A meta-analysis of microbial thermal inactivation in low moisture foods

Microbial thermal inactivation in low moisture foods is challenging due to enhanced thermal resistance of microbes and low thermal conductivity of food matrices. In this study, we leveraged the body of previous work on this topic to model key experimental features that determine microbial thermal inactivation in low moisture foods. We identified 27 studies which contained 782 mean D-values and developed linear mixed-effect models to assess the effect of microorganism type, matrix structure and composition, water activity, temperature, and inoculation and recovery methods on cell death kinetics. Intraclass correlation statistics (I2) and conditional R2 values of the linear mixed effects models were: E. coli (R2-0.91, I2-83%), fungi (R2-0.88, I2-85%), L. monocytogenes (R2-0.84, I2-75%), Salmonella (R2-0.69, I2-46%). Finally, global response surface models (RSM) were developed to further study the non-linear effect of aw and temperature on inactivation. The fit of these models varied by organisms from R2 0.88 (E. coli) to 0.35 (fungi). Further dividing the Salmonella data into individual RSM models based on matrix structure improved model fit to R2 0.90 (paste-like products) and 0.48 (powder-like products). This indicates a negative relationship between data diversity and model performance.

Alicyclobacillus mali sp. nov., Alicyclobacillus suci sp. nov. and Alicyclobacillus fructus sp. nov., thermoacidophilic sporeforming bacteria isolated from fruit beverages

Six thermo-acidophilic, spore-forming strains were isolated from a variety of juice products and were characterized genetically and phenotypically. According to 16S rRNA and rpoB gene phylogenetic analyses and average nucleotide identity comparisons against the species demarcation cutoff at <95 %, these six strains were determined to represent three novel species of Alicyclobacillus. The isolates were designated FSL-W10-0018^T, FSL-W10-0037, FSL-W10-0048, VF-FSL-W10-0049^T, FSL-W10-0057 and FSL-W10-0059^T. All six isolates were Gram-positive, motile, rod shaped, contained menaquinone 7 as the major respiratory quinone and had ω-cyclohexane C_17 : 0 as a major fatty acid. They were all able to grow aerobically in a range of acidic and moderate thermal conditions. Only isolates FSL-W10-0048 and VF-FSL-W10-0049^T were able to produce guaiacol. The following names are proposed for the three new species: Alicyclobacillus mali sp. nov. (type strain FSL-W10-0018^T =DSM 112016^T=NCIMB 15266^T); Alicyclobacillus suci sp. nov (VF-FSL-W10-0049^T=DSM 112017^T=NCIMB 15265^T); and Alicyclobacillus fructus sp. nov. (FSL-W10-0059^T=DSM 112018^T=NCIMB 15264^T).

Effect of Time, Temperature, and Transport Media on the Recovery of Listeria monocytogenes from Environmental Swabs

ABSTRACT

Environmental monitoring for Listeria monocytogenes in food processing environments is key for ensuring the safety of ready-to-eat foods. For sampling, swabs are often hydrated with a wetting or transport medium that may contain neutralizers and other ingredients. After swabbing the environment, the swabs may then be transported or shipped cold to an off-site laboratory for testing, ideally within 48 h. Extended shipping times may subject the pathogen to increased temperatures in the presence of the wetting medium, organics, and other chemicals from the processing facility that could confound detection. This study evaluated growth and detection of L. monocytogenes on stainless steel exposed to either buffer or sodium hypochlorite before drying. Swabs were rehydrated with Butterfield's phosphate buffer, neutralizing buffer, Letheen broth, or Dey-Engley neutralizing broth before swabbing. Swabs were stored in the presence of no added food, cheese whey, or ice cream under both optimal (4°C) and suboptimal (15°C) temperatures for up to 72 h. Overall, there was no growth of L. monocytogenes at 4°C through 72 h of storage, although enrichment from these swabs was dependent on the presence and type of food matrix. Pathogen growth during storage at 15°C was more variable and depended on both the food matrix and transport media used, with Dey-Engley and Letheen broths allowing for the highest population increases. Overall, more enrichments resulting in L. monocytogenes detections were observed when using Letheen broth and neutralizing buffer than Dey-Engley broth, which resulted in fewer detections at 15°C. Logistic regression and Cochran-Mantel-Haenszel analyses determined that storage temperature, transport media, and food matrix all significantly affected detection of L. monocytogenes, whereas storage time did not have a clear effect on recovery from swabs.

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Production of gaseous radiotracers for industrial applications

This paper describes prerequisite tests, analysis and the procedure for irradiation of gaseous targets and production of gaseous radioisotopes i.e. argon-41 ((41)Ar) and krypton-79 ((79)Kr) in a 100MWTh DHRUVA reactor located at Bhabha Atomic Research Center (BARC), Trombay, Mumbai, India. The produced radioisotopes will be used as radiotracers for tracing gas phase in industrial process systems. Various details and prequalification tests required for irradiation of gaseous targets are discussed. The procedure for regular production of (41)Ar and (79)Kr, and assay of their activity were standardized. Theoretically estimated and experimentally produced amounts of activities of the two radioisotopes, irradiated at identical conditions, were compared and found to be in good agreement. Based on the various tests, radiological safety analysis and standardization of the irradiation procedure, necessary approval was obtained from the competent reactor operating and safety authorities for regular production of gaseous radiotracers in DHRUVA reactor.