Shiowshuh Sheen

Mathematical modeling the cross-contamination of Escherichia coli O157:H7 on the surface of ready-to-eat meat product while slicing.

Microbial cross-contamination either at home or production site is one of the major factors of causing contamination of foods and leading to the foodborne illness. The knowledge regarding Escherichia coli O157:H7 surface transfer on ready-to-eat (RTE) deli meat and the slicer used for slicing different RTE products are needed to ensure RTE food safety. The objectives of this study were to investigate and to model the surface cross-contamination of E. coli O157:H7 during slicing operation. A five-strain cocktail of E. coli O157:H7 was inoculated directly onto a slicers round blade rim area at an initial level of ca. 4, 5, 6, 7 or 8 log CFU/blade (ca. 3, 4, 5, 6 or 7 log CFU/cm(2) of the blade edge area), and then the RTE deli meat (ham) was sliced to a thickness of 1-2 mm. For another cross-contamination scenario, a clean blade was initially used to slice ham which was pre-surface-inoculated with E. coli O157:H7 (ca. 4, 5, 6, 7 or 8 log CFU/100 cm(2) area), then, followed by slicing un-inoculated ham. Results showed that the developed empirical models were reasonably accurate in describing the transfer trend/pattern of E. coli O157:H7 between the blade and ham slices when the total inoculum level was >or=5 log CFU on the ham or blade. With an initial inoculum level at <or=4 log CFU, the experimental data showed a rather random microbial surface transfer pattern. The models, i.e., a power equation for direct-blade-surface-inoculation, and an exponential equation for ham-surface-inoculation are microbial load and sequential slice index dependent. The surface cross-contamination prediction of E. coli O157:H7 for sliced deli meat (ham) using the developed models were demonstrated. The empirical models may provide a useful tool in developing the RTE meat risk assessment.

CRITICAL EVALUATION OF CRISPY AND CRUNCHY TEXTURES: A REVIEW

Crispness and crunchiness are important factors in the enjoyment of many foods, but they are defined differently among dictionaries, consumers, and researchers. Sensory, mechanical, and acoustic methods have been used to provide data on crispness and crunchiness. Sensory measurements include biting force and sound intensity. Mechanical techniques resemble mastication and include flex, shear, and compression. Acoustical techniques measure frequency, intensity, and number of sound events. Water and oil content contribute to crispness and crunchiness, which also have temporal aspects. Information in the literature is compared in this article to develop definitions of crispness and crunchiness.

Predictive model for the reduction of heat resistance of Listeria monocytogenes in ground beef by the combined effect of sodium chloride and apple polyphenols

We investigated the combined effect of three internal temperatures (57.5, 60, and 62.5°C) and different concentrations (0 to 3.0 wt/wt.%) of sodium chloride (NaCl) and apple polyphenols (APP), individually and in combination, on the heat-resistance of a five-strain cocktail of Listeria monocytogenes in ground beef. A complete factorial design (3×4×4) was used to assess the effects and interactions of heating temperature, NaCl, and APP. All 48 combinations were tested twice, to yield 96 survival curves. Mathematical models were then used to quantitate the combined effect of these parameters on heat resistance of the pathogen. The theoretical analysis shows that compared with heat alone, the addition of NaCl enhanced and that of APP reduced the heat resistance of L. monocytogenes measured as D-values. By contrast, the protective effect of NaCl against thermal inactivation of the pathogen was reduced when both additives were present in combination, as evidenced by reduction of up to ~68% in D-values at 57.5°C; 65% at 60°C; and 25% at 62.5°C. The observed high antimicrobial activity of the combination of APP and low salt levels (e.g., 2.5% APP and 0.5% salt) suggests that commercial and home processors of meat could reduce the salt concentration by adding APP to the ground meat. The influence of the combined effect allows a reduction of the temperature of heat treatments as well as the salt content of the meat. Meat processors can use the predictive model to design processing times and temperatures that can protect against adverse effects of contaminated meat products. Additional benefits include reduced energy use in cooking, and the addition of antioxidative apple polyphenols may provide beneficial health affects to consumers.

Kinetics of Thermal Destruction of Salmonella in Ground Chicken Containing trans-Cinnamaldehyde and Carvacrol†

We investigated the heat resistance of an eight-strain cocktail of Salmonella serovars in chicken supplemented with trans cinnamaldehyde (0 to 1.0%, wt/wt) and carvacrol (0 to 1.0%, wt/wt). Inoculated meat was packaged in bags that were completely immersed in a circulating water bath and held at 55 to 71°C for predetermined lengths of time. The recovery medium was tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. D-values in chicken, determined by linear regression, were 17.45, 2.89, 0.75, and 0.29 min at 55, 60, 65, and 71°C, respectively (z = 9.02°C). Using a survival model for nonlinear survival curves, D-values in chicken ranged from 13.52 min (D(1), major population) and 51.99 min (D(2), heat-resistant subpopulation) at 55°C to 0.15 min (D(1)) and 1.49 min (D(2)) at 71°C. When the Salmonella cocktail was in chicken supplemented with 0.1 to 1.0% trans-cinnamaldehyde or carvacrol, D-values calculated by both approaches were consistently less at all temperatures. This observation suggests that the addition of natural antimicrobials to chicken renders Salmonella serovars more sensitive to the lethal effect of heat. Thermal death times from this study will be beneficial to the food industry in designing hazard analysis and critical control point plans to effectively eliminate Salmonella contamination in chicken products used in this study.

