Critical Concentration of Lecithin Enhances the Antimicrobial Activity of Eugenol against Escherichia coli.

Lecithin is a natural emulsifier used in a wide range of food and nonfood applications to improve physical stability, with no known bioactive effects. In this study, the effect of lecithin on the antimicrobial performance of a constant eugenol concentration was tested against three Escherichia coli strains (C600, 0.1229, and O157:H7 strain ATCC 700728). This is the first study, to our knowledge, focusing on lecithin at concentrations below those commonly used in foods to improve the stability of oil in water emulsions (≤10 mg/100 ml). For all three cultures, significant synergistic antimicrobial effects were observed when E. coli cultures were exposed to a constant eugenol concentration (ranging from 0.043 to 0.050% [wt/wt]) together with critical lecithin concentrations ranging from 0.5 to 1 mg/100 ml. Increasing the concentration of lecithin above 1 mg/100 ml (up to 10 mg/100 ml lecithin) diminished the antibacterial effect to values similar to those with eugenol-only treatments. The formation of aggregates (<100 nm) at the critical lecithin concentration was observed using cryo-transmission electron microscopy (cryo-TEM), together with a reduction in light absorbance at 284 nm. At critically low concentrations of lecithin, the formation of nanoscale aggregates is responsible for improving eugenol antimicrobial effects.IMPORTANCE Essential oils (EOs) are effective natural antimicrobials. However, their hydrophobicity and strong aromatic character limit the use of essential oils in food systems. Emulsifiers (e.g., lecithin) increase the stability of EOs in water-based systems but fail to consistently improve antimicrobial effects. We demonstrate that lecithin, within a narrow critical concentration window, can enhance the antimicrobial properties of eugenol. This study highlights the potential bioactivity of lecithin when utilized to effectively control foodborne pathogens.

Thermal Inactivation Kinetics of Human Norovirus Surrogates and Hepatitis A Virus in Turkey Deli Meat.

Human noroviruses (HNoV) and hepatitis A virus (HAV) have been implicated in outbreaks linked to the consumption of presliced ready-to-eat deli meats. The objectives of this research were to determine the thermal inactivation kinetics of HNoV surrogates (murine norovirus 1 [MNV-1] and feline calicivirus strain F9 [FCV-F9]) and HAV in turkey deli meat, compare first-order and Weibull models to describe the data, and calculate Arrhenius activation energy values for each model. The D (decimal reduction time) values in the temperature range of 50 to 72°C calculated from the first-order model were 0.1 ± 0.0 to 9.9 ± 3.9 min for FCV-F9, 0.2 ± 0.0 to 21.0 ± 0.8 min for MNV-1, and 1.0 ± 0.1 to 42.0 ± 5.6 min for HAV. Using the Weibull model, the tD = 1 (time to destroy 1 log) values for FCV-F9, MNV-1, and HAV at the same temperatures ranged from 0.1 ± 0.0 to 11.9 ± 5.1 min, from 0.3 ± 0.1 to 17.8 ± 1.8 min, and from 0.6 ± 0.3 to 25.9 ± 3.7 min, respectively. The z (thermal resistance) values for FCV-F9, MNV-1, and HAV were 11.3 ± 2.1°C, 11.0 ± 1.6°C, and 13.4 ± 2.6°C, respectively, using the Weibull model. The z values using the first-order model were 11.9 ± 1.0°C, 10.9 ± 1.3°C, and 12.8 ± 1.7°C for FCV-F9, MNV-1, and HAV, respectively. For the Weibull model, estimated activation energies for FCV-F9, MNV-1, and HAV were 214 ± 28, 242 ± 36, and 154 ± 19 kJ/mole, respectively, while the calculated activation energies for the first-order model were 181 ± 16, 196 ± 5, and 167 ± 9 kJ/mole, respectively. Precise information on the thermal inactivation of HNoV surrogates and HAV in turkey deli meat was generated. This provided calculations of parameters for more-reliable thermal processes to inactivate viruses in contaminated presliced ready-to-eat deli meats and thus to reduce the risk of foodborne illness outbreaks.

Determination of thermal inactivation kinetics of hepatitis A virus in blue mussel (Mytilus edulis) homogenate.

