Residue Chemistry and Predictive Microbiology Research Unit

Wyndmoor, PA, United States

Residue Chemistry and Predictive Microbiology Research Unit

Wyndmoor, PA, United States

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Liu Y.,U.S. Department of Agriculture | Morgan S.,Residue Chemistry and Predictive Microbiology Research Unit | Ream A.,U.S. Department of Agriculture | Huang L.,Residue Chemistry and Predictive Microbiology Research Unit
Journal of Industrial Microbiology and Biotechnology | Year: 2013

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. © 2013 Springer-Verlag (outside the USA).


Shen X.,Shanghai Ocean University | Sun X.,Shanghai Ocean University | Xie Q.,Shanghai Ocean University | Liu H.,Shanghai Ocean University | And 4 more authors.
Food Control | Year: 2014

This study examined the antimicrobial effect of blueberry (Vaccinium corymbosum L.) extracts obtained from four cultivars (Elliott, Darrow, Bluecrop, and Duke) on the growth of Listeria monocytogenes and Salmonella Enteritidis. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts against L. monocytogenes and S. Enteritidis in tryptic soy broth were determined. Concentrations of total phenolic compounds and four individual phenolic (chlorogenic acid, ellagic acid, quercetin, and quercetin-3-galactoside) in the extracts were determined using Folin-Ciocalteau method and HPLC analysis, respectively. All four extracts at 112.5-900mg/mL exhibited a dose-dependent growth-inhibitory effect against L.monocytogenes and S. Enteritidis. L.monocytogenes was significantly more sensitive to the antimicrobial effect of the extracts than S. Enteritidis. Phenolic compounds in the extracts such as chlorogenic acid, quercetin, ellagic acid, and quercetin-3-galactoside were the active antimicrobial compounds in the blueberry extracts. The results of this study suggest that blueberry extract or extract-derived components may be used to control pathogenic microorganisms. More studies on the use of blueberry as a natural antimicrobial in food products are warranted. © 2013 Elsevier Ltd.


Hwang C.-A.,Residue Chemistry and Predictive Microbiology Research Unit | Sheen S.,Food Safety and Intervention Technologies Research Unit | Juneja V.,Residue Chemistry and Predictive Microbiology Research Unit | Hwang C.-F.,Hungkuang University | And 2 more authors.
Food Control | Year: 2014

Acid solutions are increasingly being used for decontaminating meat surfaces. On the surfaces of acid-treated meat, the population of microorganism is reduced due to the low pH of acids, and the subsequent growth of the microorganism is reduced due to the residual acids on meat surfaces. Microbial cells on meat surfaces subjected to acid treatments may cross-contaminate untreated meat surfaces, e.g., microorganisms on the surfaces of acid-treated cooked ham cross contaminate the untreated surfaces during slicing. The objective of this study was to examine this scenario in determining the subsequent growth of acid-treated Listeria monocytogenes and Escherichia coli O157:H7 on the surfaces of untreated meat. Cells of multiple-strain L.monocytogenes or E.coli O157:H7 were exposed to HCl solutions of pH 3, 4, or 5 and deionized water at room temperature for 24h. The acid or deionized water-treated cells were inoculated separately onto cooked ham. Samples inoculated with L.monocytogenes were stored at 4 and 8°C and samples inoculated with E.coli O157:H7 were stored at 10 and 12°C. Populations of the pathogens on ham were enumerated during storage, and the lag phase durations (LPD, h) and growth rates (GR, log CFU/h) of the pathogens were determined. The populations of L.monocytogenes and E.coli O157:H7 in pH 5, 4, and 3 solutions were 1.2-3.1 and 0.6-2.4 logCFU/ml, respectively, lower than those in deionized water, indicating an increased acid stress on both microorganisms at lower pHs. L.monocytogenes subjected to pH 3 and pH 4 stresses and E.coli O157:H7 subjected to pH 3 stress exhibited significantly (p<0.05) extended LPDs and reduced GRs on cooked ham. The growth of L.monocytogenes on ham was more readily reduced by acid stress than that of E.coli O157:H7. This study showed that acid treatments reduced the viability of L.monocytogenes and E.coli O157:H7and the acid stress reduced their subsequent growth ability on untreated ham. Therefore, cross-contamination of L.monocytogenes or E.coli O157:H7 cells from acid-treated meat surfaces onto untreated meat surfaces may not impose increased risk to the product. © 2013.


