella could survive for at least 8 wk on peppers stored at 4 degrees C. Immersion of inoculated peppers in 200 ppm of sodium hypochlorite, acidified sodium chlorite, or peroxyacetic acid for 10 min reduced Salmonella on stem/calyx by 1.5 to 1.7 log units, compared with reductions of 2.1 to 2.4 log units on flesh. These results highlight the need to consider the stem/calyx as the most likely area for contamination of jalapeño peppers, and to process this commodity accordingly to minimize exposure and cross-contaminations.

Irradiation compared with chlorination for elimination of Escherichia coli O157:H7 internalized in lettuce leaves: influence of lettuce variety.

Pathogenic bacteria internalized in leaf tissues are not effectively removed by surface treatments. Irradiation has been shown to inactivate leaf-internalized bacteria, but many aspects of targeting these protected pathogens remain unknown. Bacterial cells of a cocktail mixture of 3 isolates of Escherichia coli O157:H7 were drawn into the leaves of iceberg, Boston, green leaf, and red leaf lettuce using vacuum perfusion. The inoculated leaves were treated with a 3-min wash with sodium hypochlorite solution (0, 300, or 600 ppm) or various doses of ionizing radiation (0.25 to 1.5 kGy). Leaves were stomached to recover the internalized cells and survivors enumerated. Washes with 0 ppm (water), 300 ppm, and 600 ppm chlorine solutions each gave reductions of less than 1 log. These reductions were statistically significant only in the case of green leaf lettuce. In contrast, irradiation effectively reduced E. coli O157:H7 on all varieties examined, with all doses tested being significantly reduced from the untreated control. The specific variety influenced the efficacy of irradiation. The greatest reduction obtained was 5 logs on iceberg lettuce treated with 1.5 kGy. The D(10) values (the dose necessary to achieve a 1 log reduction) were significantly (P < 0.05) different among the varieties of lettuce tested, and ranged from 0.30 kGy (iceberg) to 0.45 kGy (Boston). These values were observed to be notably higher than previous irradiation D(10) values for E. coli O157:H7 surface inoculated onto these 4 lettuce varieties. This study has shown that irradiation is able to effectively reduce viable E. coli O157:H7 cells internalized in lettuce, and that the variety of lettuce influences the specific response.

Modeling the irradiation followed by heat inactivation of Salmonella inoculated in liquid whole egg.

This study presents mathematical models that describe the inactivation of Salmonella Enteritidis, Salmonella Typhimurium, and Salmonella Senftenberg suspended in liquid whole egg (LWE) by irradiation followed by heat treatments (IR-H treatments). These models also enable prediction of cell injury in Salmonella after exposure to IR-H. Salmonella viability decreased exponentially (primary model) with heat treating time for all the radiation doses (0, 0.1, 0.3, 0.5, 1.0, and 1.5 kGy) and temperatures investigated (55, 57, and 60 degrees C). Two secondary models that related the D(T) values (time required to eliminate 90% of viable cells at a given temperature) with radiation dose, heating temperature, and recovery medium after treatments were also developed. The developed final equations enabled to establish the process criterion (combinations of irradiation doses, temperature, and heat treatment times) required to achieve a given reduction (performance criterion) in Salmonella spp. suspended in LWE or the cell damage caused by the treatments. Process criteria to obtain the established performance criteria (a 5-log(10) reduction) on any of the investigated Salmonella serovars were determined to be, 57.7 degrees C/3.5 min following 1.5 kGy when treated cells were recovered in tryptic soy agar and 59.3 degrees C/3.5 min following 0.5 kGy when cells were recovered in tryptic soy agar amended with 3% NaCl. Based on our results, current industrial LWE heat treatments (60 degrees C/3.5 min) would inactivate 3 log(10) cycles of the Salmonella population. The results of this study can be applied to engineering design and for the evaluation and optimization of the IR-H process as a new technique to obtain Salmonella-free LWE.

