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The present investigation assesses the influence of cultural attributes and heat and cold treatments on the behaviour of native toxigenic L. monocytogenes CFR 1302 and non-toxigenic L. innocua CFR 1304 in selected medium. The growth responses of L. monocytogenes and L. innocua under the influencing factors of storage temperature (10-40°C), pH level (5.5-7.5), and storage period (6-48 h) in brain heart infusion and nutrient broths revealed closeness between observed and predicted populations. Response surface plots were generated for the growth behavior of the two test cultures as a function of pH level. The toxigenic L. monocytogenes CFR 1302 could reach a higher viable population. The effect of heat treatment on Listeria spp. in selected five heating menstra showed the lowest D-value of 3.7 min at 60°C for L. innocua CFR 1304 in Milli-Q water to the highest of 8.4 min at 56°C for L. monocytogenes CFR 1302 in skim milk. The average z-value across the heating menstra for L. monocytogenes was 27.3°C as against that of 22°C for L. innocua. In the case of cold treatment, storage of 4 and 8°C resulted in appreciable increase in counts of L. monocytogenes CFR 1302 from the initial inoculum introduced in selected media. At -20°C, there was a slight decrease in the viable population. The research data helps to predict the viable populations of L. monocytogenes as a part of risk assessment in the food chain. This is of significance in providing safe and healthy food to human population.

Bacillus subtilis is a spore-forming bacterium and an important food contaminant. The aim of this study was to analyze the ability of B. subtilis spores to survive under conditions of low pH and high temperature. The package was purchased at a local supermarket, in Uberaba, Minas Gerais. A sample was collected, diluted and plated on Brain-Heart-Infusion agar (BHI). After incubation, suspected colonies of B. subtilis were transferred to BHI agar. Cell morphology, the presence of spores and Gram stain were examined, and the isolate was identified by 16S rRNA gene sequencing . The microscope evaluation indicated the presence of spores. The thermal tolerance of the spores was evaluated by the addition of 3x109spores/mL in test tubes containing peptone water. Heat treatments were carried out at 80 and 90°C at different incubation times (0, 10, 20, 30, 40, 50 and 60 min). After heating, the tubes were cooled and the number of viable spores was determined in BHI Agar. For the analysis of spore survival, D and Z values were calculated. Tolerance to acid conditions was evaluated using BHI broth with different pH values. After incubation, the bacterial concentration was determined by determining viable cell count on BHI Agar medium. The vegetative cells were transferred to the BHI broth and the pH was adjusted to different values (3, 4 or 5). Sampling were taken 8, 12 and 24 h after incubation. The samples were serially diluted in peptone water and spread in BHI Agar to determine the viable cell count . The 16S rRNA gene sequencing indicated high similarity (99.99%) with B. subtilis. D values were 17.01 min at 80°C and 13.42 min at 90°C. The Z-value was 97.13°C. B. subtilis was not able to grow at pH 3 and pH 4, but its survival was confirmed after the growth of colonies on BHI agar. At pH 5, B. subtilis grew after 24 h and the final pH changed to 7. Our results suggest that the spores of B. subtilis isolated from fruit juice-added soy beverage are tolerant to low pH and high temperature.

The effect of high-pressure processing parameters within the domain of 300−600 MPa/25−65 °C/0−30 min was evaluated on polyphenol oxidase (PPO) and peroxidase (POD) inactivation in a reduced-calorie sapodilla jam. The residual activity of PPO and POD enzymes was significantly reduced (up to 57% for PPO and 43% for POD) by temperature followed by pressure and time, and all the process parameters showed a synergistic effect represented by contour plots. However, POD was more baroresistant than PPO. The rate constants obtained from the first-order kinetics applied to enzyme inactivation during isobaric-isothermal phase varied from 2.1 × 10−3 min−1 to 1.36 × 10−2 min−1 for PPO, and 2.0 × 10−3 min−1 to 7.8 × 10−3 min−1 for POD. Various other kinetic parameters viz. D value, DP, ND, zT, zP, activation energy, and activation volume were also obtained to compare the results. Also, the HPP jam samples were microbiologically safe.

In this study, spore heat resistance and growth ability at refrigeration temperatures of Bacillus spp. and Paenibacillus spp. were determined. The spore D90°C of 67.6% (23 of 34 strains) of Bacillus and 73.9% (17 of 23 strains) of Paenibacillus was less than 15 min. The growth abilities of both genera were equivalent at 10°C. However, 71.1% (32 of 45 strains) of Paenibacillus and only 6.3% (3 of 48 strains) of Bacillus cereus group could grow at 4°C. Eight B. cereus strains formed spores with higher heat resistance compared to the other Bacillus strains assessed; however, they did not grow at tempreratures below 10°C. Conversely, four Paenibacillus strains formed spores with heat resistance equivalent to that of the eight B. cereus strains and grew at 6°C or lower. In particular, Paenibacillus sp. JCM13343 formed the highest heat-resistant spores (D90°C = 136.1 min) and grew well at 4°C. These results indicate that Paenibacillus can grow in processed foods during refrigerated storage and has the potential to cause spoilage as well as Bacillus. Therefore, Paenibacillus should be considered as one of the targets for microbiological control in refrigerated processed foods.

Persistence of Salmonella in milk powders has caused several foodborne outbreaks. The determination of proper pasteurization processing conditions requires an understanding of the thermal inactivation kinetics of Salmonella in milk powders. However, there is a lack of knowledge related to the effects of water activity (aw) and fat content on Salmonella inactivation in milk powder during thermal processing. Two types of milk powders, nonfat dry milk and whole milk powder, with different fat contents (0.62 and 29.46% wt/wt, respectively) were inoculated with a 5-strain cocktail of Salmonella and equilibrated to 3 aw levels (0.10, 0.20, and 0.30) for isothermal treatments at 75, 80, and 85°C to obtain D-values (the time required to achieve a 10-fold reduction of the bacteria at the isothermal treatment temperature) and z-values (the increase in temperature required to achieve a 90% reduction of the decimal reduction time D). Stability tests showed that the inoculation method used in this study provided a high and stable population of Salmonella for thermal inactivation studies. A moisture sorption isotherm was measured to understand the relationship between aw and moisture content of milk powders. The thermal resistance of Salmonella was found to significantly increase as aw decreased, which suggested that a higher temperature or longer processing time would be required at low aw to achieve the desired inactivation of Salmonella. The microbial inactivation kinetics were not significantly different for the 2 milk powders; therefore, data were combined to develop a universal model. A response surface model was compared with a modified Bigelow model. The modified Bigelow model performed well to predict D-values [root mean square error (RMSE) = 1.47 min] and log reductions (RMSE = 0.48 log cfu/g). The modified Bigelow model developed here could be used to estimate D-value as a function of water activity and temperature to design a thermal pasteurization system for milk powders.

Egg powders are increasingly popular ingredients, due to their functionality and compactness, in industrial food production and preparation at homes. However, there is a lack of studies that evaluate the thermal resistance of Salmonella Enteritidis PT30 and its potential surrogate Enterococcus faecium NRRL B-2354 in egg powders. This study examined the log-linear relationship between the thermal resistance of Salmonella Enteritidis (D-value) and the water activity (aw) of egg powders. The changes of aw in the egg powders with temperature were measured using a Vapor Sorption Analyzer and a high-temperature cell. The D80 ℃-value of S. Enteritidis PT30 and E. faecium inoculated in the egg powders preconditioned to three aw levels (0.3, 0.45, and 0.6) at 20 ℃ were determined using aluminum thermal death test cells. The aw values increased (P 80 ℃-values ranged from 5.3 ± 0.1 to 25.9 ± 0.2 min for S. Enteritidis while 10.4 ± 0.4 to 43.8 ± 0.4 for E. faecium in samples of the three different aw levels. S. Enteritidis PT30 showed a log-linear relationship between D80 ℃-values and aw80 ℃ for the egg powders. This study contributes to our understanding of the impact of aw on the development of thermal treatments for low-moisture foods.

