Effect of moisture on salmonella spp. heat resistance in cocoa and hazelnut shells

Izurieta, Walter Penaloza; Komitopoulou, Evangelia

doi:10.1016/j.foodres.2011.09.024

Cited by 33 publications

(13 citation statements)

References 37 publications

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“…Measurements before and after the thermal treatments at their longest time point resulted in a change in a w of less than 0.056 Ϯ 0.024 regardless of treatment temperature. This is important because it is critical to keep the food sample within the designated a w range, as a w will affect the long-term survival and resistance of bacterial cells upon treatment (28,30). Given the consistency of initial viable counts, the sequential mixing method using combined hand mixing and stomaching delivered homogeneously inoculated flour samples and an absence of bacterial cell clumps.…”

Section: Resultsmentioning

confidence: 99%

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

Forghani

Bakker

Futral

et al. 2018

Appl Environ Microbiol

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Wheat flour has been associated with outbreaks of enterohemorrhagic (EHEC), but little is known on EHEC's survival during storage and thermal processing. The objective of this study was to determine long-term viability and thermal inactivation kinetics of EHEC serogroups O26, O103, O111, and O157. Wheat flour samples were inoculated with a cocktail of five strains of a single serogroup and stored at 23 and 35°C. Inoculated samples were heated at 55, 60, 65, and 70°C. Viability was determined by plate counting. Decimal reduction time () and first decimal reduction time (δ) values were calculated with log-linear and Weibull models, respectively. At 23°C, EHEC counts declined gradually for 84 days and samples tested positive from 84 to 280 days. The thermal resistance ( and δ) values ranged from 7.5 to 8.2 and 3.1 to 5.3 days, respectively, but there were no significant differences among serogroups ( ≤ 0.05). At 35°C, no EHEC was quantifiable by day 7 and no positive samples were detected after 49 days. Heating at 55 and 65°C resulted in δ-value ranges of 15.6 to 39.7 min and 3.0 to 3.9 min, respectively, with no significant difference among serogroups either. Z values were 12.6, 6.7, 10.2, and 13.4°C for O26, O103, O111, and O157, respectively. Thermal death kinetics of EHEC in flour were better described using the Weibull model. Survival and inactivation rates of four serogroups were remarkably similar. These findings indicated that all EHEC serovars tested remained viable for at least 9 months at room temperature and survived for up to 60 min at 70°C in wheat flour. Enterohemorrhagic (EHEC) and have recently caused several gastroenteritis outbreaks and recalls of wheat flour. Because EHEC can cause illness with very low doses and there is very scarce information regarding their ability to survive storage and heating in flour, the present study was undertaken to assess the long-term survival of EHEC serogroups O26, O103, O111, and O157 in flour. These findings are relevant, as we report that EHEC can survive for more than 9 months in wheat flour during storage. In addition, results obtained suggest that thermal inactivation at 65°C for 30 min or 2 months of storage at 35°C may be feasible strategies to mitigate the risk of most EHEC serovars in wheat flour.

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Section: Resultsmentioning

confidence: 99%

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

Forghani

Bakker

Futral

et al. 2018

Appl Environ Microbiol

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“…Prior to this study, the literature investigating the effect of different inoculation methods on Salmonella survival (4,19,31) and thermal resistance (18) in low-moisture foods was limited to two inoculation methods each and two specific products (nuts and peanut butter). For most low-moisture products, the impact of inoculation methodologies on thermal resistance has not been evaluated (8,10,17,24,26); for the few products with evaluated inoculation methodologies (almond kernels, peanut butter, and flour), there are other inoculation methodologies used in the literature that have not been investigated, in terms of repeatability and inherent uncertainty (13,14,22,23,29,34). Of the five inoculation methods investigated in this study, only the methods involving lawn cultures harvested with a peptone buffer (LLI and LPI) produced results that were deemed sufficiently stable and repeatable to be used reliably when comparing or aggregating data across multiple studies or laboratories.…”

Section: Resultsmentioning

confidence: 99%

Effects of Inoculation Procedures on Variability and Repeatability of Salmonella Thermal Resistance in Wheat Flour