Inhibitory activity of honey against foodborne pathogens as influenced by the presence of hydrogen peroxide and level of antioxidant power.

Antimicrobial activity of honey has been attributed to hydrogen peroxide, which is produced by naturally occurring glucose oxidase, and phenolic compounds, although lethality of and inhibition by these and other components against microorganisms vary greatly, depending on the floral source of nectar. This study was undertaken to compare honeys from six floral sources for their inhibitory activity against Escherichia coli O157:H7, Salmonella typhimurium, Shigella sonnei, Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus. A disc assay revealed that development of zones of inhibition of growth depends on the type and concentration of honey, as well as the test pathogen. Growth of B. cereus was least affected. The inhibition of growth of S. sonnei, L. monocytogenes, and S. aureus in 25% solutions of honeys was reduced by treating solutions with catalase, indicating that hydrogen peroxide contributes to antimicrobial activity. Darker colored honeys were generally more inhibitory than light colored honeys. Darker honeys also contained higher antioxidant power. Since antimicrobial activity of the darker colored test honeys was not eliminated by catalase treatment, non-peroxide components such as antioxidants may contribute to controlling the growth of some foodborne pathogens. The antibacterial properties of honeys containing hydrogen peroxide and characterized by a range of antioxidant power need to be validated using model food systems.

Citrus juice composition does not influence radiation sensitivity of Salmonella enteritidis.

Food substrate chemistry is known to influence radiation sensitivity of pathogenic bacteria. The sensitivity of a citrus juice outbreak strain of Salmonella Enteritidis to gamma radiation was determined in five commercial orange juice formulations. The juices differed in pH (3.87 to 4.13), calcium concentration (2.1 versus 36.9 mM), juice composition (orange versus orange-tangerine blend), and antioxidant power (11,751 to 12,826 microM ferric reducing-antioxidant power units). The Dgamma (dose required to achieve 90% destruction) varied only slightly (0.35 to 0.37 kGy), with no significant (P < 0.05) differences among any of the suspending juices. These results indicate that Salmonella Enteritidis sensitivity to gamma radiation is not strongly influenced by the composition of formulated commercial orange juices.

Irradiation inactivation of four Salmonella serotypes in orange juices with various turbiditiest.

Reconstituted orange juice inoculated with Salmonella Anatum, Salmonella Infantis, Salmonella Newport, or Salmonella Stanley was treated with gamma radiation at 2 degrees C. To determine the relationship between juice antioxidant power and Dgamma (dose required to achieve 90% mortality), juice solids were removed prior to inoculation by centrifugation and/or filtration to create juice preparations of varying turbidity. In unadulterated orange juice, Salmonella Anatum (Dgamma = 0.71 kGy) was significantly more resistant than the other species tested. Salmonella Newport (Dgamma = 0.48 kGy) and Salmonella Infantis (Dgamma = 0.35 kGy) were significantly different, while Salmonella Stanley (Dgamma = 0.38 kGy) was intermediate between the two. Neither the resistance of each isolate nor the pattern of relative resistance among isolates was altered in reduced turbidity juice preparations. Although total antioxidant power was associated with the level of juice solids resuspended in phosphate buffer, antioxidant power was not significantly associated with turbidity in the juice preparations or with Dgamma of any species. The variable resistance to irradiation of the Salmonella isolates suggests this as a more significant factor than turbidity or antioxidant power in designing antimicrobial juice irradiation protocols.

Border cells and arbuscular mycorrhizae in four amaranthaceae species.

ABSTRACT Four species from the family Amaranthaceae were studied to determine border cell production and arbuscular mycorrhizal colonization. It was found that border cells, also known as sloughed root cap cells, are produced by all plant species studied and increase with increasing root length until a maximum number is reached at a root length of 25 mm. However, the increase in border cells with increasing root length is not uniform between species. Arbuscular mycorrhizal root colonization was found in all the Amaranthaceae species, and arbuscular mycorrhizal colonization was positively correlated with maximum border cell production.