Antimicrobial Wine Formulations Active Against the Foodborne Pathogens Escherichia coli O157: H7 and Salmonella enterica

ABSTRACT:  We developed wine formulations containing plant essential oils and oil compounds effective against foodborne pathogenic bacteria Escherichia coli O157:H7 and Salmonella enterica. HPLC was used to determine maximum solubility of antimicrobials in wines as well as amounts of antimicrobials extracted by wines from commercial oregano and thyme leaves. Activity of essential oils (cinnamon, lemongrass, oregano, and thyme) and oil compounds (carvacrol, cinnamaldehyde, citral, and thymol) in wines were evaluated in terms of the percentage of the sample that resulted in a 50% decrease in the number of bacteria (BA₅₀). The ranges of activities in wines (30 min BA₅₀ values) against S. enterica/E. coli were carvacrol, 0.0059 to 0.010/0.011 to 0.021; oregano oils, 0.0079 to 0.014/0.022 to 0.031; cinnamaldehyde, 0.030 to 0.051/0.098 to 0.13; citral, 0.033 to 0.038/0.060 to 0.070; lemongrass oil, 0.053 to 0.066/0.059 to 0.071; cinnamon oil 0.038 to 0.057/0.066 to 0.098; thymol, 0.0086 to 0.010/0.016 to 0.022; and thyme oil, 0.0097 to 0.011/0.033 to 0.039. Detailed studies with carvacrol, the main component of oregano oil, showed that antibacterial activity was greater against S. enterica than against E. coli and that wine formulations exhibited high activities at low concentrations of added antimicrobials. The results suggest that wines containing essential oils/oil compounds, added or extracted from oregano or thyme leaves, could be used to reduce pathogens in food and other environments.     

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 .     

APPLICATION OF CHLORINE TO REDUCE POPULATIONS OF ESCHERICHIA COLI ON BEEF

The effects of chlorine against 2 strains of E. coli attached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log ₁₀ CFU/cm ² E. coli bacteria were spray-treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, and E. coli populations enumerated. Spray treatments with water did significantly (P < 0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log ₁₀ CFU/cm ². Treatments with 500 and 800 ppm chlorine against E. coli ATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log ₁₀ CFU/cm ², respectively. At 800 ppm chlorine , E. coli O157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log ₁₀ CFU/cm ², whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of < 1 log ₁₀ CFU/cm ². Spray treatments with chlorine from sodium hypochlorite solutions reduced populations of E. coli, however, these reductions were not sufficient to completely inactivate the bacteria attached to red meat .     

Edible Apple Film Wraps Containing Plant Antimicrobials Inactivate Foodborne Pathogens on Meat and Poultry Products

ABSTRACT:  Apple-based edible films containing plant antimicrobials were evaluated for their activity against pathogenic bacteria on meat and poultry products.  Salmonella enterica  or  E. coli  O157:H7 (10⁷ CFU/g) cultures were surface inoculated on chicken breasts and  Listeria monocytogenes  (10⁶ CFU/g) on ham. The inoculated products were then wrapped with edible films containing 3 concentrations (0.5%, 1.5%, and 3%) of cinnamaldehyde or carvacrol. Following incubation at either 23 or 4 °C for 72 h, samples were stomached in buffered peptone water, diluted, and plated for enumeration of survivors. The antimicrobial films exhibited concentration-dependent activities against the pathogens tested. At 23 °C on chicken breasts, films with 3% antimicrobials showed the highest reductions (4.3 to 6.8 log CFU/g) of both  S. enterica  and  E. coli  O157:H7. Films with 1.5% and 0.5% antimicrobials showed 2.4 to 4.3 and 1.6 to 2.8 log reductions, respectively. At 4 °C, carvacrol exhibited greater activity than did cinnamaldehyde. Films with 3%, 1.5%, and 0.5% carvacrol reduced the bacterial populations by about 3, 1.6 to 3, and 0.8 to 1 logs, respectively. Films with 3% and 1.5% cinnamaldehyde induced 1.2 to 2.8 and 1.2 to 1.3 log reductions, respectively. For  L. monocytogenes  on ham, carvacrol films induced greater reductions than did cinnamaldehyde films at all concentrations tested. In general, the reduction of  L. monocytogenes  on ham at 23 °C was greater than at 4 °C. Added antimicrobials had minor effects on physical properties of the films. The results suggest that the food industry and consumers could use these films as wrappings to control surface contamination by foodborne pathogenic microorganisms.     

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 .     

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.     