Background The elimination of microbial cells is one of the most critical steps in food processing. Conventional heating is the application of diffusive and convective heat mechanisms and is traditionally applied to assure food safety. However, such process is also harmful to others thermosensitive compounds, compromising desirable sensorial characteristics. The large temperature gradients caused by conventional heating result in lower thermal efficiency, overheated zones and high processing times. To overcome these limitations, emergent technologies have been studied in the past years, such as ohmic heating. Scope and approach The aim of this review was to analyse the state of the art of microbial inactivation by ohmic heating. This study emphasizes comparisons of ohmic and conventional heating, as well as comparisons of ohmic heating in several distinct scenarios (such as variations in the frequency and electric field). Key findings and conclusions The literature analysis shows that the most analysed microbial species was Escherichia coli and studies dealing with fungi were less numerous comparing with studies dealing with bacteria. Concerning the lethality of conventional and ohmic heating, authors have shown that ohmic treated foods had smaller D values in various temperatures. The effect of frequency lacks of experimental data to explain the real impact of this parameter in the inactivation rate, once different authors have found divergent results. Moreover, increases in the electric field and salt content and decreases in the pH, fat and solid content have demonstrated higher heating rates and, therefore, higher inactivation rates.

Heat-resistant spores on a dry, heat- and water-sensitive food matrix are difficult to inactivate. Radioactive or X-ray exposure is allowed and accepted only for some selected commodities. Non-thermal atmospheric pressure plasma treatments could offer an efficient, fast, and chemical-free solution. The effectiveness of direct contact cold atmospheric plasma (CAP) generated by a dielectric barrier discharge (DBD) device and air as process gas was evaluated against spores of Bacillus spp., Geobacillus spp., and Penicillium spp. A maximum of 3 log10 cycles of inactivation was achieved for B. coagulans spores exposed for only 10 s at low surface energy of 0.18 W/cm2 determined directly at the electrodes. This corresponds to an initial decimal reduction time of D1 = 0.1 min. Spores of B. subtilis are the most resistant amongst the studied strains (D1 = 1.4 min). The determining parameter in the modeling of the inactivation curve is surface energy. Non-porous, native starch granules or shells from diatoms, a highly porous material, were also contaminated with spores and treated by DBD CAP. The inactivation level was significantly reduced by the presence of powders. Considering plasma diagnostics, it can be concluded that the spore shell is the primary and main target for a plasma-induced inactivation. The inactivation affect scales with surface energy and can be controlled directly via process time and/or discharge power.

The aim of this study is to observe and assess the performance of Psychrotrophic Gram-negative bacteria, namely Pseudomonas fluorescens, which pose a significant spoilage problem in food, under different temperature, water activity (aw) and pH conditions. Noting that at aw 0.6 and 0.75 irrespective of temperature or pH and at temperatures 600 and 1000C irrespective of water activity or pH no survival was recorded. The D-value (Decimal reduction time) at 40, 250, 370 and 420C differ significantly, with the one at 370C was significantly the highest and that at 420C was significantly the lowest. The optimum conditions were found to be at pH=6, aw=0.97 and temperature=370C showing the significantly lowest generation time (7.69 min). At pH=6, aw=0.97 and temperatures of 40 and 250C we have significantly different generation times of 46.75 and 10.9 min respectively. Concerning the z-value it was calculated at pH=4 (high acid food), pH=6 (low acid food) and pH=8 (alkaline food), at aw 0.82, 0.93 and 0.97 and from consequent D-values at temperatures 40, 250, 370 and 420C and was shown to be 25.31±3.68. Outside of the optimum conditions, Pseudomonas fluorescens died at different rates. Within all pH-values, D-values at 420C were significantly the lowest when compared to those at 40, 250 and 370C among the different aw-values. Thus changing only one factor, either storage temperature, pH or aw out of the optimum neighborhood will lead to the reduction of this bacteria, although at different rates.

Rice is prone to contamination with Bacillus cereus which causes food poisoning. The aim of this study was to investigate the presence of Bacillus cereus in cooked and uncooked rice. A total of forty samples of rice were collected from local supermarkets and tested before and after cooking for the presence of B. cereus. Half of the uncooked rice samples were B. cereus positive. In contrast B. cereus was not detected in the cooked samples when they were immediately examined for the presence of B. cereus. Storing the cooked sample at room temperature (25 °C) for twelve hours, however, gave the spores the chance to grow, and two samples showed bacterial growth higher than 1×103 Cfu/g. The D-value of B. cereus ATCC 14579 spores was found to be 2.7, 1.55, 1.35, 1.2 and 0.6 min at 80, 85, 90, 95, and 100 °C respectively. The Z-value was 9 °C. The level of bacterial growth was below the limits but it was sufficient to suggest that cooked rice should be routinely checked for B. cereus to control bacterial contamination and reheating should reach 80 °C to insure the safety.

Meta-regression models have gained in popularity during the last years as a way to create more generic models for Microbial Risk Assessments that also include variability. However, as with most meta-analyses and empirical models, systematic biases in the data can result in inaccurate models. In this article, we define experimental bias as a type of selection bias due to the practical limitations of microbial inactivation experiments. Conditions with extremely high D-values (i.e. slow inactivation) need very long experimental runs to cause significant reductions. On the other hand, when the D-value is extremely low, not enough data points can be gathered before the microbial population is below the detection limit. Consequently, experimental designs favour conditions within a practical experimental range, introducing a selection bias in the D-values. We demonstrate the impact of experimental bias in meta-regression models using numerical simulations. Models fitted to data with experimental bias overestimated the z-value and underestimated variability. We propose a rapid heuristic method to identify experimental bias in datasets, and we propose truncated regression to mitigate its impact in meta-regression models. Both methods were validated using simulated data. Thereafter the procedures were tested by building a meta-regression model for actual data for the inactivation of Bacillus cereus spores. We concluded that the dataset included experimental bias, and that it would cause an overestimation of the microbial resistance at high temperatures (>120 °C) for classical meta-regression models. This effect was mitigated when the model was built using truncated regression. In conclusion, we demonstrate that experimental bias could potentially result in inaccurate models for predictive microbiology. Therefore, checking for experimental bias should be a routine step in meta-regression modelling, and be included in guidelines on data analysis for meta-regression.

Tahini (sesame paste) is a traditional food. Numerous foodborne outbreaks have been associated with it. This study aimed to (i) explore the efficiency of 2450 MHz microwave heating at 220, 330, 440, 550, and 660 W on the inactivation of Salmonella spp, Escherichia coli O157:H7, and Listeria monocytogenes in tahini; (ii) determine the impact of desiccation and starvation stresses on pathogen survival; (iii) assess the impact of microwave heating on the physicochemical characteristics of tahini. The inoculated microorganisms in tahini were reduced with higher microwave power levels (p < 0.05) and longer exposure times. The D-values of unstressed Salmonella spp., Escherichia coli O157:H7, and L. monocytogenes ranged from 6.18 to 0.50 min, 6.08 to 0.50 min, and 4.69 to 0.48 min, respectively, at power levels of 220 to 660 W, with z-values of 410, 440, and 460 W, respectively. Generally, desiccation and starvation stress levels prior to heating increased microbial resistance to heat treatment. Microwave heating did not affect acid, peroxide, p-anisidine, or color values of tahini up to 90 °C. These findings reveal microwave heating as a potential method for lowering the risk of Salmonella spp., E. coli O157:H7 and L. monocytogenes in tahini with no compromise on quality.

