Search

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.

Water activity (aw) is a major factor affecting pathogen heat resistance in low-moisture foods. However, there is a lack of data for aw at elevated temperatures that occur during actual thermal processing conditions, and its influence on thermal tolerance of pathogens. The objective of this study was to gain an in-depth understanding of the relationship between temperature-induced changes in aw and thermal resistance of Salmonella in all purpose flour and peanut butter at elevated temperatures (80 oC). Equilibrium water sorption isotherms (water content vs. water activity) for all purpose wheat flour and peanut butter over the range of 20 to 80 °C were generated using a vapor sorption analyzer and a newly developed thermal cell. The thermal resistance (D80-values) of Salmonella in all purpose wheat flour and peanut butter with initial aw of 0.45 (measured at room temperature, ~ 20 °C) was determined via isothermal treatment of small (

Atmospheric pressure cold plasma technology is becoming increasingly popular for microbiological decontamination of food and bio-materials. In the present study, afterglow corona discharge air plasma (ACDAP) was used for the inactivation of most common food-borne pathogens, namely pathogenic Escherichia coli , Staphylococcus aureus , Salmonella typhimurium , Bacillus cereus , Listeria monocytogenes , and Vibrio parahaemolyticus . Corona discharge plasma was generated at an output voltage of 20 kV DC, and a frequency of 58 kHz. And, a centrifugal blower that provides an airflow velocity of 2.5 m/s at electrode tip level was used for generating the flowing afterglow of the plasma. During plasma exposure, about 20 °C rise in temperature and a 50% decrease in relative humidity were observed in a treatment chamber within 3 h of exposure. Upon ACDAP exposure, as high as 3.5-log (99.97%) reduction in viable cell counts of tested food pathogens, especially E. coli O157:H7, was observed over a 24-hour exposure. The pathogen inactivation pattern was better explained by using the Singh–Heldman model, which belongs to pseudo-first-order kinetics. In conclusion, ACDAP was shown to be effective for the inactivation of common food-borne pathogens.

Protective solid carriers are commonly added to probiotic cultures prior to drying. Their formulation is not trivial and depends on the drying conditions applied. In this study, we systematically investigated the influence of formulation parameters on the survival of Lactobacillus plantarum WCFS1 after drying. Low molecular weight carbohydrates (less than 2 kDa) with high glass transition temperatures provided the highest level of protection at both low (25 degrees C) and high (50 degrees C or higher) drying temperatures. Low molecular weight carbohydrates may provide stabilization by closely interacting with the lipid bilayer of the cell membranes. Meanwhile, carbohydrates with high glass transition temperatures probably provide stabilization via fixation of the cells in a glassy powder. Furthermore, adequate amounts of solid carrier are required to sufficiently stabilize the cells during drying. During drying, crystallization of solid carriers may occur. Depending on the crystal geometry, crystallization can be either beneficial (e.g. with mannitol or sorbitol) or detrimental (e.g. with lactose) to cell survival. Finally, the effect of formulation on cell viability during storage was studied. A decimal reduction time of approximately 300 days was observed when spray dried L. plantarum WCFS1 was stored at temperatures below 40 degrees C. The outcome of this study was used as a basis to construct a generalized diagram to indicate the combinations of formulation and drying conditions to maximally retain viability and operate dryers at high efficiency. (C) 2013 Elsevier Ltd. All rights reserved.

The probiotics, Lactobacillus acidophilus PTCC1643 and Lactobacillus rhamnosus PTCC1637, were encapsulated into uncoated calcium alginate beads and the same beads were coated with one or two layers of sodium alginate with the objective of enhancing survival during exposure to the adverse conditions of the gastro-intestinal tract. The survivability of the strains, was expressed as the destructive value (decimal reduction time). Particle size distribution was measured using laser diffraction technique. The thickness of the alginate beads increased with the addition of coating layers. No differences were detectable in the bead appearance by scanning electron microscopy (SEM). The alginate coat prevented acid-induced reduction of the strains in simulated gastric juice (pH 1.5, 2 h), resulting in significantly (P

The effects of continuous (50,000, 60,000 and 70,000 psi with holding times of 5 and 10 min) and discontinuous (oscillatory) (six cycles at 60,000 psi with a holding time of 20 s) high hydrostatic pressure (HHP) treatments on the viability of two Salmonella Enteriditis strains (FDA and PT30) inoculated onto raw almonds were evaluated at 25, 50, and 55 °C. Complete inactivation of the S. Enteriditis was achieved in 0.1% peptone water after continuous pressurization at 60,000 psi and 25 °C for 5 min. Continuous pressurization of raw almonds inoculated with S. Enteriditis at 60,000 psi and 50 °C for 5 min resulted in less than a log reduction (log 10 0.83) of vegetative cells. The decimal reduction time using the continuous pressurization parameters was determined to be 9.78 min. A discontinuous process consisting of six cycles of pressurization at 60,000 psi and 50 °C for 20 s provided greater than a one log reduction (log 10 1.27 for FDA and log 10 1.16 for PT30) of the S. Enteriditis concentration. The low water activity ( a w ) of the almonds was found to impart baroprotective attributes on the S. Enteriditis cells. When the almonds were directly suspended in water and then pressurized, a log 10 reduction of 3.37 was achieved. HHP of certain dry foods appears to be feasible if the food is directly suspended in the pressurizing medium (water).

