Fate of Escherichia coli O157: H7 in Chinese-Style Sausage During the Drying Step of the Manufacturing Process as Affected by the Drying Condition and Curing Agent

In this study, Chinese-style sausage was subjected to three different air-blast drying conditions commonly employed during the manufacturing process. The fate of Escherichia coli O157: H7 during the drying period was determined and compared. The effect of curing agents on the survival of E coli O157: H7 was also identified. Results showed that populations of E coli O157: H7 decreased ca 1.51 Log CFU g^-1 in sausage containing curing agents after a 6-h drying period at 50°C. However, the number of viable cells of E coli O157: H7 increased slightly in sausage without curing agents. When subjected to air-blast drying at 55°C for 6 h or at 55°C for 2·5 h and then 60°C for 3·5 h, a reduction in the number of viable cells of E coli O157: H7 was observed in sausage with or without curing agents. The reduction was more significant in sausage containing curing agents than in those without curing agents. No viable E coli O157: H7 was detected after 6 h of drying in samples containing curing agents, while the control samples still contained a viable E coli O157: H7 population of ca 2·65–4·36 Log CFU g^-1. After drying the sausage at 55°C for 4 h, inactivation of E coli O157: H7 increased in the presence of 30·00 g kg^-1 sodium chloride or 1·50 g kg^-1 sodium sorbate. On the other hand, the presence of 0·07–0·15 g kg^-1 sodium nitrite did not increase the inactivation of E coli O157: H7 compared to that in the control. © 1997 SCI.     

Behavior of Escherichia coli O157:H7 and Listeria monocytogenes in Tryptic soy broth subjected to various low temperature treatments

The inactivation and injury of Escherichia coli O157:H7 and Listeria monocytogenes in Tryptic soy broth stored at −5, −18 and −28°C were studied. Regardless of storage temperature, viable populations of E. coli O157:H7 and L. monocytogenes determined with TSA (uninjured and injured cells) or TSAB (uninjured cells), decreased as the storage time increased. However, the least surviving population of both test organisms was noted when stored at −18°C followed by those stored at −28 and −5°C. The viable populations of E. coli O157:H7 determined either with TSA or TSAB, was reduced most drastically during the first day of storage then decreased slowly thereafter. Viable populations of L. monocytogenes declined slightly and gradually during the entire storage period. Furthermore, E. coli O157:H7 was found more susceptible to the freezing storage than L. monocytogenes. After 21-day storage at −18°C, population reduction of E. coli O157:H7 determined with TSA was ca 1.72 log CFU/ml. On the other hand, a population reduction of only 0.64 log CFU/ml was noted with L. monocytogenes. Besides, the surviving population of E. coli O157:H7 contained a larger proportion of injured cells than L. monocytogenes.     

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.     

The fate of Escherichia coli O157 : H7 in Myzithra,Anthotyros, and Manouri whey cheeses during storage at 2 and 12°C

Myzithra, Anthotyros and Manouri whey cheeses were inoculated the day after production withEscherichia coli O157 : H7 at concentrations of approx. 1·8×10⁶cfu g⁻¹, and stored at 2 and 12°C for 30 and 20 days, respectively. The pH of the whey cheeses decreased from an initial value of approx. 6·20 to 5·83 or 5·60 (Myzithra) 5·75 or 5·20 (Anthotyros) and 5·80 or 5·30 (Manouri) by the end of the corresponding storage periods at 2 and 12°C, respectively. Escherichia coli O157 : H7 populations in the whey cheeses at the end of the 12°C storage period, had grown with an increase of approx. 1·3 log₁₀cfu g⁻¹. E. coli O157 : H7 populations in whey cheeses at the end of the 2°C storage period did not grow and decreased, with an approx. 2·5 log₁₀cfu g⁻¹reduction. Results showed that E. coli O157 : H7 can grow at 12°C and survive at 2°C storage in Myzithra, Anthotyros and Manouri whey cheeses, and therefore post-manufacturing contamination with this pathogen must be avoided by employing hygienic control programmes such as HACCP.     

