Beef Gravy Research Articles

Pressure resistance of cold-shocked Escherichia coli O157:H7 in ground beef, beef gravy and peptone water.

(i) To study the effects of cold shock on Escherichia coli O157:H7 cells. (ii) To determine if cold-shocked E.coli O157:H7 cells at stationary and exponential phases are more pressure-resistant than their non-cold-shocked counterparts. (iii) To investigate the baro-protective role of growth media (0·1% peptone water, beef gravy and ground beef). Quantitative estimates of lethality and sublethal injury were made using the differential plating method. There were no significant differences (P>0·05) in the number of cells killed; cold-shocked or non-cold-shocked. Cells grown in ground beef (stationary and exponential phases) experienced lowest death compared with peptone water and beef gravy. Cold-shock treatment increased the sublethal injury to cells cultured in peptone water (stationary and exponential phases) and ground beef (exponential phase), but decreased the sublethal injury to cells in beef gravy (stationary phase). Cold shock did not confer greater resistance to stationary or exponential phase cells pressurized in peptone water, beef gravy or ground beef. Ground beef had the greatest baro-protective effect. Real food systems should be used in establishing food safety parameters for high-pressure treatments; micro-organisms are less resistant in model food systems, the use of which may underestimate the organisms' resistance.

Effect of food residues on efficiency of surfactant disinfectants against food related pathogens adhered on polystyrene and ceramic surfaces

The adhesion of pathogenic bacteria on food contact surfaces increases the risk of cross-contamination in the food industry. However, food-borne disease introduced by the production process can be mitigated by surfactant use. This study investigates the effect of food residues (milk, beef gravy and tuna gravy) on the bactericidal efficiency of benzalkonium chloride (BAC) and alkyldiaminoethylglycine hydrochloride (AGH). The test was conducted on pathogenic bacteria (Escherichia coli O26, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus, and B. cereus spores) dried and adhered to the surfaces of polystyrene and ceramic dishes at room temperature for 1.5 h. The protein and lipid rich food residues protected the bacterial cells from dehydration and from the adverse effects of disinfectants, although bacterial numbers were decreased after drying and the surfaces were clearly sterilized after disinfectant treatment at typical concentrations (0.5 mg/ml–2.0 mg/ml) for 10 min. Following general and proper washing processes, the bactericidal effect of the disinfectants became clearly visible. These results indicate that applying a proper washing process prior to disinfectant treatment can prevent cross-contamination.

Behavioral Pattern of Native Food Isolates of <i>Yersinia</i> <i>enterocolitica</i> and <i>Yersinia</i> <i>intermedia</i> under Simulated Time-Temperature Combinations of the Food Chain

The public health significance of Yersinia spp. gives a new dimension to the prevailing food chain, wherein the foods do get exposed to heat and cold treatments. In this study, the effect of heat treatment on the native isolates of Yersinia enterocolitica CFR 2301 and Y. intermedia CFR 2303 revealed the D-values ranging from the lowest of 0.08 min at 65℃ in skim milk/beef gravy to the highest of 18.52 min at 50℃ in beef gravy. The heat sensitivity of both these cultures was in the order of Milli-Q water > 0.85% saline > skim milk > beef gravy. The z-values of the test cultures ranged from 7.55℃ for Y. intermedia to 12.08℃ for Y. enterocolitica. The heat sensitivity in Y. enterocolitica appeared to be related with growth incubation temperatures and also fatty acid profile of cell membrane. The effect of low temperature treatments (–20 ℃, 0℃ and 4℃ for 20 d) in water, saline and skim milk revealed the ability of Y. enterocolitica to survive more efficiently at –20℃, while Y. intermedia was more tolerant at 0℃. In packaged drinking water, Y. enterocolitica could survive and grow at 4℃ and 16℃, while at 30℃, inactivation was rapid. The findings did indicate that heat and cold treatments would not always ensure safety from Y. enterocolitica and Y. intermedia in the food chain.