Thermal inactivation of a four-strain mixture of E. coli O157:H7 was determined in lean ground turkey, lamb and pork. Inoculated meat was packaged in bags completely immersed in a circulating water bath and held at 55, 57.5, 60, 62.5, and 65°C for predetermined lengths of time. The surviving cell population was enumerated by spiral plating meat samples on tryptic soy agar overlaid with Sorbitol MacConkey agar. D-values, determined by linear regression, in turkey were 11.51, 3.59, 1.89, 0.81 and 0.29 min at 55, 57.5, 60, 62.5 and 65°C, respectively ( z =6.5°C). When a survival model was fitted to the non-linear survival curves, D-values in turkey ranged from 11.26 min at 55°C to 0.23 min at 65°C ( z =6°C). When the E. coli O157:H7 four-strain cocktail was heated in ground pork or lamb, D-values calculated by both approaches were similar at all temperatures. Thermal-death-times from this study will assist the retail food industry to design cooking regimes that ensure safety of ground muscle foods contaminated with E. coli O157:H7.

Digestive glands containing paralytic shellfish poisoning (PSP) toxins were isolated from toxic scallops. Citrate/phosphate buffers with the pH values ranging from 3 to 7 were added to achieve predetermined pH levels. The samples were heated at 90, 100, 110, 120 and 130°C using a computer controlled oil bath, and three tubes at each pH level were transferred into an ice bath immediately after predetermined heating times for up to 120 min. Both heated and unheated homogenates were analyzed for toxins qualitatively and quantitatively by high performance liquid chromatography (HPLC). Gonyautoxin (GTX) 2 and 3, saxitoxin (STX), neosaxitoxin (NEO) and C toxins were identified by HPLC. All toxins were most sensitive to higher temperatures and higher pH values. However, under gentle heating conditions and low pH, GTX 2 and 3 increased slightly. One explanation for this could be the increased extraction efficiency by heating. However, the conversion of sulfocarbamate toxins to highly toxic carbamate toxins upon heating in the presence of acid known as “Proctor” enhancement, could be another possible explanation for the apparent conversion of C1 and C2 toxins to GTX 2/3. The increase in STX may possibly be due to the conversion of GTX 2/3 and NEO into STX. The kinetics of thermal destruction were qualitatively similar to the thermal destruction of microorganisms. That is, the log survival of heated toxins was inversely proportional to time of heating and log decimal reduction time inversely related to temperature of heating. Efficacy of thermal destruction was highly dependent on pH, with more rapid thermal destruction at higher pH levels. The levels of individual toxins in the homogenate and those generated during heating could be reduced significantly by heating at 130°C at pH 6–7.

Destruction kinetics of two selected spoilage microorganisms, Saccharomyces cerevisiae and Lactobacillus plantarum in apple juice were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a water bath. Inoculated apple juice was heated in a microwave oven (700 W, 2450 MHz) under continuous-flow conditions to selected exit temperatures (52.5–65°C). Aliquots of inoculated juice were also subjected to batch thermal treatments (50–80°C) in a well-stirred water bath. Time-temperature profiles obtained both during heating and cooling of test samples were used to correct both come-up and come-down times. The time-corrected D-values under microwave heating were 4.8, 2.1 and 1.1 s at 52.5, 55 and 57.5°C, respectively, for S. cerevisiae and 14, 3.8 and 0.79 s at 57.5, 60 and 62.5°C, respectively, for L. plantarum with corresponding z-values of 7 and 4.5°C. D-values under batch thermal heating were 58, 25, 10 and 1.9 s at 50, 55, 60 and 70°C, respectively, for S. cerevisiae and 52, 22, 8.4 and 1.2 s at 55, 60, 70 and 80°C, respectively, for L. plantarum with corresponding z-values of 13.4 and 15.9°C. Microbial destruction thus occurred much faster under microwave heating than under thermal heating suggesting some contributory enhanced effects to be associated with microwave heating.

