Lihan Huang

Eastern Idaho Regional Medical Center, Айдахо-Фолс, Idaho, United States

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Publications (57)131.44 Total impact

  • Changcheng Li · Lihan Huang · Cheng-An Hwang · Jinquan Chen ·
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    ABSTRACT: The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 °C, were analyzed by curve-fitting to the Huang and Baranyi models using the USDA IPMP 2013. The experimental results showed that L. monocytogenes in salted samples exhibited approximately 40% longer lag times than the cells in unsalted samples under the same temperature condition, while the rates of bacterial growth were not affected by the addition of salt. The Ratkowsky square-root (RSR) model, Huang square-root (HSR) model, and an Arrhenius-type model were all shown suitable for evaluating the effect of temperature on specific growth rates. The estimated nominal minimum growth temperature in the RSR model was −0.5 °C, whereas the minimum growth temperature in HSR model was 2.57 °C. The HSR models may be more suitable for describing the temperature effect in salted salmon roe. The lag times of L. monocytogenes were found to change log-linearly with the specific growth rates. The mean h0 in the Baranyi model was 0.742 in unsalted samples and 1.193 in salted samples, and did not appear to change with temperature in a systematic manner. In summary, kinetic models were developed for examining the effect of temperature on growth of L. monocytogenes in unsalted and salted salmon roe samples. The results may be used by the food industry and regulatory agencies to estimate the growth of L. monocytogenes in salmon roe, and to conduct risk assessments of this microorganism.
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    ABSTRACT: Shiga toxin-producing Escherichia coli (STEC) is a major foodborne pathogen causing serious illnesses and hospitalizations in the United States. Bacteria that are exposed to environmental stresses during food processing may exhibit different growth patterns in the subsequent growth environment. The purpose of this study was to examine the effect of environmental stresses on the growth of O15H and non-O157 STEC in lettuce or cantaloupe. Strains of O157:H7 and non-O157 STEC (O26:H11, O103:H1, O104:H4, and O145:NM) were subjected to four selected stresses including 2 ppm of chlorine, aw of 0.97 (osmotic stress), and pH 5 (acid stress) at 22 °C for 24 h, or starvation (lack of nutrients) at 22 °C for 15 d. A cocktail mix of stressed or non-stressed (control) O157 or non-O157 at 3 log CFU/g (control or stressed) was inoculated on lettuce or cantaloupe and incubated at 10 and 22 °C for four weeks. While there were significant differences (p < 0.05) in the growth of stressed and unstressed cells of non-O157 STEC, no difference was observed in the growth of stressed and unstressed O157 STEC cells. Osmotic-stressed non-O157 STEC had significantly higher cell populations than control with 2 log difference (9.0 vs. 6.8 log CFU/g) at 10 °C on lettuce and 1 log difference (9.3 vs. 8.3 log CFU/g) at 22 °C on cantaloupe after 4 weeks. Acid-stressed non-O157 STEC had significantly higher cell populations than control at 10 °C after 4 weeks with >1 log difference (7.7 vs. 6.3 log CFU/ml) on cantaloupe. Starvation-stressed non-O157 STEC showed significantly higher cell populations than control with 1 log difference (8.4 vs. 7.2 log CFU/g) at 22 °C on cantaloupe after 4 weeks. The results indicated that osmotic, acid, or starvation stress may enhance the growth of non-O157 STEC on lettuce or cantaloupe and lead to a greater safety risk.
    Food Control 09/2015; 55. DOI:10.1016/j.foodcont.2015.02.040 · 2.81 Impact Factor
  • Yoon-Ki Hong · Lihan Huang · Won Byong Yoon ·
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    ABSTRACT: Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the growth kinetics of C. sporogenes in cooked beef under different temperature conditions.Ground beef samples, inoculated with C. sporogenes spores, were incubated at temperatures between 8 and 47 °C to examine the growth of this microorganism. Two primary models (Huang and Baranyi models) were used to analyze the growth data. The Ratkowsky square-root model was used as the secondary model to evaluate the effect of temperature on bacterial growth rate and lag time. The USDA IPMP 2013, a free data analysis tool for predictive microbiology, was used in data analysis.No growth of C. sporogenes was observed at temperatures below 15 °C for up to 25 days. At temperatures between 20 and 47 °C, C. sporogenes grew in cooked beef. The growth curves could be analyzed by both Huang and Baranyi models. The root mean squared error (RMSE) was 0.375 for the Huang model, and 0.441 for the Baranyi model with a global h0 of 10.46. The nominal minimum growth temperature (T0) estimated from the Huang model was 15.5 °C, which was 12.7 °C for the Baranyi model. The maximum growth temperature was 48.0 and 48.3 °C for the Baranyi and Huang models, respectively. The lag times and specific growth rates of C. sporogenes observed in this study were reasonably close to the data reported in the literature for C. botulinum under comparable conditions, suggesting that C. sporogenes may be used as a potential surrogate for evaluating the growth of C. botulinum in cooked meats during cooling. However, a direct comparison of growth kinetics between the two microorganisms is needed to confirm the suitability of C. sporogenes as a surrogate of C. botulinum.