Characterization of the Key Aroma Compounds in Beef and Pork Vegetable Gravies á la Chef by Application of the Aroma Extract Dilution Analysis

By application of the aroma extract dilution analysis (AEDA) on an aroma distillate isolated from a freshly prepared, stewed beef/vegetable gravy, 52 odor-active compounds were detected in the flavor dilution (FD) factor range of 4-4096. On the basis of high FD factors in combination with the results of the identification experiments, 3-(methylthio)propanal (cooked potato), 3-mercapto-2-methylpentan-1-ol (gravy-like), (E,E)-2,4-decadienal (deep-fried, fatty), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (lovage-like), vanillin (vanilla-like), (E,E)-2,4-nonadienal (deep-fried), and (E)-2-undecenal (metallic) are suggested as key contributors to the aroma of the gravy. To get an insight into the role of the vegetables as sources of gravy odorants, a beef gravy was prepared without vegetables. The AEDA results revealed that, in particular, onions and leek are important sources of gravy aroma compounds, adding particularly the very potent, gravy-like smelling 3-mercapto-2-methylpentan-1-ol to the overall aroma profile. Further compounds that were clearly derived from the vegetables and, thus, are important modifiers of the overall aroma were 4-vinyl-2-methoxyphenol, (E)-beta-damascenone, beta-ionone, 2-isopropyl-3-methoxypyrazine, and 2-(sec-butyl)-3-methoxypyrazine. Interestingly, none of the key odorants detected in the gravy can be assumed to be formed from a reaction between beef and vegetable constituents. A comparison of the odorants in the beef/vegetable gravy with a gravy prepared according to the same procedure, but substituting beef by pork meat, indicated that most of the aroma compounds were identical-although different in FD factors-but the tallowy smelling 12-methyltridecanal was detected as key odorant only in the beef/vegetable gravy.

Quantitation of 13 Heterocyclic Aromatic Amines in Cooked Beef, Pork, and Chicken by Liquid Chromatography−Electrospray Ionization/Tandem Mass Spectrometry

The concentrations of heterocyclic aromatic amines (HAAs) were determined, by liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI-MS/MS), in 26 samples of beef, pork, and chicken cooked to various levels of doneness. The HAAs identified were 2-amino-3-methylimidazo[4,5- f]quinoline, 2-amino-1-methylimidazo[4,5- b]quinoline, 2-amino-1-methylimidazo[4,5- g]quinoxaline (I gQx), 2-amino-3-methylimidazo[4,5- f]quinoxaline, 2-amino-1,7-dimethylimidazo[4,5- g]quinoxaline (7-MeI gQx), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline, 2-amino-1,6-dimethyl-furo[3,2- e]imidazo[4,5- b]pyridine, 2-amino-1,6,7-trimethylimidazo[4,5- g]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline, 2-amino-1,7,9-trimethylimidazo[4,5- g]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-9 H-pyrido[2,3- b]indole, and 2-amino-3-methyl-9 H-pyrido[2,3- b]indole. The concentrations of these compounds ranged from <0.03 to 305 parts per billion (micrograms per kilogram). PhIP was the most abundant HAA formed in very well done barbecued chicken (up to 305 microg/kg), broiled bacon (16 microg/kg), and pan-fried bacon (4.9 microg/kg). 7-MeI gQx was the most abundant HAA formed in very well done pan-fried beef and steak, and in beef gravy, at concentrations up to 30 microg/kg. Several other linear tricyclic ring HAAs containing the I gQx skeleton are formed at concentrations in cooked meats that are relatively high in comparison to the concentrations of their angular tricyclic ring isomers, the latter of which are known experimental animal carcinogens and potential human carcinogens. The toxicological properties of these recently discovered I gQx derivatives warrant further investigation and assessment.