Effectiveness of Active Packaging on Control of Escherichia Coli O157:H7 and Total Aerobic Bacteria on Iceberg Lettuce

Contaminated leafy green vegetables have been linked to several outbreaks of human gastrointestinal infections. Antimicrobial interventions that are adoptable by the fresh produce industry for control of pathogen contamination are in great demand. This study was undertaken to evaluate the efficacy of sustained active packaging on control of Escherichia coli O157:H7 and total aerobic bacteria on lettuce. Commercial Iceberg lettuce was inoculated with a 3‐strain mixture of E. coli O157:H7 at 10² or 10⁴ CFU/g. The contaminated lettuce and un‐inoculated controls were placed respectively in 5 different active packaging structures. Traditional, nonactive packaging structure was included as controls. Packaged lettuce was stored at 4, 10, or 22 °C for 3 wk and sampled weekly for the population of E. coli O157:H7 and total aerobic bacteria. Results showed that packaging structures with ClO₂ generator, CO₂ generator, or one of the O₂ scavengers effectively controlled the growth of E. coli O157:H7 and total aerobic bacteria under all storage conditions. Packaging structure with the ClO₂ generator was most effective and no E. coli O157:H7 was detected in samples packaged in this structure except for those that were inoculated with 4 log CFU/g of E. coli O157:H7 and stored at 22 °C. Packaging structures with an oxygen scavenger and the allyl isothiocyanate generator were mostly ineffective in control of the growth of the bacteria on Iceberg lettuce. The research suggests that some of the packaging structures evaluated in the study can be used to control the presence of foodborne pathogens on leafy green vegetables.     

Critical Factors Affecting the Destruction of Escherichia coli O157:H7 in Apple Cider Treated with Fumaric Acid and Sodium Benzoate

Destruction of Escherichia coli O157:H7 in apple cider treated with fumaric acid and sodium benzoate (0.15% and 0.05% w/v, respectively) was determined under pH and storage temperatures that commonly occur in apple cider. At 5°C storage, while destruction of E. coli O157:H7 in the presence of preservatives increased with time, there was little decline in E. coli O157:H7 populations in the absence of the preservatives. Increasing storage temperatures to 15°C and 25°C significantly increased the rate of destruction of E. coli O157:H7 in cider with the preservatives (P < 0.05). Increasing the pH of cider (from 3.2 to 4.7) decreased the rate of destruction of E. coli O157:H7.     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

Survival and detection of Escherichia coli O157:H7 and Listeria monocytogenes during the manufacture of dry sausage using two different starter cultures

A sausage batter (35% pork, 35% beef, 30% fat) was inoculated with high (5·46–5·68), medium (3·78–4·54) or low (2·30–2·60 log₁₀cfug⁻¹) levels of Escherichia coli O157:H7 and with high (5·05–5·41) or medium (2·92–3·35 log₁₀cfug⁻¹) levels of Listeria monocytogenes serovar 4b and fermented using starter cultures A (Staphylococcus xylosus DD-34 with bacteriocin-producingPediococcusacidilactici PA-2 and Lactobacillus bavaricus MI-401) and B(S. carnosus MIII withLb. curvatus Lb3). Sausages were manufactured (fermented and dried) in a smoke chamber at 17–23°C for 15 days and further stored at 15–17°C for 34 days. The numbers of E. coli O157:H7 decreased more using starter B than starter A (first experiment P<0·0015, second experiment P<0·0002) but the organism was not eliminated. Small numbers of E. coli O157:H7 were more often detected after enrichment for 18–24 h than for 6 h (P=0·0044) when tested after deep freezing. By contrast, L. monocytogenes decreased more rapidly in the high-inoculum sausages produced with starter A (P<0·0001) but no significant difference was detected between the starters in the medium-inoculum sausages. L. monocytogenes was eliminated from the medium-inoculum sausages after 49 days.     