  • Ting Fang · Lihan Huang · Lijun Liu · Fan Mei · Jinquan Chen ·
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    ABSTRACT: The main objective of this study was to develop the primary and secondary models to describe the growth kinetics of Salmonella as well as background microorganisms in raw, shucked oysters. Samples, inoculated with a cocktail of two Salmonella serotypes, S. Typhimurium (CICC22956) and S. Enteritidis (CICC21482), were incubated at 4, 8, 12, 16, 20, 25, 30, 33, 37, 40, and 43 °C. Growth of Salmonella was observed at all temperatures, except at 4 °C. The background microorganisms grew at all temperatures. All growth curves clearly exhibited lag, exponential and stationary phases, and were analyzed using the Huang growth model. Three secondary models (Ratkowsky square-root, Huang square-root, and Cardinal parameter models) were compared for evaluating the effect of temperature on bacterial growth rates. Data analysis was performed using IPMP 2013, a free predictive microbiology software tool developed by the USDA ARS.
    Food Control 07/2015; 53. DOI:10.1016/j.foodcont.2014.12.036 · 2.81 Impact Factor
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    Dike O Ukuku · Lihan Huang · Christopher Sommers ·
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    ABSTRACT: For health reasons, people are consuming fresh-cut fruits with or without minimal processing and, thereby, exposing themselves to the risk of foodborne illness if such fruits are contaminated with bacterial pathogens. This study investigated survival and growth parameters of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and aerobic mesophilic bacteria transferred from cantaloupe rind surfaces to fresh-cut pieces during fresh-cut preparation. All human bacterial pathogens inoculated on cantaloupe rind surfaces averaged ∼4.8 log CFU/cm(2), and the populations transferred to fresh-cut pieces before washing treatments ranged from 3 to 3.5 log CFU/g for all pathogens. A nisin-based sanitizer developed in our laboratory and chlorinated water at 1,000 mg/liter were evaluated for effectiveness in minimizing transfer of bacterial populations from cantaloupe rind surface to fresh-cut pieces. Inoculated and uninoculated cantaloupes were washed for 5 min before fresh-cut preparation and storage of fresh-cut pieces at 5 and 10°C for 15 days and at 22°C for 24 h. In fresh-cut pieces from cantaloupe washed with chlorinated water, only Salmonella was found (0.9 log CFU/g), whereas E. coli O157:H7 and L. monocytogenes were positive only by enrichment. The nisin-based sanitizer prevented transfer of human bacteria from melon rind surfaces to fresh-cut pieces, and the populations in fresh-cut pieces were below detection even by enrichment. Storage temperature affected survival and the growth rate for each type of bacteria on fresh-cut cantaloupe. Specific growth rates of E. coli O157:H7, Salmonella, and L. monocytogenes in fresh-cut pieces were similar, whereas the aerobic mesophilic bacteria grew 60 to 80 % faster and had shorter lag phases.