Resistances to benzalkonium chloride of bacteria dried with food elements on stainless steel surface

To confirm the importance of washing food sediments from the surface of food-related environments, we examined resistances against benzalkonium chloride of pathogenic bacterial ( Escherichia coli O26, Pseudomonas aeruginosa and Staphylococcus aureus) cells dried and adhered on stainless steel dishes with milk, beef gravy or tuna gravy. Suspensions (0.1 ml) of these bacteria (8–9 log cfu/ml) were put on a 5 cm ϕ stainless steel dish and dried at room temperature (20–24 °C) for 90 min in a bio-clean bench with ventilation. Though these bacteria suspended with distilled water decreased 30–40 fold during the drying period, milk and the gravies protected the bacteria. Without the food elements, the adhered E. coli and Stap. aureus were decreased from 6 to<2 log cfu/dish by 0.5 mg/ml benzalkonium chloride (BKC) for 10 min treatment. Although Ps. aeruginosa showed resistance to BKC, the adhered cells were inactivated by 2.0 mg/ml BKC. However, the bactericidal effect disappeared by the food elements, particularly with milk, even at 1.0 and/or 2.0 mg/ml BKC levels. The protective efficiency of milk on bacteria disappeared if washed with water.

Heat resistance kinetics variation among various isolates of Escherichia coli

This paper reports an investigation of serotype-specific differences in heat resistance kinetics of clinical and food isolates of Escherichia coli. Heat resistance kinetics for 5 serotypes of E. coli at 60 °C were estimated in beef gravy using a submerged coil heating apparatus. The observed survival curves were sigmoidal and there were significant differences ( p=0.05) of the survival curves among the serotypes. Consequently, a model was developed that accounted for the sigmoidal shape of the survival curves and the serotype effects. Specifically, variance components for serotypes and replicates within serotypes were estimated using mixed effect nonlinear modeling. If it is assumed that the studied serotypes represent a random sample from a population of E. coli strains or serotypes, then, from the derived estimates, probability intervals of the expected lethality for random selected serotypes can be computed. For example, expected serotype-specific lethalities at 60 °C for 10 min are estimated to range between 5 and 9 log 10 with 95% probability. On the other hand, to obtain a 6-log 10 lethality, the expected minutes range, with 95% probability, from 6 to 12 min. The results from this study show that serotypes of E. coli display a wide range of heat resistance with nonlinear survival curves. Industrial relevance This paper is of high current interest since it deals with the ongoing international debate on log linear vs. non-log linear microbial inactivation curves observed during thermal and non-thermal processing. The data on 5 serotypes of E. coli indicate a clear need for further studies with more strains to fully characterize the heat resistance kinetics for E. coli.

Mathematical description of non-linear survival curves of Listeria monocytogenes as determined in a beef gravy model system at 57.5 to 65 °C

This paper presents a non-linear model for predicting the inactivation of Listeria monocytogenes, suspended in beef broth after heat treatment. A five-strain cocktail of L. monocytogenes was used in developing inactivation data at 57.5, 60, 62.5 and 65 °C, where maximum observed lethalities were more than 7 log 10 for the latter three temperatures. For all four temperatures, the survival curves, i.e. the common logarithms (base 10) of the numbers of surviving cells vs. times, were distinctly convex. Four functions, based on different assumptions underlying the shape of the survival curves, were compared. The assumptions involve the asymptotic behavior of the survival curves. Mechanistic considerations were used in deriving some of the functions considered. The function selected for further modeling was the logistic function, where the natural logarithm of time is the independent variable. Using this function, a model for predicting the amount of inactivation for temperatures between 57.5 and 65 °C was determined. The model presented in this paper is different from models that have been presented in the predictive microbiology literature, in that the parameters that describe the model are assumed to be random variables. Thus, a full description of the model includes standard deviations of parameter values, which were estimated using a mixed-effects analysis. Other research has indicated a logistic function adequately describes survival curves of L. monocytogenes. The use of this function entails that there are not non-zero asymptotic D-values. In conclusion, there is a substantial body of evidence suggesting that non-linear models are needed for characterizing survival curves of L. monocytogenes.

Growth and heat resistance kinetic variation among various isolates of Salmonella and its application to risk assessment.

