Recovery of heat-stressed E. coli O157:H7 from ground beef and survival of E. coli O157:H7 in refrigerated and frozen ground beef and in fermented sausage kept at 7°C and 22°C

A study was undertaken to obtain information on survival of Escherichia coli O157:H7 in ground beef subjected to heat treatment, refrigeration and freezing and on survival of E. coli O157:H7 in fermented sausage kept at 7°C and 22°C. For the challenge test, a mixture of E. coli O157:H7 strains (EH 321, EH 385, EH 302) was used and enumeration was performed on an isolation medium suitable for recovery of stressed organisms: modified Levine's eosin methylene blue agar (mEMB). Heat resistance of E. coli O157:H7 decreased after pre-incubation at a reduced temperature.Escherichia coli O157:H7 was more susceptible to heat inactivation after storage at 7°C and die-off was even more enhanced if cultures were frozen prior to heat inactivation. The enhanced reduction of the pathogen at 56°C after prior storage under refrigeration was confirmed in a test with inoculated ground beef.Escherichia coli O157:H7 was able to survive in ground beef at 7°C for 11 days and at −18°C for 35 days showing maximal one log reduction during the storage period. Thus, ground beef contaminated with E. coli O157:H7 will remain a hazard even if the ground beef is held at low or freezing temperatures. At both 7°C and 22°C, a gradual reduction of E. coli O157:H7 was noticed in fermented sausage over the 35 days storage period resulting in a 2 log decrease of the high inoculum (10⁶cfu 25 g⁻¹). For the low inoculum (10³cfu 25 g⁻¹) a 2·5 log reduction was obtained in 7 and 28 days storage at respectively 22 and 7°C. Application of good hygienic practices and implementation of HACCP in the beef industry are important tools in the control of E. coli O157:H7.     

Survival of Escherichia coli O157:H7 in dry fermented sausages containing micro-encapsulated probiotic lactic acid bacteria

Escherichia coli O157:H7 is capable of surviving the rigorous processing steps during the manufacture of dry fermented sausages. The effect of adding two probiotic organisms, Lactobacillus reuteri and Bifidobacterium longum as co-cultures with the meat starter cultures Pediococcus pentosaceus and Staphylococcus carnosus on the viability of E. coli O157:H7 in dry fermented sausages was studied. A 5 strain cocktail of E. coli O157:H7 was added at 7.4 log cfu/g to the sausage batter and challenged with either or both Lb. reuteri or B. longum before or after they were micro-encapsulated. Sausages were fermented at < or = 26 degrees C and 88% relative humidity (RH) followed by drying at 75% RH and 13 degrees C for 25 d. The pH, water activity (aw), protein, moisture, and numbers of all inoculated organisms were monitored during processing. The pH and aw decreased from 5.7 and 0.98 to 4.9 and 0.88 at the end of fermentation and drying, respectively. These processes reduced E. coli O157:H7 by 1.0 and 0.7 log cfu/g at the end of fermentation and drying, respectively. Unencapsulated Lb. reuteri with or without B. longum reduced E. coli O157:H7 by 3.0 log cfu/g and B. longum caused a 1.9 log cfu/g reduction. While micro-encapsulation increased survival of Lb. reuteri and B. longum, it reduced their inhibitory action against E. coli O157:H7.     

Growth and survival of Escherichia coli O157:H7 during the fermentation and storage of diluted cultured milk drink

The fate of various Escherichia coli O157:H7 strains including 933, A8993-C32, MF6707, 18731A, EK250 and EF304 during the fermentation and storage of diluted cultured milk drink fermented with Lactobacillus casei ssp.casei CCRC 11197 or L. delbrueckii ssp. bulgaricus CCRC 14009 were investigated in this study. E. coli O157:H7, regardless of strains, grew rapidly in skim milk and reached a maximum population of c. 8·0–9·0 log cfu ml⁻¹after c. 24 h of cultivation in mixed cultures with L. casei ssp. casei or L. delbrueckii ssp. bulgaricus. However, the population of E. coli O157:H7, depending on the strain and the lactic acid bacteria present, declined as cultivation proceeded further. With the inoculation of c. 5·0 log cfu ml⁻¹E. coli O157:H7, viable cells of this pathogen reduced to non-detectable level in the non-sugar-added cultured drink (pH 3·5) prepared with L. delbrueckii ssp.bulgaricus after one day storage at 7°C. Depending on the strains, E. coli O157:H7 survived in the non-sugar-added cultured drink prepared with L. casei ssp. casei for a period of <1–4 days. Adding sugar to cultured drink extended the survival period of E. coli O157:H7. The extent of the sugar-protective effect varied with different strains of E. coli O157:H7 and the amount of sugar added to the drink.     