This project was undertaken to determine the kinetic parameters of thermal inactivation of Listeria monocytogenes on pecans, macadamia nuts, and sunflower seeds subjected to heat treatments simulating industry processes. Five strains were grown in nonselective medium, mixed, and resuspended before inoculating macadamia nuts, pecans, and sunflower seeds (6 to 9 Log CFU/g). Redried inoculated pecans and macadamia nuts were heated in an oven at a temperature range of 90 to 140°C. Unshelled sunflower seeds were heated in sunflower seed oil. The thermal inactivation was determined by measuring viable cell counts using standard microbiological methods. Average count data were fit to the log-linear model, and thermal-death kinetics were calculated. On pecans, the viable Listeria counts were reduced by 3 and 3.5 Log CFU/g after 40 min at 110°C and 8 min at 140°C, respectively. On macadamia nuts, the L. monocytogenes population was reduced by 5 Log CFU/g after 20 min at 120°C. Unshelled sunflower seeds were subjected to heat treatment via a hot-oil bath. On sunflower seeds, >7 Log CFU/g reductions were observed after 15 min at 120°C. The thermal resistance (D value) for inactivation on pecans at 140°C was 3.1 min and on macadamia nuts at 120°C was 4.4 min. The inactivation of L. monocytogenes was influenced by the kind of nut or seed. These results suggest that L. monocytogenes has a relatively high thermal tolerance. The findings from this study will contribute to the assessment of the effectiveness of heat treatment for control of this pathogen on nuts and seeds. IMPORTANCE Listeria monocytogenes is a major concern for the food industry in ready-to-eat (RTE) foods. In recent years, large-scale recalls have occurred with contaminated sunflower seeds and macadamia nuts that triggered product withdrawals. These events stress the importance of understanding Listeria’s ability to survive heat treatments in these low-water activity foods. Nuts and seeds are subjected to a variety of thermal treatments typically referred as roasting. To date, no listeriosis outbreak has been linked to nuts and seeds, but the recent recognition that this pathogen can be detected in commercial products stresses the need for research on thermal treatments. The characterization of heat inactivation kinetics at temperatures typically used during roasting processes will be very beneficial for validation studies. This manuscript reports inactivation rates of L. monocytogenes strains inoculated onto macadamia nuts, sunflower seeds, and pecan halves subjected to temperatures between 90 and 140°C.

Despite the importance of biofilm formation in contamination of meat by pathogenic Escherichia coli at slaughter plants, drivers for biofilm have been unclear. To identify selection pressures for biofilm, we evaluated 745 ‘Top 7’ from cattle and 700 generic E. coli from two beef slaughter plants for motility, expression of curli and cellulose, and biofilm-forming potential. Top 7 were also screened for serogroup, stx1, stx2, eae and rpoS. Generic E. coli were compared by source (hide of carcass, hide-off carcass, processing equipment) before and after implementation of antimicrobial hurdles. The proportion of E. coli capable of forming biofilms was lowest (7.1%; P < 0.05) for cattle isolates and highest (87.3%; P < 0.05) from equipment. Only one enterohemorrhagic E. coli (EHEC) was an extremely-strong biofilm-former, in contrast to 73.4% of E. coli from equipment. Isolates from equipment after sanitation had a greater biofilm-forming capacity (P < 0.001) than those before sanitation. Most Top 7 were motile and expressed curli, although these traits along with expression of cellulose and presence of rpoS were not necessary for biofilm formation. In contrast, isolates capable of forming biofilms on equipment were almost exclusively motile and able to express curli. Results of the present study indicate that cattle would rarely carry EHEC capable of making strong biofilms to slaughter plants. However, if biofilm-forming EHEC contaminated equipment, current antimicrobial hurdles would inadvertently perpetuate the most robust biofilm-forming strains. Accordingly, new and effective anti-biofilm hurdles are required for meat-processing equipment, to reduce future instances of food-borne disease.ImportanceAs the majority of enterohemorrhagic E. coli (EHEC) are not capable of forming biofilms, sources were undetermined of the biofilm-forming EHEC isolated from ‘high-event periods’ in beef slaughter plants. This study demonstrated that sanitation procedures used on beef-processing equipment inadvertently select for survival of the most robust biofilm-forming strains of E. coli. Cattle only rarely carry EHEC capable of forming strong biofilms (1/745 isolates evaluated), but sanitation of equipment markedly increased (P < 0.001) biofilm-forming capacity of E. coli. In contrast, chilling carcasses for 3 days at 0°C reduced (P < 0.05) biofilm-forming capacity of E. coli. Consequently, an additional anti-biofilm hurdle for meat-processing equipment, perhaps involving cold exposure, is necessary to further reduce the risk of food-borne disease.

The influence of chilling, freezing, and dry-ing preservation methods on morphological properties and viability of four yeast cultures, isolated Saccharomyces boulardii (SB1 and SB2), Saccharomyces cerevisiae (SC), and Kluyveromyces lactis (KL), was studied. chilling preservation had no effect on yeast colony morphology parameters till the end of the preservation period in contrast with freez-ing and drying preservation methods. Drying preservation resulted in the highest viability decrement % of yeast cultures ranged between 59.38 to 40.21% as compared with other preservation methods. There is a noticeable re-duction in D values of preserved yeast cultures by drying, which varied from (33 to 26 day) in comparison to chilling and freezing preserva-tion that recorded (119 to 83 and 180 to 57 day), respectively. The obtained results re-vealed that chilling preservation under proper conditions, as well as freezing, is more prefer-able for the preservation of studied yeast cul-tures than that preserved yeast by the drying method.

The effect of moderate-temperature (≤60 °C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product-matrix, aw, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to aw 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 °C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and aw level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of aw was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing aw in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 °C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 °C as a microbial kill step.

The thermal-death times of Listeria monocytogenes were determined in inoculated restructured goat steak at 60°C, 65°C, and 70°C of sous-vide temperatures. D-values of L. monocytogenes in inoculated restructured goat steak ranged from 7.27 min at 60°C to 0.46 min at 70°C. Times need to yield at least a 6 log reduction of L. monocytogenes at their temperatures for this product were 47, 12, and 3 min, respectively. After sous-vide, all microbial counts in non-inoculated samples were not detectable, except the aerobic and anaerobic mesophilie and lactic acid bacteria counts were lower than 2 Log CFU/g. For sous-vided and grilled sous-vided samples, sous-vide loss and surface shrinkage were the lowest in samples sous-vided at 60°C for 47 min (p

In this research the effect of edible coatings based on aloe vera and cassava starch on the physicochemical properties and the kinetic parameters of degradation of ascorbic acid (AA) in pineapple minimally processed during 16 days of storage at 4 ° C was evaluated. Five treatments (T1, T2, T3, T4 and T5) were tested, pineapple “honey gold” with coating solutions of different aloe vera / starch concentrations (100/0, 75/25, 50/50, 25/75 and 0/100 respectively), and a control treatment (T6 ) that corresponds to fruit without coating. The coatings were carried out by immersing the fruit previously processed for 1 minute. The results show that the treatment with the best pH values, titratable acidity (AT) and maturity index (IM) was T3 (pH: 3.61, AT: 0.0480, IM: 2.915), in terms of moisture and soluble solids (SS) the T1 treatment (% Moisture: 81.725) and T4 (SS: 11.19) showed the most optimal values. The model that best described the degradative behavior of AA is zero order, being the T4 treatment the most adequate to preserve vitamin C with a value (k: 0.781), a half-life (t ½: 28 days) and a decimal reduction time (D: 93 days).