Inactivation ofEscherichia coliO157:H7 by combinations of GRAS chemicals and temperature

Reported outbreaks of foodborne illness involvingEscherichia coliO157:H7 have increased in the United States during the last decade, with a variety of food products being implicated as vehicles of infection. Studies were carried out to determine the efficacy of combinations of various GRAS chemicals and moderate temperatures to killE. coliO157:H7. A five-strain mixture ofE. coliO157:H7 of approximately 10⁸cfu ml⁻¹was inoculated into 0·1% peptone solutions containing 1·0 or 1·5% lactic acid plus 0·1% hydrogen peroxide, 0·1% sodium benzoate or 0·005% glycerol monolaurate. The solutions were incubated at 8°C for 0, 15 and 30 min; at 22°C for 0, 10 and 20 min; or at 40°C for 0, 10 and 15 min; populations ofE. coliO157:H7 were determined at each sampling time. At 40°C, the pathogen was inactivated to undetectable levels within 10 min of incubation in the presence of 1·0 or 1·5% lactic acid plus hydrogen peroxide, and within 15 min of incubation in the presence of 1·5% lactic acid plus sodium benzoate or glycerol monolaurate. At 22°C, complete inactivation ofE. coliO157:H7 was observed after 20 min of exposure to 1·5% lactic acid plus 0·1% hydrogen peroxide, whereas a reduction of 5 log₁₀cfu ml⁻¹was observed with a treatment of 1·5% lactic acid plus glycerol monolaurate. None of the treatments resulted in total inactivation of the pathogen at 8°C. The aforementioned treatments could potentially be used to inactivate or reduceE. coliO157:H7 populations on raw produce.     

Survival and growth of foodborne pathogens in minimally processed vegetables at 4 and 15 °C

Abstract: We conducted this study to investigate the survival and growth of pathogens on fresh vegetables stored at 4 and 15 °C. Vegetables (romaine lettuce, iceberg lettuce, perilla leaves, and sprouts) were inoculated with 4 pathogens (Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli O157:H7) and stored at 2 different temperatures for different periods of time (3, 6, 9, 12, and 15 d at 4 °C and 1, 2, 3, 5, and 7 d at 15 °C). Populations of the 4 pathogens tended to increase on all vegetables stored at 15 °C for 7 d. Populations of E. coli O157:H7 and S. Typhimurium increased significantly, by approximately 2 log₁₀CFU/g, on loose and head lettuce stored at 15 °C for 1 d. No significant differences were observed in the growth of different pathogens on vegetables stored at 4 °C for 15 d. E. coli O157:H7 did not survive on sprouts stored at 15 or 4 °C. The survival and growth of food pathogens on fresh vegetables were very different depending on the pathogen type and storage temperature. Practical Application: Survivals and growth of pathogens on various vegetables at 4 and 15 °C were observed in this study. Survivals and growth of pathogens on vegetables were different depending on the pathogen type and storage temperature. Therefore, vegetables should be stored under refrigerated conditions (below 4 °C) prior to consumption. This recommendation may vary depending on the type of vegetable.     

Survival of Escherichia coli O157:H7 in Apple Cider as Affected by Dimethyl Dicarbonate, Sodium Bisulfite, and Sodium Benzoate

Survival of Escherichia coli O157:H7 in apple cider containing no preservatives, 0.025% dimethyl dicarbonate (DMDC), 0.045% sodium benzoate (SB), 0.0046% sodium bisulfite (NaS; 65.5% sulfur dioxide), or a combination of NaS and SB (NaS/SB) and stored at 4, 10, and 25°C was evaluated. E. coli O157:H7 survived for up to 18 days at 4,10, and 25°C in unpreserved apple cider. At 4 and 10°C, DMDC was most efficient at inactivating E. coli O157:H7, generally followed by NaS/SB SB, and NaS (p<0.05). E coli O157:H7 was more resistant to preservatives at 4°C than at 25°C (P < 0.05). E. coli O157:H7 was sublethally injured in cider containing preservatives, and to a lesser extent, in unpreserved cider. Generally, injury was more pronounced in cider containing DMDC, followed by NaS/SB, SB, and NaS (p<0.05).     

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.     

