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In this study, the thermal inactivation kinetics of Paenibacillus sanguinis 2301083PRC and Clostridium sporogenes JCM1416MGA were determined in full and low fat “requeijao cremoso”. Requeijao cremoso” is a type of processed cheese widely produced and consumed in Brazil. From a total of 79 strains of six different species of sporeforming bacteria isolated from “requeijao cremoso”, 12 strains of P. sanguinis , 14 strains of B. thuringiensis , and 21 strains of C. sporogenes survived to heat shock at 140°C/1 min. Then, two strains ( P. sanguinis 2301083PRC and C. sporogenes JCM1416MGA) were selected for the determination of inactivation kinetic parameters in full and low fat “requeijao cremoso” in the range of 85 °C–115 °C. The inactivation curves did not follow first order kinetic and Weibull model was used to estimate inactivation kinetic parameters. Significantly higher δ values were found for P. sanguinis 2301083PRC in low fat “requeijao cremoso” compared to full fat “requeijao cremoso” at 85 °C and 105 °C, showing that the formulation affected heat inactivation kinetics of this microorganism (p C. sporogenes JCM1416MGA was more heat resistant than P. sanguinis 2301083PRC, with δ (time for the first decimal reduction) values of 10, 3 and 1.3 min at 105, 110 and 115 °C, respectively. The 4D times (time for four decimal reductions) for this strain reached 19 min at 115 °C. The z values of P. sanguinis 2301083PRC and C. sporogenes JCM1416MGA were 8.1 °C and 14.2 °C and 5.9 °C and 10.8 °C in low fat and full fat “requeijao cremoso”, respectively. The results obtained in this study show that current thermal processes applied during “requeijao cremoso” production will have a minor impact on the concentration of spores of the most heat resistant strains such as C. sporogenes JCM1416MGA. Despite this, C. sporogenes JCM1416MGA could serve as an adequate target for the design of the thermal process to be applied in full-fat and low-fat formulations of “requeijao cremoso”.

We have developed a novel roller conveyer plasma device, which generates gas plasma via atmospheric pressure dielectric barrier discharge (APDBP) on rollers. High voltage and earth electrodes are incorporated into the rollers, which are covered with a silicon sheet. Bactericidal activity of the device was measured against Xanthomonas campestris pv. campestris (Xcc), which was spotted onto aluminium plates and subjected to gas plasma treatment generated by APDBD. After treatment, viable cell number of Xcc decreased with a decimal reduction time (D value) of 0.90 min (initial population: 5.0 × 108 CFU/ml) and below 0.34 min (initial population: 9.8 × 105 CFU/ml). APDBD treatment induced slight morphological changes to Xcc along with significant degradation of lipopolysaccharides (LPS) and degradation/oxidation of genomic DNA to form 8-hydroxy-2'-deoxyguanosine (8-OHdG). Reactive chemical products (hydrogen peroxide, nitrite and nitrate), ultraviolet light (UV-A) and slight temperature elevations were observed during operation of the device. Our results suggest hydrogen peroxide and nitrite generated during operation of the device cause oxidation and degradation of the genomic DNA as well as the degradation of LPS, which are potential mechanisms for inactivation. In addition, the successful inactivation of Xcc on cabbage leaf by the device suggests the method could have practical applications.

High-fat low-moisture foods are often implicated in outbreaks of Salmonellosis. Research has suggested that the fat content in peanut butter may play an important role in protecting Salmonella from thermal inactivation. Our recent studies indicate that the water activity (aw) of oil reduces sharply with increasing temperature, which causes desiccation to the bacteria and consequently enhances their thermal resistance. Therefore, a humid heating environment may help accelerate the thermal inactivation rate of bacteria inside oil. In this research, we selected Enterococcus faecium NRRL B-2354 (E. faecium) as a surrogate of Salmonella to study how the bacterium inside oil responds to thermal treatments under different relative humidities (RHs). Specially, we determined the decimal reduction time (D-value) of E. faecium in peanut oil which was exposed to different RHs (0–100%) at 80 °C. The data revealed that the D80 of E. faecium in 0.51 mm oil layers reduced exponentially from 6335.8 to 9.6 min with increasing RH (0–61%), then stayed constant (7.7 ± 1.5 min) at higher RH levels (61–100%). Further experiments with reduced sample thicknesses (0.26 & 0.10 mm) revealed significantly lower D80 values in thinner oil layers than in thicker oil layers at those high RH levels (61%–100%). The results of this study indicate that the water vapor equilibration was not reached in oil in short-time high-RH thermal treatments. This study suggests that oil protects bacteria from thermal inactivation not only through desiccation of bacterial cells but also by serving as a moisture barrier to hinder environmental water vapor from rehydrating the bacteria during short-time high-RH thermal processing.