Modeling the impact of chlorine on the behavior of Listeria monocytogenes on ready-to-eat meats.

Listeria monocytogenes (Lm) continues to pose a food safety hazard in ready-to-eat (RTE) meats due to potential cross-contamination. Chlorine is commonly used to sanitize processing equipment and utensils. However, Lm may survive the treatment and then contaminate food products. The objective of this study was to characterize the behavior of chlorine-exposed Lm on RTE ham during refrigerated storage. A two strain cocktail of Lm serotype 4b was pre-treated with chlorine (0, 25, and 50 ppm) for one hour, and then inoculated onto the surface of RTE ham to obtain an inoculum of about 3.0 log CFU/g. The inoculated ham samples were stored at 4, 8, and 16 °C, and Lm was enumerated periodically during the storage. The growth characteristics (lag time and growth rate) of Lm were estimated using the DMFit software. The results indicated that Lm growth was suppressed by the chlorine treatment. At 4 °C, the lag time of Lm with no (0 ppm) chlorine exposure (4.2 days) was shorter than those exposed to 25 ppm (5.4 days) and 50 ppm (6.8 days). The lag time decreased with the increase of temperature, e.g., at 25 ppm, the lag times were 5.2, 3.8 and 2.6 days for 4, 8 and 16 °C, respectively, and increased with the increase of chlorine concentration, e.g., at 16 °C, the lag times were 1.2, 2.6 and 4.0 days for 0, 25 and 50 ppm, respectively. However, growth rate increased with the increase of temperature and decreased with the increase of chlorine concentration. The lag time and growth rate as a function of chlorine concentration and temperature can be described using a modified Ratkowsky model and a modified Zwietering model, respectively. The results showed that the growth of Lm on RTE ham was delayed by pre-exposure to chlorine (at ≤ 50 ppm). The predictive models developed will contribute to microbial risk assessments of RTE meats.

Food Surface Texture Measurement Using Reflective Confocal Laser Scanning Microscopy

Confocal laser scanning microscopy (CLSM) was used in the reflection mode to characterize the surface texture (roughness) of sliced food surfaces. Sandpapers with grit size between 150 and 600 were used as height references to standardize the CLSM hardware settings. Sandpaper particle sizes were verified by scanning electron microscopy (SEM). The mean amplitude (in micrometers) of surface variation along line segments of the scanned sandpaper topographical image sets showed very close agreement between the measured result and the grit particle size (based on the U.S. Coated Abrasive Manufactures Inst. {CAMI], standard). The verified instrument settings were then used to measure the surface texture of mechanically sliced food surfaces, including cooked ham, salami, and cheese. Sliced food surface texture parameters of Ra (average height of a line segment), Rs (surface area ratio), Pa (average height on a region of interest), and Pq (root-mean-square height on a region of interest) were evaluated by this method. Values of the surface roughness of sliced ham, salami, and cheese were found to be comparable to the range of dimensions of selected sandpapers. The CLSM method may be useful for other surface texture measurements, and to investigate the impact of food surface texture on microbial adhesion or attachment, which might play a significant role in microbial transfer from one surface to another.

Growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham under refrigerated and temperature abuse conditions.

This study examined the growth characteristics of Listeria monocytogenes as affected by a native microflora in cooked ham at refrigerated and abuse temperatures. A five-strain mixture of L. monocytogenes and a native microflora, consisting of Brochothrix spp., isolated from cooked meat were inoculated alone (monocultured) or co-inoculated (co-cultured) onto cooked ham slices. The growth characteristics, lag phase duration (LPD, h), growth rate (GR, log(10) cfu/h), and maximum population density (MPD, log(10) cfu/g), of L. monocytogenes and the native microflora in vacuum-packed ham slices stored at 4, 6, 8, 10, and 12 °C for up to 5 weeks were determined. At 4-12 °C, the LPDs of co-cultured L. monocytogenes were not significantly different from those of monocultured L. monocytogenes in ham, indicating the LPDs of L. monocytogenes at 4-12 °C were not influenced by the presence of the native microflora. At 4-8 °C, the GRs of co-cultured L. monocytogenes (0.0114-0.0130 log(10) cfu/h) were statistically but marginally lower than those of monocultured L. monocytogenes (0.0132-0.0145 log(10) cfu/h), indicating the GRs of L. monocytogenes at 4-8 °C were reduced by the presence of the native microflora. The GRs of L. monocytogenes were reduced by 8-7% with the presence of the native microflora at 4-8 °C, whereas there was less influence of the native microflora on the GRs of L. monocytogenes at 10 and 12 °C. The MPDs of L. monocytogenes at 4-8 °C were also reduced by the presence of the native microflora. Data from this study provide additional information regarding the growth suppression of L. monocytogenes by the native microflora for assessing the survival and growth of L. monocytogenes in ready-to-eat meat products.

