LACTIC ACID INACTIVATION OF SALMONELLA TYPHIMURIUM ATTACHED TO CATFISH SKIN

This study was conducted to test sanitizer efficacy of lactic acid on Salmonella typhimurium populations that were firmly attached or loosely attached on catfish skin with or without mucus. For both cell types, counts of S. typhimurium were reduced from 5.9 log¹⁰ CFU/skin to below the limit of detection of 2.0 log¹⁰ CFU/skin by a 5 min exposure to 2% lactic acid. Exposure for 1 min reduced a 10⁴ CFU/skin inoculum to below the limit of detection. Catfish skin mucus slightly decreased the antimicrobial effect of lactic acid against firmly attached S. typhimurium.     

EFFECT OF ELECTRICAL STIMULATION ON KILLING SALMONELLA TYPHIMURIUM IN VARIOUS SALT SOLUTIONS

Electrical stimulation was evaluated as a method to kill Salmonella typhimurium in various salt solutions at different concentration . Salmonella typhimurium at 2 × 10⁵ CFU/ml was treated at 22–24C for 60 min in each salt solution using electricity at 10 mA/cm² current, 1 kHz frequency, and 50% duty cycle. Samples taken at various times were serially diluted, plated on tryptic soy agar and xylose lysine desoxycholate agar, and incubated at 37C for 18–24 h. To detect injured cells, samples were also pre-enriched in buffered peptone water at 37C for 4–5h before being plated. Results indicated all salmonellae were electrically killed at 5 min in NaCl, at 30 min in NaNO₃, and at 45 min in NaC₂H₃O₂ at 0.15 and 0.015 M concentrations. Salmonellae were also killed at 45 min in Na₃PO₄ and at 60 min in Na₂CO₃ at 0.0015 M concentration by electricity in combination with high pH .     

MICROBIOLOGICAL STATUS OF EGYPTIAN SALTED MEAT (BASTERMA) AND FRESH SAUSAGE

The microbiological quality of 125 samples of the most popular Egyptian meat products (75 Egyptian fresh sausage "EPS" and 50 basterma) was determined. The aerobic plate count (APC) and Lactobacillaceae count of basterma ranged from 1 × 10⁴ to 9 × 10⁶ CFU/g, respectively . Enterobacteriaceae, mold and yeast counts for basterma were similar (<1 × 10² CFU/g). Artificially contaminated slices of meat and garlic paste of basterma showed that the paste inhibited growth of Salmonella typhimurium. APC and Enterobacteriaceae counts of EFS ranged from 1.1 × 10⁴ to 1 × 10⁸ and from 1 × 10² to 1 × 10⁷ CFU/g, respectively. Nearly 26% and 29% of EFS were positive for Clostridium perfringens and coagulase-positive Staphylococcus aureus, respectively . Salmonella could not be detected in any examined samples. Bacteriologically, EFS might pose a potential health hazard, making it imperative to institute sanitary measures during its production and sale .; Accepted for Publication July 2, 1997     

HYGIENIZATION OF INDIAN CHICKEN MEAT BY IONIZING RADIATION

Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 10⁵ - 2.6 × 10⁶/g), mainly with Staphylococcus spp. (1.5 × 10⁴ - 2.8 × 10⁵/g). All the chicken samples also showed the presence of Salmonellae (3 × 10¹ - 2.1 × 10²/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D₁₀ values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (10⁸ cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .     

REDUCTION OF SALMONELLA ON POST-CHILL CHICKEN CARCASSES BY TRISODIUM PHOSPHATE (NA3PO4) TREATMENT

The use of trisodium phosphate (TSP) in rinsing chicken carcasses was evaluated for salmonellae reduction. Post-chill carcasses were dipped into a 10%-TSP solution at 10 or 50C for 15 s. After storing 0, 1 or 6 days at 4C, the incidence and reduction of salmonellae were measured using a nitrocellulose (NC) membrane lifting technique, conventional culture methods and most probable number (MPN) technique. In a trial using non-inoculated carcasses, the incidences of salmonellae were decreased from 12 ∼ 24% in controls to 0 ∼ 8% in TSP-treated groups. When the carcasses were inoculated with S. typhimurium (2×10⁴ CPU/carcass), the NC membrane lifting method detected 27 ∼ 46% less incidences of salmonellae in TSP-treated groups. However, culture methods failed to show any difference between TSP-treated and untreated carcasses. Another trial using MPN method showed a significant reduction of salmonellae (1.6 ∼ 1.8 logs) in TSP-treated groups (P < 0.01) at both 1 and 6 days. Although 50C-TSP treatment gave 0.4 log greater reduction than 10C-treatment, the difference was not statistically significant. Total plate counts (TPC) revealed a similar reduction trend to MPN results of salmonellae.     

