With recent improvements in the commercial feasibility of high pressure pasteurization units, the technology is gaining rapid acceptability across various sectors of food manufacturing, thus requiring extensive validation studies for effective adoption. Various times (1 min to 10 min) and intensity levels (0 MPa to 380 MPa) of elevated hydrostatic pressure were investigated for decontamination of mesophilic background microflora and inoculated Salmonella in orange juice. Results were analyzed by GLM procedure of SAS using Tukey- and Dunnett-adjusted ANOVA, additionally the Kmax and D-values were calculated using best-fitted (maximum R2) model obtained by GInaFit software. At 380 MPa, for treatments of 1 min to 10 min, D-value of 1.35, and inactivation Kmax of 3.34 were observed for Salmonella serovars. D-values were 5.90 and 14.68 for treatments of 241 MPa and 103 MPa, respectively. Up to 1.01 and >7.22 log CFU/mL reductions (p < 0.05) of habituated Salmonella serovars at planktonic stages were achieved using application of pressure at 380 MPa for 1 min and 10 min, respectively. Mesophilic background microflora counts were reduced (p < 0.05) by 1.68 to 5.29 log CFU/mL after treatment at 380 MPa for 1 min and 10 min, respectively. Treatments below two minutes were less efficacious (p ≥ 0.05) against the pathogen and background microflora, in vast majority of time and pressure combinations.
The current study investigated synergism of elevated hydrostatic pressure, habituation, mild heat, and antimicrobials for inactivation of O157 and non-O157 serogroups of Shiga toxin-producing Escherichia coli. Various times at a pressure intensity level of 450 MPa were investigated at 4 and 45 °C with and without carvacrol, and caprylic acid before and after three-day aerobic habituation in blueberry juice. Experiments were conducted in three biologically independent repetitions each consist of two replications and were statistically analyzed as a randomized complete block design study using ANOVA followed by Tukey- and Dunnett’s-adjusted mean separations. Under the condition of this experiment, habituation of the microbial pathogen played an influential (p < 0.05) role on inactivation rate of the pathogen. As an example, O157 and non-O157 serogroups were reduced (p < 0.05) by 1.4 and 1.6 Log CFU/mL after a 450 MPa treatment at 4 °C for seven min, respectively, before habituation. The corresponding log reductions (p < 0.05) after three-day aerobic habituation were: 2.6, and 3.3, respectively at 4 °C. Carvacrol and caprylic acid addition both augmented the pressure-based decontamination efficacy. As an example, Escherichia coli O157 were reduced (p < 0.05) by 2.6 and 4.2 log CFU/mL after a seven-min treatment at 450 MPa without, and with presence of 0.5% carvacrol, respectively, at 4 °C.
The current study investigated Listeria monocytogenes inactivation using mild heat with elevated hydrostatic pressure and nisin under buffered condition. A four-strain pathogen mixture was exposed to 0 (control) and up to 9 min of (1) 4 °C elevated pressure; (2) 4 °C elevated pressure and nisin; (3) 4 °C nisin; (4) heat at 40 °C; (5) 40 °C elevated pressure; (6) 40 °C elevated pressure and nisin; and (7) 40 °C nisin. Elevated hydrostatic pressure at 400 MPa (Hub880 Explorer, Pressure BioScience Inc., Easton, MA, USA) and nisin concentration of 5000 IU/mL were used in the trials. Analyses of variance were conducted, followed by Dunnett’s- and Tukey-adjusted means separations. Under conditions of these experiments, nisin augmented (p < 0.05) decontamination efficacy of 40 °C heat and elevated hydrostatic pressure treatments, particularly at treatment interval of 3 min. This synergism with nisin faded away (p ≥ 0.05) as the treatment time for thermal, high-pressure, and thermal-assisted pressure processing increased. The results of our study, thus, exhibit that practitioners and stakeholders of pressure-based technologies could benefit from synergism of mild heat and nisin for short-term, high-pressure pasteurization treatments to achieve microbial safety and economic feasibility comparable to traditional heat-treated products.
As many as 99% of illnesses caused by Listeria monocytogenes are foodborne in nature, leading to 94% hospitalizations, and are responsible for the collective annual deaths of 266 American adults. The current study is a summary of microbiological hurdle validation studies to investigate synergism of mild heat (up to 55 °C) and elevated hydrostatic pressure (up to 380 MPa) for decontamination of Listeria monocytogenes and natural background microflora in raw milk and phosphate-buffered saline. At 380 MPa, for treatments of 0 to 12 min, d-values of 3.47, 3.15, and 2.94 were observed for inactivation of the pathogen at 4, 25, and 50 °C. Up to 3.73 and >4.26 log CFU/mL reductions (p < 0.05) of habituated Listeria monocytogenes were achieved using pressure at 380 MPa for 3 and 12 min, respectively. Similarly, background microflora counts were reduced (p < 0.05) by 1.3 and >2.4 log CFU/mL after treatments at 380 MPa for 3 and 12 min, respectively. Treatments below three min were less efficacious (p ≥ 0.05) against the pathogen and background microflora, in the vast majority of time and pressure combinations. Results of this study could be incorporated as part of a risk-based food safety management system and risk assessment analyses for mitigating the public health burden of listeriosis.
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