The abilities of cells of a particular type of bacteria to leave lag phase and begin the process of dividing or surviving heat treatment can depend on the serotypes or strains of the bacteria. This article reports an investigation of serotype-specific differences in growth and heat resistance kinetics of clinical and food isolates of Salmonella. Growth kinetics at 19 degrees C and 37 degrees C were examined in brain heart infusion broth and heat resistance kinetics for 60 degrees C were examined in beef gravy using a submerged coil heating apparatus. Estimates of the parameters of the growth curves suggests a small between-serotype variance of the growth kinetics. However, for inactivation, the results suggest a significant between-serotype effect on the asymptotic D-values, with an estimated between-serotype CV of about 20%. In microbial risk assessment, predictive microbiology is used to estimate growth and inactivation of pathogens. Often the data used for estimating the growth or inactivation kinetics are based on measurements on a cocktail--a mixture of approximately equal proportions of several serotypes or strains of the pathogen being studied. The expected growth or inactivation rates derived from data using cocktails are biased, reflecting the characteristics of the fastest growing or most heat resistant serotype of the cocktail. In this article, an adjustment to decrease this possible bias in a risk assessment is offered. The article also presents discussion of the effect on estimating growth when stochastic assumptions are incorporated in the model. In particular, equations describing the variation of relative growth are derived, accounting for the stochastic variations of the division of cells. For small numbers of cells, the expected value of the relative growth is not an appropriate "representative" value for actual relative growths that might occur.

Increased thermotolerance of Clostridium perfringens spores following sublethal heat shock

Beef gravy samples inoculated with Clostridium perfringens spores were heat shocked at 75 °C for 20 min, and then thermotolerance at 100 °C was assessed using a submerged-coil heating apparatus. Survivors were enumerated on Shahidi Ferguson Perfringens agar. An association of the heat resistance with the origin of the C. perfringens could not be established due to significant variations in the heat resistance among strains. Interestingly, deviations from classical logarithmic linear declines in the log numbers with time were not observed in both control and heat shocked samples. D-values at 100 °C for C. perfringens spores ranged from 15.5 to 21.4 min. Heat shocked spores of 9 out of 10 strains had significantly higher ( p<0.05) D-values at 100 °C than unstressed spores. Proteins with epitopic and size similarity to Escherichia coli GroEL and Bacillus subtilis small acid-soluble protein, SspC, were present in spores. However, heat shock treated spores did not appear to significantly increase expression of these proteins. Acquired thermotolerance is of substantial practical importance to food processors and should provide useful information for designing thermal treatments to eliminate C. perfringens spores in ready-to-eat foods.

HEAT RESISTANCE OF CLOSTRIDIUM PERFRINGENS VEGETATIVE CELLS AS AFFECTED BY PRIOR HEAT SHOCK1

ABSTRACT This study quantified the heat resistance and the effects of a heat shock on the subsequent heat resistance of 10 strains of Clostridium perfringens. Beef gravy samples inoculated with vegetative cells of the pathogen were subjected to sublethal heating at 48C for 10 min, and then heated to a final temperature of 58C using a submerged‐coil heating apparatus. Heat‐treated samples were spiral plated on Shahidi‐Ferguson Perfringens agar to determine surviving bacterial population. No correlation between the heat resistance and the origin of the C. perfringens could be established due to significant variations in the heat resistance among strains. Inactivation kinetics of both heat‐shocked and nonheat‐shocked samples exhibited log‐linear decline in the number of surviving cells with time. D‐values at 58C for C. perfringens vegetative cells ranged from 1.21 to 1.60 min. Heat shocking allowed the organism to survive longer and the increase in heat resistance was as high as 1.5 fold. Also, heat shock resulted in the overexpression of proteins exhibiting epitopic and size similarity to E. coli GroEL and B. subtilis small acid soluble proteins. Increased heat resistance due to heat shock must be considered while designing cooking/reheating regimes that ensure safety of ready‐to‐eat foods contaminated with high numbers of C. perfringens vegetative cells.