Changes of microbiological quality in meatballs after heat treatment

The effects of different cooking processes (grilling, oven and microwave cooking) on the microbial flora of the raw meatballs inoculated with E. coli O157:H7 at the level 2×10⁴ cfu/ml were investigated. The meatballs were stored at 4 °C. The flora of the raw meatballs is described in this paper. While Salmonella was found in each sample, none of the samples contained C. perfringens or E. coli O157:H7. The processes of grill cooking or microwave cooking decreased the microbial flora by 2–3 log cycles. E. coli O157:H7 was completely destroyed by all cooking methods. E. coli O157:H7 count of the raw meatball samples increased for 1.5 log cycles at the end of storage compared to beginning.     

Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi

Acid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 °C) and commercial Amasi fermented at 30 °C for 24 h and stored at 7 °C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log₁₀ cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p ? 0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p ? 0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.     

Fate of Escherichia coli O157:H7 in field-inoculated lettuce

Impact of drip and overhead sprinkler irrigation on the persistence of attenuated Escherichia coli O157:H7 in the lettuce phyllosphere was investigated using a split-plot design in four field trials conducted in the Salinas Valley, California, between summer 2007 and fall 2009. Rifampicin-resistant attenuated E. coli O157:H7 ATCC 700728 (BLS1) was inoculated onto the soil beds after seeding with a backpack sprayer or onto 2- or 4-week-old lettuce plant foliage with a spray bottle at a level of 7 log CFU ml⁻¹. When E. coli O157:H7 was inoculated onto 2-week-old plants, the organism was recovered by enrichment in 1 of 120 or 0 of 240 plants at 21 or 28 days post-inoculation, respectively. For the four trials where inoculum was applied to 4-week-old plants, the population size of E. coli O157:H7 declined rapidly and by day 7, counts were near or below the limit of detection (10 cells per plant) for 82% or more of the samples. However, in 3 out 4 field trials E. coli O157:H7 was still detected in lettuce plants by enrichment 4-weeks post-inoculation. Neither drip nor overhead sprinkler irrigation consistently influenced the survival of E. coli O157:H7 on lettuce.     

Survival of Escherichia coli O157:H7 in cucumber fermentation brines

Abstract: Bacterial pathogens have been reported on fresh cucumbers and other vegetables used for commercial fermentation. The Food and Drug Administration currently has a 5‐log reduction standard for E. coli O157:H7 and other vegetative pathogens in acidified pickle products. For fermented vegetables, which are acid foods, there is little data documenting the conditions needed to kill acid resistant pathogens. To address this knowledge gap, we obtained 10 different cucumber fermentation brines at different stages of fermentation from 5 domestic commercial plants. Cucumber brines were used to represent vegetable fermentations because cabbage and other vegetables may have inhibitory compounds that may affect survival. The 5‐log reduction times for E. coli O157:H7 strains in the commercial brines were found to be positively correlated with brine pH, and ranged from 3 to 24 d for pH values of 3.2 to 4.6, respectively. In a laboratory cucumber juice medium that had been previously fermented with Lactobacillus plantarum or Leuconostoc mesenteroides (pH 3.9), a 5‐log reduction was achieved within 1 to 16 d depending on pH, acid concentration, and temperature. During competitive growth at 30 °C in the presence of L. plantarum or L. mesenteroides in cucumber juice, E. coli O157:H7 cell numbers were reduced to below the level of detection within 2 to 3 d. These data may be used to aid manufacturers of fermented vegetable products determine safe production practices based on fermentation pH and temperature. Practical Application: Disease causing strains of the bacterium E. coli may be present on fresh vegetables. Our investigation determined the time needed to kill E. coli in cucumber fermentation brines and how E. coli strains are killed in competition with naturally present lactic acid bacteria. Our results showed how brine pH and other brine conditions affected the killing of E. coli strains. These data can be used by producers of fermented vegetable products to help assure consumer safety.     