EVALUATION OF BACTERIOLOGICAL QUALITY IN SELECTED COMMERCIAL INFANT FORMULAS AVAILABLE IN POLAND AND EGYPT

One hundred samples of commercial infant formula bought in shops in the Poznan region (Poland) and Cairo region (Egypt) were investigated. Samples were analyzed for aerobic plate counts (APC), total Bacillus cereus (TBC), and incidences of Bacillus spp. and coliforms. The mean APC and TBC did not show any important variation with country, being practically the same in products bought in Poland and Egypt. All commercial infant formula analyzed immediately after opening were of satisfactory bacteriological quality, exhibiting APC lower than 10⁴ CFU g⁻¹ (mean 4.9 × 10²) and TBC lower than 10³ CFU g⁻¹ (mean 1.1 × 10²). However, 60% of the examined fruit juice and ready-to-feed infant formula presented TBC above the recommendation safety limit after storage at 22C for 72 h and at 35C for 48 h. In most cases the mean log APC and TBC were highest (P > 0.05) for fruit juice and ready-to-feed infant formula stored at elevated temperature (35 ± 1C).     

Synergistic Effect of Electrolyzed Water and Citric Acid Against Bacillus Cereus Cells and Spores on Cereal Grains

ABSTRACT:  The effects of acidic electrolyzed water (AcEW), alkaline electrolyzed water (AlEW), 100 ppm sodium hypochlorite (NaClO), and 1% citric acid (CA) alone, and combinations of AcEW with 1% CA (AcEW + CA) and AlEW with 1% CA (AlEW + CA) against Bacillus cereus vegetative cells and spores was evaluated as a function of temperature (25, 30, 40, 50, or 60 °C) and dipping time (3 or 6 h). A 3-strain cocktail of Bacillus cereus cells or spores of approximately 10⁷ CFU/g was inoculated in various cereal grains (brown rice, Job's tear rice, glutinous rice, and barley rice). B . cereus vegetative cells and spores were more rapidly inactivated at 40 °C than at 25 °C. Regardless of the dipping time, all treatments reduced the numbers of B . cereus vegetative cells and spore by more than 1 log CFU/g, except the deionized water (DIW), which showed approximately 0.7 log reduction. The reductions of B . cereus cells increased with increasing dipping temperature (25 to 60 °C). B . cereus vegetative cells were much more sensitive to the combined treatments than spores. The effectiveness of the combined electrolyzed water (EW) and 1% CA was considerable in inhibiting B . cereus on cereal grains. The application of combined EW and CA for controlling B . cereus cells and spores on cereal grains has not been previously reported. Therefore, the synergistic effect of EW and CA may provide a valuable insight on reducing foodborne pathogens on fruits, vegetables, and cereal grains.     

Thermal Inactivation and Postthermal Treatment Growth during Storage of Multiple Salmonella Serotypes in Ground Beef as Affected by Sodium Lactate and Oregano Oil

ABSTRACT:  We assessed the heat resistance of  Salmonella  in raw ground beef in both the absence and presence of sodium lactate, oregano oil, and in combinations of these 2 GRAS-listed ingredients, and determined their bactericidal or bacteriostatic activities during postthermal treatment storage at 15 °C. A cocktail of 8 serotypes of  Salmonella  spp. was inoculated into ground beef supplemented with sodium lactate (NaL) (1.5% and 3%) and/or oregano oil (0.5% and 1%) to obtain approximately 8 log CFU/g. The ground beef samples (3 g) were vacuum-packed and heated at 60, 65, or 71 °C in a circulating water bath for selected times to inactivate approximately 5 to 6 log CFU/g of the pathogen, and then stored at 15 °C for 15 and 30 d. Results show that especially at the lower cooking temperatures, addition of oregano oil increased the inactivation rate of  Salmonella  spp., whereas addition of NaL alone exhibited a protective effect against lethality and decreased the rate. Addition of combinations of oregano oil and NaL overcame this protective effect. During subsequent posttreatment storage for 15 d,  Salmonella  populations in the controls and in samples containing 0.5% oregano (60 and 65 °C) or 1% oregano oil (60 °C) increased to 4.5 to 6 log CFU/g. The values for all other samples were at or near undetectable levels. Results from the 30-d storage study were similar. These findings indicate that lactate and oregano oil may be used to render  Salmonella  spp. more susceptible to the lethal effect of heat and to inhibit growth of  Salmonella  spp. that survive heat treatments.     