Hildebrandt

Marks

Ryser

et al. 2016

Journal of Food Protection

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Limited prior research has shown that inoculation methods affect thermal resistance of Salmonella in low-moisture foods; however, these effects and their repeatability have not been systematically quantified. Consequently, method variability across studies limits utility of individual data sets and cross-study comparisons. Therefore, the objective was to evaluate the effects of inoculation methodologies on stability and thermal resistance of Salmonella in a low-moisture food (wheat flour), and the repeatability of those results, based on data generated by two independent laboratories. The experimental design consisted of a cross-laboratory comparison, both conducting isothermal Salmonella inactivation studies in wheat flour (~0.45 water activity, 80°C), utilizing five different inoculation methods: (i) broth-based liquid inoculum, (ii) lawn-based liquid inoculum, (iii) lawn-based pelletized inoculum, (iv) direct harvest of lawn culture with wheat flour, and (v) fomite transfer of a lawn culture. Inoculated wheat flour was equilibrated ~5 days to ~0.45 water activity and then was subjected to isothermal treatment (80°C) in aluminum test cells. Results indicated that inoculation method impacted repeatability, population stability, and inactivation kinetics (α = 0.05), regardless of laboratory. Salmonella inoculated with the broth-based liquid inoculum method and the fomite transfer of a lawn culture method exhibited instability during equilibration. Lawn-based cultures resulted in stable populations prior to thermal treatment; however, the method using direct harvest of lawn culture with wheat flour yielded different D-values across the laboratories (α = 0.05), which was attributed to larger potential impact of operator variability. The lawn-based liquid inoculum and the lawn-based pelletized inoculum methods yielded stable inoculation levels and repeatable D-values (~250 and ~285 s, respectively). Also, inoculation level (3 to 8 log CFU/g) did not affect D-values (using the lawn-based liquid inoculum method). Overall, the results demonstrate that inoculation methods significantly affect Salmonella population kinetics and subsequent interpretation of thermal inactivation data for low-moisture foods.

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“…There were also studies with capillary tubes using water bath for apple juice 12 , and glass vials with an oven-heated sand bath for crushed cocoa bean and hazelnut shells to determine the bacteria's thermo-tolerance 13 . Although these devices are common tools with water or oil bath for characterizing heat-resistant bacterial spores in foods, various thermo-tolerances of the same bacatria have been frequently reported from different heating methods 4,6,[14][15][16]18 developed a new apparatus to control sample surface temperatures during rapid heating and cooling cycles.…”

Section: Knowledge Of Bacteria's Heat Resistance Is Essential For Devmentioning

confidence: 99%

Performance of a heating block system designed for studying the heat resistance of bacteria in foods

Kou¹,

Li²,

Wang³

2016

2016 ASABE International Meeting

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Knowledge of bacteria's heat resistance is essential for developing effective thermal treatments.Choosing an appropriate test method is important to accurately determine bacteria's heat resistances. Although being a major factor to influence the thermo-tolerance of bacteria, the heating rate in samples cannot be controlled in water or oil bath methods due to main dependence on sample's thermal properties. A heating block system (HBS) was designed to regulate the heating rates in liquid, semi-solid and solid foods using a temperature controller. Distilled water, apple juice, mashed potato, almond powder and beef were selected to evaluate the HBS's performance by experiment and computer simulation. The results showed that the heating rates of 1, 5 and 10 °C/min with final set-point temperatures and holding times could be easily and precisely achieved in five selected food materials. A good agreement in sample central temperature profiles was obtained under various heating rates between experiment and simulation. The experimental and simulated results showed that the HBS could provide a sufficiently uniform heating environment in food samples. The effect of heating rate on bacterial thermal resistance was evaluated with the HBS. The system may hold potential applications for rapid and accurate assessments of bacteria's thermo-tolerances.Knowledge of bacteria's heat resistance is of great importance in developing effective food processing methods. Selection of appropriate heating parameters can effectively reduce the target microorganism populations while achieving minimal thermal impacts on food quality. In addition to growth temperatures, stages of growth, bacterial strains, sample compositions, and the pH of the heating medium, heat resistance of bacteria is mainly affected by final temperature, holding time and heating rate 1-3 . Thermal death time (TDT) test is a common method to determine the heat resistance of bacteria 1,[4][5][6][7] . The device used for those TDT tests needs to meet the basic requirements, such as precisely controlled sample temperatures, a short come-up time (CUT) to avoid thermal adaptation of bacteria, and isothermal conditions for uniform sample temperature distributions 5 . Therefore, choosing an appropriate test method is important to obtain accurate determination of bacteria's heat resistance.There have been many studies on TDT test devices in foods. Odlaug et al. 8 used aluminum tubes in a miniature retort system to study thermal destruction of Clostridium botulinum spores in tomato juice. Gaze et al. 9 placed samples of ground meat in 0.5-to 1-mm thick sterile bags, and then immerged them in a shaking water bath. Kotrola et al.10 placed turkey meat samples into a TDT sealed tube heated by a shaking oil bath. Chung et al.11 designed an aluminum test cell heated in oil bath for determining the heat resistance of Clostridium sporogenes in selected foods. There were also studies with capillary tubes using water bath for apple juice 12 , and glass vials with an oven-heated sand bat...

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Effect of moisture on salmonella spp. heat resistance in cocoa and hazelnut shells

Cited by 33 publications

References 37 publications

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

Effects of Inoculation Procedures on Variability and Repeatability of Salmonella Thermal Resistance in Wheat Flour

Performance of a heating block system designed for studying the heat resistance of bacteria in foods

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