Survival ofEscherichia coliO157:H7,Listeria monocytogenesandSalmonella kentuckyin Norwegian fermented,dry sausage

Raw, newly produced sausages containing a mixed starter culture of lactobacilli and micrococci were each inoculated at separate locations (using a syringe) with low (10³–10⁴cfu) and high (10⁵–10⁷cfu) numbers of eitherEscherichia coliO157:H7, Listeria monocytogenes orSalmonella kentucky. Three identically prepared sausages were analysed at each sampling day during fermentation, maturation and storage at 4 and 20°C. In the low-inoculum samples, growth was observed initially (2 days) during fermentation forE. coliO157:H7 (3log₈increase in cfu) andL. monocytogenes(five-fold increase in cfu) but not forS. kentuckywhich decreased below the detection limit (150cfu sample^–1). None of the pathogens was detected after 5.5 months, neither at 4 nor 20°C. In the high-inoculum samples there was a decrease during fermentation and maturation for all the pathogens. After 5.5-months storage at 4°C, there was only about 90% reduction of the original inoculate ofL. monocytogenes, whereasE. coliO157:H7 survived at a low number (500cfu sample^–1) andS. kentuckydisappeared below the detection limit. After 5.5-months storage at 20°C, all the pathogens had disappeared below the detection limit. These results indicate that, from a safety point of view, it may be better to store these kinds of sausages at room temperature than in the cold, provided that the sensory qualities are retained and that similar results are obtained with other food pathogens.     

Determination of the effect of sodium lactate on the survival and heat resistance of Escherichia coli O157:H7 in two commercial beef patty formulations

The effect of 4% sodium lactate (NaL) in beefburger patty formulations on the survival and heat resistance of Escherichia coli O157:H7 was investigated. Fresh beef trimmings were inoculated with E. coli O157:H7 to a concentration of 6·0–7·0 log₁₀ cfu g⁻¹ and subjected to the processing stages of beefburger patty production. Two commercial beefburger patty formulations were produced: a ‘quality’ patty (100% beef) and an ‘economy’ patty (70% beef, 30% other ingredients, including onion, water, salt, seasoning, rusk and soya concentrate). Sodium lactate (4% w/v) was added to the beefburger patties during mincing and the formed patties were frozen and stored for 1 month. Beefburger patties without added NaL were used as controls. After frozen storage for 1 month, patties were examined for E. coli O157:H7 counts. There was a synergistic effect between freezing and NaL, which resulted in a small but significant reduction (P<0·05) (approximately 0·5 log₁₀ cfu g⁻¹) in E. coli O157:H7 numbers. The frozen beefburger patties were also heat-treated at 50, 55 and 60°C and the data analysed to derive D -values for E. coli O157:H7 cells. At each temperature treatment, theD -values of the quality and economy beefburger patties with 4% NaL were significantly lower (P<0·001) than the D -values of the patty formulations without NaL. The study demonstrates that the presence of 4% NaL in beefburger patty formulations can reduce the overall risks posed to consumers by the presence ofE. coli O157:H7 by, first; reducing pathogen survival during freezing and frozen storage of the uncooked product; and, second, by increasing the susceptibility of the pathogen to heat during normal cooking processes.     

Influence of gamma irradiation on growth and survival of Escherichia coli O157:H7 and quality of cig kofte, a traditional raw meat product

Cig kofte is a traditional Turkish food containing raw ground meat. Samples inoculated with Escherichia coli O157:H7 were irradiated at 0.5–6 kGy with a ⁶⁰Co source and stored at 4 and 25 °C. Total aerobic mesophilic count decreased with increasing irradiation doses, D₁₀ value was 0.83 kGy. Escherichia coli O157:H7 count decreased from 5.1 log₁₀ CFU g^?1 to an undetectable level (<1 log₁₀ CFU g^?1) after 1‐day storage at 4 °C following irradiation at 2 kGy, D₁₀‐value was 0.29 kGy. Irradiation doses up to 2 kGy did not affect sensory quality after 1 day. There was colour loss in samples irradiated at 2 kGy or above and stored for longer periods. Storage of the irradiated products at abused temperature must be avoided for safety assurance. Irradiation at 2 kGy has a great potential for extending the shelf‐life of cig kofte and assuring safety by decreasing the number of E. coli O157:H7 and other bacteria, but further studies with suitable package designs are needed to decrease quality degradation during extended storage.     