Effect of stress induced by suboptimal growth factors on survival of Escherichia coli O157:H7

This study investigated the growth and survival of E. coli O157:H7 exposed to a combination of suboptimal factors (22°C, 7°C, −18°C/0.5% NaCl, 5.0% NaCl/pH 7.0, pH 5.4, pH 4.5/addition of lactic acid) in a simulation medium for red meat (beef gravy). Prolonged survival was noted as the imposed stress was more severe, and as multiple growth factors became suboptimal. At a defined temperature (7°C or −18°C), survival was prolonged at the more acid, more suboptimal pH (pH 4.5>pH 5.4>pH 7.0) while at a defined pH (pH 4.5), better survival was observed at 7°C than at 22°C. This suggests that application of the hurdle concept for preservation of food may inhibit outgrowth but induce prolonged survival of E. coli O157:H7 in minimal processed foods. At both 22°C and 7°C, the addition of lactic acid instead of HCl to reduce pH (to pH 4.5) resulted in a more rapid decrease of E. coli O157:H7. High survival was observed in beef gravy, pH 5.4 at −18°C (simulation of frozen meat)—reduction of log 3.0 to log 1.9 after 43 days—and in beef gravy, pH 4.5 and 5% NaCl at 7°C (simulation of a fermented dried meat product kept in refrigeration)—less than 1 log reduction in 43 days. In these circumstances, however, a high degree of sublethal damage of the bacterial cells was noted. The degree of sublethal damage can be estimated from the difference in recovery of the pathogen on the non-selective TSA medium and the selective SMAC medium.

Predictive Thermal Inactivation Model for Listeria monocytogenes with Temperature, pH, NaCl, and Sodium Pyrophosphate as Controlling Factors

The effects and interactions of heating temperature (55 to 65°C), pH (4 to 8), salt (NaCl; 0 to 6%, wt/vol), and sodium pyrophosphate (SPP; 0 to 0.3%, wt/vol) on the heat inactivation of a four-strain mixture of Listeria monocytogenes in beef gravy were examined. A factorial experimental design comparing 48 combinations of heating temperature, salt concentration, pH value, and SPP content was used. Heating was carried out using a submerged-coil heating apparatus. The recovery medium was plate count agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. Decimal reduction times (D-values) were calculated by fitting a survival model to the data with a curve-fitting program. The D-values were analyzed by second-order response surface regression for temperature, pH, NaCl, and SPP levels. Whereas increasing the NaCl concentration protected L. monocytogenes against the lethal effect of heat, high SPP concentrations increased heat sensitivity. Also, low pH values increased heat sensitivity of L. monocytogenes. The four variables interacted to affect the inactivation of the pathogen. Thermal resistance of L. monocytogenes can be lowered by combining these intrinsic factors. A predictive model that described the combined effect of temperature, pH, NaCl, and SPP levels on thermal resistance of L. monocytogenes was developed. The model can predict D-values for any combination of temperature, pH, NaCl, and SPP that are within the range of those tested. Using this predictive model, food processors should be able to design adequate thermal regimes to eliminate L. monocytogenes in thermally processed foods.

PREDICTIVE MODEL FOR THE COMBINED EFFECT OF TEMPERATURE, pH, SODIUM CHLORIDE, AND SODIUM PYROPHOSPHATE ON THE HEAT RESISTANCE OF ESCHERICHIA COLI O157:H71

ABSTRACT The effects and interactions of heating temperature (5–62.5C), pH (4 – 8), NaCl (0 – 6%, w/v), and sodium pyrophosphate (0 – 0.3%, w/v) on the heat resistance of a four strain mixture of Escherichia coli O157:H7 in beef gravy were examined. Thermal death times were determined using a submerged coil heating apparatus. The recovery medium was plate count agar supplemented with 1% sodium pyruvate. Decimal reduction times (D‐values) were calculated by fitting a survival model to the data with a curve fitting program. The D‐values were analyzed by second order response surface regression for temperature, pH, NaCl and sodium pyrophosphate levels. The four variables interacted to affect the inactivation of the pathogen. Thermal resistance of E. coli O157:H7 can be lowered by combining these intrinsic factors. A mathematical model describing the combined effect of temperature, pH, NaCl and sodium pyrophosphate levels on the thermal inactivation of E. coli O157:H7 was developed. The model can predict D‐values for any combinations of temperature, pH, NaCl and sodium pyrophosphate that are within the range of those tested.