Nowadays, fortified vegetable oils with vitamin D3 are widely available in different countries and are consumed daily. The reduction rate of added vitamin D3 in fortified canola oil during heating process, the changes in oxidative status, and the thermal kinetic degradation of vitamin D3 in the fortified oil were investigated. For this purpose, canola oil was fortified at two levels of vitamin D3 with 5.625 µg/mL (low concentration or LC) and 13.585 µg/mL (a high concentration or HC). Samples were heated isothermally at 100, 150, and 180 °C for 30 min. The vitamin D3 concentration was determined by the high-performance liquid chromatographic method. The retention of vitamin D3 in samples treated at 100 °C for 30 min showed no significant reduction. Samples treated at 150 and 180 °C depending on the initial concentration showed the retention of 67.5% to 72.97% and 33.16% to 40.35% of vitamin D3 , respectively. An inverse relationship was found between the increment of lipid oxidation products (peroxide and anisidine values) and the retention of vitamin D3 . Kinetic parameters such as rate constant, activation energy, decimal reduction time, and quotient indicator were also calculated. An Arrhenius relationship was used for the assessment of temperature dependence of vitamin D3 degradation. Activation energies for vitamin D3 in LC and HC between 100 and 180 °C were found to be 44.01 and 38.77 kJ/mol, respectively. PRACTICAL APPLICATION: The oil can be fortified with vitamin D3 at low cost and offers a good bioavailability. A high-temperature cooking method may not be appropriate for the fortified products containing high lipid content.

Inulinases are used for the production of high-fructose syrup and fructooligosaccharides, and are widely utilized in food and pharmaceutical industries. In this study, different carbon sources were screened for inulinase production by Aspergillus niger in shake flask fermentation. Optimum working conditions of the enzyme were determined. Additionally, some properties of produced enzyme were determined [activation (Ea)/inactivation (Eia) energies, Q10 value, inactivation rate constant (kd), half-life (t1/2), D value, Z value, enthalpy (ΔH), free energy (ΔG), and entropy (ΔS)]. Results showed that sugar beet molasses (SBM) was the best in the production of inulinase, which gave 383.73 U/mL activity at 30 °C, 200 rpm and initial pH 5.0 for 10 days with 2% (v/v) of the prepared spore solution. Optimum working conditions were 4.8 pH, 60 °C, and 10 min, which yielded 604.23 U/mL, 1.09 inulinase/sucrase ratio, and 2924.39 U/mg. Additionally, Ea and Eia of inulinase reaction were 37.30 and 112.86 kJ/mol, respectively. Beyond 60 °C, Q10 values of inulinase dropped below one. At 70 and 80 °C, t1/2 of inulinase was 33.6 and 7.2 min; therefore, inulinase is unstable at high temperatures, respectively. Additionally, t1/2, D, ΔH, ΔG values of inulinase decreased with the increase in temperature. Z values of inulinase were 7.21 °C. Negative values of ΔS showed that enzymes underwent a significant process of aggregation during denaturation. Consequently, SBM is a promising carbon source for inulinase production by A. niger. Also, this is the first report on the determination of some properties of A. niger A42 (ATCC 204,447) inulinase.

Improper food processing is one of the major causes of foodborne illness. Accurate prediction of the thermal destruction rate of foodborne pathogens is therefore vital to ensure proper processing and food safety. When bacteria are subjected to pH and thermal stresses during growth, sublethal stresses can occur that may lead to differences in their subsequent tolerance to thermal treatment. As a preliminary study to test this concept, the current study evaluated the effect of prior pH and thermal stresses on thermal tolerance of Salmonella and Staphylococcus using a tryptic soy broth supplemented with yeast extract. Bacteria incubated at three pH values (6.0, 7.4, and 9.0) and four temperatures (15, 25, 35, and 45°C) for 24 hr were subjected to thermal treatments at 55, 60, and 65°C. At the end of each treatment time, bacterial suspensions were surface‐plated on standard method agar for quantification of bacterial survival and further calculation of the thermal death decimal reduction time (D‐value) and thermal destruction temperature (z‐value). The effect of pH stress alone during the incubation on the thermal tolerance of both bacteria was generally insignificant. An increasing pattern of D‐value was observed with the increment of thermal stress (incubation temperature). The bacteria incubated at 35°C required the highest z‐value to reduce the 90% in D‐values. Staphylococcus mostly displayed higher tolerance to thermal treatment than Salmonella. Although further research is needed to validate the current findings on food matrices, findings in this study clearly affirm that adaptation of bacteria to certain stresses may reduce the effectiveness of preservation procedures applied during later stage of food processing and storage.

A prototype of microwave pasteurizer has been proposed as an alternative for holder pasteurization (HP) routinely used in Human Milk Bank (HMB), ensuring microbiological safety of human milk (HM). It was shown that the time of heat generation was about 15–16 min shorter by applying the microwave than in HP. Total inactivation of heat-sensitive bacteria Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis, suspended in milk, occurred in the temperature 62–72 °C in HP. In the case of heat-resistant enterococci the level of inactivation depended on the conditions of the process and the properties of the strains. The application of microwave heating allows to obtain lower D-value than those achieved during HP. The using of microwave heating at 62.5 or 66 °C for 5 or 3 min, respectively, allows to inactivation of HM microbiota. Appropriate microbiological quality of milk is critical for the effectiveness of the pasteurization process. Industrial relevance Looking for new methods of donor human milk (HM) preservation is dictated by the necessity of providing microbiological safety and, at the same time, maintain its high nutritional and biological value. The holder pasteurization used in the Human Milk Banks (HMB) (heating at 62 °C for 30 min) leads to inactivation of all vegetative forms of microorganisms. Unfortunately, this method causes significant reduction of health benefitting properties of HM. The paper demonstrates the possibility of using the new microwave pasteurizer for preservation of HM, allowing for quick heating of milk to the appropriate temperature and maintaining it in these conditions for a required time. It was shown that the decimal reduction times (D) for strains inoculated to UHT or human milk are several times shorter by using microwave heating than in the commercial pasteurization method. The total inactivation of HM microbiota is obtained after heating at 62.5 and 66 °C for 5 and 3 min, respectively.

Human noroviruses (HNoVs) cause significant gastrointestinal disease outbreaks worldwide. Tulane virus (TV) is a cultivable HNoV surrogate widely used to determine control measures against HNoVs. The objective of this study was to determine the heat inactivation kinetics (D- and z-values) of TV in cell-culture media and on spiked homogenized spinach using the first-order and Weibull models. TV in cell-culture media at approximately 7 log PFU/mL (PFU-plaque forming unit) in 2-mL glass vials was heated at 52, 54, and 56 °C for up to 10 min in a circulating water bath. Survivors were enumerated using confluent host LLC-MK2 cells in six-well plates by plaque assay. Data from three replicate treatments assayed in duplicate were analyzed statistically. D-values by the first-order model for TV in cell-culture media at 52, 54, and 56 °C were 4.59 ± 0.05, 2.91 ± 0.05, and 1.74 ± 0.07 min, respectively, with a z-value of 9.09 ± 0.01 °C (R2 = 0.997). The Weibull model showed td = 1 values of 2.53 ± 0.08, 1.99 ± 0.10, and 0.57 ± 0.64 min, respectively, at the same temperatures. The D-values for TV in spinach were 7.94 ± 0.21, 4.09 ± 0.04, and 1.43 ± 0.02 min and the z-value was 10.74 ± 0.01 °C (R2 = 0.98) by the first-order model and 4.89 ± 0.02, 3.21 ± 0.45, and 0.25 ± 0.38 min for the Weibull model at 50, 54, and 58 °C, respectively. In comparison to previously reported results for the cultivable HNoV surrogate, murine norovirus -1, TV in cell-culture media and spiked on spinach homogenates showed lower D- and z-values. TV may not be an ideal HNoV surrogate for heat inactivation studies in cell-culture media or homogenized spinach in vacuum bags.

