Inactivation of E. coli 8739 in Enriched Soymilk Using Pulsed Electric Fields

ABSTRACT: Soymilk enriched with dairy proteins was subjected to pulsed electric fields (PEF) to evaluate the inactivation of Escherichia coli 8739 and the extension of microbial shelf-life. The maximum thermal exposure level of sample was 60 °C for 1.6 s during a PEF treatment. A 5.7-log reduction was achieved using PEF at 41.1 kV/cm for 54 μs. PEF inactivation of E. coli 8739 followed a 1st-order kinetic model. D-values of E. coli 8739 were 31.9,18.6, and 11.0 μs at 30,35, and 40 kV/cm, respectively. PEF treatment at 41.1 kV/cm for 54 μs significantly extended the microbial shelf-life at 4 °C ( P < 0.05). No significant change in brightness and viscosity of PEF-treated samples was observed during a 30-d storage at 4 °C. PEF was found effective in inactivation of E. coli in and extension of microbial shelf-life of enriched soymilk.     

Inactivation of Escherichia coli with Power Ultrasound in Apple Cider

The use of acoustic energy to secure apple cider safety was explored. Inactivation tests were performed with Escherichia coli K12 at 40 °C, 45 °C, 50 °C, 55 °C, and 60 °C with and without ultrasound, followed by a validation test with E. coli O157:H7 at 60 °C. The cell morphology was observed with environmental scanning electron microscopy for samples treated at 40 °C and 60 °C. Physical quality attributes of the apple cider (pH, titratable acidity, °Brix, turbidity, and color) were compared for treated samples. The inactivation tests showed that sonication increased E. coli K12 cell destruction by 5.3‐log, 5.0‐log, and 0.1‐log cycles at 40 °C, 50 °C, and 60 °C, respectively. The additional destruction due to sonication was more pronounced at sublethal temperatures. At the lethal temperature of 60 °C, the rate of death by ultrasound was not significantly different compared with the thermal‐alone treatment. The inactivation of E. coli K12 with heat was described by 1st‐order kinetics, especially at 50 °C and 60 °C. For ultrasound treatments, concave upward survival curves were observed, which had a shape factor in the range of 0.547 to 0.720 for a Weibull distribution model. Extensive damage for ultrasound treated E. coli K12 cells, including cell perforation, was observed. Perforation is a unique phenomenon found on ultrasound‐treated cells that could be caused by liquid jets generated by cavitation. Titratable acidity, pH, and °Brix of the cider were not affected by ultrasound treatment. Minor changes in color and turbidity for ultrasound treated samples, especially for sonication at 40 °C for 17.7 min, were observed.     

Inactivation of in Apple Juice by Radio Frequency Electric Fields

ABSTRACT: Heat pasteurization may detrimentally affect the quality of fruit and vegetable juices; hence, nonthermal pasteurization methods are actively being developed. Radio frequency electric fields processing has recently been shown to inactivate yeast in water at near-ambient temperatures. The objective of this study was to extend the radio frequency electric fields (RFEF) technique to inactivate bacteria in apple juice. A converged-field treatment chamber was developed that enabled high-intensity RFEF to be applied to apple juice using a 4-kW power supply. Finite element analyses indicated that uniform fields were generated in the treatment chamber. Escherichia coli K12 in apple juice was exposed for 0.17 ms to electric field strengths of up to 26 kV/cm peak over a frequency range of 15 to 70 kHz. The population of E. coli was reduced by 1.8 log following exposure to an 18 kV/cm field at an outlet temperature of 50 °C. Raising the temperature increased inactivation. Intensifying the electric field up to 16 kV/cm increased inactivation; however, above this intensity, inactivation remained constant. Radio frequencies of 15 and 20 kHz inactivated E. coli better than frequencies of 30 to 70 kHz. Inactivation was independent of the initial microbial concentration between 4.3 and 6.2 log colony-forming units (CFU)/mL. Applying 3 treatment stages at 50 °C increased inactivation to 3 log. The electric energy for the RFEF process was 300 J/mL. The results of the present study provide the 1st evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.     