SHELF-LIFE OF FRESH FILLED PASTA. HAZARD ANALYSIS AND CRITICAL CONTROL POINTS OF THE MANUFACTURING PROCESS AND HOUSEHOLD PRACTICES

Hazard Analysis and Critical Control Point (HACCP) approach was used to assess the safety of a fresh filling pasta (ricotta-filled ravioli) manufacturing plant in La Plata region, Argentina. Household practices like cooking and holding meals before serving were also evaluated. Samples of ricotta, main raw material of the filling, showed colony counts of Enterobacteriaceae total microorganisms, molds and yeasts of (5 × 10³-1 × 10⁵), (1x10⁵−1x10⁸) and 1 × 10⁵ CFU/g, respectively. E. coli was also detected in one out of five samples, suggesting a hazardous condition of this raw material. Salmonella spp. was not isolated from any of the dough samples tested. Ricotta filling showed high colony counts of mesophilic microorganisms (6 × 10⁶ CFU/g), Enterobacteriaceae (1 × 10⁵ - 1 × 10⁶ CFU/g), while E. Coli was detected in 20% of the samples. Counts of B. cereus, S. aureus were less than 1 × 10² CFU/g in the analyzed materials. In the finished product (ricotta-filled ravioli), the colony counts of mesophilic microorganisms and Enterobacteriaceae were 3 × 10⁸ and 8 × 10⁵ CFU/g, respectively. Critical Control Points found were cooking and holding time before serving. The implementation of suggested corrections allowed the microbial quality of the final product (ricotta-filled ravioli) to be improved considerably. The growth of total microbial counts during refrigerated storage (0, 4, 8 and 10C) were measured and the shelf-life of ricotta and ricotta-filled ravioli was calculated.     

Rapid dye reduction tests for the determination of microbiological quality of meat

Rapid dye reduction tests have been developed to determine the quality of meat. Three chemical indicators, resazurin and two tetrazolium compounds, were used to correlate the microbial numbers and reduction times in meat samples. Twenty-five surface samples from sheep carcasses were subjected to each reduction test. Total viable counts given were obtained at 37°C. Resazurin reduction time was 90–120 min when the bacterial counts ranged from 1.5×10⁶ to 7.7×10⁶/cm². Samples showing bacterial counts between 1.5×10⁶ and 6.0×10⁶/cm² reduced tetrazolium (NBT) in 360–390 min whereas samples containing bacterial counts of 2.1×10⁶/cm² took 420–450 min to reduce iodophenyl nitrophenyl tetrazolium (INT) dye. Regression equations relating the number of organisms per cm² and reduction time were applied to predict the microbiological quality of meat samples from reduction time data. Among the three dyes, resazurin gave the lowest reduction time.     

INFLUENCE OF WASHING TREATMENT ON NATIVE MICROFLORA AND ESCHERICHIA COLI POPULATION OF INOCULATED CANTALOUPES

The influence of chlorine or hydrogen peroxide treatment on populations of Escherichia coli 25922 on the external surface of inoculated cantaloupe was investigated. Surface treatment with 70% EtOH, followed by immersion in 10⁸ CFU/mL E. coli inoculum deposited an average of 4.4 log₁₀CFU/cm² cell population on the cantaloupe surface. The efficncy of washing inoculated cantaloupe was dependent on storage interval between inoculation and treatment. Dipping the cantaloupes in solutions containing 1000 mg/L chlorine or 5% peroxide for 5 min, within 24 h of inoculation, caused a 2 log₁₀ CFU/cm² reduction of the indigenous surface microflora and a 3–4.0 log₁₀ CFU/cm² reduction in E. coli. The efficacy was less when the interval between inoculation and treatment exceeded 24 h. Chlorine appeared in be a better antimicrobial agent than hydrogen peroxide against F. coli ATCC 25922 inoculated on cantaloupe surfaces while hydrogen peroxide was better in reducing surface microflora of cantaloupe.     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