Fermented fish, including rusip and bekasam, contains lactic acid bacteria, some of which have probiotic properties. Considering the beneficial effect, the count of viable cells in probiotic carrier foods must be at least 106 CFU/g throughout the product shelf-life. The processing and storage condition significantly affect the viability of probiotics in carrier foods. This research was conducted to determine the heat resistance of probiotic candidate Enterococcus faecalis R22B isolated from rusip in three different media: bekasam, rusip, and physiological saline solution (NaCl 0.85%). E. faecalis R22B was heated in each medium at a temperature of 70 °C for 0, 2, 4, 8, and 12 min. The media characteristics showed differences within the parameters included pH values of 4.41-6.99; aw 0.67-0.92; moisture content 72.56-98.09%; ash content 0.69-12.32%; protein content 0-14.7%; fat content 0-0.84%; and carbohydrate content from 0-4.93%. The results showed that the difference in the heating medium had no significant effect (p>0.05) on the heat resistance of the bacteria, as indicated by the D70 value. The required average heating time at 70 oC to decrease E. faecalis R22B cells by 1log10 (D70 value) in bekasam, rusip, and physiological saline media were 3.17, 3.29, and 3.55 min, respectively. Despite having a lower DT-value, the reduction of bacteria cells in three media heated at 70 oC showed no difference (p>0.05); therefore, bekasam and rusip are suitable for probiotic carrier food.

Aichi virus (AiV) that results in gastroenteritis worldwide, is spread through contaminated shellfish and water. The resistance/tolerance of AiV to common inactivation processes along with the absence of commercially available vaccines makes it necessary to study its thermal inactivation kinetics. This research evaluated the heat inactivation of AiV in cell-culture media using 2-ml sterile glass vials by the linear and Weibull models. Heat treatments of AiV titers of 7 log plaque forming units (PFU)/ml were conducted thrice in a water-bath at 50, 54, and 58 °C for up to 90 min. Plaque assays for each dilution in duplicate were used to determine infectious virus titers. Linear model D-values for AiV at 50 ± 1 °C (± = standard error) (come-up time = 68 s), 54 ± 0.7 °C (130 s), and 58 ± 0.6°C (251 s) were 43.3 ± 4.23 (R2 = 0.40, RMSE = 0.56), 5.69 ± 0.28 (R2 = 0.80, RMSE = 0.43), and 1.20 ± 0.63 min (R2 = 0.69, RMSE = 0.39), respectively, and the linear model z-value was 5.14 ± 0.39°C (R2 = 0.99, RMSE = 0.08). For the same temperatures, the Weibull model td = 1 values were 20.98 ± 8.8 (R2 = 0.62, RMSE = 0.46, α (scale parameter) = 2.30, β (shape parameter) = 0.38), 3.84 ± 0.69 (R2 = 0.85, RMSE = 0.38, α = 1.08, β = 0.66), and 0.87 ± 0.10 min (R2 = 0.80, RMSE = 0.32, α = 0.22, β = 0.61), respectively and the z-value (using Td = 1 ) was 5.79 ± 0.22 °C (R2 = 1.0, RMSE = 0.03). A better fit was obtained with the Weibull model for log reductions versus time with higher R2 and lower RMSE values. Application of AiV inactivation parameters can help reduce the risk of AiV outbreaks.

A predictive model was made for the logarithm of the thermal decimal reduction time (logD) of Salmonella enterica (D = time to 90% reduction by inactivation). The model was fitted with multiple linear regression from 521 logD-values reported in literature for laboratory media and foods highly varying in water activity and pH. The single regression model with temperature as the only variable had a high residual standard error (RSE) of 0.883 logD and no predictive value (fraction of variance explained (R2) < 0.001). Adding water activity, sugar content and pH as predictors resulted in a model with a lower RSE of 0.458 logD and an adjusted R2 of 0.73. The model was validated by comparing 985 predicted with observed logD for S. enterica from other publications. The model was subsequently validated with 1498 published logD-values for inactivation of vegetative cells of nine other pathogenic bacteria genera (mainly Listeria monocytogenes, Escherichia coli, Clostridium perfringens, Cronobacter spp., Staphylococcus aureus, Yersinia enterocolitica) in or on a variety of laboratory media, meat, fish, dairy, nuts, fruits and vegetables. Regression analyses for validation with the 985 logD of S. enterica and 2483 logD of all genera show deviations from the expected slope of 1 (both 0.81) and the expected intercept of 0 (0.04 and 0.19 logD respectively). However, only 0.7% and 2% respectively of the new logD (expected: 0.5%) were observed above the 99% prediction interval of the original S. enterica model based on 521 logD. The findings suggest that i) the variability of thermal resistance of strains within species is larger than between genera and species; ii) one generic predictive model, also accounting for variability, suffices for designing the thermal inactivation of a variety of vegetative pathogenic bacteria in many food types.

International audience; The leading causes of foodborne viral disease outbreaks are human norovirus and hepatitis A virus (HAV). Their environmental persistence enables contamination of kitchen surfaces and crops often consumed raw, such as berries. Many decontamination procedures are inefficient and unsuitable for surfaces of industrial kitchen environments and soft fruits. In this study, we investigated the efficiency of a novel surface decontamination technology, combining steam and ultrasound (steam-ultrasound). Plastic, steel or raspberry surfaces were spiked with the norovirus surrogate, murine norovirus (MNV), and HAV, and steam-ultrasound treated at 85, 90 and 95 °C for 0–5 s. Post treatment viruses were titrated for survival by plaque assay and for genome stability by real-time quantitative PCR (RT-qPCR) of nucleic acid extracts. Survival of viruses were estimated in a log-linear model and the treatment time requirements for each decimal reduction (D value) in viral survival were calculated. The estimated D values of MNV or HAV were 0.4–0.2 or 1.1–0.8 s on plastic, 0.9–0.7 or 1.4–0.8 s on steel and 1.6–1.7 or 3.2–4.7 s on raspberries. No clear trend of genome reduction was observed with tested treatment parameters. Raspberries treated up to 4 s retained its natural texture and visual appeal similar to untreated controls whilst monitored for 7 days. In conclusion, steam-ultrasound treatment can within seconds reduce the titre of foodborne viruses on surfaces of plastic, steel and raspberries. This may particularly benefit industrial scale production of soft fruits for raw consumption and for swift non-hazardous decontamination of industrial kitchen surfaces.

Intervention technologies for inactivating Salmonella on whole chia seeds are currently limited. Determination of the thermal inactivation kinetics of Salmonella on chia seeds and selection of an appropriate nonpathogenic surrogate will provide a foundation for selecting and optimizing thermal pasteurization processes for chia seeds. In this study, chia seed samples from three separate production lots were inoculated with a five-strain Salmonella cocktail or Enterococcus faecium NRRL-B2354 and equilibrated to a water activity of 0.53 at room temperature (25°C). After equilibration for at least 3 days, the inoculated seeds were subjected to isothermal treatments at 80, 85, or 90°C. Samples were removed at six time points, and surviving bacteria were enumerated. Whole chia seeds were diluted in a filter bag at 1:30 because bacterial recovery with this method was similar to that obtained from ground seeds. Survivor data were fitted to consolidated models: one primary model (log linear or Weibull) and one secondary model (Bigelow). E. faecium had higher thermal resistance than did Salmonella, suggesting that E. faecium may be a suitable conservative nonpathogenic surrogate for Salmonella. The Weibull model was a better fit for the survivor data than was the log-linear model for both bacteria based on the lower root mean square error and corrected Akaike's information criterion values. Lipid oxidation measurements and fatty acid concentrations were significantly different from those of the control samples, but the overall magnitude of the differences was relatively small. The thermal inactivation kinetics of Salmonella and E. faecium on chia seeds may be used as a basis for developing thermal pasteurization processes for chia seeds. HIGHLIGHTS

The presence of Listeria monocytogenes in Mozzarella di Bufala Campana Protected Designation of Origin cheeses may depend on curd stretching conditions and post contaminations before packaging. To avoid cross-contamination, thermal treatment of water, brines and covering liquid may become necessary. The present study aimed to improve knowledge about L. monocytogenes thermal resistance focusing on the influence of some cheese making operations, namely curd stretching and heat treatment of fluids in contact with cheese after molding, in order to improve the safety of the cheese, optimize efficacy and sustainability of the processes. Moreover, the role that cheese curd stretching plays in L. monocytogenes inactivation was discussed. The 12 tested strains showed a very heterogeneous heat resistance that ranged from 7 to less than 1 Log10 Cfu/mL reduction after 8 min at 60°C. D-values (decimal reduction times) and z-values (thermal resistance constant) calculated for the most heat resistant strain among 60 and 70°C were highly affected by the matrix and, in particular, heat resistance noticeably increased in drained cheese curd. As cheese curd stretching is not an isothermal process, to simulate the overall lethal effect of an industrial process a secondary model was built. The lethal effect of the process was estimated around 4 Log10 reductions. The data provided may be useful for fresh pasta filata cheese producers in determining appropriate processing durations and temperatures for producing safe cheeses.