Ahmed O.M.,University of Tennessee at Knoxville | Ahmed O.M.,Suez Canal University | Pangloli P.,University of Tennessee at Knoxville | Hwang C.-A.,Residue Chemistry and Predictive Microbiology Research Unit | And 4 more authors.
Food Control | Year: 2015

Listeria monocytogenes is a psychrotrophic foodborne pathogen that has been isolated from ready-to-eat meat and poultry products (RTE meats). The purpose of this study was to quantify lactate and acetate levels in retail RTE meats that had been tested in a previous study for the presence of L.monocytogenes to correlate the occurrence of L.monocytogenes to the acid levels. Products were extracted after blending 50g of each sample with de-ionized water, and the extracts were quantified for lactate and acetate using HPLC. In general, the concentrations of both acids in samples varied with product types and manufacturers (p<0.05). The mean concentrations of lactate and acetate ranged from 10.71 to 23.03mg/g (1.07-2.30%) and 0.66-1.56mg/g (0.066-0.156%), respectively. The mean concentrations of lactate and acetate in L.monocytogenes-positive samples were 1.13-24.05mg/g (0.11-2.4%) and 0-5.74mg/g (0-0.574%), respectively. Results of this study indicate that RTE meats containing low levels of lactate were more likely to be positive for L.monocytogenes while samples with higher concentrations of lactate and acetate were less likely to be positive for the pathogen. Therefore, the addition of lactate and acetate as antimicrobials is helpful as part of an overall Listeria control program. However, a rigorous sanitation and an effective HACCP program are also essential for control of Listeria. © 2014.


Medina M.B.,Residue Chemistry and Predictive Microbiology Research Unit
Journal of Agricultural and Food Chemistry | Year: 2011

A new method for the detection of phenolics in food systems was developed. This method is based on interactions of phenolics with Fast Blue BB diazonium salt in alkali pH, forming azo complexes, with the absorbance measured at 420 nm after 60 min. The linear regression correlations (R2) of gallic acid calibration standards were >0.99. The phenolic content (gallic acid equivalent) of samples analyzed yielded higher ratios (1.7-6.6) of the total phenolics by Fast Blue BB to Folin-Ciocalteu methods in most beverages and grain samples, but in flaxseed and some juice blends, the ratios were <1. The lower ratios suggest the presence of non-phenolic reducing constituents measured with the Folin-Ciocalteu method as "total phenolics". This method is simple and inexpensive and can be used to rapidly assess the total phenolics of foods and beverages. © This article not subject to U.S. Copyright. Published 2011 by the American Chemical Society.


Gurtler J.B.,U.S. Department of Agriculture | Marks H.M.,U.S. Department of Agriculture | Bailey R.B.,U.S. Department of Agriculture | Juneja V.,Residue Chemistry and Predictive Microbiology Research Unit | Jones D.R.,U.S. Department of Agriculture
Foodborne Pathogens and Disease | Year: 2013

The goal of this study was to determine the inactivation kinetics of Salmonella in commercial 10% salted liquid whole egg (LWE) to assist the U.S. Department of Agriculture in writing new liquid egg pasteurization guidelines. Current data are not sufficient for predicting thermal inactivation kinetics of Salmonella spp. for use in updating pasteurization guidelines for many types of liquid egg products, including salted LWE (SLWE). This is, in part, due to variations in Salmonella strains and changes in the processing of liquid egg products that have arisen in the past 40 years. Pasteurization guidelines are currently being reevaluated in light of recent risk assessments. Heat-resistant Salmonella serovars Enteritidis and Oranienburg were composited and mixed into 10% SLWE, resulting in final populations of approximately 5.7-7.8 log colony-forming units (CFU)/mL. Inoculated egg was injected into glass capillary tubes, flame-sealed, and heated in a water bath at 60, 62.2, 63.3, 64.3, or 66 C. Contents were surface-plated and incubated at 37 C for 24 h. Survival curves were not log-linear (log levels versus time), but decreased rapidly, and after initial periods became linear. Asymptotic decimal reduction values at each temperature were calculated from survivor curves with a minimum inactivation of 5.0 log CFU/mL. The asymptotic thermal D-values for SLWE were 3.47, 2.23, 1.79, 1.46, and 1.04 min at 60, 62.2, 63.3, 64.3, or 66 C, respectively. The calculated thermal z-value was 11.5 C. A model that predicts lethality for given times and temperatures that was developed predicted that the current pasteurization requirements for 10% SLWE (i.e., 63.3 C for 3.5 min, or 62.2 C for 6.2 min) are not sufficient to inactivate 7 log CFU/mL of Salmonella and only achieve approximately 4 log CFU/mL inactivation. This model will assist egg-products manufacturers and regulatory agencies in designing pasteurization processes to ensure product safety. © Mary Ann Liebert, Inc.