Piezoelectric Flow Injection Analysis Biosensor for the Detection of Salmonella Typhimurium

ABSTRACT: Piezoelectric biosensors have the potential to provide direct detection of food contaminants, such as pathogens. In this study, Protein A antibody immobilization was used for the activation of the piezoelectric biosensor to detect Salmonella typhimurium. The overall system consisted of a new design for a flow cell and flow injection analysis system. The flow cell made possible a baseline stability of ± 1 Hz out of 5 MHz for hours. The sensor had responses of 5 to 65 Hz in 30 min with R²= 0.95 for S. typhimurium concentrations of 10⁷to 10⁹ CFU/ml under continuous flow, and 3 to 75 Hz in 40 min with R²= 0.96 for S. typhimurium concentrations of 10⁶ to 10¹⁰ CFU/ ml under stop flow. Cross-reactivity tests were performed with nonpathogenic Escherichia coli, Escherichia coli O157:H7, Listeria monocytogenes , and Vibrio parahaemolyticus and showed less than 10% response.     

THE EFFECT OF AEROBIC MESOPHILIC MICROFLORAL LEVELS ON THE ISOLATION OF INOCULATED LISTERIA MONOCYTOGENES STRAIN LM82 FROM SELECTED FOODS

The effect of aerobic mesophilic microfloral concentration on the isolation of Listeria monocytogenes LM82 was studied in 31 (18 cheeses and 7 noncheese) retail foods having standard plate counts of 10¹ to 10⁸ colony forming units (CFU)/g. Foods were spiked with L. monocytogenes and enriched at 30°C for 24 h in a selective enrichment broth used in a U.S. Food and Drug Administration method. Inoculum levels for isolation on modified McBride agar ranged from 0.1 to > 5 × 10³ with a geometric mean value of 5 inoculated CFU/g or 1.4 CFU/g. Pure Enterococcus (Streptococcus) faecalis ( 0 to 6 × 10⁶ inoculated CFU/mL ) in the absence of food matrix had no effect on the enrichment of L. monocytogenes. Ease of isolation of LM82 was independent of the food microflora concentration both generally and in the specific food type of 9 Brie cheeses. Competition, when it occurs, therefore, may be due to specific bacterial competitors rather than bacterial numbers .     

SURVIVAL OF CAMPYLOBACTER JEJUNI IN MARINATED AND NONMARINATED CHICKEN PRODUCTS

Consumption of chicken products has been increasing. Most of these products in Finland are sold as fresh marinated pieces in consumer packages. The impact of marination on the survival of enteric pathogens is not known. We studied the survival of Campylobacter jejuni on marinated chicken drumsticks and sliced breast strips stored at a refrigerator temperature of +4C. The marinade was an emulsion of vegetable oil and water with spices, NaCl (5.9% wt/wt) and its pH was adjusted to 4.5 with lactic and acetic acid. The survival of C. jejuni was similar in marinated and nonmarinated chicken drumsticks and strips. The organisms were detected for at least nine days at the higher inoculum level (10¹– 10² CFU/mL) and for at least five days at the lower inoculum level (10¹– 10² CFU/mL). C. jejuni, inoculated into plain marinade and stored at 4C, was detected after 24 h but not after 48 h. Our results revealed that marination procedure used to reduce and prevent the growth of spoilage organisms does not significantly decrease the survival of Campylobacter jejuni in chicken products.     

Influence of catfish skin mucus on trisodium phosphate inactivation of attached Salmonella Typhimurium,Edwardsiella tarda,and Listeria monocytogenes