Hepatitis A virus (HAV) is a food-borne enteric virus responsible for outbreaks of hepatitis associated with shellfish consumption. The objectives of this study were to determine the thermal inactivation behavior of HAV in blue mussels, to compare the first-order and Weibull models to describe the data, to calculate Arrhenius activation energy for each model, and to evaluate model efficiency by using selected statistical criteria. The times required to reduce the population by 1 log cycle (D-values) calculated from the first-order model (50 to 72°C) ranged from 1.07 to 54.17 min for HAV. Using the Weibull model, the times required to destroy 1 log unit (tD = 1) of HAV at the same temperatures were 1.57 to 37.91 min. At 72°C, the treatment times required to achieve a 6-log reduction were 7.49 min for the first-order model and 8.47 min for the Weibull model. The z-values (changes in temperature required for a 90% change in the log D-values) calculated for HAV were 15.88 ± 3.97°C (R(2), 0.94) with the Weibull model and 12.97 ± 0.59°C (R(2), 0.93) with the first-order model. The calculated activation energies for the first-order model and the Weibull model were 165 and 153 kJ/mol, respectively. The results revealed that the Weibull model was more appropriate for representing the thermal inactivation behavior of HAV in blue mussels. Correct understanding of the thermal inactivation behavior of HAV could allow precise determination of the thermal process conditions to prevent food-borne viral outbreaks associated with the consumption of contaminated mussels.

Impacts of sample preparation methods on solubility and antilisterial characteristics of essential oil components in milk.

Essential oil components (EOCs) have limited water solubility and are used at much higher concentrations in complex food matrices than in growth media to inhibit pathogens. However, the correlation between solubility and activity has not been studied. The objective of this work was to characterize the solubility of EOCs in solvents and milk and correlate solubility with antilisterial activity. The solubilities of four EOCs, thymol, carvacrol, eugenol, and trans-cinnamaldehyde, in water was significantly increased in the presence of 5% (vol/vol) ethanol. In milk, the solubility of EOCs was lower than in water, with lower solubility in higher-fat milk. EOCs applied to milk as stock solutions (in 95% aqueous ethanol) enabled quicker dissolution and higher solubility in milk serum than other methods of mixing, such as end to end, and greater reductions of Listeria monocytogenes Scott A after 0 and 24 h. When the EOC concentration detected in milk serum was above the minimum bactericidal concentration, complete inhibition of L. monocytogenes in tryptic soy broth resulted. Therefore, the antilisterial properties in milk could be correlated with the solubility by comparison to the minimum inhibitory or bactericidal concentrations of EOCs. While the EOCs applied using ethanol generally had solubility and activity characteristics superior to those of other mixing methods, ethanol is not used to a great extent in nonfermented foods. Therefore, mixing methods without an organic solvent may be more readily adaptable to enhancing the distribution of EOCs in complex food systems.

A comparison of the thermal inactivation kinetics of human norovirus surrogates and hepatitis A virus in buffered cell culture medium.

Human noroviruses and hepatitis A virus (HAV) are considered as epidemiologically significant causes of foodborne disease. Therefore, studies are needed to bridge existing data gaps and determine appropriate parameters for thermal inactivation of human noroviruses and HAV. The objectives of this research were to compare the thermal inactivation kinetics of human norovirus surrogates (murine norovirus (MNV-1), and feline calicivirus (FCV-F9)) and HAV in buffered medium (2-ml vials), compare first-order and Weibull models to describe the data, calculate Arrhenius activation energy for each model, and evaluate model efficiency using selected statistical criteria. The D-values calculated from the first-order model (50-72 °C) ranged from 0.21-19.75 min for FCV-F9, 0.25-36.28 min for MNV-1, and 0.88-56.22 min for HAV. Using the Weibull model, the tD = 1 (time to destroy 1 log) for FCV-F9, MNV-1 and HAV at the same temperatures ranged from 0.10-13.27, 0.09-26.78, and 1.03-39.91 min, respectively. The z-values for FCV-F9, MNV-1, and HAV were 9.66 °C, 9.16 °C, and 14.50 °C, respectively, using the Weibull model. For the first order model, z-values were 9.36 °C, 9.32 °C, and 12.49 °C for FCV-F9, MNV-1, and HAV, respectively. For the Weibull model, estimated activation energies for FCV-F9, MNV-1, and HAV were 225, 278, and 182 kJ/mol, respectively, while the calculated activation energies for the first order model were 195, 202, and 171 kJ/mol, respectively. Knowledge of the thermal inactivation kinetics of norovirus surrogates and HAV will allow the development of processes that produce safer food products and improve consumer safety.