The survival of pathogenic bacteria in, and the microbial spoilage of, salads, containing meat, fish and vegetables

Summary. An investigation was carried out on the fate at 9° and 20°C of: (i) two types of non-spore-bearing bacteria, causing food-borne disease, viz. Staphylococcus aureus and Salmonella spp., and two spore-bearing entero-pathogens ( Clostridium perfringens and Bacillus cereus ); and (ii) Lactobacillaceae and yeasts in one type of meat and vegetable salad (pH = 4.2, acetic acid content 0.5%) and in one type of shrimp salad (pH = 5.3, acetic acid content 0.3%), preserved at two levels of benzoic acid plus sorbic acid. the pathogens were inoculated at initial densities of 10⁴-10⁹/g; for lactic acid bacteria and yeast reliance was placed on naturally occurring organisms.
The non-spore-bearing pathogens died out under all conditions, albeit much faster at 20°C. Spore-bearing cells of the Bacillaceae tested remained mostly dormant under the conditions of the tests. Lactobacillaceae developed fast, also at 9°C and eventually caused souring of the products. Yeasts appeared to play a role at 3°C only. the main antibacterial effect of the salads was demonstrated to be due to its vinegar content and pH.     

REMOVAL OF SALMONELLA TYPHIMURIUM ATTACHED TO CHICKEN SKIN BY RINSING WITH TRISODIUM PHOSPHATE SOLUTION: SCANNING ELECTRON MICROSCOPIC EXAMINATION

The effect of trisodium phosphate (TSP) on Salmonella typhimurium attached to chicken skin was investigated by using scanning electron microscopy (SEM). Chicken drumsticks were inoculated with Salmonella typhimurium (2 × 10⁸ CFU/mL) for 30 min. Both inoculated and non-inoculated drumsticks were rinsed with 10% TSP solution at 10 or 50C for 15 s, and skin pieces were cut and fixed for SEM examination. For inoculated skins, a significant difference was noticed between TSP-rinsed and control skins (water-rinsed) at both temperatures. While control skins were covered with salmonellae (4 × 10⁵∼ 1 × 10⁶ CFU/cm²) and miscellaneous debris, TSP-rinsed skins, either at 10 or 50C, showed clean skin surfaces (<8×10³ CFU/cm²). For non-inoculated skins, it was difficult to see the difference in the number of attached bacteria due to their low numbers, however, water-rinsed skins still showed the debris on the surface. Above observations suggest that one of the major mechanisms of TSP on salmonellae reduction is detachment of contaminants from the skin surface.     

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.     

Mechanism of inactivation of heat-tolerant spores of Bacillus stearothermophilus IFO 12550 by Rapid Decompression

The effect of three rapid decompression methods to clear the mechanism of inactivation of heat tolerant spores of Bacillus stearothermophilus IFO 12550 was investigated. Pressurization of the spores at 200 MPa and 75°C for 60 min caused a kill of 10⁴ CFU/mL by the link-motion system but the nonrotational rod valve and E.G. seal methods gave a kill of about 10³ CFU/mL. Sterilization was due to the physical breakdown of spore coat, and was induced by its physical permeability of water at high pressure and temperature. Rapid decompression by the link-motion system at 200 MPa decreased the D-value of the spores from 3000 min (100°C, one atmosphere) to 6 min, 11 min, and 17 min at 95, 85, and 75°C, respectively.     

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     

Portable Electronic Nose for Detection of Spoiling Alaska Pink Salmon (Oncorhynchus gorbuscha)

ABSTRACT:  The ability of a portable hand-held electronic nose (EN) in detecting spoilage of whole Alaska pink salmon ( Oncorhynchus gorbuscha ) stored at 14 °C and in slush ice (1 °C) was investigated. Fish were sampled daily at 14 °C for up to 3 d, while fish stored in slush ice were sampled at various intervals up to 16 d. Sensory evaluations indicated that fish were rejected at day 3 when stored at 14 °C and at day 12 when stored in slush ice. Aerobic bacteria counts for fish skin at 14 °C ranged from 3.4 log₁₀ colony-forming units (CFU)/cm² (day 0) to 4.8 log₁₀ CFU/cm² (day 3) and for fish stored in slush ice ranged from 3.4 log₁₀ CFU/cm² (day 0) to 5.5 log₁₀ CFU/cm² (day 16). The correct classification rate using forward stepwise general discriminate analysis was 85% and 92% for EN analysis of belly cavity volatiles for fish held at 14 °C and in slush ice, respectively. A predictive model may be developed for spoilage of whole Alaska pink salmon by analyzing belly cavity odors using the EN.     