This study examined the antimicrobial effectiveness of trisodium phosphate (TSP) on Edwardsiella tarda, Listeria monocytogenes, and Salmonella Typhimurium attached to catfish skin with and without mucus. Salmonella Typhimurium and E. tarda attached more readily to catfish skin than did L monocytogenes. At high inoculum levels (10(7) CFU/ml), TSP treatments (at 2 to 6%) for 10 min reduced bacterial counts of E. tarda by >2.5 to >3.3 log10 CFU per skin sample for firmly attached cells and by 3.5 to 3.6 log10 CFU per skin sample for loosely attached cells. Counts of L. monocytogenes declined by 0.6 to >1.8 log10 CFU per skin sample for firmly attached cells and by 1.2 to 2.2 log10 CFU per skin sample for loosely attached cells. Counts of Salmonella Typhimurium were reduced by 3.6 to >3.8 log10 CFU per skin sample for firmly attached cells and by 3.5 to >3.8 log10 CFU per skin sample for loosely attached cells. Overall, counts of firmly attached bacteria on TSP-treated skins with mucus were higher than counts on skin without mucus. Firmly attached L. monocytogenes was more resistant to TSP than was firmly attached Salmonella Typhimurium or E. tarda. The presence of mucus on skins slightly decreased the antimicrobial effect of TSP Significant (P < 0.05) reduction in the numbers of all three bacteria can be achieved by treatment with 6% TSP for 10 min.     

Decontamination Efficacy of Combined Chlorine Dioxide with Ultrasonication on Apples and Lettuce

ABSTRACT:  The bacterial reduction of Salmonella and Escherichia coli O157:H7-inoculated apples and lettuce by ClO₂ at 0, 5, 10, 20, and 40 ppm with and without 170-kHz ultrasonic treatments for 3, 6, and 10 min, respectively, have been studied. The treatments of ClO₂ at 20 and 40 ppm for 3, 6, and 10 min or at 5 and 10 ppm for 6 and 10 min with 170-kHz ultrasonication caused 3.115 to 4.253 log reductions in Salmonella and 2.235 to 3.865 log reduction in E. coli O157:H7 on inoculated apples. Using combined ClO₂ and ultrasonication to treat 4.48 × 10⁴ CFU/g Salmonella and 1.07 × 10⁵ CFU/g E. coli O157:H7-inoculated lettuce, the bacterial reductions were 2.257 to 2.972 and 1.357 to 2.264 log, respectively. The residual ClO₂ decreased with increasing treatment times, over 80% of ClO₂ was detected after the 3-min treatment, and more than 70% remained after the 10-min treatment time. No bacteria were recovered from the posttreatment solutions of ClO₂ or ClO₂ combined with ultrasonication. The temperature of the ClO₂ treatment was 20.1 °C, and it increased to 40.1, 44.9, and 50.3 °C, with 170-kHz ultrasonic treatments for 3, 6, and 10 min, respectively, on apples.     

RELEASE OF PROPYL PARABEN FROM A POLYMER COATING INTO WATER AND FOOD SIMULATING SOLVENTS FOR ANTIMICROBIAL PACKAGING APPLICATIONS

The release phenomena of propyl paraben from a polymer coating to water and three food simulating solvents (10% aqueous ethanol, 50% aqueous ethanol, n-heptane) were studied for antimicrobial packaging applications. The effects of food simulating solvent, initial concentration in the coating and temperature on the propyl paraben release were examined. The initial concentration of propyl paraben in the coating ranged from 1.26 × 10⁴ to 10.52 × 10⁴ g/m³ and the temperature from 5.5 to 30C. For water, the release was controlled by Fickian diffusion with constant diffusion coefficient (7±11 × 10^-11 cm²/s at 30C), and independent of the initial concentration. For 10% ethanol, the release followed again the Fickian model with constant diffusion coefficient (30±40 × 10^-11 cm²/s at 30C). For 50% ethanol and n-heptane, the release was instantaneous and not controlled by Fickian diffusion. For the release into water, the activation energy for diffusion from the Arrhenius relationship was around 88 kJ/mole.     

INHIBITION OF STAPHYLOCOCCUS AUREUS AND BACILLUS CEREUS ON A VEGETARIAN FOOD TREATED WITH NISIN COMBINED WITH EITHER POTASSIUM SORBATE OR SODIUM BENZOATE