Nanocapsular dispersion of thymol for enhanced dispersibility and increased antimicrobial effectiveness against Escherichia coli O157:H7 and Listeria monocytogenes in model food systems.

Essential oils are marginally soluble in water, making it challenging to evenly disperse them in foods and resulting in an increased tendency to bind with food lipids and proteins, resulting in lowered antimicrobial efficacy. In the current study, free and nano-dispersed (ND) thymol were compared in terms of their antimicrobial efficacies against Escherichia coli O157:H7 ATCC 43889 and 43894 and Listeria monocytogenes strains Scott A and 101 in apple cider and 2% reduced-fat milk. Apple cider was adjusted to pHs 5.5 and 3.5, and antimicrobial tests were performed at 0.3-, 0.5-, 0.75-, and 1.0-g/liter thymol concentrations at 35, 32, 25, and 4°C. Overall, 0.5 and 1.0 g/liter thymol in nano-dispersion and along with free thymol were inhibitory and bactericidal, respectively, against bacterial strains under all treatment conditions. At pH 5.5, 0.5 g/liter ND thymol was bacteriostatic against L. monocytogenes and E. coli for up to 48 h. At pH 3.5, L. monocytogenes controls did not survive beyond 12 h but E. coli survived and was inhibited by 0.5 g/liter ND thymol after 12 and 48 h in apple cider. E. coli strains were significantly sensitive to 4°C and pH 3.5 (P < 0.05). When bacteria were tested in 2% reduced-fat milk at 35 or 32°C, ND and free thymol demonstrated inhibition at 4.5 g/liter. Thus, the current technology seems to be promising and novel, enabling thymol-containing nano-dispersions that are not only transparent but also effective against pathogens in food applications, especially in clear beverages.

Effectiveness of chitosan on the inactivation of enteric viral surrogates.

Chitosan is known to have bactericidal and antifungal activity. Although human noroviruses are the leading cause of non-bacterial gastroenteritis, information on the efficacy of chitosan against foodborne viruses is very limited. The objective of this work was to determine the effectiveness of different molecular weight chitosans against the cultivable human norovirus and enteric virus surrogates, feline calicivirus, FCV-F9, murine norovirus, MNV-1, and bacteriophages, MS2 and phiX174. Five purified chitosans (53, 222, 307, 421, ~1150 kDa) were dissolved in water, 1% acetic acid, or aqueous HCl pH = 4.3, sterilized by membrane filtration, and mixed with equal volume of virus to obtain a final concentration of 0.7% chitosan and 5 log(10) PFU/ml virus. Virus-chitosan suspensions were incubated for 3 h at 37 °C. Untreated viruses in PBS, in PBS with acetic acid, and in PBS with HCl were tested as controls. Each experiment was run in duplicate and replicated at least twice. Water-soluble chitosan (53 kDa) reduced phiX174, MS2, FCV-F9 and MNV-1 titers by 0.59, 2.44, 3.36, and 0.34 log(10) PFU/ml respectively. Chitosans in acetic acid decreased phiX174 by 1.19-1.29, MS2 by 1.88-5.37, FCV-F9 by 2.27-2.94, and MNV-1 by 0.09-0.28 log(10) PFU/ml, respectively. Increasing the MW of chitosan corresponded with an increasing antiviral effect on MS2, but did not appear to play a role for the other three tested viral surrogates. Overall, chitosan treatments showed the greatest reduction for FCV-F9, and MS2 followed by phiX174, and with no significant effect on MNV-1.

Survival and inactivation of human norovirus surrogates in blueberry juice by high-pressure homogenization.