    Journal of food protection 07/2015; 78(7):1288-1295. DOI:10.4315/0362-028X.JFP-14-233 · 1.85 Impact Factor
  • Cheng-An Hwang · Lihan Huang · Vijay Juneja ·
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    ABSTRACT: The surfaces of ready-to-eat meats are susceptible to postprocessing contamination by Listeria monocytogenes. This study quantified the lag-phase durations (LPD) and growth rates (GR) of L. monocytogenes on the surfaces of cooked ham as affected by sorbate solutions of different concentrations and pH levels. Slices of cooked ham inoculated with a four-strain mixture of L. monocytogenes (ca. 10(3) CFU/g) were surface treated with sorbate solutions of 0 to 4% (wt/vol) at pH 4.0 to 6.5, vacuum packaged, and stored at 4 to 12°C for up to 45 days. The LPD and GR of L. monocytogenes were used to develop response surface models. The models estimated that the LPD of L. monocytogenes in samples treated with solutions of pH 4.0 to 5.5 (no sorbate) were 0 to 11 days and the GR were 0.25 to 0.36 log CFU/day, respectively, at 4°C. With the treatments of 2 and 4% (wt/vol) sorbate solutions, the LPD were estimated to be extended to 2 to 26 days and 34 to >45 days, and the GR were reduced to 0.15 to 0.30 and 0 to 0.19 log CFU/day, respectively. At 4°C, increasing sorbate concentrations by 1% (wt/vol) to 2, 3, and 4% (wt/vol) at pH 5.5 to 4.0 led to an extension of LPD by 2 to 11, 10 to 19, and 18 to 27 days, whereas the GR were reduced by 0.037 to 0.055, 0.048 to 0.066, and 0.060 to 0.078 log CFU/day, respectively. Sorbate also extended the LPD and reduced the GR of L. monocytogenes at 8 and 12°C. Results indicated that sorbate concentration and pH level were significant factors affecting the LPD and GR of L. monocytogenes and that the combination of sorbate and low pH has potential for use as a surface treatment to control L. monocytogenes on meat surfaces.
    Journal of food protection 06/2015; 78(6):1154-60. DOI:10.4315/0362-028X.JFP-14-408 · 1.85 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: The objective of this study was to develop a new approach using a one-step approach to directly construct predictive models for describing the growth of Salmonella Enteritidis (SE) in liquid egg white (LEW) and egg yolk (LEY). A five-strain cocktail of SE, induced to resist rifampicin at 100 mg/L, was used to inoculate LEW and LEY. Kinetic studies were conducted isothermally at different temperatures between 8 and 43°C to generate growth curves at each temperature.
    Food Control 04/2015; 57. DOI:10.1016/j.foodcont.2015.03.051 · 2.81 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: The objective of this research was to develop a new one-step methodology that uses a dynamic approach to directly construct a tertiary model for prediction of the growth of Clostridium perfringens in cooked beef. This methodology was based on simultaneous numerical analysis and optimization of both primary and secondary models using multiple dynamic growth curves obtained under different conditions. Once the models were constructed, the bootstrap method was used to calculate the 95% confidence intervals of kinetic parameters, and a Monte Carlo simulation method was developed to validate the models using the growth curves not previously used in model development. The results showed that the kinetic parameters obtained from this study accurately matched the common characteristics of C. perfringens, with the optimum temperature being 45.3°C. The results also showed that the predicted growth curves matched accurately with experimental observations used in validation. The mean of residuals of the predictions is -0.02logCFU/g, with a standard deviation of only 0.23logCFU/g. For relative growths <1logCFU/g, the residuals of predictions are <0.4logCFU/g. Overall, 74% of the residuals of predictions are <0.2logCFU/g, 7.7% are >0.4logCFU/g, while only 1.5% are >0.8logCFU/g. In addition, the dynamic model also accurately predicted four isothermal growth curves arbitrarily chosen from the literature. Finally, the Monte Carlo simulation was used to provide the probability of >1 and 2logCFU/g relative growths at the end of cooling. The results of this study will provide a new and accurate tool to the food industry and regulatory agencies to assess the safety of cooked beef in the event of cooling deviation. Published by Elsevier B.V.