Lacombe A.,University of Maine, United States | Tadepalli S.,University of Maine, United States | Hwang C.-A.,Residue Chemistry and Predictive Microbiology Research Unit | Wu V.C.H.,University of Maine, United States
Foodborne Pathogens and Disease | Year: 2013

The antimicrobial activity and model of action of polyphenolic compounds extracted from lowbush wild blueberries (LWB) were studied against Escherichia coli O157:H7. Polyphenols in LWB were extracted using 80% vol/vol methanol and designated as total blueberry phenolics (TBP). The fraction was further separated by a C-18 Sep-Pak cartridge into monomeric phenolics acids (MPA) and anthocyanins plus proanthocyanidins (A&P). The A&P fraction was further separated into anthocyanins and proanthocyanidins using a LH-20 Sephadex column. Each fraction was diluted in 0.85% wt/vol NaCl, inoculated with E. coli O157:H7 to achieve 8 log colony-forming units (CFU)/mL, and incubated at 25 C for 1 h. The survival populations of E. coli O157:H7 in the phenolic fractions were determined by a viable cell counts method. The permeability of the cell membrane of E. coli O157:H7 was determined using LIVE/DEAD viability assay, and the damage was visualized by using transmission electron microscopy (TEM). Significant (p<0.05) reductions of 5 log CFU/mL of E. coli O157:H7 were observed for MPA at 0.4 g/L gallic acid equivalents (GAE), A&P at 0.9 g/L GAE, and anthocyanins at 0.65 g/L GAE. Reductions of 6-7 CFU/mL were observed for MPA at 0.8 g/L GAE, A&P at 1.8 g/L GAE, and anthocyanins at 1.3 g/L GAE compared to the control. The cell membrane of E. coli O157:H7 exhibited a significantly increased permeability when treated with proanthocyanidins (0.15 g/L GAE), A&P (0.45 g/L GAE), anthocyanins (0.65 g/L GAE), and TBP (0.14 g/L GAE). TEM confirmed the inactivation and increased membrane permeability of E. coli O157:H7. This study demonstrated the antimicrobial effect of polyphenols from LWB against E. coli O157:H7 and the probable mode of action. © 2013, Mary Ann Liebert, Inc.


Hwang C.-A.,Residue Chemistry and Predictive Microbiology Research Unit | Huang L.,Residue Chemistry and Predictive Microbiology Research Unit
Journal of Food Processing and Preservation | Year: 2014

This study examined the growth of Listeria monocytogenes in ham salads of various pHs and sorbate concentrations. Ham was inoculated with L.monocytogenes and mixed with potassium sorbate (0-0.2%) and mayonnaise to achieve salad pHs of 5.4-5.8. The population increases of L.monocytogenes in salads stored at 4C for 4 weeks were correlated to salad pH and sorbate concentration. In salads with pHs of 5.4-5.8 containing 0.0, 0.1, 0.15 and 0.2% sorbate, the populations of L.monocytogenes increased 2.7-6.4, 2.4-5.2, 1.0-3.7 and 0.2-2.0log cfu/g, respectively. A polynomial model was developed to describe the population increases as a function of salad pH and sorbate concentration. It indicated that the increases of L.monocytogenes were significantly lower (P<0.05) in salads containing higher sorbate concentrations. Results from this study will help identify the salad pH and sorbate levels that reduce the hazard of L.monocytogenes in mayonnaise-based salads. © 2014 Wiley Periodicals, Inc.


PubMed | University of Bío Bío, University of Santiago de Chile, University ChileSantiago and Residue Chemistry and Predictive Microbiology Research Unit
Type: | Journal: Frontiers in microbiology | Year: 2016

Cronobacter spp. have been responsible for severe infections in infants associated with consumption of powdered infant formula and follow-up formulae. Despite several risk assessments described in published studies, few approaches have considered the tremendous variability in cell response that small micropopulations or single cells can have in infant formula during storage, preparation or post process/preparation before the feeding of infants. Stochastic approaches can better describe microbial single cell response than deterministic models as we prove in this study. A large variability of lag phase was observed in single cell and micropopulations of 50 cells. This variability increased as the heat shock increased and growth temperature decreased. Obviously, variability of growth of individual Cronobacter sakazakii cell is affected by inoculum size, growth temperature and the probability of cells able to grow at the conditions imposed by the experimental conditions should be taken into account, especially when errors in bottle-preparation practices, such as improper holding temperatures, or manipulation, may lead to growth of the pathogen to a critical cell level. The mean probability of illness from initial inoculum size of 1 cell was below 0.2 in all the cases and for inoculum size of 50 cells the mean probability of illness, in most of the cases, was above 0.7.


PubMed | Safety Technologies, Dairy and Functional Foods Research Unit, Residue Chemistry and Predictive Microbiology Research Unit and 1815 iversity St
Type: Journal Article | Journal: Journal of dairy science | Year: 2016

In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100g (WPC34) and 76.8 g of protein/100g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35 C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35 C but at least 18 mo at lower temperatures, which should extend the market for these products.

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