Human noroviruses (HNoV) have been implicated in gastrointestinal outbreaks associated with fresh produce, juices, and ready-to-eat foods. In order to determine the risk of HNoV transmission by contaminated blueberry juice, survival characteristics of cultivable HNoV surrogates (murine norovirus, MNV-1; feline calicivirus, FCV-F9; and bacteriophage MS2) in blueberry juice (pH = 2.77) after 0, 1, 2, 7, 14, and 21 days at refrigeration temperatures (4°C) were studied. High-pressure homogenization (HPH) was studied as a novel processing method for noroviral surrogate inactivation in blueberry juice. Blueberry juice or phosphate-buffered saline (PBS; pH 7.2 as control) was inoculated with each virus, stored over 21 days at 4°C or subjected to HPH, and plaque assayed. FCV-F9 (∼5 log(10) PFU/mL) was undetectable after 1 day in blueberry juice at 4°C. MNV-1 (∼4 log(10) PFU/ml) showed minimal reduction (1 log(10) PFU/mL) after 14 days, with greater reduction (1.95 log(10) PFU/mL; p < 0.05) after 21 days in blueberry juice at 4°C. Bacteriophage MS2 (∼6 log(10) PFU/mL) showed significant reduction (1.93 log(10) PFU/mL; p < 0.05) after 2 days and was undetectable after 7 days in blueberry juice at 4°C. FCV-F9 remained viable in PBS for up to 21 days (2.28 log(10) PFU/mL reduction), while MNV-1 and MS2 survived after 21 days (1.08 and 0.56 log(10) PFU/mL reduction, respectively). Intriguingly, FCV-F9 and bacteriophage MS2 showed reduction after minimal homogenization pressures in blueberry juice (pH = 2.77), possibly due to the combination of juice pH, juice components, and mechanical effects. MNV-1 in blueberry juice was only slightly reduced at 250 (0.33 log(10) PFU/mL) and 300 MPa (0.71 log(10) PFU/mL). Virus surrogate survival in blueberry juice at 4°C correlates well with the ease of HNoV transmission via juices. HPH for viral inactivation in juices is dependent on virus type, and higher homogenization pressures may be needed for MNV-1 inactivation.

Thermal inactivation of Escherichia coli O157:H7 when grown statically or continuously in a chemostat.

The objective of this study was to determine if survivor curves for heat-inactivated Escherichia coli O157:H7 were affected by the physiological state of the cells relative to growth conditions and pH of the heating menstruum. A comparison was made between the log-linear model and non-log-linear Weibull approach. Cells were grown statically in aerobic culture tubes or in an aerobic chemostat in tryptic soy broth (pH 7.2). The heating menstruum was unbuffered peptone or phosphate buffer (pH 7.0). Thermal inactivation was carried out at 58, 59, 60, and 61°C, and recovery was on a nonselective medium. Longer inactivation times for statically grown cells indicated potential stress adaptation. This was more prevalent at 58°C. Shape response was also significantly different, with statically grown cells exhibiting decreasing thermal resistance over time and chemostat cells showing the opposite effect. Buffering the heating menstruum to ca. pH 7 resulted in inactivation curves that showed less variability or scatter of data points. Time to specific log reduction values (t(d)) for the Weibull model were conservative relative to the log-linear model depending upon the stage of reduction. The Weibull model offered the most accurate fit of the data in all cases, especially considering the log-linear model is equivalent to the Weibull model with a fixed shape factor of 1. The determination of z-value for the log-linear model showed a strong correlation between log D-value and process temperature. Correlations for the Weibull model parameters (log δ and log p) versus process temperature were not statistically significant.

Properties and potential food applications of lauric arginate as a cationic antimicrobial.

Lauric arginate (LAE, ethyl-Nα-lauroyl-L-arginate hydrochloride) is synthesized from food components lauric acid and L-arginine and is quickly hydrolyzed to lauric acid and L-arginine in vivo. The antimicrobial properties and low toxicity are the basis for approval as a generally recognized as safe (GRAS) preservative at a level of up to 200 ppm in certain food products in the United States such as meat, poultry, and cheese and a safe food preservative up to 225 ppm in the European Union. These developments have generated great interest to apply LAE to improve the safety and quality of food products. In the present review, physicochemical and toxicological properties are first discussed. Antimicrobial properties and mechanisms of LAE in microbiological media, and antimicrobials used in combination with LAE aiming to achieve synergistic activities are then reviewed. The physical basis of reduced antimicrobial activities of LAE in food matrices is discussed, and studies applying LAE in meat, poultry, dairy, produce, and low-moisture foods and food-contact surfaces are summarized. Antimicrobial properties of LAE in emulsion systems and potential packaging films are also discussed for potential novel applications to improve the application in food systems. Finally, the possible impact of LAE on food sensory properties is reviewed along with some perspectives on research needs in the science and technology of LAE for use as a food antimicrobial preservative.