Acid and alcohol tolerance of Escherichia coli O157:H7 in pulque, a typical Mexican beverage

Pulque is a traditional Mexican fermented alcoholic beverage produced from the nectar of maguey agave plants. No data exist on the behavior of Escherichia coli O157:H7 in agave nectar and pulque. An initial trial was done of the behavior of E. coli O157:H7 during fermentation of nectar from a single producer, a nectar mixture from different producers and "seed" pulque. A second trial simulating artisanal pulque production was done by contaminating fresh nectar with a cocktail of three E. coli O157:H7 strains, storing at 16 ° and 22 °C for 14 h, adding seed pulque and fermenting until pulque was formed. A third trial used pulque from the second trial stored at 22 °C as seed to ferment fresh nectar at 22 °C for 48 h (fermentation cycle). This procedure was repeated for an additional two fermentation cycles. During incubation at 16 ° or 22 °C in the first trial, the E. coli O157:H7 strains multiplied in both the single producer nectar and nectar mixture, reaching maximum concentration at 12h. E. coli O157:H7 cell concentration then decreased slowly, although it survived at least 72 h in both fermented nectars. E. coli O157:H7 did not multiply in the seed pulque but did survive at least 72 h. In the second trial, the numbers of E. coli O157:H7 increased approximately 1.5 log CFU/ml at 22 °C and 1.2 log CFU/ml at 16 °C after 14 h. After seed pulque was added, E. coli O157:H7 concentration decreased to approximately 2 log CFU/ml, and then remained constant until pulque was produced. In the third trial, the E. coli O157:H7 cells multiplied and survived during at least three nectar fermentation cycles. The results suggest that E. coli O157:H7 can develop acid and alcohol tolerance in pulque, and constitutes a public health risk for pulque consumers.     

Efficacy of Slightly Acidic Electrolyzed Water and UV‐Ozonated Water Combination for Inactivating Escherichia Coli O157:H7 on Romaine and Iceberg Lettuce during Spray Washing Process

Spray washing is a common sanitizing method for the fresh produce industry. The purpose of this research was to investigate the antimicrobial effect of spraying slightly acidic electrolyzed water (SAEW) and a combination of ozonated water with ultraviolet (UV) in reducing Escherichia coli O157:H7 on romaine and iceberg lettuces. Both romaine and iceberg lettuces were spot inoculated with 100 μL of a 3 strain mixture of E. coli O157:H7 to achieve an inoculum of 6 log CFU/g on lettuce. A strong antimicrobial effect was observed for the UV‐ozonated water combination, which reduced the population of E. coli by 5 log CFU/g of E. coli O157:H7 on both lettuces. SAEW achieved about 5 log CFU/g reductions in the bacterial counts on romaine lettuce. However, less than 2.5 log CFU/g in the population of E. coli O157:H7 was reduced on iceberg lettuce. The difference may be due to bacteria aggregation near and within stomata for iceberg lettuce but not for romaine lettuce. The UV light treatment may stimulate the opening of the stomata for the UV‐ozonated water treatment and hence achieve better bacterial inactivation than the SAEW treatment for iceberg lettuce. Our results demonstrated that the combined treatment of SAEW and UV‐ozonated water in the spray washing process could more effectively reduce E. coli O157:H7 on lettuce, which in turn may help reduce incidences of E. coli O157:H7 outbreaks.     

A model study of Escherichia coli O157:H7 survival in fermented dry sausages--influence of inoculum preparation, inoculation procedure, and selected process parameters