Thermal Inactivation of Escherichia coli O157:H7 in Cooked Turkey Products

Survival of Escherichia coli O157:H7 when heated in commercial-type turkey products was determined. Thermal death times (TDT) were determined at 52–60°C in ground turkey with no additives, 3% fat; ground turkey with no additives, 11% fat; turkey ham batter, 11% fat; turkey frank batter, 17% fat; and turkey sausage batter, 31% fat. Mean D₅₂-values ranged from 44.9 to 116 min; D₅₅-values from 6.63 to 39.4 min; D₅₇-values from 2.20 to 11.7 min; D₆₀-values from 0.68 to 5.86 min. At all temperatures, survival of E. coli O157:H7 was greater in formulated products than in turkey meat with no additives. Greatest survival occurred in the turkey frank batter. Using our z-value data, times to provide a 5 D kill of E. coli O157:H7 in turkey franks cooked at 60°C, 65.6°C, or 71°C would be 26, 3.1, or 0.37 min, respectively.     

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     

Survival of Escherichia coli O157:H7 during Manufacture and Storage of White Brined Cheese

Escherichia coli O157:H7 is a major foodborne pathogen that causes severe disease in humans. Survival of E. coli O157:H7 during processing and storage of white brined cheese was investigated. Cheeses were prepared using pasteurized milk inoculated with a 4 strain E. coli O157:H7 cocktail (7 log₁₀ CFU/g) with or without yogurt starter culture (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. thermophilus) and stored in 10% or 15% NaCl brine at 10 and 21 ºC for 28 d. NaCl concentration, water activity (a_w), pH, and numbers of E. coli O157:H7 and lactic acid bacteria (LAB) were determined in cheese and brine. E. coli O157:H7 was able to survive in cheese stored in both brines at 10 and 21 ºC regardless of the presence of starter LAB, although the latter significantly enhanced E. coli O157:H7 reduction in cheese or its brine at 10 ºC. E. coli O157:H7 numbers were reduced by 2.6 and 3.4 log₁₀ CFU/g in cheese stored in 10% and 15% NaCl brine, respectively, in the presence of starter LAB and by 1.4 and 2.3 log₁₀ CFU/g, respectively, in the absence of starter LAB at 10 ºC. The pathogen survived, but at lower numbers in the brines. The salt concentration of cheese stored in 10% brine remained about 5% during ripening, but in 15% brine, the NaCl level increased 1.6% to 8.1% (w/w) by 28 d. Values of pH and a_w slightly decreased 1 d after exposure to brine and reached 5.5 to 6.6 and 0.88 to 0.94, respectively, in all treatments.     

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.     

Plum Coatings of Lemongrass Oil‐incorporating Carnauba Wax‐based Nanoemulsion

Nanoemulsions containing lemongrass oil (LO) were developed for coating plums and the effects of the nanoemulsion coatings on the microbial safety and physicochemical storage qualities of plums during storage at 4 and 25 °C were investigated. The emulsions used for coating were produced by mixing a carnauba wax‐based solution (18%, w/w) with LO at various concentrations (0.5% to 4.0%, w/w) using dynamic high pressure processing at 172 MPa. The coatings were evaluated for their ability to inhibit the growth of Salmonella Typhimurium and Escherichia coli O157:H7 and their ability to preserve various physicochemical qualities of plums. Uniform and continuous coatings on plums, formed with stable emulsions, initially inhibited S. Typhimurium and E. coli O157:H7 by 0.2 to 2.8 and 0.8 to 2.7 log CFU/g, respectively, depending on the concentration of LO and the sequence of coating. The coatings did not significantly alter the flavor, fracturability, or glossiness of the plums. The antimicrobial effects of the coatings against S. Typhimurium and E. coli O157:H7 were demonstrated during storage at 4 and 25 °C. The coatings reduced weight loss and ethylene production by approximately 2 to 3 and 1.4 to 4.0 fold, respectively, and also retarded the changes in lightness and the concentration of phenolic compounds in plums during storage. The firmness of coated plums was generally higher than uncoated plums when stored at 4 °C and plum respiration rates were reduced during storage. Coatings containing nanoemulsions of LO have the potential to inhibit Salmonella and E. coli O157:H7 contamination of plums and may extend plum shelf life.