A comparative study was performed to assess the efficacy of UV-C light emitting diodes (UV–C LEDs) at 277 nm and a low-pressure mercury (LPM) lamp at 253.7 nm to inactivate Penicillium expansum spores on apple skin at 4 °C or 25 °C. In saline solution, the D value for the inactivation of spores using 277 nm at 25 °C was 6.62 mJ cm−2 and 7.19 mJ cm−2 at 4 °C, both of which were significantly lower than the D value at 253.7 nm (9.26 mJ cm−2). The UV-mediated inactivation of spores on the surface of apple skin followed non-linear kinetics with an initial linear phase followed by tailing. The calculated D values for spores on apple surface were significantly higher compared to within saline (14.49 and 18.80 mJ cm−2 with 277 nm at 25 °C and 4 °C, respectively, compared to 23.00 mJ cm−2 with 253.7 nm). This could be due to protective effects of apple peel constituents or the non-uniform energy distribution due to the uneven apple surface. Yet, the log reductions achieved (>2 log CFU) were equivalent to washing in hypochlorite solution (200 mg L−1 free-chlorine) which is the current industrial practice. UV-C light at 277 and 253.7 nm (500 mJ cm−2) was shown to prevent growth of blue mould and subsequent spoilage of inoculated and stored apples (28 days) if treated prior to damage. The UV-C treatments at doses corresponding to reduction of 2 log CFU of P. expansum did not impact apple physico-chemical quality parameters during 12 weeks of storage at 25 °C.

Salmonella is one of the most important causative agents of food borne infections in terms of food hygiene. In this study, we investigated whether N 2 gas plasma, generated by applying a short high-voltage pulse to N 2 using a static induction thyristor power supply (1.5 kilo pulse per second), exhibited a bactericidal/disinfecting effect against Salmonella . Viable cell number of Salmonella was efficiently decreased with a decimal reduction time ( D value) of 0.178 min (initial slope) and 3.105 min (single-slope approximation). Plasma treatment altered the surface structure of Salmonella , as observed by scanning electron microscopy. In addition, this treatment induced a marked degradation in O antigen. Polymerase chain reaction (PCR) analysis also suggested that the Salmonella genomic DNA was damaged by the plasma treatment. Reactive chemical products (hydrogen peroxide-like chemicals), ultraviolet light (UV-A) and slight temperature elevations were observed during the operation of the gas plasma device. Viable cell number versus intensity of each potential bactericidal factor were used to identify the primary mechanism of disinfection of Salmonella . Although equivalent levels of UV-A or heat treatment did not inactivate Salmonella , treatment with a low concentration of hydrogen peroxide efficiently inactivated the bacteria. Our results suggest the N 2 gas plasma generates reactive chemical species that alter components of Salmonella such as the cell surface as well as damaging the genomic DNA. The combined effect of these reactive species is to induce cell death.

Shigatoxin-producing Escherichia coli (STEC) are one of the important pathogens of concern in various foods and beef in particular. Ultra violet radiation (UV) is an important non thermal treatment that can be very effective in controlling STEC. Current research was aimed at studying the resistance of various STEC to UV and determining suitability of nalidixic acid adapted (Nal) STEC strains for UV inactivation studies. A total of 20 parent strains and 20 Nal strains of E. coli O157:H7, O26, O45, O103, O104, O111, O121 and O145 along with nonpathogenic surrogates (ATCC 1427 and 1428) were used in this study (individual strain and cocktail). Pure cultures of the respective pathogens were treated with UV at three different intensities (1.04, 1.92 and 3.02 mW/cm2). The D values (time needed for one log reduction at a particular intensity) were determined from the linear portion of the inactivation curves. The results show that among the five E. coli O157:H7 strains tested, strain 5 was the most resistant strain with a D value of 86.8 s at 1.04 mW/cm2 UV intensity and E. coli O104:H4 was the most resistant non-O157 serogroup with D value of 65.8 s. An overall comparison of the entire parent STEC strains shows that the serogroup E. coli O157:H7 was the most resistant one to UV. It was observed that the D values of parent strains except for E. coli O157:H7 strain E932 were significantly higher (p