Heat shock and thermotolerance of Escherichia coli O157:H7 in a model beef gravy system and ground beef.

Duplicate beef gravy or ground beef samples inoculated with a suspension of a four-strain cocktail of Escherichia coli O157:H7 were subjected to sublethal heating at 46 degrees C for 15-30 min, and then heated to a final internal temperature of 60 degrees C. Survivor curves were fitted using a linear model that incorporated a lag period (TL), and D-values and 'time to a 4D inactivation' (T4D) were calculated. Heat-shocking allowed the organism to survive longer than non-heat-shocked cells; the T4D values at 60 degrees C increased 1.56- and 1.50-fold in beef gravy and ground beef, respectively. In ground beef stored at 4 degrees C, thermotolerance was lost after storage for 14 h. However, heat-shocked cells appeared to maintain their thermotolerance for at least 24 h in ground beef held to 15 or 28 degrees C. A 25 min heat shock at 46 degrees C in beef gravy resulted in an increase in the levels of two proteins with apparent molecular masses of 60 and 69 kDa. These two proteins were shown to be immunologically related to GroEL and DnaK, respectively. Increased heat resistance due to heat shock must be considered while designing thermal processes to assure the microbiological safety of thermally processed foods.

Effects of nisin and temperature on survival, growth, and enterotoxin production characteristics of psychrotrophic Bacillus cereus in beef gravy.

The presence of psychrotrophic enterotoxigenic Bacillus cereus in ready-to-serve meats and meat products that have not been subjected to sterilization treatment is a public health concern. A study was undertaken to determine the survival, growth, and diarrheal enterotoxin production characteristics of four strains of psychrotrophic B. cereus in brain heart infusion (BHI) broth and beef gravy as affected by temperature and supplementation with nisin. A portion of unheated vegetative cells from 24-h BHI broth cultures was sensitive to nisin as evidenced by an inability to form colonies on BHI agar containing 10 micrograms of nisin/ml. Heat-stressed cells exhibited increased sensitivity to nisin. At concentrations as low as 1 microgram/ml, nisin was lethal to B. cereus, the effect being more pronounced in BHI broth than in beef gravy. The inhibitory effect of nisin (1 microgram/ml) was greater on vegetative cells than on spores inoculated into beef gravy and was more pronounced at 8 degrees C than at 15 degrees C. Nisin, at a concentration of 5 or 50 micrograms/ml, inhibited growth in gravy inoculated with vegetative cells and stored at 8 or 15 degrees C, respectively, for 14 days. Growth of vegetative cells and spores of B. cereus after an initial period of inhibition is attributed to loss of activity of nisin. One of two test strains produced diarrheal enterotoxin in gravy stored at 8 or 15 degrees C within 9 or 3 days, respectively. Enterotoxin production was inhibited in gravy supplemented with 1 microgram of nisin/ml and stored at 8 degrees C for 14 days; 5 micrograms of nisin/ml was required for inhibition at 15 degrees C. Enterotoxin was not detected in gravy in which less than 5.85 log10 CFU of B. cereus/ml had grown. Results indicate that as little as 1 microgram of nisin/ml may be effective in inhibiting or retarding growth of and diarrheal enterotoxin production by vegetative cells and spores of psychrotrophic B. cereus in beef gravy at 8 degrees C, a temperature exceeding that recommended for storage or for most unpasteurized, ready-to-serve meat products.