Theil error splitting method for selecting the "best model" in microbial inactivation studies.

Escherichia coli K-12 was grown under unbuffered, buffered, and starving environmental conditions and then subjected to isothermal inactivation at 58 degrees C for up to 30 min. Survival versus time data were used to evaluate three models reported as suitable for the prediction of microbial inactivation by thermal means. The error splitting method proposed by Theil was used to divide the average squared difference between each observed and predicted datum into three orthogonal error sources: bias, regression, and random error. The method is based on the hypothesis that if the model is accurate, the overall average predicted and observed values should be the same and a plot of observed versus predicted inactivation values should have a slope of 1. The bias fixed error term quantifies the overall average difference between predicted and observed inactivation values. The regression fixed error term quantifies the difference between observed and predicted values near the end of the predictive region, where shoulders and tails may occur. The random error term quantifies the random variability of the predicted versus observed inactivation values. Statistical tests were proposed to determine the significance of each fixed error term and the normality of the random error source. The method was used to discuss the goodness of fit for the three models for Escherichia coli. The best model was the one that minimized total residual error, maximized random error sources (i.e., fixed error terms are not significant), and maximized the coefficient of correlation between observed and predicted inactivation values.

Escherichia coli thermal inactivation relative to physiological state.

Studies have explored the use of various nonlinear regression techniques to better describe shoulder and/or tailing effects in survivor curves. Researchers have compiled and developed a number of diverse models for describing microbial inactivation and presented goodness of fit analysis to compare them. However, varying physiological states of microorganisms could affect the measured response in a particular population and add uncertainty to results from predictive models. The objective of this study was to determine if the shape and magnitude of the survivor curve are possibly the result of the physiological state, relative to growth conditions, of microbial cells at the time of heat exposure. Inactivation tests were performed using Escherichia coli strain K-12 in triplicate for three growth conditions: statically grown cells, chemostat-grown cells, and chemostat-grown cells with buffered (pH 6.5) feed media. Chemostat cells were significantly less heat resistant than the static or buffered chemostat cells at 58 degrees C. Regression analysis was performed using the GInaFiT freeware tool for Microsoft Excel. A nonlinear Weibull model, capable of fitting tailing effects, was effective for describing both the static and buffered chemostat cells. The log-linear response best described inactivation of the nonbuffered chemostat cells. Results showed differences in the inactivation response of microbial cells depending on their physiological state. The use of any model should take into consideration the proper use of regression tools for accuracy and include a comprehensive understanding of the growth and inactivation conditions used to generate thermal inactivation data.

Thermal Inactivation Kinetics of Tulane Virus in Cell-Culture Medium and Spinach.

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.

Nonthermal inactivation of Escherichia coli K-12 on spinach leaves, using dense phase carbon dioxide.

While the use of some chemical sanitizers is approved for inactivation of microbes on the surfaces of fruits and vegetables, these compounds often degrade product quality with limited improvement in product safety. The application of dense phase carbon dioxide (DPCD, or high-pressure CO2) is a nonthermal process for inactivation of foodborne pathogens inoculated into various juices and model solutions. In this work, DPCD was evaluated for its potential to inactivate Escherichia coli K-12 inoculated on fresh spinach leaves. Inoculated leaves were exposed for up to 40 min to DPCD at a subcritical condition (5 MPa, 40 degrees C) and two supercritical conditions (7.5 and 10 MPa, 40 degrees C) at a flow rate of 50 g of CO2/min. E. coli K-12 populations were reduced to nondetectable levels (approximately 5-log reduction) using supercritical treatment conditions at exposure times as short as 10 min; efficacy of DPCD at the subcritical state was limited. This research demonstrates that DPCD has potential as a pasteurization technology for application to leafy green vegetables, although issues with discoloration and other quality measures will need more extensive evaluations.