Thermal stability (D-value and pasteurization) and gastric acid resistance of spore forming and nonspore forming probiotic strains were evaluated in this study. Bacillus coagulans MTCC 5856 spores showed highest thermal resistance (D-value 35.71 at 90 °C) when compared with other Bacillus strains and Lactobacillus species. B. coagulans strains exhibited significantly higher resistance to simulated gastric juice (pH 1.3, 1.5, and 2.0) compared to Lactobacillus strains. It also showed high resistance to cooking conditions of chapati (whole wheat flour-based flatbread) (88.94% viability) and wheat noodles (and 94.56% viability), suggesting remarkable thermal resistance during food processing. Furthermore, B. coagulans MTCC 5856 retained 73% viability after microwave cooking conditions (300 s, at 260 °C) and 98.52% in milk and juice at pasteurization temperature (420 min, at 72 °C). Thus, B. coagulans MTCC 5856 clearly demonstrated excellent resistance to gastric acid and high temperature (90 °C), thereby suggesting its extended application in functional foods (milk, fruit juices, chapati, and wheat noodles) wherein high temperature processing is involved.

Decontamination practices, which often involve thermal treatments, are routinely performed in beef packing plants and have generally improved the safety of meat in North America. We investigated whether Escherichia coli in the beef production chain is becoming more heat resistant due to those treatments. Cattle isolates (n = 750) included seven serogroups (O157, O103, O111, O121, O145, O26, and O45) which were collected between 2002 and 2017. Beef plant isolates (n = 700) from carcasses, fabrication equipment, and beef products were included. Heat resistance was determined in Luria-Bertani broth at 60°C and by PCR screening for the locus of heat resistance (LHR). The decimal reduction for E. coli at 60°C (D(60ºC) values) ranged from 0 to 7.54 min, with 97.2% of the values being 2 min was not significantly different (P > 0.05) among cattle and meat plant isolates. E. coli from equipment before sanitation (median, 1.03 min) was more heat resistant than that after sanitation (median, 0.9 min). No significant difference in D(60ºC) values was observed among E. coli isolates from different years, from carcasses before and after antimicrobial interventions, or from before and during carcass chilling. Of all isolates, 1.97% harbored LHR, and the LHR-positive isolates had greater median D(60ºC) values than the LHR-negative isolates (3.25 versus 0.96 min). No increase in heat resistance in E. coli was observed along the beef production chain or with time. IMPORTANCE The implementation of multiple hurdles in the beef production chain has resulted in substantial improvement in the microbial safety of beef in Canada. In this study, we characterized a large number of Escherichia coli isolates (n = 1,450) from various sources/stages of beef processing to determine whether the commonly used antimicrobial interventions would give rise to heat-resistant E. coli on meat, which in turn may require alternatives to the current control of pathogens and/or modifications to the current cooking recommendations for meat. The findings show that the degree and rate of heat resistance in E. coli did not increase along the production chain or with time. This furthers our understanding of man-made ecological niches that are required for the development of heat resistance in E. coli.

Aluminum based reflective nanolens arrays were developed via a series of aluminum electropolishing and anodization steps with subsequent selective dissolution of anodic aluminum oxide (AAO). The diameter of nanolenses (d) on arrays can be controlled by altering electrolytes and voltages used for aluminum anodization. The d values of arrays produced by anodization in 0.3 M oxalic acid at 40, 60, and 80 V, and in 1.0 M phosphoric acid at 100, 110, and 120 V were 71.94, 121.90, and 161.53 nm, and 220.16, 252.06, and 274.78 nm, respectively. The effectiveness of UV (254 nm) inactivation of Escherichia coli O157:H7 and Listeria monocytogenes at concentrations of 5–6 log CFU/mL in water and in a 10% (w/v) sucrose solution was improved using a nanolens array having a d value of 252.06 nm. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10068-020-00765-z) contains supplementary material, which is available to authorized users.

Alicyclobacillus acidoterrestris is a spore-forming bacterium of importance to the fruit juice industry due to its remarkable heat resistance and production of guaiacol taint. Whole genome sequencing analysis reveals species demarcation corresponds to the two major genotypic groups to which A. acidoterrestris isolates belong. Heat resistance was significantly different between genotypic groups 1 and 2 with D90 values of 15.5 and 9.3 min, respectively (p

The inactivation and damage of histamine-forming bacteria (HFB), Enterobacter aerogenes and Staphylococcus capitis, in a 0.1 M potassium phosphate buffer (pH 6.8) and marlin meat slurry by high hydrostatic pressure (HHP) treatments were studied using viability measurement and scanning electron microscopy (SEM). HHP treatments showed first order destruction kinetics to E. aerogenes and S. capitis during the pressure holding period. HFB in marlin meat slurry had higher D values and were more resistant to HHP treatments than in phosphate buffer. In phosphate buffer, E. aerogenes had higher D values than S. capitis at &gt, 380 MPa of pressure, whereas the reverse trend was noticed at lower pressures (&lt, 380 MPa). In marlin meat slurry, S. capitis had a higher D value than E. aerogenes at the same treatment pressure, indicating that S. capitis was more resistant to HHP treatment. To our knowledge, this is the first report to demonstrate that HHP can be used to inactivate HFB, E. aerogenes, and S. capitis, by causing disruption to bacterial cell membrane and cell wall as demonstrated by SEM micrographs.

Understanding the thermal inactivation of biopreservatives in food matrixes is essential for their proper use in the food industry, enabling reduction of heating time and optimization of heating temperature. With this aim in mind, the effect of heat treatment on the activity and thermostability of commercial nisin from Lactococcus lactis was investigated. Residual activity tests performed for 90 min in the 70–86 °C temperature range at pH 3.0 demonstrated that bacteriocin thermoinactivation followed first-order kinetics. Low values of the inactivation rate constant (0.0089–0.0892 min−1) and high values of the decimal reduction time (25.8 ≤ D-value ≤ 258.4 min) indicated excellent nisin thermostability in the lower end of the investigated temperature range, but the thermal resistance constant (z-value) was only 15.4 °C, which pointed out poor thermoresistance at the higher end. Thermodynamic parameters estimated for nisin irreversible thermal inactivation were energy, enthalpy and Gibbs free energy of activation of 155.1, 152.2–152.3 and 83.5–86.6 kJ mol−1, respectively, and activation entropy of 188.6–192.5 J mol−1 K−1. If on the one hand these results taken together confirm the thermostability of nisin as a biopreservative in use in the food industry, on the other hand suggest the importance of looking for new more thermostable antimicrobials to use in operations at higher temperatures.

The objective of the study was the evaluation of the efficacy of plasma activated water (PAW) for Escherichia coli inoculated on soybean seed surface. PAW was prepared by high-power atmospheric pressure air plasma jet. The inactivation kinetics, explained by Bigelow log-linear and Weibull models, showed the significant antibacterial potential of PAW in comparison to the control (sterile distilled water). PAW treatment for 25 min let to log10 CFU/g reduction of E. coli from 6.8 to 3.6 and its antibacterial effect persisted further 44 h (2.7 log10 CFU/g). Decimal reduction time (D-value) for tested bacteria was 7 min. Furthermore, the influence on PAW on the polyphenolics content and antioxidant activity was evaluated. To identify the PAW chemistry, physical properties, including pH, redox potential, and conductivity were estimated. The levels of H2O2, nitrate (NO3−) and nitrite anions (NO2−) as long-lived species were measured and compared to SDW without plasma activation.