Various amounts of nisin (0, 10³ and 5 × 10³ IU/g) in combination with either potassium sorbate (0, 2, and 3%) or sodium benzoate (0, 0.06 and 0.12%) were tested for effectiveness in inhibiting growth of Staphylococcus aureus C10 and Bacillus cereus B7 inoculated on a vegetarian food. The strains used were isolated from vegetarian foods obtained commercially in Taiwan, and the test food, spice and dried bean curd, was selected for the study based on ability to support the growth of these organisms. After treatment with a preservative combination, the surfaces of sterilized food samples were inoculated, samples were stored in vacuum or nonvacuum packages at either 4C or 30C, and at appropriate times, tested for microbial growth. Growth of both isolates was unaffected by vacuum-packaging treatment; however, a bacteriostatic effect was found at 4C. Data indicated that during the 14-day storage at 4C, vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 0.12% sodium benzoate significantly (p < 0.05) decreased the counts of S. aureus C10 and B. cereus B7 by 2.61 and 3.02 log₁₀ CFU/g, respectively. In the vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 3% potassium sorbate, counts for C10 and B7 were decreased by 2.35 and 2.64 log₁₀ CFU/g, respectively. Thus, the combined treatment extended the shelf-life of the vegetarian food .     

Spectroscopic Differentiation and Quantification of Microorganisms in Apple Juice

ABSTRACT: A fast and easy-to-operate Fourier Transform Infrared (FTIR) spectrometry-based approach was developed for microbial differentiation and quantification in apple juice. Eight different microorganisms were evaluated: Enterobacter cloacae, Salmonella typhimurium, Enterobacteraerogenes, Salmonella choleraesuis, Serratia marcescens, Pseudomonas vulgaris, Vibrio cholerae , and Hafnia alvei . FTIR spectroscopy combined with chemometrics could differentiate the microorganisms studied at low concentration level of 10³ colony-forming units (CFU) /mL in apple juice. The chemometric models developed to count microorganisms in apple juice were validated by an independent test set consisting of 18 samples and correlated against plate counts satisfactorily up to a detection limit of 10³ CFU/mL.     

EXAMINATION OF THE MICROBIAL STATUS OF SELECTED INDIGENOUS FERMENTED FOODS IN NIGERIA

Four Nigerian traditionally fermented foods (wara, nono, ogi and kununzaki) were evaluated for the presence of some microorganisms of public health concern. Among the dairy foods , Staphylococcus aureus and Klebsiella sp. were isolated from wara while Escherichia coli, Salmonella sp. and Klebsiella sp. were isolated from nono. The cereal-based fermented foods (ogi and kunu-zaki) contained Bacillus subtilis, E. coli, S. aureus, Klebsiella sp. and Enterococcus faecalis. The mesophilic aerobic counts were: 5 × 10⁵ for wara; nono, 1.53 × 10⁷; ogi, 3.6 × 10⁶ and kunu-zaki, 2.6 × 10⁶ cfu/mL. The enterobacteriaceae counts on nono, wara, ogi and kunu-zaki were 1.79 × 10⁷, 4.5 × 10⁵, 4.0 × 10⁵ and 1.2 × 10⁶ cfu/mL, respectively. No Vibrio count (detection limit: <10 cfu/mL) was recorded in all the food samples considered. The yeast and mold counts ranged from 1.0 × 10⁵– 3.31 × 10⁷ among the food products. The antimicrobial susceptibility patterns of the organisms isolated from dairy products (nono and wara) revealed that they were resistant to ampicillin (100%) and sensitive to gentamicin (100%) and nalidixic acid (100%). Most isolates from cereal based products (ogi and kunu-zaki) were 100% resistant to penicillin, ampicillin and chloramphenicol. This work highlights the need to maintain hygienic standards in the preparation of our locally fermented cereal and dairy foods.     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.     

An Objective Evaluation of Changes in Firmness of Ripening Bananas Using a Sonic Technique

SUMMARY— Firmness in fruits is sometimes evaluated as being the force necessary to attain a given deformation within the product. Since modulus of elasticity is defined as the ratio of stress to strain, it should measure resistance to force and, hence, the firmness of a material. Using a sonic technique, the resonant frequencies of cylindrical specimens of flesh from Valery bananas were measured and Young's modulus of elasticity was calculated. Softening of the banana during ripening was associated with a decrease in Young's modulus of elasticity from 272 × 10⁵ dynes/cm² at ripeness corresponding to a light green peel color to 85 × 10⁵ dynes/cm² at the yellow stage. Modulus of elasticity was significantly and directly correlated with starch content, but inversely correlated with luminous reflectance and the logarithm of percent reducing sugars.