Resistance ofListeria monocytogenesto ultrasonic waves under pressure at sublethal (manosonication) and lethal (manothermosonication) temperatures

The influence of amplitude of ultrasonic waves, static pressure and temperature on the inactivation rate ofListeria monocytogenesby ultrasonic waves under pressure (manosonication; MS) has been investigated. Also the influence of growth temperature, pH and composition of treatment medium, and the presence of sodium chloride in the recovery medium on the MS resistance ofL. monocytogeneshas been investigated and compared with its heat resistance. The inactivation ofL. monocytogenesby high power ultrasonic waves (20 kHz, 117 μm) at ambient temperature and pressure was low (D_UW=4.3 min). The increase of relative pressure (MS) to 200 kPa decreasedD_MSto 1.5 min and the increase to 400 kPa to 1.0 min. Inactivation rate by MS increased exponentially with the amplitude of ultrasonic waves in the range of 62-150 μm. An amplitude increase of 100 μm decreased the MS resistance of approximately six times. The inactivation rate by MS was not influenced by treatment temperature up to 50°C. However at higher temperatures the lethality of this combined process (MTS) increased considerably. Inactivation by MTS was the result of the inactivation by heat in addition to that by ultrasound under pressure. Cells grown at 37°C were twice more heat resistant than those grown at 4°C but no differences were found between decimal reduction time values to MS (117 μm, 200 kPa, 40°C) of both suspensions. While the inactivation rate by heat in pH 4 buffer was two- and five-fold higher than in pH 7 buffer and skimmed milk respectively, the differences amongD_MS-value in these media were lower than 60%. The addition of 57% of sucrose to the treatment medium increasedD₆₁from 0.22 to 5.7 min andD_MSfrom 1.5 to 3.1 min. The addition of 3% sodium chloride to the recovery medium decreasedD₆₀by 1/3 but did not modifyD_MS-values.     

Effect of High Hydrostatic Pressure on Cashew Apple (Anacardium occidentale L.) Juice Preservation

ABSTRACT:  High hydrostatic pressure is an alternative to thermal processing to inactivate spoilage and pathogenic microorganisms. Cashew apple juice has a pleasant flavor and is rich in vitamin C. Studies to determine the effect of high pressure on microorganisms in cashew apple juice are still lacking. In this study, the inactivation of natural micropopulation and inoculated Escherichia coli by high pressure was evaluated in fresh cashew apple juice. The microbiological stability of pressure-treated juice was also evaluated. The applied high pressure levels ranged from 250 to 400 MPa for periods of 3 to 7 min. Treatments with 350 MPa for 7 min and 400 MPa for either 3 or 7 min reduced the aerobic mesophilic bacteria count to a level below the detection limit. Pressure treatments were also efficient in inactivating yeast and filamentous fungi. The inoculated E. coli (10⁶ CFU/mL) was reduced to below 10 CFU/mL after a pressure treatment of 400 MPa for 3 min. The inactivation of this microorganism followed a 1st-order reaction kinetics. The decimal reduction time ( D- value) ranged from 1.21 to 16.43 min, while pressure resistance value ( z -value) was 123.46 MPa. Neither natural micropopulation growth nor E. coli repair was observed in postprocessed (400 MPa for 3 min) cashew apple juice kept under refrigerated storage (at 4 °C) during 8 wk. The results of this study demonstrated the efficacy of high-pressure treatment for preserving cashew apple juice.     

Antimicrobial Activity and Synergistic Effect of Cinnamon with Sodium Benzoate or Potassium Sorbate in Controlling Escherichia coli O157:H7 in Apple Juice

ABSTRACT: Antimicrobial effects of cinnamon, sodium benzoate, potassium sorbate, and combinations were examined against Escherichia coli O157:H7 in apple juice at 8°C and 25°C. E. coli O157:H7 was reduced by 1.6 log colony-forming units (CFU)/mL at 8°C and 2.0 log CFU/mL at 25°C by 0.3% cinnamon. At 8°C, 5.2 log CFU/mL of E. coli O157:H7 was eliminated in 11 d by 0.3% cinnamon with 0.1% sodium benzoate, and in 14 d by 0.3% cinnamon with 0.1% potassium sorbate. At 25°C, 5.3 log CFU/mL E. coli O157:H7 was eliminated in 3 d by the same combinations. A synergistic effect was observed between cinnamon and preservatives against E. coli O157:H7 at 8°C and 25°C.     