    International Journal of Food Microbiology 12/2014; 195C:20-29. DOI:10.1016/j.ijfoodmicro.2014.11.025 · 3.08 Impact Factor
  • ChangCheng Li · Lihan Huang · Jinquan Chen ·
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    ABSTRACT: Peanut butter has been implicated in multi-state outbreaks of salmonellosis in recent years. Studies have shown that Salmonella exhibited increased thermal resistance in peanut butter. However, little is known about the effect of product formulation on the kinetics of survival of Salmonella during thermal treatment. Therefore, the objective of this research was to compare the thermal resistance of Salmonella in four commercially available peanut butter and spread products, and evaluate the effect of product formulation on the survival of this pathogen during heating. Four peanut butter and spread samples, including Omega 3 (A), regular fat (B), reduced sugar (C), and reduced fat (D), inoculated with a 6-strain cocktail of Salmonella spp., were heated at 70, 75, 80, 85, and 90 °C. Experimental results showed that the highest thermal resistance of Salmonella was found in the samples with reduced fat, while the least in the samples with Omega 3 formulation. No significant difference in the bacterial thermal resistance was observed in the regular fat and reduced sugar formulations. The Weibull survival model was used to describe the survival curves. Results showed that the average exponent (shape factor) of the model ranged from 0.38 to 0.662, suggesting progressively decreased rate of inactivation during heating. The scale (rate) coefficients of the model increased linearly with temperature. The calculated minimum lethal temperature for Salmonella was 54.8, 59.8, 59.5, and 63.9 °C in samples A, B, C, and D, respectively. No tail effect was observed. The results of this study suggest that proper formulation of peanut butter and spread may enhance thermal inactivation of Salmonella.
    Food Control 11/2014; 45:143–149. DOI:10.1016/j.foodcont.2014.04.028 · 2.81 Impact Factor
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    ABSTRACT: Most fresh produce, such as strawberries, receives minimal processing and is often eaten raw. Contamination of produce with pathogenic bacteria may occur during growth, harvest, processing, transportation, and storage (abuse temperature) and presents a serious public health risk. Strawberries have been implicated in an outbreak of Escherichia coli O157:H7 infection that sickened 15 people, including one death. Strawberries may also be contaminated by other serogroups of non-O157 Shiga toxin-producing E. coli (STEC), including O26, O45, O103, O111, O121 and O145, which have become known as the “Big Six” or “Top Six” non-O157 STECs. The objective of this research was to explore the potential application of high pressure processing (HPP) treatment to reduce or eliminate STECs in fresh strawberry puree (FSP). FSP, inoculated with a six-strain cocktail of the “Big Six” non-O157 STEC strains or a five-strain cocktail of E. coli O157:H7 in vacuum-sealed packages, were pressure-treated at 150, 250, 350, 450, 550, and 650 MPa (1 MPa = 106 N/m2) for 5, 15, and 30 min. HPP treatment, at 350 MPa for ≥5 min, significantly reduced STECs in FSP by about 6-log CFU/g from the initial cell population of ca. 8-log CFU/g. Cell rupture, observed by scanning electron microscopy (SEM), demonstrated that the HPP treatments can be potentially used to control both non-O157 and O157:H7 STECs in heat sensitive products.
    Food Microbiology 06/2014; 40:25–30. DOI:10.1016/ · 3.33 Impact Factor
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    ABSTRACT: Unlabelled: The aim of this study was to determine the growth kinetics of Listeria monocytogenes, with and without cold-adaption, on fresh-cut cantaloupe under different storage temperatures. Fresh-cut samples, spot inoculated with a 4-strain cocktail of L. monocytogenes (∼3.2 log CFU/g), were exposed to constant storage temperatures held at 10, 15, 20, 25, or 30 °C. All growth curves of L. monocytogenes were fitted to the Baranyi, modified Gompertz, and Huang models. Regardless of conditions under which cells grew, the time needed to reach 5 log CFU/g decreased with the elevated storage temperature. Experimental results showed that there were no significant differences (P > 0.05) in the maximum growth rate k (log CFU/g h(-1) ) and lag phase duration λ (h) between the cultures of L. monocytogenes with or without previous cold-adaption treatments. No distinct difference was observed in the growth pattern among 3 primary models at various storage temperatures. The growth curves of secondary modeling were fitted on an Arrhenius-type model for describing the relationship between k and temperature of the L. monocytogenes on fresh-cut cantaloupe from 10 to 30 °C. The root mean square error values of secondary models for non- and cold-adapted cells were 0.018, 0.021, and 0.024, and 0.039, 0.026, and 0.017 at the modified Gompertz, Baranyi, and Huang model, respectively, indicating that these 3 models presented the good statistical fit. This study may provide valuable information to predict the growth of L. monocytogenes on fresh-cut cantaloupes at different storage conditions. Practical application: Listeriosis has occurred and increased along with the increased demand of fresh and fresh-cut fruits and vegetables. This study was conducted to predict the growth of non- and cold-adapted L. monocytogenes on fresh-cut cantaloupe at different temperature using mathematical model. These results can be helpful for risk assessments of L. monocytogenes in fresh-cut cantaloupe. This study provides valuable information to food handlers to choose proper storage temperatures for extending the shelf-life of fresh-cut cantaloupe.