Control of Enterotoxic Bacillus cereus on Poultry or Red Meats and in Beef Gravy by Gamma Irradiation

The gamma-radiation resistance of five enterotoxic and one emetic isolate of Bacillus cereus vegetative cells and endospores was tested in mechanically deboned chicken meat (MDCM), ground turkey breast, ground beef round, ground pork loin and beef gravy. The D10 values for B. cereus ATCC 33018 were 0.184, 0.431 and 2.56 kGy for logarithmic-phase cells, stationary-phase cells, and endospores at 5°C on MDCM, respectively. Neither the presence nor absence of air during irradiation significantly affected radiation resistance of vegetative cells or endospores of B. cereus ATCC 33018 when present on MDCM. Irradiation temperature (−20 to +20°C) did affect the radiation resistance of stationary-phase vegetative cells and to a limited extent that of spores on MDCM. Impedance studies indicated that surviving vegetative cells were severely injured by radiation. A dose of 7.5 kGy at 5°C was required to eliminate a challenge of 4.6 × 103B. cereus ATCC 33018 from temperature-abused MDCM (24 h at 30°C). The radiation resistance of a mixture of endospores of six strains to gamma radiation was 2.78 kGy in ground beef round, ground pork loin and beef gravy, but 1.91 kGy in turkey and MDCM. The results indicate that irradiation of meat or poultry can provide significant protection from vegetative cells but not from endospores of B. cereus.

USE OF MEAT ISOLATE, LACTOBACILLUS BAVARICUS MN, TO INHIBIT LISTERIA MONOCYTOGENES GROWTH IN A MODEL MEAT GRAVY SYSTEM

ABSTRACT The ability of Lactococcus lactis 11454, Pediococcus pentosaceus 43200 and Lactobacillus bavaricus MN, originally isolated from dairy, vegetable, and meat products, respectively, to inhibit growth of Listeria monocytogenes Scott A in a model beef gravy was examined. In the first series of experiments, where the lactic acid bacteria and L. monocytogenes were inoculated at levels of 105 CFU/mL and 103 CFU/mL, respectively only L. bavaricus inhibited listerial growth at 10C. Subsequent experiments using L. bavaricus MN confirmed that the inhibition was caused by a bacteriocin, occurred at temperatures at low as 4C, and could be initiated by 103 CFU/mL L. bavaricus in the presence of L. monocytogenes at levels 10‐fold higher. Although the inhibitory agent was protease‐sensitive and inhibition occurred in the absence of a fermentable carbohydrate, the presence of acid enhanced efficacy of the bacteriocin.

Oxidation‐Reduction Potentials of Canned Foods and Their Ability to Support Clostridium Botulinum Toxigenesis

ABSTRACTOxidation‐reduction potentials (Eh) of canned foods ranged from ‐18 to ‐438 mV. Foods packed in glass had higher redox potentials than those packed in cans. Only 4 out of 26 products tested reached positive redox values after exposure to air for 24 hr at 4°C. Inoculated containers of mushrooms, whole corn, cream corn, asparagus, beef gravy, kidney beans, green beans, cream of mushroom soup, cheddar cheese soup, and lima beans supported toxin production by C. botulinum; potatoes and beets did not.

Thermal Inactivation of Clostridium perfringens Enterotoxin

Thermal inactivation studies of Clostridium perfringens enterotoxin revealed that biological activity was destroyed within 5 min at 60 C, whereas about 10% or less residual serological activity could be detected even after 80 min of exposure at 60 C in saline or in phosphate buffer, pH 7.0 or 8.0. Loss of serological activity was more rapid at 60 C at pH 5.4 or 6.0 than at pH 7.0 or 8.0. Flocculation of enterotoxin was visible in phosphate buffer after 20 min of exposure at 60 C, pH 5.4, 70 min at pH 6.0 but not at all at pH 7.0 or 8.0. Rapid loss of serological activity also occurred at 60 C in cooked turkey, chicken gravy, beef gravy as well as in 5, 10, and 20% bovine serum albumin and gelatin. Up to about 12% of the heat-inactivated serological activity could be recovered by treating toxin in the food samples with urea for 1 h at room temperature. However, serological activity of toxin heated in phosphate buffer could not be reactivated by urea treatment.