Postharvest Microbiology of Farm-reared, Tropical Freshwater Prawn (Macrobrachium Rosenbergii)

ABSTRACT: The microbiological quality of farm-reared, tropical freshwater prawn ( Macrobrachium rosenbergii ) stored at 2 different temperatures was studied. The prawn muscle was found to have the initial bacterial load of 10⁴ cfu/g. The lactics and vibrios were in the range of 10² cfu/g, while the E. coli , aeromonads, staphylococci, anaerobes, and molds were in the level of 10¹ cfu/g. Salmonella and Vibrio cholerae were present in the prawn muscle. The prawn muscle held at room temperature (28 ± 2 °C) was organoleptically acceptable up to 8 h, when the bacterial load was more than 10⁶ cfu/g. However, the prawn muscle stored at freezer temperatures (−10 to −15 °C) was found to be in acceptable condition even after 30 d of storage and the bacterial load was fluctuating in the range of 10³ to 10⁴ cfu/g.     

Acidified Sodium Chlorite as an Alternative to Chlorine for Elimination of Salmonella on Alfalfa Seeds

ABSTRACT:  The health and environmental hazard associated with the use of chlorine for food processing has been documented previously. This study was conducted to determine if acidified sodium chlorite (ASC) could be used to replace calcium hypochlorite (Ca[OCl]₂) for disinfection of alfalfa seeds. Contaminated seeds containing approximately 1.5 × 10⁷ CFU/g of Salmonella were treated with ASC or Ca(OCl)₂ at different concentrations and for different periods of time. Results showed that the efficacy of ASC and Ca(OCl)₂ for elimination of Salmonella on contaminated seeds could be improved greatly by extending the treatment time from the traditional 15 to 45 min. Treatment of seeds with 800 ppm of ASC for 45 min reduced the number of Salmonella by 3.9 log units, approximately 1.2 log units higher than that treated with 20000 ppm of Ca(OCl)₂. Treatment of seeds with a lower concentration (100 to 400 ppm) of ASC for 45 min reduced the number of Salmonella by 1.3 to 2.2 log units. Soaking alfalfa seeds in 800 ppm of ASC for 45 min did not affect seed germination. However, soaking seeds in 20000 ppm of Ca(OCl)₂ for 45 min reduced seed germination by 20%. Unlike Ca(OCl)₂, antimicrobial efficiency of ASC was not affected by pre-exposure to alfalfa seeds. Data presented also showed that Salmonella on newly inoculated seeds that had been stored at 4 °C for less than 7 d were more sensitive to sanitizer treatment than those on seeds that had been stored for 4 wk or longer.     

Effect of irradiation and modified atmosphere packaging on the microbiological safety of minced pork stored under temperature abuse conditions

The safety of irradiated pork packed in 25% CO₂:75% N₂ and stored at abuse temperature (10 or 15°C) was assessed by inoculation studies involving Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica and Clostridium perfringens . Irradiation to a dose of 1.75 kGy reduced pathogen numbers to below the detection limit of 10² cells g^-1. When higher inoculum levels were used (10⁶ cells g^-1) irradiation at 1.75 kGy reduced pathogen numbers by 1 –>5 log₁₀ cycles depending on strain. Clostridium perfringens was the most resistant, and Y. enterocolitica the most sensitive of the pathogens studied.
In all cases when high numbers (10⁶ to 10⁷g^-1) of spoilage and/or pathogenic bacteria were present initially on the pork the meat appeared spoiled, and although irradiation reduced the number of microorganisms, the meat was still unacceptable from a sensory viewpoint after treatment.
It was concluded that the microbiological safety of irradiated, modified atmosphere packaged (MAP) pork is better than that of unirradiated MAP pork.     

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.     

Reduction of Streptococcus thermophilus in a whey protein isolate by low moisture extrusion cooking without loss of functional properties

A whey protein isolate powder (WPI) (4–5% water) inoculated with 5x10⁵ viable Streptococcus thermophilus per g, was continuously processed in a twin screw extruder under the following conditions (barrel length = 500 or 1000 mm; screw profile = forward transport and compression elements; moisture content during extrusion = 4–5%; feed rate = 10 kg h^-1; barrel temperature ( T_b ) = 80–204°C; speed of screw rotation = 50 r.p.m.). The minimum residence time determined by pulse injection of erythrosin was 20–25 s (500 mm barrel) or 35–40 s (1000 mm barrel).
Reduction values of viable Streptococcus thermophilus of 10^4.2-fold (500 mm barrel, T_b = 143°C) or 10^4.9-fold (1000 mm barrel, T_b = 133°C) were obtained without any modification of protein solubility or gelling properties. WPI extruded at the highest barrel temperatures (182–204°C) underwent limited browning and reduction of protein solubility. Gel permeation and hydrophobic interaction chromatography of the soluble constituents did not show any aggregates of β-lactoglobulin or α-lactalbumin.
Gels prepared from control or extruded WPI ( T_b 143°C with a barrel length = 500 mm or T_b 133°C with a barrel length = 1000 mm) were identical, as judged by scanning electron microscopy and rheological evaluations.