    Journal of Food Science 04/2014; 79(6). DOI:10.1111/1750-3841.12468 · 1.70 Impact Factor
  • Hsin-Yun Hsu · Lihan Huang · James Swi-Bea Wu ·
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    ABSTRACT: Raw whole strawberries, if contaminated with pathogens, such as Escherichia coli O157:H7, must be pasteurized prior to consumption. Therefore, the objective of this research was to investigate the thermal inactivation kinetics of E. coli O157:H7 in strawberry puree (SP), and evaluate the changes in anthocyanins and color, and the survival of yeasts and molds (YM) after thermal processing. Inoculated with a 5-strain cocktail, fresh SP, with or without added sugar (20 and 40 °Brix), was heated at 50, 52, 54, 57.5, 60, and 62.5 °C to determine the thermal resistance of E. coli O157:H7. In raw SP, the average D-values of E. coli O157:H7 were 909.1, 454.6, 212.8, 46.1, and 20.2 s at 50, 52, 54, 57.5, and 60 °C, respectively, with a z-value of 5.9 °C. While linearly decreasing with temperature, the log D-values of E. coli O157:H7 increased slightly with sugar concentration. The log degradation rates of anthocyanins increased linearly with temperature, but decreased slightly with sugar concentrations. These results suggest that sugar may provide some protection to both E. coli O157: H7 and anthocyanins in SP. The browning index was not affected by heating at 50 and 52 °C at low sugar concentrations, but increased by an average of 1.28%, 2.21%, and 10.1% per min when SP was exposed to heating at 54, 57.5, and 60 °C, respectively. YM was also inactivated by heating. This study demonstrated that properly designed thermal processes can effectively inactivate E. coli O157:H7 and YM in contaminated SP, while minimizing the changes in anthocyanins and color.
    Journal of Food Science 03/2014; 79(1):M74-80. DOI:10.1111/1750-3841.12327 · 1.70 Impact Factor
  • Ting Fang · Lihan Huang ·
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    ABSTRACT: Peeled hard-boiled eggs (HBE) are ready-to-eat products susceptible to surface contamination by Listeria monocytogenes. This study investigated the growth and survival of L. monocytogenes between 4 and 43 °C in egg whites cooked under different conditions (70 °C for 15 min, 80 °C for 20 min, and 100 °C for 10 min). L. monocytogenes inoculated to samples cooked at 100 °C could grow uninhibitedly between 4 and 40 °C, exhibiting no lag phases, but failed to grow at 43 °C. The growth process was described by a 3-parameter logistic primary model, with the specific growth rates fitted equally well to the Ratkowsky square-root and Cardinal models. According to the Ratkowsky square-root model, the estimated minimum (nominal) and maximum growth temperatures were −0.3 and 47 °C, which were 1.6 and 44.3 °C, respectively, according to the Cardinal model.
    Food Control 02/2014; 36(1):191-198. DOI:10.1016/j.foodcont.2013.08.034 · 2.81 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: Predictive microbiology is an area of applied research in food science that uses mathematical models to predict the changes in the population of pathogenic or spoilage microorganisms in foods exposed to complex environmental changes during processing, transportation, distribution, and storage. It finds applications in shelf-life prediction and risk assessments of foods. The objective of this research was to describe the performance of a new user-friendly comprehensive data analysis tool, the Integrated Pathogen Modeling Model (IPMP 2013), recently developed by the USDA Agricultural Research Service. This tool allows users, without detailed programming knowledge, to analyze experimental kinetic data and fit the data to known mathematical models commonly used in predictive microbiology. Data curves previously published in literature were used to test the models in IPMP 2013. The accuracies of the data analysis and models derived from IPMP 2013 were compared in parallel to commercial or open-source statistical packages, such as SAS® or R. Several models were analyzed and compared, including a three-parameter logistic model for growth curves without lag phases, reduced Huang and Baranyi models for growth curves without stationary phases, growth models for complete growth curves (Huang, Baranyi, and re-parameterized Gompertz models), survival models (linear, re-parameterized Gompertz, and Weibull models), and secondary models (Ratkowsky square-root, Huang square-root, Cardinal, and Arrhenius-type models). The comparative analysis suggests that the results from IPMP 2013 were equivalent to those obtained from SAS® or R. This work suggested that the IPMP 2013 could be used as a free alternative to SAS®, R, or other more sophisticated statistical packages for model development in predictive microbiology.
