International Journal of Food Sciences and Nutrition Growth and survival of Escherichia coli O157:H7 in fresh tropical fruit juices at ambient and cold temperatures (original) (raw)
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International journal of food sciences and nutrition, 2005
The survival of Escherichia coli O157:H7 in acidic foods and its enhanced survival in refrigerated acid foods are well documented. This prompted the present study to evaluate the growth potential of E. coli O157:H7 in fresh tropical fruit juices. The pH of the various juices ranged between 3.57 (pineapple) and 6.2 (avocado). Samples were separately inoculated with a mixture of four E. coli O157:H7 strains at initial levels of approximately 10(3) cfu/ml, and stored at refrigeration (4 degrees C) and ambient (20-25 degrees C) temperatures for 120 h. In pineapple juice, some decline in count was noted during ambient temperature storage but complete inhibition was not observed. At refrigeration temperature, the test strains survived without a noticeable decline in number. The pH remained unchanged throughout the experiment at both incubation temperatures. In papaya and avocado juices, counts of the test strains increased at varying rates at both storage temperatures. A decrease in pH wa...
International Journal of Food Sciences and Nutrition
The survival of Escherichia coli O157:H7 in acidic foods and its enhanced survival in refrigerated acid foods are well documented. This prompted the present study to evaluate the growth potential of E. coli O157:H7 in fresh tropical fruit juices. The pH of the various juices ranged between 3.57 (pineapple) and 6.2 (avocado). Samples were separately inoculated with a mixture of four E. coli O157:H7 strains at initial levels of approximately 10 3 cfu/ml, and stored at refrigeration (48C) and ambient (20 Á/258C) temperatures for 120 h. In pineapple juice, some decline in count was noted during ambient temperature storage but complete inhibition was not observed. At refrigeration temperature, the test strains survived without a noticeable decline in number. The pH remained unchanged throughout the experiment at both incubation temperatures. In papaya and avocado juices, counts of the test strains increased at varying rates at both storage temperatures. A decrease in pH was also noted in the stored juice. This study demonstrated that E. coli O157:H7 can survive well in acidic pineapple juice at both incubation temperatures and could also grow luxuriously in fruit juices with relatively higher pH values ( /5.7) when stored at ambient and refrigeration temperatures.
Journal of Food Protection, 2001
The adaptation of Escherichia coli O157:H7 cells to acid conditions has been reported. This study showed the behavior of three strains of E. coli O157:H7 in two different physiological stages (acid shocked and control cells), inoculated in five fruit pulps stored at 4°C for up to 30 days. The three strains of E. coli O157:H7 inoculated in grape pulp could be recovered up to day 30. E. coli O157:H7 strains survived for 4 days in all fruit pulps tested with different pH values (2.51 to 3.26), with the exception of acid-shocked cells of E. coli O157:H7 strain 933, which did not survive in “cajá” (Spodias lutea L.) pulp. The results clearly indicated that acid resistance can persist for long periods during storage at 4°C. The protection conferred by acid adaptation suggests that acid-resistant organisms will be better equipped to outlast these acid challenges. The survival of E. coli O157:H7 in fruit pulps with a low pH, stored under refrigeration, is of extreme importance due to the hi...
Survival of Escherichia coli O157:H7 during the Manufacture and Storage of Fruit Yogurt
Journal of Food Safety, 2013
The objectives of the study were to assess the behavior of Escherichia coli O157:H7 during the manufacture of fruit yogurt at different fermentation and storage temperatures. Reconstituted milk was fermented at 37, 40 or 45C; the resultant product was stored at 4, 10 or 15C for 7 days. Samples of milk and yogurt were analyzed. E. coli O157:H7 and lactic acid bacteria (LAB) counts; pH of samples was recorded. During fermentation, E. coli O157:H7 grew in the presence or absence of LAB regardless of temperature. E. coli O157:H7 increased in presence of thermophilic LAB more than 2.75 log cfu/mL. The growth of LAB in all samples showed the same trend. The pH values of milk containing E. coli O157:H7 and LAB decreased gradually to reach 4.6 Ϯ 0.1 at the end of fermentation period. During cooling, there was neither growth nor death of E. coli O157:H7 at 4 and 10C, while a slight increase at 15C. All the experiments showed significant differences in the population of E. coli O157:H7 in the presence or absence of LAB. During storage, E. coli O157:H7 number declined for all experiments and approached undetectable levels at the end of storage. The sensitivity of E. coli O157:H7 to acidity and lowered temperature was noticed during storage. PRACTICAL APPLICATIONS Escherichia coli O157:H7 has emerged as a major foodborne pathogen and has been implicated in several outbreaks involving milk and dairy products. The results of the present study indicate that E. coli cannot tolerate the acidity and storage temperature. Applying quality control systems in the processing line will ensure that the E.coli will not survive in the commercially prepared fruit yogurt.
Journal of Food Protection, 2014
Numerous outbreaks involving fresh juices contaminated with Escherichia coli O157:H7 have occurred in the United States and around the world, raising concern for the safety of these products. Until now, only a few studies regarding the thermal tolerance of this pathogen in acidic juices over a wide range of pH values have been published. Therefore, the effect of varying the pH with different organic acids on the thermal inactivation of non–acid-adapted and acid-adapted E. coli O157:H7 (strain C7927) was determined. The decimal reduction times (D-values) and the change in temperature required for the thermal destruction curve to traverse 1 log cycle (z-values) were calculated for non–acid-adapted E. coli in an apple-carrot juice blend (80:20) adjusted to three pH values (3.3, 3.5, and 3.7) by the addition of lactic, malic, or acetic acid and at a pH of 4.5 adjusted with NaOH. Thermal parameters were also determined for acid-adapted cells in juices acidified with malic acid. The effec...