The influence of inoculum preparation, inoculation level, and inoculation procedure on Escherichia coli O157:H7 inactivation during the manufacture of fermented sausage was evaluated in a model study. Prior growth in glucose-enriched tryptone soya broth, which provided exposure to mildly acidic conditions (pH 4.8), had no effect on the later survival of E. coli O157: H7 strains 5-1 and ATCC 43894 under extremely acidic conditions (pH 2), but the same strains became sensitive to acidity after 7 days of incubation on the surface of refrigerated beef (as per the normal contamination route from slaughter to further processing). In subsequent sausage production trials, the extent of destruction observed for E. coli O157:H7 strains F-90, 5-1, and ATCC 43894 inoculated directly into the meat batter was unchanged when the inoculation level was decreased from 7.3 to 4.7 log CFU/g, but the level of inactivation was ca. 1 log higher when the surfaces of beef cuts, rather than the batter, were inoculated 7 days prior to processing. Regardless of processing conditions (fermentation to a pH of < or = 5.0 at 24 or 37 degrees C, drying at 14 degrees C to a water activity [a(w)] value of 0.91 or 0.79), strains F-90, 5-1, and ATCC 43894 showed similar survival capacities during the manufacture of sausage. A approximately 2-log reduction in pathogen numbers was generally obtained after samples were dried to an a(w) of 0.91, irrespective of fermentation temperature. The addition of a 5-day predrying holding stage at the fermentation temperature significantly (P < 0.05) increased pathogen inactivation when fermentation was carried out at 37 degrees C (but not when it was carried out at 24 degrees C). However, significant pathogen reductions (4 to 5 log CFU/g) were achieved only for extensively dried products (a(w) = 0.79).     

Efficacy of Chlorine Dioxide, Ozone, and Thyme Essential Oil or a Sequential Washing in Killing Escherichia coli O157:H7 on Lettuce and Baby Carrots

Chlorine dioxide (ClO₂), ozone, and thyme essential oil has been found to be effective in reducing pathogens, including Escherichia coli O157:H7, on selected produce. The efficacy of these sanitizers was evaluated, alone or through their sequential washing to achieve a 3 or more log reduction of mixed strains of E. coli O157:H7 on shredded lettuce and baby carrots. Samples sprinkle inoculated with mixed strains of E. coli O157:H7 were air-dried for 1 h at 22±2°C in a biosafety cabinet, stored at 4°C for 24 h, and then treated with different concentrations of disinfectants and exposure time. Sterile deionized water washing resulted in approximately 1log reduction ofE. coli O157:H7 after 10 min washing of lettuce and baby carrots. Gaseous treatments resulted in higher log reductions in comparison to aqueous washing. However, decolorization of lettuce leaves was observed during long exposure time. A logarithmic reduction of 1.48-1.97log₁₀ cfu/g was obtained using aqueous ClO₂ (10.0 mg/L for 10 min) ozonated water (9.7 mg/L for 10 min) or thyme oil suspension (1.0 mL/L for 5 min) on lettuce and baby carrots. Of the three sequential washing treatments used in this study, thyme oil followed by aqueous ClO₂/ozonated water, or ozonated water/aqueous ClO₂ were significantly (P<0.05) more effective in reducing E. coli O157:H7 (3.75 and 3.99log, and 3.83 and 4.34 log reduction) on lettuce and baby carrots, respectively. The results obtained from this study indicate that sequential washing treatments could achieve 3-4log reduction of E. coli O157:H7 on shredded lettuce and baby carrots.     

Survival of Escherichia coli O157:H7 in dry sausage fermented by probiotic lactic acid bacteria

Probiotic Lactobacillus rhamnosus GG, L rhamnosus E‐97800, L rhamnosus LC‐705 and commercial Pediococcus pentosaceus were studied for their ability to inhibit the growth of Escherichia coli O157:H7 in dry sausage. The strains were able to produce technologically high‐quality dry sausage. The number of E coli O157:H7 decreased from approximately 5 to approximately 2 log cfu g⁻¹ It was concluded that the above‐mentioned strains and the commercial culture were equally effective in inhibiting E coli O157:H7. © 2000 Society of Chemical Industry     

Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

The fate of Listeria monocytogenes, Salmonella Typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on teewurst, a traditional raw and spreadable sausage of Germanic origin. Multi-strain cocktails of each pathogen (ca. 5.0 log CFU/g) were used to separately inoculate teewurst that was subsequently stored at 1.5, 4, 10, and 21 °C. When inoculated into commercially-prepared batter just prior to stuffing, in general, the higher the storage temperature, the greater the lethality. Depending on the storage temperature, pathogen levels in the batter decreased by 2.3 to 3.4, ca. 3.8, and 2.2 to 3.6 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, during storage for 30 days. When inoculated onto both the top and bottom faces of sliced commercially-prepared finished product, the results for all four temperatures showed a decrease of 0.9 to 1.4, 1.4 to 1.8, and 2.2 to 3.0 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, over the course of 21 days. With the possible exceptions for salt and carbohydrate levels, chemical analyses of teewurst purchased from five commercial manufacturers revealed only subtle differences in proximate composition for this product type. Our data establish that teewurst does not provide a favourable environment for the survival of E. coli O157:H7, S. Typhimurium, or L. monocytogenes inoculated either into or onto the product.     