Milk inoculated with Clostridium botulinum spores (PA9508B) (107 CFU/mL) was subjected to high-pressure high-temperature treatment (HPHT) (700–900 MPa; 90–110 °C for 0–24 min) using an insulated sample chamber, as well as in a water bath (90–100 °C) (conventional) and surviving spores were enumerated. Destruction kinetics were well described by a first order kinetic model. Conventional heating D values ranged from 156 to 12 min with a z value of 7.8 °C. During HPHT, higher pressures and temperatures resulted in accelerated spore destruction rates. At 900 MPa, the associated D values were 14.5, 1.8 and 0.35 min at 90, 100 and 110 °C, respectively, much lower than the conventional D values. The pressure dependent ZT values were 11.2, 12.3, 12.4 °C at 700, 800, 900 MPa respectively, increasing with pressure. The temperature dependent ZP values were 470, 630, and 800 MPa at 90, 100, and 110 °C, respectively. By comparing ZT with ZP values, it was clear the spores were relatively more sensitive at higher temperatures than at higher pressures in this temperature-pressure range. D value trends beyond 120 °C indicated thermal inactivation was the principal mode of spore destruction and high pressure can protect spores under these conditions.

Salmonella Enteritidis is a major foodborne pathogen exposed to various environmental and preservation stresses in the food chain. Because adaptive responses of viable bacterial cells in the presence of sublethal stress can induce cross-protection against different stresses, we investigated the heat resistance of Salmonella Enteritidis at 60 °C under prolonged exposure to acid-salt combined stress and subsequent refrigeration. Salmonella Enteritidis was grown in tryptic soy broth at four pH values (4.5, 5.4, 6.4, and 7.3) and four NaCl concentrations (0%, 1%, 2%, and 3%) at 37 °C for 24 h and then incubated at 4 °C for 0, 1, 4, or 7 days. For 0 and 1 day-refrigerated cultures, previous adaptation to single stresses (acid or salt stress) increased the heat resistance of Salmonella Enteritidis, resulting in increased D-values, whereas the combination of acid and salt stress reduced heat tolerance; acid stress played a more critical role in mediating this effect than salt concentration. To elucidate the related mechanisms, the expression levels of heat shock sigma factors (rpoH) and heat shock genes (dnaK and groEL) were analyzed and found to be associated with the heat resistance of Salmonella Enteritidis. The refrigeration period was negatively correlated (P 0.01) with the D-value (r = -0.505) and with the transcript levels of rpoH (r = -0.654), dnaK (r = -0.652), and groEL (r = -0.645). Our findings demonstrated that acid-salt combined preservation techniques and subsequent refrigeration may prevent S. Enteritidis survival in heat-pasteurized food products caused by cross-protection of acid or salt adapted cells.

In-shell pecans are susceptible to microbial contamination. This study was performed to investigate feasibility of using hot water treatment as a kill-step for food-borne pathogens during pecan shelling. In-shell pecans were subjected to hot water at 70, 80 or 90 °C for 1, 2, 3, 4 or 5 min. The time-temperature treatments to achieve a 5-log reduction of Salmonella enterica, Escherichia coli O157:H7, Listeria monocytogenes, and non-pathogenic Enterococcus faecium were determined. Thermal death values were determined for each tested condition. L. monocytogenes was most susceptible to heat treatment and were reduced by 4.6 ± 0.35 log CFU/g at 70 °C for 5 min, while 3–5 min at 80 and 90 °C treatments was required to achieve a similar reduction level for S. enterica, E. coli O157:H7, and E. faecium. S. enterica were most resistant and required 4 min treatment time to achieve a 5-log reduction at 80 and 90 °C. The D-values ranged from 1.15 to 1.72, 0.83 to 1.19, and 0.41–0.92 min at 70, 80 and 90 °C, respectively. E. faecium had the highest D-value (1.72 min at 70 °C), indicating a potential surrogate for process validation for pecan industries. Utilizing proper hot water treatment during pecan shelling could reduce food safety risk.

Thermal processing is usually used by the fruit juice industry for enzyme and microbial inactivation, thus limiting organoleptic changes that affect shelf life and quality of products. Mainly the inactivation of enzymes is necessary to avoid quality changes related to cloud loss, using mild temperature that allows minor alterations in product’s sensory as well as in nutritive traits. Pineapple juice, a product obtained by diluting the concentrate juice and pasteurizing afterword shipped to Europe, has a high residual pectin methylesterase (PME) activity. In this view, the present work provides a detailed kinetic study of the effect of pasteurization on inactivation of PME in pineapple juice. The fresh juice was treated with temperatures ranging from 70 to 95 °C, for various times, until the complete denaturation of PME occurred. Results of thermal stabilization treatments showed that enzyme inactivation behaviour follows a first-order kinetic process, in the studied temperature range. Moreover, the reaction rate constants for denaturation of PME were determined; in particular, activation energy (Ea), decimal reduction time (Dref), and z value (z), were 78.2 ± 4.5 kJ/mol, 16 s (at reference temperature of 106 °C) and 36 ± 3 °C, respectively. Based on the thermal resistance data here reported to inactivate PME, a treatment of 106 °C with a mean holding time of 1 min should be employed in order to preserve cloudiness of pasteurized pineapple juice.

Decimal reduction time ( D-value) was calculated for six non-O157 Shiga toxin-producing Escherichia coli (STEC) in a laboratory medium and ground beef. For the laboratory medium, an overnight culture of each strain of STEC was divided into 10-mL sample bags and heated in a water bath for a specific time on the basis of the temperatures. Survival curves were generated by plotting the surviving bacterial population against time, and a linear-log primary model was used to estimate the D-values from survival curves. The z-values (the temperature raised to reduce the D-value by one-tenth) were calculated by plotting the log D-values against temperature. Similarly, for ground beef, six fat contents, 5, 10, 15, 20, 25, and 30% of ground beef were formulated for this study. Inoculated meat was divided into 5-g pouches and submerged in a water bath set at specific temperatures (55, 60, 65, 68, and 71.1°C). The average D-value for these strains in a laboratory medium was 17.96 min at 55°C, which reduced significantly ( P0.05) to 1.58 min at 60°C, and then further reduced ( P0.05) to 0.46 min at 65°C. In ground beef, a negative correlation ( P0.05) between fat content of ground beef and D-values was observed at 55°C. However, at temperatures greater than 60°C, there was no impact ( P0.05) of fat content of ground beef on the thermal resistance of non-O157 STECs. Irrespective of the fat content of ground beef, the D-values ranged from 15.93 to 11.69, 1.15 to 1.12, and 0.14 to 0.09 min and 0.05 at 55, 60, 65, and 68°C, respectively. The data generated from this study can be helpful for the meat industry to develop predictive models for thermal inactivation of non-O157 STECs in ground beef with varying fat content.

Heat treatments can cause degradation in tomatoes of lycopene which has important antioxidant effects. No information about decimal reduction time (D100) of lycopene is available. D-value is the time required at a given temperature to reduce 90% of the molecule. This study for the first time determine the kinetic of lycopene thermal degradation. The content was measured at regular intervals of pasteurization using canned tomato paste to determinate D value. Microbiological analysis was carried out to verify product stability after packaging. Yeasts, molds and lactic acid bacteria were determined. The pasteurization time allowed to observe a loss of the red color. Lycopene content, after an increase at 8 min, decreased at 32 min of pasteurization. D100 value was calculated at 75 min; a diminution of 90% in lycopene content in the concentrated tomato paste was observed. Microbiological analysis confirmed the stability of products after 8 min of pasteurization.