Influence of Storage Temperature on the Kinetics of the Changes in Anthocyanins, Vitamin C, and Antioxidant Capacity in Fresh-Cut Strawberries Stored under High-Oxygen Atmospheres

ABSTRACT:  Changes in the main antioxidant properties of fresh-cut strawberries stored under high-oxygen atmospheres (80 kPa O₂) were studied at selected temperatures (5 to 20 °C). The suitability of zero- and 1st-order kinetics as well as a model based on Weibull distribution function to describe changes in experimental data is discussed. A non-Arrhenius approach was used to determine the temperature dependence of the estimated rate constants. A Weibull kinetic model most accurately  ( R ²_adj≥ 0.800)  estimated changes in anthocyanins and antioxidant capacity of fresh-cut strawberries throughout the storage period, whereas a 1st-order model adequately fitted  ( R ²_adj≥ 0.982)  the variation of vitamin C. The temperature dependency of the kinetic rate constants for each antioxidant property was successfully modeled through the non-Arrhenius approach  ( R ²_adj≥ 0.709)  . The T_c obtained for anthocyanins, vitamin C, and antioxidant capacity degradation were 290, 284, and 289 K, respectively, indicating the temperature at which a marked acceleration of the losses in the antioxidant potential of strawberry wedges occurs. These findings will help to describe the variation of the antioxidant potential of fresh-cut strawberries upon storage time and temperature.     

Inactivation of Listeria monocytogenes and Escherichia coli by Ultrasonic Waves Under Pressure at Nonlethal (Manosonication) and Lethal Temperatures (Manothermosonication) in Acidic Fruit Juices

The inactivation of Listeria monocytogenes and Escherichia coli suspended in apple and orange juices by ultrasound under pressure at nonlethal (manosonication, MS) and lethal temperatures (manothermosonication, MTS) was evaluated. Significant differences were found in the MS resistance (35 °C, 110 μm, 200 kPa) of three strains of L. monocytogenes and three of E. coli in pH 3.5 buffer, L. monocytogenes STCC 5672 and E. coli O157:H7 being the most resistant strains. Regarding the interspecific differences, L. monocytogenes showed higher MS resistance than E. coli. Although the pH and treatment medium composition did not significantly change the bacterial MS resistance, the effectiveness of ultrasound increased by both raising the amplitude of ultrasonic waves and the pressure. The energy transmitted to the fruit juices by ultrasonic waves at different combinations of amplitudes (46.5, 90, 110, and 130.5 μm) and pressures (0, 100, and 200 kPa) was also studied, obtaining an exponential relationship between the D _MS values and power input: an increase of 116 W increased the inactivation rate approximately 10-fold in both juices. The MS resistance of both species decreased when heat was applied jointly with ultrasound (MTS), which was more effective in inactivating L. monocytogenes and E. coli than the sum of MS and heat acting simultaneously but independently. Therefore, MTS showed a synergistic lethal effect in acidic juices, whose magnitude was dependent on the treatment conditions.     

Effects of ultraviolet-light emitting diodes (UV-LEDs) on microbial inactivation and quality attributes of mixed beverage made from blend of carrot,carob, ginger,grape and lemon juice

Efficacy of ultraviolet light-emitting diodes (UV-LEDs) with peak and coupled emissions at 280, 365 and 280/365 nm on inactivation of E. coli K12 in mixed beverage (MB) was investigated. MB comprised of 31.6% carrot, 44.3% carob, 8.7% grape, 10.2% ginger, and 5.2% lemon juice. The impact of UV-LEDs on some physicochemical and phytochemical properties of MB was compared to that of heat treatment (70 °C, 120 s). While, UV-LED irradiation using coupled 280/365 nm for 40 min resulted in the highest inactivation of E. coli K12 (>4 log) out of tested wavelengths, the number of mesophilic bacteria (TAC), and yeast and molds (YM) in mixed beverage were reduced by 2.59 log CFU/mL (from 5.69 log CFU/mL of initial load), and 0.17 log CFU/mL (from 3.28 log CFU/mL of the initial load), respectively. Although, the color parameters slightly changed after irradiation, the color of MB did not show visual difference (ΔE = 0.94) compared to untreated samples. UV-LED treatment caused a significant increase in total phenolic compound (1.75-fold) and antioxidant capacity (4.60 fold) compared to heat-treated samples (p < 0.05). UV-LED treatment caused a decrease in carotenoid content (71.3%) lower than that of heat-treated samples (88.9%), indicating that UV-LED irradiation preserved the total carotenoid content better than the heat treatment.Industrial relevanceLight-emitting diodes (LEDs) are new sources of ultraviolet light utilized for non-thermal processing of foods. In this study, a static bench top unit was designed to investigate the efficacy of UV-LEDs with different treatment times and peak emissions by considering the inactivation of E. coli K12 in newly formulated mixed drink (MB). UV-LED irradiation of MB using coupled 280/365 nm for 40 min provided the highest microbial inactivation and preserved bioactive compounds better than the heat treatment. It can be proposed as an effective method for the processing of fruit juices which is rich in bioactive constituents.     