CONDITIONS AFFECTING AUTOINDUCER‐2‐BASED QUORUM‐SENSING OF ESCHERICHIA COLI O157:H7 ON FRESH BEEF

ABSTRACT

This study evaluated whether inoculated (none, 1, 5 log colony‐forming units [cfu]/cm²) Escherichia coli O157:H7 would result in detection of autoinducer (AI)‐2‐like activity on beef. Inoculated fresh beef, containing low (LNB) or high (HNB) initial levels of natural flora, was analyzed for bacterial populations and AI‐2‐like activity during aerobic or vacuum‐packaged storage (4, 10, 25C). As expected, no growth of E. coli O157:H7 was detected at 4C, while at 10C, growth was detected only on LNB samples stored aerobically; AI‐2‐like activity was minimal (P ≥ 0.05) at both temperatures. E. coli O157:H7 showed more growth in LNB than HNB, and in aerobically than vacuum‐packaged samples inoculated with 1 log cfu/cm² of the pathogen during storage at 25C. AI‐2‐like activity was generally higher in LNB than HNB samples stored aerobically at 25C, while no significant AI‐2‐like activity was detected in samples stored in vacuum packages. The results indicated that E. coli O157:H7 may exhibit AI‐2‐like activity on aerobically stored beef in the presence of lower initial levels of natural flora, and at temperatures allowing prolific growth of the pathogen. Thus, AI‐2‐based quorum‐sensing of E. coli O157:H7 may not be of importance in beef stored at low temperatures.

PRACTICAL APPLICATIONS

This study presents evidence that Escherichia coli O157:H7 showed autoinducer (AI)‐2 activity and involved in quorum‐sensing on fresh beefcontaining low initial levels of natural flora during aerobic storage at abusive storage temperatures. Thus, AI‐2‐based quorum‐sensing of E. coli O157:H7 may not be important in beef stored at recommended low temperatures.     

Validation of a manufacturing process for fermented, semidry Turkish soudjouk to control Escherichia coli O157:H7

Two soudjouk batters were prepared from ground beef (20% fat) and nonmeat ingredients and inoculated with a five-strain mixture of Escherichia coli O157:H7 to yield an initial inoculum of 7.65 log10 CFU/g. One batter contained a commercial-starter culture mixture (approximately 8.0 log10 CFU/g) and dextrose (1.5%), while the other batter relied upon a natural fermentation with no added carbohydrate. Following mixing, sausage batters were held at 4 degrees C for 24 h prior to stuffing into natural beef round casings. Stuffed soudjouk sticks were fermented and dried at 24 degrees C with 90 to 95% relative humidity (RH) for 3 days and then at 22 degrees C with 80 to 85% RH until achieving a product moisture level of approximately 40%. After fermentation and drying with an airflow of 1 to 1.5 m/s, the sticks were either not cooked or cooked to an instantaneous internal temperature of 54.4 degrees C (130 degrees F) and held for 0, 30, or 60 min. The sticks were then vacuum packaged and stored at either 4 or 21 degrees C. For each of three trials, three sticks for each treatment/batter were analyzed for numbers of E. coli O157:H7 after inoculation, after fermentation, after cooking, and after storage for 7, 14, 21, and 28 days. Reductions in numbers of E. coli O157:H7 after fermentation and drying for sticks fermented by the starter culture (pH 4.6) and for sticks naturally fermented (pH 5.5) were 1.96 and 0.28 log10 CFU/g, respectively. However, cooking soudjouk sticks produced with a starter culture and holding at 54.4 degrees C for 0, 30, or 60 min reduced pathogen numbers from an initial level after fermentation and drying of 5.69 log10 CFU/g to below a detectable level by either direct plating (<1.0 log10 CFU/g) or by enrichment. In contrast, cooking soudjouk sticks produced without an added starter culture decreased pathogen numbers from an initial level after fermentation and drying of 7.37 to 5.65 log10 CFU/g (54.4 degrees C, no hold), 5.04 log10 CFU/g (54.4 degrees C, 30 min hold), and 4.67 log10 CFU/g (54.4 degrees C, 60 min hold). In general, numbers of E. coli O157:H7 within both groups of soudjouk sticks decreased faster during storage at 21 degrees C compared to 4 degrees C. After 28 days of storage, total reductions in pathogen numbers in soudjouk sticks produced using a starter culture but that were not subsequently cooked were 7.65 and 3.93 log10 CFU/g at 21 and 4 degrees C, respectively. For naturally fermented soudjouk, total reductions varied from 4.47 to 0.45 log10 CFU/g, depending on the cooking time and storage temperature. These data provide guidelines for manufacturers of dry sausage of ethnic origin, including soudjouk, to assess the safety of their processes for control of E. coli O157:H7.     