This study investigated the thermal inactivation of five Campylobacteraceae species (Campylobacter coli, Campylobacter helveticus, Campylobacter concisus, Campylobacter fetus subsp. fetus and Arcobacter butzleri) at 55 and 60 °C using an immersed coil heating apparatus. The applicability of nine different models, including log linear and Weibull type models, some of which accounted for shoulders and tailing populations at the start or end of the heat treatment, was assessed to describe the thermal inactivation of each species. The Weibull model with tailing effect provided a good fit with low RMSE value (0.07–0.27), AICc (−88.12 to −6.82) and high R2 values (0.97–0.99) depending on the temperature and the species. The Weibull + tail model showed a significantly high D value for Arcobacter butzerli (180.2 s) at 55 °C and a low D value for C. helveticus (23.9 s) at 60 °C, with a high degree of variability in thermal tolerance noted across the species. Moreover, the Weibull + tail model also indicated high thermal sensitivity for C. fetus subsp. fetus at both temperatures investigated. This study highlights the value of assessing various inactivation models to describe the D value to get the model which best describes the survival data. These model predictions enhance knowledge about the survival characteristics and behaviour of fastidious Campylobacteraceae in the food chain.

The individual and combined effects of high pressure carbon dioxide (HPCD) and nisin (200 IU/mL) on the inactivation of Escherichia coli O157:H7 suspended in physiological saline (PS, pH 5.60), phosphate-buffered saline (PBS, pH 5.60 or 7.00) or carrot juice (pH 6.80) were evaluated. The pressure in this study was 5 and 8 MPa, the temperature was 25 °C–45 °C, and the treatment time was 5–65 min. Inactivation of cells in PS (pH 5.60) by HPCD followed first order kinetics, the k (the inactivation rates) increased while the D (decimal reduction time) decreased in the presence of nisin, however, the acid solution dissolving nisin rather than nisin itself played a prominent role in this combination effect with HPCD in PS buffer. The inactivation kinetics of cells in PBS (pH 5.60 or 7.00) and carrot juice (pH 6.80) by HPCD followed slow-to-fast two-stage kinetics and was fitted by the modified Gompertz equation. The M (the time at which the absolute death rate is maximum) significantly decreased in the presence of nisin. HPCD enhanced the sensitization of E. coli to nisin and the time for the complete inactivation was shortened by 2.5–5 min in PBS buffer and carrot juice by combination of HPCD and nisin (HPCD + nisin) than by HPCD alone. Regression coefficients (R2) and mean square error (MSE) were used to evaluate the model performance, indicating that the models could provide a good fitting to the experimental data.

In the present study, the synergistic disinfection efficacy of low concentration electrolyzed water (LcEW) (free available chlorine, 4 mg/L) combined with brief heat enhancement was evaluated and the bactericidal mechanism was investigated by atomic force microscopy (AFM). The inactivation kinetics of Escherichia coli O157:H7 and Salmonella Typhimurium on organic carrot were fitted with Weibull model to evaluate the synergistic effects. LcEW is effective at inactivating E. coli O157:H7 and S . Typhimurium on organic carrots, and the efficacy is dependent on the temperature. The combined treatment with LcEW at 80 °C resulted in decimal reduction time ( T R ) of 7.42 and 3.27 s for E. coli O157:H7 and S. Typhimurium, respectively. The reactive oxygen species generated from LcEW were responsible for the microbial inactivation. In addition, AFM observation of E. coli O157:H7 and S. Typhimurium revealed morphological alterations in the bacterial cell structure, which illustrated the damage of cell membrane injury and intracellular component leakage. Quality attributes of carrot treated with LcEW and short-time heating (70 °C, 1 min) were not significantly different from controls. Compared to the control group, the combined treatment exhibited significantly ( P