Inactivation of Cronobacter sakazakii by manothermosonication in buffer and milk

The inactivation of Cronobacter sakazakii by heat and ultrasound treatments under pressure at different temperatures [manosonication (MS) and manothermosonication (MTS)] was studied in citrate-phosphate pH 7.0 buffer and rehydrated powdered milk. The inactivation rate was an exponential function of the treatment time for MS/MTS treatments (35−68 °C; 200 kPa of pressure; 117 μm of amplitude of ultrasonic waves) in both media, and for thermal treatments alone when buffer was used as heating media. Survival curves of C. sakazakii during heating in milk had a concave downward profile. Up to 50 °C, the lethality of ultrasound under pressure treatments was independent of the treatment temperature in both media. At temperatures greater than 64 °C in buffer and 68 °C in milk, the inactivating effect of MTS was equivalent to that of the thermal treatments alone at the same temperature. Between 50 and 64 ºC for buffer and 50 and 68 °C for milk, the lethality of MTS was the result of a synergistic effect, where the total lethal effect was higher than the lethal effect of heat added to that of ultrasound under pressure at room temperature. The maximum synergism was found at 60 °C in buffer and at 56 °C in milk. A heat treatment of 12 min (60 °C) or 4 min of an ultrasound under pressure at room temperature treatment (35 °C; 200 kPa; 117 μm) would be necessary to guarantee the death of 99.99% of C. sakazakii cells suspended in milk. The same level of C. sakazakii inactivation can be achieved with 1.8 min of a MTS treatment (60 °C; 200 kPa; 117 μm). Damaged cells were detected after heat treatments and after ultrasound under pressure treatments at lethal but not at non-lethal temperatures.     

Heat-moisture Treatments of Cowpea Flour and Their Effects on Phytase Inactivation

ABSTRACT: Samples of finely ground cowpea flour with moisture content adjusted to 10%, 25%, 35% (dry basis) were heated in sealed retort pouches at 70 to 95°C for periods of 2 to 32 min. Phytase showed a high thermal resistance with residual activity ranging between 50% and 95%. Thermal inactivation of cowpea phytase was adequately described by a fractional conversion model based on a 1st-order rate equation. Overall, increasing temperature and initial moisture content resulted in increased enzyme inactivation. Estimated activation energies between 70 and 95°C were 33.3, 37.9, and 43.4 kJ/mol at 10%, 25%, and 35% moisture, respectively. The kinetic models generated were successfully used to predict phytase activity in cowpea flour.     

Survival of Escherichia coli O157:H7 in yogurt drink, plain yogurt and salted (tuzlu) yogurt: Effects of storage time, temperature, background flora and product characteristics

The survival of Escherichia coli O157:H7 at 4 and 22°C in yogurt drink, plain yogurt and salted yogurt (yogurt native to Hatay, Turkey) was studied. Total aerobic plate count (TPC), total mould and yeast count, pH and titratable acidity during the storage period were measured. pH and TPC count of the samples at 22°C were significantly higher than those of samples at 4°C ( P <  0.01). E. coli O157:H7 survived in the products at both 4 and 22°C, whereas survival of E. coli O157:H7 was significantly lower at 4°C than at 22°C ( P <  0.05). Multiple linear regression models were used to determine factors affecting the survival of E. coli O157:H7.     

Inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in Liquid Egg White Using Pulsed Electric Field

ABSTRACT: The effects of temperature and pulsed electric field (PEF) intensity on inactivation of pathogens such as Escherichia coli O157:H7 and Salmonella enteritidis in egg white was investigated. Liquid egg white inoculated with 10⁸ colony-forming units (CFU)/mL of each pathogen was treated with up to 60 pulses (each of 2 JAS width) at electric field intensities of 20 and 30 kV/cm. The processing temperatures were 10°C, 20°C, and 30°C. After treatment, uninjured and total viable cells were enumerated in selective and nonselective agars, respectively. Maximum inactivations of 3.7 and 2.9 log units were obtained for S. enteritidis and E. coli O157:H7, respectively, while injured cells accounted for 0.5 and 0.9 logs for E. coli O157:H7 and S. enteritidis , respectively. For both bacteria, increasing treatment temperature tended to increase the inactivation rate. There was synergy between electric field intensity and processing temperature. The inactivation rate constant k _T values for E. coli O157:H7 on both selective and nonselective agars were 8.2 × 10^-3 and 6.6 × 10^-3/μS, whereas the values for S. enteritidis were 16.2 × 10^-3 and 12.6 × 10^-3/μS, respectively. The results suggest that E. coli O157:H7 was more resistant to heat-PEF treatment compared with S. enteritidis.     

Temperature Effect on Inactivation Kinetics of Escherichia coli O157:H7 by Electron Beam in Ground Beef, Chicken Breast Meat, and Trout Fillets

ABSTRACT:  Ground beef, boneless skinless chicken breast meat, and boneless skinless trout fillets were inoculated with Escherichia coli O157:H7 and incubated to approximately 10⁹ colony forming units per gram (CFU/g). Following incubation, temperature of the meat samples was equilibrated to −20, 4, and 22 °C. The meat samples at different temperatures were subjected to one-sided electron beam (e-beam) with fixed energy at 10 million electron volts (MeV) and doses at 0 (control), 0.5, 1.0, 2.0, 2.5, and 3.0 kGy. The survivors were enumerated using a standard spread-plating method. The survivor curves were plotted on logarithmic scale as a function of e-beam dose for each meat sample subjected to e-beam at different temperatures. The D -values were calculated as a negative reciprocal of the slope of the survivor curves. The D -values for E. coli ranged from 0.22 to 0.35 kGy in trout at 4 °C and chicken at −20 °C, respectively. The D -values were different between meat types. Regardless of temperature, E. coli in chicken had highest D -value followed by beef and trout. The D -values for E. coli in frozen samples were higher than D -values in samples irradiated at 4 and 22 °C regardless of species. Although there were numerical differences between D -values for samples subjected to e-beam while chilled (4 °C) or frozen (−20 °C), they were statistically insignificant. Water radiolysis is considered as an indirect mechanism for microbial inactivation. Therefore, while the physical state of water (frozen or unfrozen) in foods seems the major contributor to microbial inactivation by e-beam due to water radiolysis, product temperature most likely plays a minor role.     

Comparative Study of Thermal Inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in Ground Pork

ABSTRACT: Thermal inactivation of Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes in ground pork was compared. The D (decimal reduction time at a certain heating temperature) values of E. coli O157:H7, Salmonella , and L. monocytogenes at 55 to 70°C were 33.44 to 0.048 min, 45.87 to 0.083 min, and 47.17 to 0.085 min, respectively. The z (temperature rise for 1 log10 reduction of D) value of E. coli O157:H7, Salmonella , and L. monocytogenes in ground pork was 4.94°C, 5.89°C, and 5.92°C, respectively. Significant difference was found on the D and z values between E. coli O157:H7 and Salmonella or between E. coli O157:H7 and L. monocytogenes . The D and z values of Salmonella in ground pork were not significantly different from L. monocytogenes .     

Effects of pH,temperature, and pre-pulsed electric field treatment on pulsed electric field and heat inactivation of Escherichia coli O157:H7

This investigation was undertaken to study the inactivation of Escherichia coli O157:H7 by pulsed electric field (PEF) treatment and heat treatment after exposure to different stresses. E. coli O157:H7 cells exposed to different pHs (3.6, 5.2, and 7.0 for 6 h). different temperatures (4, 35, and 40 degrees C for 6 h), and different pre-PEF treatments (10, 15, and 20 kV/cm) were treated with PEFs (20, 25, and 30 kV/cm) or heat (60 degrees C for 3 min). The results of these experiments demonstrated that a pH of 3.6 and temperatures of 4 and 40 degrees C caused significant decreases in the inactivation of E. coli O157:H7 by PEF treatment and heat treatment (P < 0.05). Pre-PEF treatments, pHs of 5.2 and 7.0, and a temperature of 35 degrees C, on the other hand, did not result in any resistance of E. coli O157:H7 cells to inactivation by PEF treatment and heat treatment (P > 0.05).     