Behavior of Shiga-toxin-producing Escherichia coli in ewe milk stored at different temperatures and during the manufacture and ripening of a raw milk sheep cheese (Zamorano style)

This study was conducted to assess the survival of 2 wild Shiga toxin-producing Escherichia coli strains (one serotype O157:H7 and one non-O157:H7) in ewe milk stored at different conditions and to examine the fate of the O157 strain during the manufacture and ripening of a Spanish sheep hard variety of raw milk cheese (Zamorano). The strains were selected among a population of 50 isolates, which we obtained from ewe milk, because of their high resistance to 0.3% lactic acid. Both strains were inoculated (approximately 2 log₁₀ cfu/mL) in raw and heat-treated (low-temperature holding, LTH; 63°C/30 min) ewe milk and stored for 5 d at 6, 8, and 10°C and also according to a simulation approach for assessing the effects of failures in the cold chain. The minimum growth temperature for the O157:H7 strain in LTH and raw ewe milk was 8°C. For the non-O157:H7 strain, the lowest temperature showing bacterial growth in LTH ewe milk was 6°C, but it did not grow at any of the tested conditions in raw milk. It appears that the O157 strain was more susceptible to cold stress but was likely a better competitor than the non-O157 strain against the milk autochthonous microbiota. For manufacture of Zamorano cheese, raw milk was inoculated with approximately 3 log₁₀ cfu/mL, and after 2 mo of ripening at 10 to 12°C, the cheeses showed the expected general characteristics for this variety. The O157:H7 strain increased 0.9 log₁₀ cfu/g after whey drainage and during ripening and storage decreased by 2.9 log₁₀ cfu/g. Nevertheless, its detectable level (estimated at 6.2 cfu/g) after 2 mo of ripening suggests that Zamorano cheese manufactured from raw ewe milk contaminated with E. coli O157:H7 could represent a public health concern.     

Edible films containing carvacrol and cinnamaldehyde inactivate Escherichia coli O157:H7 on organic leafy greens in sealed plastic bags

The antimicrobial effects of apple-, carrot-, and hibiscus-based edible films containing carvacrol and cinnamaldehyde against Escherichia coli O157:H7 on organic leafy greens in sealed plastic bags were investigated. Fresh-cut Romaine and Iceberg lettuce, and mature and baby spinach leaves were inoculated with E. coli O157:H7 and placed into Ziploc® bags. Edible films were then added to the bags, which were stored at 4°C. The evaluation of samples taken at days 0, 3, and 7 showed that on all leafy greens, 3% carvacrol-containing films had the greatest effect against E. coli O157:H7, reducing the bacterial population by about 5 log CFU/g on day 0. All three types of 3% carvacrol-containing films reduced E. coli O157:H7 by about 5 log CFU/g at day 0. The 1.5% carvacrol-containing films reduced E. coli O157:H7 by 1–4 logs CFU/g at day 7. Films with 3% cinnamaldehyde showed reduction of 0.6–3 logs CFU/g on different leafy greens.     