Extraction of nisin from a 2.5% commercial nisin product using methanol and ethanol solutions.

Nisin is a class Ia bacteriocin used widely in the food industry to inhibit a number of gram-positive pathogens. Although this peptide exhibits activity against many gram-positive bacteria, its effectiveness can vary significantly depending upon the food application. Encapsulation is one method that has been investigated for improving the activity of nisin. Improvement of the encapsulation efficiency of nisin requires purification of the compound, which can be accomplished utilizing organic solvents. The objective of this study was to use methanol and ethanol solutions to extract and concentrate nisin from a commercial preparation containing 2.5% nisin. Commercial nisin was extracted with different concentrations of ethanol or methanol in sterile water for up to 8 h. Approximately 75% of the nisin activity was recovered with 10 or 50% ethanol compared with less than 1% recovery with an ethanol concentration higher than 90%. Extraction with 10 or 50% methanol was approximately as effective as that with lower concentrations of ethanol. However, yields were significantly greater for extraction with methanol at concentrations greater than 90%. The solubility of the nisin likely influenced the extraction profiles for the conditions used. Purification for an 8-h extraction using 10 and 50% ethanol was 1.36 and 1.93 times, respectively. Purification was less than 0.1 at higher ethanol concentrations due to poor extraction. For methanol treatments, purification factors were all 1.09 to 5.98, and they increased as methanol concentration increased. This method for extracting and purifying nisin from dairy proteins using organic solvents may provide an alternative means for preparing and concentrating nisin for encapsulation and other applications.

Inactivation of Escherichia coli K-12 exposed to pressures in excess of 300 MPa in a high-pressure homogenizer.

Homogenization is used widely in the dairy industry to improve product stability and quality. High-pressure homogenization (HPH) of fluid foods up to pressures of 300 MPa has demonstrated excellent potential for microbial inactivation. Microbial inactivation can be enhanced during HPH with the inclusion of antimicrobial compounds. Escherichia coli K-12 cells, grown statically or in chemostat, were exposed to HPH processing pressures of 50 to 350 MPa in the absence or presence of the antimicrobial nisin. Valve temperature was regulated by a water bath and pressure, and temperature data were recorded continuously after process initiation. Survivors were enumerated via plating on nonselective growth media. Pressure and temperature at the valve outlet port exhibited a quadratic relationship (R(2) = 0.9617, P < 0.05). Significant HPH-induced inactivation of the gram-negative microorganism was observed in the range of 100 to 250 MPa. Above 300 MPa, heat was the main factor promoting microbial inactivation, regardless of whether cells were grown in chemostat or statically. Chemostat-grown cells were significantly (P < 0.05) more resistant to HPH processing than were statically grown cells. Data indicate potential synergistic effects of nisin and HPH on the inactivation of bacterial contaminants. This study represents the first report of inactivation of a bacterium with HPH pressures in excess of 300 MPa in the presence and absence of an antimicrobial.

Antimicrobial efficacy of eugenol microemulsions in milk against Listeria monocytogenes and Escherichia coli O157:H7.

The antimicrobial activity of eugenol microemulsions (eugenol encapsulated in surfactant micelles) in ultrahigh-temperature pasteurized milk containing different percentages of milk fat (0, 2, and 4%) was investigated. Antimicrobial microemulsions were prepared from a 5% (wt) aqueous surfactant solution (Surfynol 485W) with 0.5% (wt) eugenol. Two strains each of Listeria monocytogenes and Escherichia coli O157:H7 previously shown to be the least and most resistant to the microemulsion in microbiological media were used to inoculate sterile milk (10(4) CFU/ml). Samples were withdrawn and plated at 0, 1, 3, 6, 12, and 24 h for enumeration. Microemulsions completely prevented growth of L. monocytogenes for up to 48 h in skim milk and reduced both strains of E. coli O157:H7 to less than detectable levels in less than 1 h. Similarly, in 2% fat milk, eugenol-Surfynol combinations reduced both strains of E. coli O157:H7 to less than detectable levels in less than 1 h but only increased the lag phase of both strains of L. monocytogenes. In full-fat milk (4% fat), microemulsions inhibited growth of the least resistant strains of L. monocytogenes and E. coli but were ineffective against the two resistant strains. Unencapsulated eugenol was slightly more or as inhibitory as microemulsions against target pathogens. Results were attributed to diffusional mass transport of antimicrobials from microemulsions to the macroemulsion (milk). Results suggest that food composition, especially fat level, may affect the efficiency of targeting of foodborne pathogens with surfactant-encapsulated antimicrobials.