    International journal of food microbiology 11/2013; 171C:100-107. DOI:10.1016/j.ijfoodmicro.2013.11.019 · 3.08 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: The objective of this research is to determine the thermal inactivation kinetics of Listeria monocytogenes in chicken breast meat under both isothermal and dynamic conditions. A four-strain cocktail of L. monocytogenes was inoculated to chicken breast meat. Isothermal studies were performed by submerging samples under hot water maintained at constant temperatures ranging from 54 to 66 °C. The D values at each temperature were determined and used to calculate the z value, using log(D) = log(D0) − T/z. Dynamic studies were conducted by submerging samples in a water bath with its temperature programmed to increase linearly from 30 to 65 °C at 1.25 °C/min or 1.73 °C/min. A method was developed to determine the kinetic parameters from linear heating temperature profiles.The thermal inactivation of L. monocytogenes in chicken breast meat followed the first-order kinetics. The z value determined from the isothermal studies was 4.95 °C, which is very close to the values reported in the literature. The dynamic method can also be used to determine the thermal inactivation kinetics of L. monocytogenes. The average z value (4.10 °C) determined by the dynamic method was slightly lower than that determined by the isothermal method. However, the parameters (D0 and z) determined from both isothermal and dynamic methods can be used to estimate the survival of L. monocytogenes exposed to linear heating temperature profiles, with statistically equal accuracies.The dynamic method explored in this study can be used to determine the D0 and z values of microorganisms that exhibit first-order kinetics and are exposed to linear heating temperature profiles. Compared to the isothermal method, the dynamic method requires few data points and is equally accurate.
    Food Control 10/2013; 33(2):484–488. DOI:10.1016/j.foodcont.2013.03.049 · 2.81 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: The objective of this work was to optimize a mathematical equation for use as a primary kinetic model that employed a new approach to describe the three-phase growth of bacteria under constant temperature conditions. This research adopted an optimization algorithm in combination with the Runge–Kutta method to solve the differential form of the new growth model in search of an optimized lag phase transition coefficient (LPTC), which is used to define the adaption and duration of lag phases of bacteria prior to exponential growth. Growth curves of Listeria monocytogenes, Escherichia coli O157:H7, and Clostridium perfringens, selected from previously published data, were analyzed to obtain an optimized LPTC for each growth curve and a global LPTC for all growth curves. With the new optimized LPTC, the new growth model could be used to accurately describe the bacterial growth curves with three distinctive phases (lag, exponential, and stationary). The new optimized LPTC significantly improved the performance and applicability of the new model. The results of statistical analysis (ANOVA) suggested that the new growth model performed equally well with the Baranyi model. It can be used as an alternative primary model for bacterial growth if the bacterial adaption is more significant in controlling the lag phase development.
    Food Control 07/2013; 32(1):283–288. DOI:10.1016/j.foodcont.2012.11.019 · 2.81 Impact Factor
  • Ting Fang · Yanhong Liu · Lihan Huang ·
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    ABSTRACT: The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.