Inhibitory effects of microencapsulated allyl isothiocyanate (AIT) against Escherichia coli O157:H7 in refrigerated, nitrogen packed, finely chopped beef

Allyl isothiocyanate (AIT) is an effective inhibitor of various pathogens, but its use in the food industry is limited by its volatility and pungency. The objective of this study was to overcome the volatility of AIT by microencapsulation and evaluate its antimicrobial effectiveness against Escherichia coli O157:H7 in chopped beef. Chopped beef was aseptically prepared and inoculated with a five-strain cocktail of E. coli O157:H7 to yield 4 or 8 log10 cfu/g. AIT was microencapsulated in gum acacia to yield 3.7-54.8 mg AIT/g at a ratio of 1:4 and freeze dried. Microcapsules at 5% or 10% (w/w) were then added to experimental samples that were packed under nitrogen, and stored at 4 degrees C for 18 days. Samples were analyzed for numbers of E. coli O157:H7 and the aerobic mesophilic bacteria (TAC) at 3-day intervals. AIT at 4980 ppm eliminated both low and high levels of inoculated E. coli O157:H7 after 15 and 18 days of storage, respectively. AIT at 2828 ppm reduced E. coli by 2.7 log10 cfu/g by 18 days of storage. AIT levels <1000 ppm were not more effective in reducing E. coli survival than the control treatment without AIT addition. AIT at 170-1480 ppm had negligible effects on the TAC, and while 4980 ppm kept TAC levels 相似文献   

Efficacy of various plant hydrosols as natural food sanitizers in reducing Escherichia coli O157:H7 and Salmonella Typhimurium on fresh cut carrots and apples

In the present study, inhibitory effects of the hydrosols of thyme, black cumin, sage, rosemary and bay leaf were investigated against Salmonella Typhimurium and Escherichia coli O157:H7 inoculated to apple and carrots (at the ratio of 5.81 and 5.81 log cfu/g for S. Typhimurium, and 5.90 and 5.70 log cfu/g for E. coli O157:H7 on to apple and carrot, respectively). After the inoculation of S. Typhimurium or E. coli O157:H7, shredded apple and carrot samples were washed with the hydrosols and sterile tap water (as control) for 0, 20, 40 and 60 min. While the sterile tap water was ineffective in reducing (P > 0.05) S. Typhimurium and E. coli O157:H7, 20 min hydrosol treatment caused a significant (P < 0.05) reduction compared to the control group. On the other hand, thyme and rosemary hydrosol treatments for 20 min produced a reduction of 1.42 and 1.33 log cfu/g respectively in the E. coli O157:H7 population on apples. Additional reductions were not always observed with increasing treatment time. Moreover, thyme hydrosol showed the highest antibacterial effect on both S. Typhimurium and E. coli O157:H7 counts. Inhibitory effect of thyme hydrosol on S. Typhimurium was higher than that for E. coli O157:H7. Bay leaf hydrosol treatments for 60 min reduced significantly (P < 0.05) E. coli O157:H7 population on apple and carrot samples. In conclusion, it was shown that plant hydrosols, especially thyme hydrosol, could be used as a convenient sanitizing agent during the washing of fresh-cut fruits and vegetables.     

Growth and survival of Escherichia coli O157:H7 during the manufacture and ripening of raw goat milk lactic cheeses

The behaviour of Escherichia coli O157:H7 was studied during the manufacture and ripening of raw goat milk lactic cheeses. Cheese was manufactured from raw milk in the laboratory and inoculated with E. coli O157:H7 to a final concentration of 10, 100 and 1000 cfu ml(-1). E. coli O157:H7 was counted by CT-SMAC (Mac Conkey Sorbitol Agar with cefixim and tellurite) and O157:H7 ID throughout the manufacturing and ripening processes. When the milk was inoculated with 10, 100 or 1000 cfu ml(-1), counts decreased to less than 1 log(10) g(-1) in curds just prior to moulding. However, viable E. coli O157:H7 were found in cheeses throughout processing, and even after 42 days of ripening. Results indicate that E. coli O157:H7 survives the lactic cheese manufacturing process. Thus, the presence of low numbers of E. coli O157:H7 in milk destined for the production of raw milk lactic cheeses can constitute a threat to the consumer.