Potential of Cinnamon Oil Emulsions as Alternative Washing Solutions of Carrots.

The objective of this study was to evaluate the potential of cinnamon oil emulsions as alternative washing solutions to improve the microbial safety of carrots. Whey protein concentrate (WPC), gum arabic (GA), lecithin, and their combinations were used to prepare cinnamon oil emulsions. The emulsions were characterized for their hydrodynamic diameter (Dh) during 7 days of storage and their antimicrobial activity against cocktails of Salmonella enterica , Escherichia coli O157:H7, and Listeria monocytogenes . The Dh of the emulsion prepared with the GA+WPC blend did not change significantly (195.0 to 184.1 nm), whereas all other emulsions showed varying degrees of increases in Dh. Compared with free cinnamon oil dissolved in 5% ethanol, all emulsions showed similar or lower MICs and MBCs. Emulsions prepared with GA and equal masses of GA and WPC were chosen and diluted to 0.2 and 0.5% cinnamon oil to wash carrots that were surface inoculated with bacterial cocktails because of their lower MICs and MBCs than free oil. Emulsions resulted in significantly higher reductions of pathogens on carrots than free cinnamon oil, 3.0 to 3.7 versus 2.1 to 2.3 log CFU/g at 0.5% cinnamon oil and 2.0 to 3.0 versus 1.0 to 1.7 log CFU/g at 0.2% cinnamon oil. No transfer of bacteria from inoculated carrots to wash solutions and no effects of organic load on log reductions were only observed for wash treatments with 0.5% emulsified cinnamon oil. Thus, the cinnamon oil emulsions are potential alternative postharvest washing solutions for fresh produce production.

Antimicrobial properties of microemulsions formulated with essential oils, soybean oil, and Tween 80.

It was previously found that blending soybean oil with cinnamon bark oil (CBO), eugenol or thyme oil, Tween 80, and equal masses of water and propylene glycol could be used to prepare microemulsions. In the present study, the objective was to determine the antimicrobial activity of the microemulsions in tryptic soy broth (TSB) and 2% reduced fat milk. In TSB, the minimum inhibitory concentration (MIC) of CBO solubilized in microemulsions was up to 625 ppm against cocktails of Listeria monocytogenes, Salmonella enterica or Escherichia coli O157:H7, which was equal to or higher in concentration than free CBO dissolved in ethanol. However, MICs of eugenol or thyme oil in microemulsions were much higher than that of free antimicrobials. Therefore, microemulsions of CBO were chosen to do further study. Inactivation curves of L. monocytogenes or E. coli O157:H7 in TSB or 2% reduced fat milk were tested and fitted using the Weibull model. In TSB, a gradual decrease in cell viability of L. monocytogenes and E. coli O157:H7 was observed with the microemulsion treatments at 625 ppm CBO, which was in contrast to the more rapid and greater inactivation by free CBO. Gradual inactivation of L. monocytogenes in 2% reduced fat milk was also observed in the treatment with 10,000 ppm free or microemulsified CBO. When fitted using the Weibull model, the predicted time to obtain a 3-log decrease of L. monocytogenes and E. coli O157:H7 in TSB or 2% reduced fat milk increased with an increased amount of soybean oil in microemulsions. Additionally, increasing the amount of Tween 80 in mixtures with different mass ratios of Tween 80 and essential oils significantly decreased the log reductions of L. monocytogenes in TSB. Our study showed that microemulsions can be used to dissolve EOs and control the rate of inactivating bacteria, but the composition of microemulsions is to be carefully chosen to minimize the reduction of antimicrobial activities.