Mark. T. Morgan

Pasteurization has long been the standard method to extend the shelf-life of dairy products, as well as a means to reduce microbial load and the risk of food-borne pathogens. However, the process has limitations, which include cost effectiveness, high energy input, and reduction of product quality/organoleptic characteristics. In an effort to reduce these limitations and extend shelf-life, this study examined a novel low temperature, short time (LTST) method in which dispersed milk in the form of droplets was treated with low heat/pressure variation over a short treatment time, in conjunction with pasteurization. Lactobacillus fermentum and Pseudomonas fluorescens Migula were exposed to conventional pasteurization treatments with and without LTST. Using these organisms, the LTST addition was able to reduce microbial load below detection limits; 1.0 × 101 cfu/mL, from approximately 1.2 × 108 and 1.0 × 107 cfu/mL for L. fermentum and P. fluorescens Migula, respectively. In addition, the shelf-life of the treated, raw, and uninoculated product was prolonged from 14 to 35 days, compared with standard pasteurization, to as long as 63 days with the LTST amendment. Sensory analysis of samples also demonstrated equal or greater preference for LTST + pasteurization treated milk when compared to pasteurization alone (α = 0.05). Conventional pasteurization was effective at reducing the above mentioned microorganisms by as much as 5.0 log10 cfu/mL. However, LTST was able to achieve 7.0–8.0 log10 cfu/mL reduction of the same microorganisms. In addition, BActerial Rapid Detection using Optical scattering Technology detected and identified microorganisms isolated both pre- and post-treatment, of which the only organisms surviving LTST were Bacillus spp. Increased lethality, improved shelf-life, and equal or better organoleptic characteristics without increased energy consumption demonstrate the effectiveness of the incorporation of LTST. The improved shelf-life may potentially have major impacts in the dairy industry in terms of shipping and overall sustainability.

Acute gastroenteritis caused by human norovirus is a significant public health issue. Fresh produce and seafood are examples of high-risk foods associated with norovirus outbreaks. Food contact surfaces also have the potential to harbor noroviruses if exposed to fecal contamination, aerosolized vomitus, or infected food handlers. Currently, there is no effective measure to decontaminate norovirus on food contact surfaces. Chlorine dioxide (ClO ₂ ) gas is a strong oxidizer and is used as a decontaminating agent in food processing plants. The objective of this study was to determine the kinetics and mechanism of ClO ₂ gas inactivation of a norovirus surrogate, murine norovirus 1 (MNV-1), on stainless steel (SS) coupons. MNV-1 was inoculated on SS coupons at the concentration of 10 ⁷ PFU/coupon. The samples were treated with ClO ₂ gas at 1, 1.5, 2, 2.5, and 4 mg/liter for up to 5 min at 25°C and a relative humidity of 85%, and virus survival was determined by plaque assay. Treatment of the SS coupons with ClO ₂ gas at 2 mg/liter for 5 min and 2.5 mg/liter for 2 min resulted in at least a 3-log reduction in MNV-1, while no infectious virus was recovered at a concentration of 4 mg/liter even within 1 min of treatment. Furthermore, it was found that the mechanism of ClO ₂ gas inactivation included degradation of viral protein, disruption of viral structure, and degradation of viral genomic RNA. In conclusion, treatment with ClO ₂ gas can serve as an effective method to inactivate a human norovirus surrogate on SS contact surfaces.

Previous studies show that treatment of cantaloupes with chlorine dioxide (ClO2) gas at 5 mg/liter for 10 min results in a significant reduction (P < 0.05) in initial microflora, an increase in shelf life without any alteration in color, and a 4.6- and 4.3-log reduction of Escherichia coli O157:H7 and Listeria monocytogenes, respectively. However, this treatment could result in the presence of chloroxyanion residues, such as chloride (Cl−), chlorite (ClO2−), chlorate (ClO3−), and perchlorate (ClO4−), which, apart from chloride, are a toxicity concern. Radiolabeled chlorine dioxide (36ClO2) gas was used to describe the identity and distribution of chloroxyanion residues in or on cantaloupe subsequent to fumigation with ClO2 gas at a mean concentration of 5.1 ± 0.7 mg/liter for 10 min. Each treated cantaloupe was separated into rind, flesh, and mixed (rind and flesh) sections, which were blended and centrifuged to give the corresponding sera fractions. Radioactivity detected, ratio of radioactivity to mass ...

Significant food-borne disease outbreaks have occurred from consumption of ready-to-eat foods, including produce, contaminated withListeria monocytogenes. Challenging food matrices (e.g., cantaloupe, sprouts) with limited processing steps postharvest to reduce pathogen loads have underscored a need for new mitigation strategies. Chlorine dioxide (ClO₂) is increasingly being used in produce and other food systems to reduce food-borne pathogen levels. The goal of this study was to characterize the transcriptional response and survival ofL. monocytogenes10403S exposed to ClO₂. The transcriptional profile of log-phase cells exposed to 300 mg/liter ClO₂for 15 min was defined by whole-genome microarray. A total of 340 genes were significantly differentially expressed. Among the differentially expressed genes, 223 were upregulated (fold change ≥ 1.5; adjustedPvalue < 0.05) in role categories responsible for protein fate, cellular processes, and energy metabolism. There were 113 and 16 genes differentially expressed belonging to regulatory networks of σ^Band CtsR, respectively. We assessedL. monocytogenes10403S survival after exposure to 100, 300, and 500 mg/liter aqueous ClO₂in brain heart infusion (BHI) broth; there was a significant difference between cells exposed to 500 mg/liter ClO₂and those exposed to all other conditions over time (Pvalue < 0.05). Isogenic ΔsigBand ΔctsRmutants exposed to 300 mg/liter ClO₂were more sensitive to ClO₂than the wild type under the same conditions. These results provide an initial insight into the mechanisms thatL. monocytogenesemploys to survive sublethal ClO₂and further our understanding of the inactivation mechanisms of this increasingly used sanitizer.

A multivariate data analysis was performed on responses of an impedimetric biosensor to quantify Salmonella typhimurium. To develop the impedimetric biosensor, an interdigitated microelectrode (IME) was fabricated by using a semiconductor fabrication process. Anti-Salmonella antibodies were immobilized based on streptavidin–biotin binding on the surface of the IME to form an active sensing layer. The impedance spectra of the biosensor were measured at frequencies ranging between 10 Hz and 1 MHz with different concentrations of S. typhimurium in PBS and pork samples. Partial-least squares (PLS) regression models were developed and evaluated as a multivariate data analysis method. The best PLS regression model developed from impedance spectra that were acquired with different individual biosensors had the correlation coefficient of determination (R²) 0.75 and 0.59 for PBS and pork samples, respectively. The PLS models estimated the concentration of S. typhimurium with 1.49 and 1.96 Log CFU mL⁻¹ of root mean square of error in prediction (RMSEP) for PBS and pork samples, respectively. The PLS model built with impedance data from the same biosensor improved R² to 0.85 and 0.89, and reduced the RMSEPs to 1.13 and 1.02 Log CFU mL⁻¹ for PBS and pork samples, respectively. This study showed the feasibility of quantifying S. typhimurium by performing multivariate analysis on responses from the impedimetric biosensor.