    Food Microbiology 05/2013; 34(1):174-81. DOI:10.1016/ · 3.33 Impact Factor
  • Yanhong Liu · Shannon Morgan · Amy Ream · Lihan Huang ·
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    ABSTRACT: Listeria monocytogenes is a food-borne pathogen of significant threat to public health. Nisin is the only bacteriocin that can be used as a food preservative. Due to its antimicrobial activity, it can be used to control L. monocytogenes in food; however, the antimicrobial mechanism of nisin activity against L. monocytogenes is not fully understood. The CtsR (class III stress gene repressor) protein negatively regulates the expression of class III heat shock genes. A spontaneous pressure-tolerant ctsR deletion mutant that showed increased sensitivity to nisin has been identified. Microarray technology was used to monitor the gene expression profiles of the ctsR mutant under treatments with nisin. Compared to the nisin-treated wild type, 113 genes were up-regulated (>2-fold increase) in the ctsR deletion mutant whereas four genes were down-regulated (<-2-fold decrease). The up-regulated genes included genes that encode for ribosomal proteins, membrane proteins, cold-shock domain proteins, translation initiation and elongation factors, cell division, an ATP-dependent ClpC protease, a putative accessory gene regulator protein D, transport and binding proteins, a beta-glucoside-specific phosphotransferase system IIABC component, as well as hypothetical proteins. The down-regulated genes consisted of genes that encode for virulence, a transcriptional regulator, a stress protein, and a hypothetical protein. The gene expression changes determined by microarray assays were confirmed by quantitative real-time PCR analyses. Moreover, an in-frame deletion mutant for one of the induced genes (LMOf2365_1877) was constructed in the wild-type L. monocytogenes F2365 background. ΔLMOf2365_1877 had increased nisin sensitivity compared to the wild-type strain. This study enhances our understanding of how nisin interacts with the ctsR gene product in L. monocytogenes and may contribute to the understanding of the antibacterial mechanisms of nisin.
    Journal of Industrial Microbiology 03/2013; 40(5). DOI:10.1007/s10295-013-1243-0 · 2.44 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: The objective of this work was to develop a numerical simulation method to study the heat transfer process and inactivation of Escherichia coli O157:H7 during gas grilling of non-intact beef steaks (NIBS). A finite difference and optimization algorithm was developed to determine the effective heat transfer parameters during grilling. After validation, these parameters were used in a finite element method to simulate the temperature profiles at various locations of NIBS (2.54 cm in thickness). The computer simulation results showed that E. coli O157:H7 may survive the heating processes if normal grilling conditions for intact beef steaks were used. Computer simulation results also suggested that E. coli O157:H7 might be effectively inactivated if NIBS (2.54 cm) were evenly flipped (every 4 min) and cooked for 16 min during cooking. The result of this study may help the food service industry to develop more adequate grilling methods and conditions to cook NIBS.
    Journal of Food Engineering 12/2012; 113(3):380–388. DOI:10.1016/j.jfoodeng.2012.07.003 · 2.77 Impact Factor
  • Lihan Huang ·
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    ABSTRACT: This study was conducted to investigate the growth of non-O157 Shiga toxin-producing Escherichia coli (STEC) in spinach leaves and to develop kinetic models to describe the bacterial growth. Six serogroups of non-O157 STEC, including O26, O45, O103, O111, O121, and O145, were used in the growth studies conducted isothermally at 4, 8, 15, 20, 25, 30, and 35°C. Both STEC and background microflora were enumerated to develop kinetic models. Growth of STEC in spinach leaves was observed at elevated temperatures (15-35°C), but not at 4 and 8°C. This study considered the dynamic interactions between the STEC cells and the background microflora. A modified Lotka-Volterra and logistic equation was used to simulate the bacterial growth. In combination with an unconstrained optimization procedure, the differential growth equations were solved numerically to evaluate the dynamic interactions between the STEC cells and the background microflora, and to determine the kinetic parameters by fitting each growth curve to the growth equations. A close agreement between the experimental growth curves and the numerical analysis results was obtained. The analytical results showed that the growth of STEC in spinach leaves was unhindered when the population was low, but the growth was suppressed by the background microflora as the STEC population approached the maximum population density. The effect of temperature on the growth of both STEC and background microflora was also evaluated. Secondary models, evaluating the effect of temperature on growth rates, were also developed. The estimated apparent minimum growth temperature for STEC was 11°C in commercial spinach leaves. The methodology and results of this study can be used to examine the dynamic interactions and growth between different bacteria in foods, and to conduct risk assessments of STEC in spinach leaves.
    International journal of food microbiology 11/2012; 160(1):32-41. DOI:10.1016/j.ijfoodmicro.2012.09.019 · 3.08 Impact Factor

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556 Citations
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  • 2002-2015
    • Eastern Idaho Regional Medical Center
      Айдахо-Фолс, Idaho, United States
  • 2012
    • United States Department of Agriculture
      • Agricultural Research Service (ARS)
      Washington, Washington, D.C., United States
    • Fujian Agriculture and Forestry University
      Min-hou, Fujian, China
  • 2011
    • Franklin and Marshall College
      Lancaster, California, United States