Effect of salt, smoke compound, and temperature on the survival of Listeria monocytogenes in salmon during simulated smoking processes.

The objectives of this study were to examine and develop a model to describe the survival of Listeria monocytogenes in salmon as affected by salt, smoke compound (phenol), and smoking process temperature. Cooked minced salmon containing selected levels of salt (0%, 2%, 4%, and 6%) and smoke compound (0, 5, 10, and 15 ppm phenol) were inoculated with a 6-strain mixture of L. monocytogenes to an inoculum level of 6.0 log(10) CFU/g. The populations of L. monocytogenes in salmon during processing at 40, 45, 50, and 55 degrees C that simulated cold- and hot-smoking process temperatures were determined, and the effects of salt, phenol, and temperature on the survival of L. monocytogenes in salmon were analyzed and described with an exponential regression. At 40 degrees C, the populations of L. monocytogenes in salmon decreased slightly with inactivation rates of <0.01 log(10) CFU/h, and at 45, 50, and 55 degrees C, the inactivation rates were 0.01 to 0.03, 0.15 to 0.30, and 2.8 to 3.5 log(10) CFU/h, respectively. An exponential regression model was developed and was shown to closely describe the inactivation rates of L. monocytogenes as affected by the individual and combined effects of salt, phenol, and smoking process temperature. Temperature was the main effector in inactivating L. monocytogenes while salt and phenol contributed additional inactivation effects. This study demonstrated the inactivation effects of salt, smoke compound, and temperature on L. monocytogenes in salmon under a smoking process. The data and model can be used by manufacturers of smoked seafood to select concentrations of salt and smoke compound and alternative smoking process temperatures at 40 to 55 degrees C to minimize the presence of L. monocytogenes in smoked seafood.

Antimicrobial Effects of Allyl Isothiocyanate and Modified Atmosphere on Pseduomonas Aeruginosa in Fresh Catfish Fillet under Abuse Temperatures

The effects of allyl isothiocyanate (AIT; 18 and 36 μg/L) in vapor phase, modified atmosphere (MA; 49% CO2 , 0.5% O2 , and 50.5% N2 ), and their combinations on the growth behavior of Pseduomonas aeruginosa in fresh catfish fillet at different abuse temperatures (8, 15, and 20 °C) were evaluated in this study. Lag phase, maximum growth rate, and shelf life were used as parameters to analyze the antimicrobial effects. Both gaseous AIT and MA alone inhibited the growth potential of P. aeruginosa effectively, prolonging the shelf life by 1.5 to 3.4 times compared to the control at abuse temperatures between 8 and 20 °C. The synergistic effect was observed at 8 °C, extending the shelf life of fresh catfish by more than 6.5 times (≥ 550 h). In addition, the maximum growth rate decreased with decreasing storage temperature, but it was not significantly influenced by the addition of AIT or MA. Hence, the combination of AIT and MA may be used as an effective antimicrobial system to reduce the microbial risks due to temperature abuse and to improve the shelf life of fresh catfish fillet. The proper combination of AIT and MA may be further optimized for industrial applications.

Inactivation of Uropathogenic Escherichia coli in Ground Chicken Meat Using High Pressure Processing and Gamma Radiation, and in Purge and Chicken Meat Surfaces by Ultraviolet Light

Extraintestinal pathogenic Escherichia coli, including uropathogenic E. coli (UPEC), are common contaminants in poultry meat and may cause urinary tract infections after colonization of the gastrointestinal tract and transfer of contaminated feces to the urethra. Three non-thermal processing technologies used to improve the safety and shelf-life of both human and pet foods include high pressure processing (HPP), ionizing (gamma) radiation (GR), and ultraviolet light (UV-C). Multi-isolate cocktails of UPEC were inoculated into ground chicken which was then treated with HPP (4°C, 0–25 min) at 300, 400, or 500 MPa. HPP D10, the processing conditions needed to inactivate 1 log of UPEC, was 30.6, 8.37, and 4.43 min at 300, 400, and 500 MPa, respectively. When the UPEC was inoculated into ground chicken and gamma irradiated (4 and -20°C) the GR D10 were 0.28 and 0.36 kGy, respectively. The UV-C D10 of UPEC in chicken suspended in exudate and placed on stainless steel and plastic food contact surfaces ranged from 11.4 to 12.9 mJ/cm2. UV-C inactivated ca. 0.6 log of UPEC on chicken breast meat. These results indicate that existing non-thermal processing technologies such as HPP, GR, and UV-C can significantly reduce UPEC levels in poultry meat or exudate and provide safer poultry products for at-risk consumers.