Compressed Saccharomyces cerevisiae yeasts were dried in a modified Yamato Pulvis GA 22 fluidized bed dryer and also exposed to moist heat in classical thermal death time experiments. The results showed that dehydration and not moist heat, dry heat, or oxidation was responsible for viability decreases during fluidized bed drying. It was determined that the viabilities of the compressed yeasts placed in the dryer were not substantially affected by the drying temperature during the warming-up and constant-rate drying periods (when moisture contents were greater than 15%). However, at moisture contents below 15% when compressed yeasts were in the falling-rate drying period, viability decreased sharply. Phantom thermal death time curves were constructed in order to distinguish between the kinetics of death due to moist heat (classical thermal death time experiments) and the kinetics of death due to dehydration in the fluidized bed dryer. For both compressed yeasts below 50 °C, moist heat D (thermal decimal reduction time) values were found to be greater than dD (dehydration decimal reduction time) values which indicates that at such temperatures, the death of both compressed yeasts due to moist heat is less vital than death due to dehydration. As temperatures increased above 50 °C, moist heat became more responsible for killing the compressed yeasts than dehydration. When compressed yeast was dried in the presence of trehalose (a known dehydration protectant), 30% higher viability was seen compared to the same yeast dried without trehalose.

Moisture levels, drying rates, and yeast cell viabilities (survival curves) were determined for two commercial compressed baker's yeasts dried in a modified fluidized bed dryer. Unlike the survival curves seen for microbes examined by classical thermal death procedures, the survival curves for both compressed yeasts stabilized—each at a different, distinct viability—as temperatures were changed in the fluidized bed dryer. The D and z values describing drying kinetics were determined from survival curves. The D values obtained for both compressed yeasts showed a linear relationship with drying temperature. Using air at 80 °C, compressed yeast no. 1 exhibited a D value of 4.20 minutes while the D value for compressed yeast no. 2 was 8.34 minutes. The z value for compressed yeast no. 1 was 28.4 °C and for compressed yeast no. 2 it was 27.5 °C. It was determined that the viability of the compressed yeasts in the fluidized bed dryer was not significantly affected by the drying temperature used during the warming-up and constant-rate drying periods (when moisture contents were greater than 15%). Mechanisms of death for fluidized bed drying appear to be very different from that reported for spray drying as evidenced by the ~200-fold differences in D values at the same temperature.

Ultra high pressure treatments ranging from 0 to 720 min were applied to freshly squeezed, non-pasteurized orange juice and reconstituted frozen orange juice at pressures in the range 100 to 400 MPa to investigate the pressure inactivation kinetics of pectin methyl esterase (PME) activity. Freshly squeezed orange juice was adjusted to pH 3.7 or 3.2 (12.6 ° Brix) while the reconstituted frozen concentrate orange juice was adjusted to 10, 20, 30 and 40 ° Brix at pH 3.7. The frozen concentrated orange juice was initially heat treated to inactivate the natural enzymes and then fortified with commercial PME prior to inactivation studies. Analyses of kinetic data revealed the presence of a dual-effect of pressure inactivation: the first one, designated as an instantaneous pressure kill (IPK), which depended only on the pressure level; and a second one, which depended on the holding time at each pressure level, described by first-order reaction kinetics (characterized by a rate constant, k , or by the more familiar decimal reduction time, D ). The associated IPK were higher and D values were lower at the lower pH and lower soluble solid contents. The pressure sensitivity of D values were adequately described by a z p value which represented the range of applied pressure between which the D values change by a factor of 10.

Thermal stability of lysozyme in aqueous buffer solutions was studied at selected temperatures (73–100 °C), pH values (4.2–9.0) and levels of sucrose (0%, 5%, 15%) and sodium chloride (0, 0.1 M, 1 M). The results, fitted to a first-order model and expressed in terms of decimal reduction time ( D ), inactivation rate constant ( k ), decimal reduction temperature ( z ) and Arrhenius activation energy ( E a ) indicated that lysozyme was most stable at pH 5.2, and thermal stability decreased sharply as the pH increased to 9.0. A regression equation for prediction of k as a function of pH and temperature was derived, with the best fit obtained for the model in the pH range of 5.2–7.2 (adjusted multiple r 2 = 0.98). At pH 7.2 and 9.0, sodium chloride had a clear stabilizing effect against heat inactivation of lysozyme. Sucrose stabilized lysozyme against heat inactivation at 75 °C but not at 91 °C. Thermal inactivation kinetics of lysozyme and its potential to prevent or delay microbial growth were investigated in beer. Lysozyme at concentrations of 10 and 50 ppm appeared to delay growth of the spoilage bacteria L. brevis and P. damnosus in beer, but did not prevent growth of the bacteria.

Thermal destruction of the biotin-binding activity of avidin was estimated by thermal destruction time (TDT) experiments between 73·3°C and 125·6°C. Decimal reduction time at 121·1°C was 24·5 min while the response to temperature change was described by a z value of 33 C°. Heat stability of the biotin-binding site of avidin was shown to be much greater than previously inferred from DSC protein denaturation studies of avidin.