高压均质对芒果汁中大肠杆菌的杀菌动力学

为预测高压均质(high pressure homogenization,HPH)对芒果汁中大肠杆菌的杀菌作用,进行了压力40~190 MPa、进料温度20~60℃和均质次数1~5次的HPH实验,并运用Weibull模型对杀菌致死曲线进行动力学分析。研究表明:随压力、进料温度和均质次数的升高,HPH对芒果汁中大肠杆菌的杀菌效果增强。50℃HPH处理芒果汁,压力由40 MPa升高至190 MPa时,大肠杆菌降低量由0.46(lg(CFU/mL))增加至5.16(lg(CFU/mL)),达到美国食品药物管理局规定的非热加工杀菌卫生安全要求;70 MPa HPH处理芒果汁,进料温度由20℃升高至60℃时,大肠杆菌降低量由0.34(lg(CFU/mL))增加至5.02(lg(CFU/mL));20℃、190 MPa HPH处理芒果汁,均质次数由1增加至4时,大肠杆菌降低量由1.73(lg(CFU/mL))增加至5.15(lg(CFU/mL))。通过Weibull模型拟合杀菌致死曲线,并对模型进行简化,发现简化的Weib ull模型在20~50℃、40~190 MPa均质1次和20~40℃、190 MPa均质1~5次时拟合性较好(R~20.92)。简化的Weibull模型可用于预测进料温度-压力和进料温度-均质次数的杀菌效果,可为芒果汁的HPH生产过程中微生物安全性的控制提供理论依据。     

Heat Curing of Soy Protein Films at Atmospheric and Sub-atmospheric Conditions

ABSTRACT: The effect of heat curing at atmospheric or subatmospheric conditions on selected properties (moisture content, water vapor permeability (WVP), color, tensile strength (TS), elongation (E), and total soluble matter (TSM) content) of cast soy protein isolate films was investigated. Films were heat cured at 85 °C for 6, 12, 18, or 24 h at absolute pressures of 101.3, 81.32, or 61.32 kPa. Heat-cured films had increased (P < 0.05) TS and decreased (P < 0.05) WVP and E compared to control, unheated films. Heat treatment under vacuum reduced the WVP of films faster than heat curing at atmospheric pressure. High TS values, low E values, and low TSM values were also reached within short heating time under vacuum. However, vacuum treatment increased the size and number of cavities in cured films as evidenced by scanning electron micrographs.     

Inactivation of Salmonella Senftenberg 775W by ultrasonic waves under pressure at different water activities

The inactivation of Salmonella Senftenberg 775W by ultrasonic waves (20 kHz, 117 microm) under pressure (175 kPa) treatments at sublethal (manosonication; MS) and lethal temperatures (manothermosonication; MTS) in media of different water activities has been investigated. Heat decimal reduction time values increased up to eighteen fold when the water activity was decreased from >0.99 to 0.93 at 65 degrees C, but hardly increased the MS resistance. In reduced water activity media (a(w) of 0.96 and 0.93) a synergistic lethal effect was observed between heat and ultrasound under pressure, being the inactivation rate of Salmonella Senftenberg 775W three times faster than the expected additive rate considering an effect of both bacterial lethal processes. An empirical mathematical equation enabled to predict the D(MS) and D(MTS) values obtained at different temperatures and a(w) in the ranges investigated of Salmonella serovars and also the microbial level of inactivation due to the synergistic lethal effect of MTS treatments in media of reduced a(w). This work could be useful for improving sanitation and preservation treatments of foods, especially those in which components protect microorganisms to heat.     

Combined Carbon Dioxide and High Pressure Inactivation of Pectin Methylesterase, Polyphenol Oxidase, Lactobacillus plantarum and Escherichia coli

ABSTRACT: High pressure processing (HPP) and CO₂have both been shown to increase food product shelf-life. CO₂ was added at approximately 0.2 molar % to solutions processed at 500 to 800 MPa in order to further inactivate pectin methylesterase (PME), polyphenol oxidase (PPO), L. plantarum ATCC 8014, and E. coli K12. An interaction was found between CO₂ and pressure at 25 °C and 50 °C for PME and PPO, respectively. Activity of PPO was decreased by CO₂ at all pressure treatments. The interaction between CO₂ and pressure was significant for L. plantarum with a significant decrease in survivors due to the addition of CO₂ at all pressures studied. No significant effect on E. coli survivors was seen with CO₂ addition.