Restaurants used to prepare tenderloin beef medallions using different frying parameters in order to satisfy their customers. However, some of those cooking methods are not in accordance with food safety recommendations, because they do not reach internal temperatures recognized as save, in countries such as US, Canada and Brazil. This study aimed to assess the microbial inactivation in tenderloin beef medallions fried to five pre-determined degrees of doneness. Two different frying techniques were investigated, allowing beef pieces to reach the following degrees of doneness: rare, medium-rare, medium, medium-well and well-done. Before thermal processing, tenderloin beef medallions were artificially contaminated with approximately 106 CFU/g of Escherichia coli and the survival of this microorganism and mesophilic total counts were measured using VRBA + MUG and BHI plates, respectively. Bacterial colonies grew on BHI plates were also analyzed by Matrix-Assisted Laser and Time-Of-Flight desorption/ionization mass spectrometry (MALDI-TOF/MS) in order to identify survivors. Results indicated that complete E. coli inactivation was only observed on tenderloin beefs subjected to well-done degree established by both techniques, given that Technique 1 recommended a final heating inside oven after frying. Without this final oven processing, which is not always done in restaurants, more than 2 log CFU/g of viable E. coli were detected. Modeling of the kinetic parameters by GInaFIT revealed a D value (time needed to reduce 90% of the bacterial population) of 1.67 min for Technique 1 and D = 3.81 min for Technique 2 and this difference was associated to the difference of temperatures of olive oil. MALDI-TOF analyses demonstrated high diversity in natural microbiota of tenderloin beef pieces and among the main identified survivor genera was Citrobacter, Enterobacter, Hafnia, Serratia, Raoultella, Bacillus, Lactobacillus, Micrococcus, Pseudomonas, Serratia and Staphylococcus. Pathogens such as Salmonella and Listeria monocytogenes were not found. Based on the results, we recommend the use of high microbiological quality beef for the preparation of tenderloin beef medallions and the validation of frying process considering specific conditions of restaurants, because different degrees of fried may result in different counts and types of bacterial survivors.

This study reports on the influence of heat and hydrogen peroxide combination on the inactivation kinetics of two heat resistant molds: Neosartorya fischeri and Paecilomyces variotii. Spores of different ages (1 and 4 months) of these molds were prepared and D-values (the time required at certain temperature/hydrogen peroxide combination to inactivate 90% of the mold ascospores) were determined using thermal death tubes. D-values found for P. variotii ranged from 1.2 to 25.1 s after exposure to different combinations of heat (40 or 60 °C) and hydrogen peroxide (35 or 40% w/w) while for N. fischeri they varied from 2.7 to 14.3 s after exposure to the same hydrogen peroxide concentrations and higher temperatures (60 or 70 °C). The influence of temperature and hydrogen peroxide concentration on the d-values varied with the genus of mold and their ages. A synergistic effect of heat and hydrogen peroxide in reducing D-values of Paecilomyces variotti and N. fischeri has been observed. In addition to strict control of temperature, time and hydrogen concentration, hygienic storage and handling of laminated paperboard material must be considered to reduce the probability of package’s contamination. All these measures together will ensure package’s sterility that is imperative for the effectiveness of aseptic processing and consequently to ensure the microbiological stability of processed foods during shelf-life.

Two strains of Escherichia coli (K-12 and O157:H7), Salmonella ( enteritidis and typhimurium ) and Listeria monocytogenes (AS-1 and M24-1) were individually suspended in phosphate-buffered saline (PBS) and apple juice prior to exposure to UV radiation (220–300 nm) and heating at 55 °C. The calculated decimal reduction times ( D value, min) varied with suspending medium and mode of inactivation. The AS-1 and M24-1 strains of L. monocytogenes were found to be most resistant to UV in PBS (0.28–0.29 min) while the AS-1 strain was most resistant in juice (1.26 min). The AS-1 strain of L. monocytogenes and E. coli O157:H7 were most heat resistant when suspended in PBS (4.41 min) and juice (4.43 min), respectively. Results obtained from this study may be used by apple juice processors in selecting appropriate organisms for UV irradiation or heat treatment lethality validations.