Food Microbiology, 2000
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 71 after 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 71 E. 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 78C. 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 51^4 days. Adding sugar to cultured drink extended the survival period of E. coli O157:H7. The extent of the sugar-protective e¡ect varied with di¡erent strains of E. coli O157:H7 and the amount of sugar added to the drink.
Behavior of Escherichia coli O157:H7 in tomato and processed tomato products
Food Research International, 2003
The survival of E. coli O157:H7 in acid foods for weeks and its prolonged survival in refrigerated acid foods are well documented. This prompted the study to evaluate survival of E. coli O157:H7 in tomato and processed tomato products. The pH of the various products ranged from 4.2 to 4.8 and some products contained preservatives such as vinegar. Samples were separately inoculated with a mixture of four E. coli O157:H7 strains previously isolated from hamburger meat at lower and higher initial inoculum levels, incubated at 4 and 25 C and assayed for survival at regular intervals. In fresh whole tomato, growth was detected until day 4 and complete elimination was observed at day 7 at room temperature incubation. At refrigeration temperature, counts decreased slightly but survival was noted until day 10. In processed whole tomato, similar patterns were seen at room temperature incubation, but elimination was not observed until day 16. At refrigeration temperatures counts at day 16 were higher than the initial inoculum level. In processed tomato juice, the test strains kept on growing for over 20 days at room temperature storage, whereas at refrigeration temperature, the initial number was more or less maintained until day 23. In processed tomato sauce, incubated at room temperature, a sharp decline in number until day 6 was followed by a sharp increase in number until day 16. At refrigeration temperature, the test strain survived until day 16 with slight decrease in number. The test strains were eliminated in ketchup within 2 days at room temperature, whereas elimination was not achieved until day 8 at refrigeration temperature. In pasta sauce and snack sauce, although elimination was observed at days 11 and 7, respectively, at room temperature incubation, the test strains survived for about 22 days at refrigeration temperature without much decrease in count. Patterns were similar at higher levels of initial inoculation, but it took longer to achieve elimination of the test strains. This study demonstrated that E. coli O157:H7 can survive markedly in various tomato products, and the survival is notably prolonged at refrigeration temperatures.
Journal of Food Protection, 2011
The purpose of the present study was to determine the heat resistance of six non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes in comparison to E. coli O157:H7 in single-strength apple juice without pulp. The thermal parameters for stationary-phase and acid-adapted cells of E. coli strains from serogroups O26, O45, O103, O111, O121, O145, and O157:H7 were determined by using an immersed coil apparatus. The most heat-sensitive serotype in the present study was O26. Stationaryphase cells for serotypes O145, O121, and O45 had the highest D 56uC -value among the six non-O157 serotypes studied, although all were significantly lower (P , 0.05) than that of E. coli O157:H7. At 60uC E. coli O157:H7 and O103 demonstrated the highest D-values (1.37 ¡ 0.23 and 1.07 ¡ 0.03 min, respectively). The D 62uC for the most heat-resistant strain belonging to the serotype O145 was similar (P . 0.05) to that for the most resistant O157:H7 strain (0.61 ¡ 0.17 and 0.60 ¡ 0.09 min, respectively). The heat resistance for stationary-phase cells was generally equal to or higher than that of acid-adapted counterparts. Although E. coli O157:H7 revealed D-values similar to or higher than the individual six non-O157 STEC serotypes in apple juice, the z-values for most non-O157 STEC tested strains were greater than those of E. coli O157:H7. When data were used to calculate heat resistance parameters at a temperature recommended in U.S. Food and Drug Administration guidance to industry, the D 71.1uC for E. coli O157:H7 and non-O157 STEC serotypes were not significantly different (P . 0.05).
Food Science and Nutrition, 2019
Chlorine‐based solutions are commonly used to sanitize orange fruits prior to juice extraction. We used flow cytometry (FCM) to investigate the physiology of Escherichia coli following its subjection to chlorine‐based solutions and alternative sanitizing agents (H2O2 and organic acids). Green fluorescent protein (GFP)‐generating E. coli K‐12 were washed with 50–200 ppm available chlorine (AC), 1%–5% H2O2, 2%–4% citric acid, 4% acetic acid, or 4% lactic acid, after which they were added to 1.2 μm filtered orange juice (OJ). Cell physiology was investigated with FCM during storage at 4°C, and culturability was determined using plate counting. Analysis of GFP fluorescence allowed estimation of intracellular pH (pHi). FCM results demonstrated an inverse relationship between the concentration of AC or H2O2 and cellular health in OJ. Higher concentrations of sanitizer also resulted in a significantly greater number of viable but nonculturable (VBNC) cells. Real‐time FCM showed that supplementation of AC with 2% citric acid, but not with 100 ppm of Tween‐80, led to a significant reduction in pHi of the cells incubated in OJ, and that the majority of the reduction in pHi occurred during the first 2 min of incubation in OJ. Organic acids were found to be more effective than both AC and H2O2 in reducing the pHi, viability, and culturability of the cells in OJ. The results confirmed the hypothesis that consecutive subjection of E. coli to maximum legally permitted concentrations of sanitizers and OJ induces the VBNC state. Furthermore, we demonstrate successful application of FCM for monitoring the efficacy of washing procedures.