Heat treatments are widely used in food processing often with the aim of reducing or eliminating spoilage microorganisms and pathogens in food products. The efficacy of applying heat to control microorganisms is challenged by the natural diversity of microorganisms with respect to their heat robustness. This review gives an overview of the variations in heat resistances of various species and strains, describes modeling approaches to quantify heat robustness, and addresses the relevance and impact of the natural diversity of microorganisms when assessing heat inactivation. This comparison of heat resistances of microorganisms facilitates the evaluation of which (groups of) organisms might be troublesome in a production process in which heat treatment is critical to reducing the microbial contaminants, and also allows fine-tuning of the process parameters. Various sources of microbiological variability are discussed and compared for a range of species, including spore-forming and non-spore-forming pathogens and spoilage organisms. This benchmarking of variability factors gives crucial information about the most important factors that should be included in risk assessments to realistically predict heat inactivation of bacteria and spores as part of the measures for controlling shelf life and safety of food products.

Cloudy apple juice has been treated by high pressure carbon dioxide (HPCD) as non-thermal technology to inactive polyphenoloxidase and pectinmethylesterase in batch mode. Stirring speed (from 200 to 600 rpm) induced an increase in the enzyme inactivation rate while a triple cycle of pressurization/depressurization led to the same enzyme inactivation efficiency. Enzyme inactivation kinetics were determined at different temperatures (from 35 to 45 °C) and pressures (from 10 to 20 MPa). Data were described by the first order kinetic model and the Weibull model. For the first order kinetic model, decimal reduction time for HPCD treatment was found to be smaller than for mild heating, in the same temperature range. The same tendency was observed for the first decimal reduction time in the Weibull model. HPCD treatment resulted in a homogenization effect reflected in the shifting of the particle size distribution towards smaller diameters after treatment. HPCD treatment did not result in a change of water and oxalate soluble pectin content, total phenolic compounds and hidroxymethylfurfural content., Spanish Government (MINECO) and the European Regional Development Fund for financial support of project CTQ2015-64396-R and AEI’s contract.

Liquid cultures are commonly used to inoculate low-moisture foods. However, liquid-inoculation may generate varied results due to differences in preparation methods, and the introduction of liquid into a low-moisture matrix may cause stickiness and clumping. The objectives of this study were to develop a dry-inoculation method using freeze-dried Enterococcus faecium NBRL-2354, and to evaluate the stability of freeze-dried inoculum over time (35 days at −20 °C) in terms of survival and heat resistance. Two protectants, freeze-drying buffer and skim milk, mixed separately with liquid E. faecium were freeze-dried and their preservative effects were compared. Heat resistance of freeze-dried inoculum was determined by decimal reduction time at 80 °C (D80) in wheat flour (water activity 0.45 at room temperature). Freeze-drying buffer and skim milk formed slimy layers around bacterial cells and yielded freeze-dried inoculum with high survivability. D80-values of freeze-dried E. faecium protected by freeze-drying buffer or skim milk were 6.67 ± 0.22 min and 5.92 ± 0.39 min, respectively. Freeze-dried inoculum was stable with a high population concentration (>10.0 log CFU/g), while skim milk-protected inoculum showed stable heat resistance throughout storage. In summary, freeze-dried E. faecium protected by skim milk was the optimum dried inoculum and can be used as a substitute for liquid-inoculum in low-moisture foods.

Wheat germ is scrapped during milling due to their unfavourable baking properties and rapid deterioration. Although it is a low-cost by-product with remarkable nutritional features, its widespread utilisation is limited by the action of enzymes. On that basis, the effect of the germ stabilisation process by fluidisation with hot air was studied. Fluidisation, carried out with air between 90 and 150 °C, generated notable lipase inactivation, which reached a minimum residual activity of 15.5% from original. The total tocopherol contents of stabilised samples were not significantly affected. Colour attributes of treated samples showed slight changes compared with raw wheat germ. A mathematical model was fitted to colour data to predict the changes due to heat. A first-order kinetic model was applied to descript the thermal lipase inactivation. The inactivation rate constant, D value, Z value and the activation energy were calculated for this process. The results obtained in this study are expected to contribute to the optimisation of wheat germ stabilisation by fluidisation. This process may enable to obtain a food with good nutritional features for human consumption from a co-product of the wheat milling industry at a short time and high temperature. Fil: Gili, Renato Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencia y Tecnología de Alimentos Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Ciencia y Tecnología de Alimentos Córdoba; Argentina Fil: Penci, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencia y Tecnología de Alimentos Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Ciencia y Tecnología de Alimentos Córdoba; Argentina Fil: Torrez Irigoyen, Ricardo Martin. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Giner, Sergio Adrian. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina Fil: Ribotta, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencia y Tecnología de Alimentos Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Ciencia y Tecnología de Alimentos Córdoba; Argentina

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”.

Supercritical carbon dioxide (SCCD) was applied for the inactivation of tissue enzymes in beetroot juice. The SCCD process parameters had a significant effect on the inactivation kinetics of polyphenol oxidase (PPO), peroxidase (POD), pectin esterase (PE) and polygalacturonase (PG). The use of traditional pasteurization (TP) resulted in a higher level of inactivation of the tested enzymes than SCCD. The lowest decimal reduction time was noted for PG and the highest for POD. The PG, PE, PPO and POD inactivation kinetic constants were calculated as 0.90, 0.85, 0.82 and 0.6 × 10−2 min−1 for k-values and 256, 271, 281 and 384 min for D-values, respectively, based on the first order kinetic model. The highest degradation of bethacyanins, bethaxanthins and polyphenols occurred at 60 MPa at 55 °C, for 30 min: 58, 32 and 30%, respectively. Overall, SCCD treatment is a promising technique to obtain high quality non-acidified beetroot juice but further studies should concentrate on additional factors affecting the inactivation of tissue enzymes.

Optimally ripened commercial cabbage kimchi is considered the main cause of enteric norovirus (NoV) outbreaks in Korea. This study investigated the effect of 1-10kGy gamma radiation on the inactivation of murine norovirus-1 (MNV-1; initial inoculum of 5-6log10PFU/ml), used as a human NoV surrogate, in kimchi. The effects of gamma radiation on the pH and acidity were also examined to address the index of quality and fermentation, respectively. Titers of MNV-1 significantly reduced (p 0.05). The D-value (1-log reduction) for MNV-1 in kimchi, calculated using first-order kinetics, was 5.75kGy (R2=0.98, RMSE=0.10). Therefore, this study suggests that the use of ≥5.75kGy gamma radiation in the kimchi manufacturing industry could be very effective in reducing NoV contamination by >90% (1 log), without causing changes in quality and fermentation.

This study evaluates the potential of continuous wave Ultraviolet C light (UV-C) and broad-spectrum intense pulsed light (in this study referred to as High Intensity Light Pulses, HILP) for the inactivation of pathogens of public concern in powdered infant formula (PIF) producers. To achieve this goal a sequential set of experiments were performed, firstly in clear liquid media, secondly on the surface of spherical beads under agitation and, finally in PIF. L. innocua was the most sensitive microorganism to both technologies under all conditions studied with reductions exceeding 4 log10 cycles in PIF. In the clear liquid medium, the maximum tolerance to light was observed for C. sakazakii against UV-C light and for B. subtilis spores against HILP, with a fluence of approximately 17 mJ/cm2 required for a 1 log10 cycle inactivation (D value) of each species. In PIF it was possible to inactivate >99% of the vegetative cell populations by HILP with a fluence of 199 mJ/cm2 and of B. subtilis spores by doubling the fluence. By contrast, for UV-C treatments a fluence of 2853 mJ/cm2 was needed for 99.9% reduction of C. sakazakii, which was the most light-resistant microorganism to UV-C. Results here obtained clearly show the potential for light-based interventions to improve PIF microbiological safety.