Survival of Escherichia coli O157:H7 during manufacture and storage of traditional and low lactose yogurt (original) (raw)
Related papers
Ciência Animal Brasileira
The purpose of this study was to evaluate the behavior of E. coli O157:H7 during lactose hydrolysis and fermentation of traditional and low lactose yogurt. It also aimed to verify E. coli O157:H7 survival after 12 h of storage at 4 ºC ±1 ºC. Two different types of yogurts were prepared, two with whole milk and two with pre-hydrolyzed whole milk; in both groups one yogurt was inoculated with E. coli O157:H7 and the other one was not inoculated. The survival of E. coli and pH of yogurt were determined during fermentation and after 12-h refrigeration. The results showed that E. coli O157:H7 was able to grow during the fermentation period (from 4.34 log CFU.mL-1 to 6.13 log CFU.mL-1 in traditional yogurt and 4.34 log CFU.mL-1 to 6.16 log CFU.mL-1 in low lactose yogurt). The samples with E. coli O157:H7 showed gas formation and syneresis. Thus, E. coli O157:H7 was able to survive and grow during fermentation of traditional and low lactose yogurts affecting the manufacture technology. Mor...
Survival of Escherichia coli O157 : H7 in yoghurt during preparation and storage at 4oC
Letters in Applied Microbiology, 1997
S . M AS S A, C. A LT IE R I, V. Q UA RA N TA AN D R. DE P AC E. 1997. Cow's milk was inoculated with ca 10 3 and 10 7 cfu ml −1 Escherichia coli O157 : H7. After fermentation at 42°C for 0-5 h, the yoghurt was stored at 4°C. Two kinds of yoghurt were used : traditional yoghurt (TY), made with Streptococcus thermophilus and Lactobacillus bulgaricus starter cultures, and 'bifido' yoghurt (BY), made with the two starter cultures plus Bifidobacterium bifidum. After 7 d E. coli O157 : H7 decreased from 3·52 to 2·72 log 10 cfu ml −1 and from 7·08 to 5·32 log 10 cfu ml −1 in TY, and from 3·49 to 2·73 log 10 cfu ml −1 and from 7·38 to 5·41 log 10 cfu ml −1 in BY. The pH values of yoghurt dropped from 6·6 to 4·5 and 4·4 in TY (for low and high pathogen inocula, respectively), and from 6·6 to 4·6 and 4·5 in BY (for low and high pathogen inocula, respectively).
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.
Survival of Escherichia coli O157:H7 in traditional African yoghurt fermentation
International Journal of Food Microbiology, 2002
Growth and survival of a nontoxigenic strain of Escherichia coli O157:H7 (ATCC 43888) was determined in traditionally fermented pasteurized milk. Preheated milk was inoculated with 1% (v/v) of a mixed culture of Lactobacillus delbrueckii ssp. bulgaricus (NCIMB 11778) and Streptococcus salivarius ssp. thermophilus (NCIMB 110368) and incubated at 25, 30, 37 or 43 jC for 24 h. E. coli O157:H7 (10 5 CFU/ml) were introduced into the milk pre-and post-fermentation. Fermented milk samples were subsequently stored at either 4 jC (refrigerator temperature) or 25 jC (to mimic African ambient temperature) for 5 days. After 24 h of fermentation, the pH of the samples fermented at the higher temperatures of 37-43 jC decreased from 6.8 to 4.4-4.0 (F 0.2) whereas at the lower temperature of 25 jC, the pH decreased to pH 5.0 F 0.1. During this period, viable counts for E. coli O157:H7 increased from 10 5 to 10 8-10 9 CFU/ml except in milk fermented at 43 jC wherein viability declined to 10 4 CFU/ml. In fermented (25-30 jC) milk stored at 4 jC for 5 days, E. coli O157:H7 viability decreased from 10 8-9 to 10 6-7 CFU/ml whereas milk fermented at 43 jC resulted in loss of detectable cells. In contrast, storage of fermented milk samples at 25 jC for 5 days eventually resulted in complete loss of viability irrespective of fermentation temperature. Stationary phase E. coli O157:H7 inoculated post-fermentation (25 and 43 jC) survived during 4 jC storage, but not 25 jC storage. Fermentation temperature and subsequent storage temperature are critical to the growth and survival of E. coli O157:H7 in traditional fermented products involving yoghurt starter cultures.
ISRN Microbiology (Print), 2013
The purpose of this study was to determine the viability of Mycobacterium avium subsp. paratuberculosis (MAP), Escherichia coli (E. coli), and Salmonella Enteritidis (S. Enteritidis) during preparation and refrigerated storage of yogurt. Three yogurts were prepared using pasteurized commercial milk. Each yogurt was artificially contaminated with (1) MAP, (2) E. coli + S. Enteritidis, and (3) MAP + E. coli + S. Enteritidis. Samples were taken during and after the fermentation process until day 20 after inoculation. MAP was not detected during their preparation and short-term storage but was recuperated after starting at 180 min after inoculation storage. Live bacterial counts of E. coli, and S. Enteritidis increased during the first 24 hours, followed by a slight decrease towards the end of the study. In this study it was shown how MAP, E. coli, and S. Enteritidis resisted the acidic conditions generated during the preparation of yogurt and low storage temperatures. This work contributes to current knowledge regarding survival of MAP, E. coli, and S. Enteritidis during preparation and refrigerated storage of yogurt and emphasizes the need to improve hygiene measures to ensure the absence of these pathogenic microorganisms in dairy products.
Survival and detection of coliforms, Enterobacteriaceae, and gram-negative bacteria in Greek yogurt
Journal of Dairy Science, 2017
Despite the widespread use of coliforms as indicator bacteria, increasing evidence suggests that the Enterobacteriaceae (EB) and total gram-negative groups more accurately reflect the hygienic status of high-temperature, short-time pasteurized milk and processing environments. If introduced into milk as postpasteurization contamination, these bacteria may grow to high levels and produce a wide range of sensory-related defects. However, limited information is available on the use and survival of bacterial hygiene indicators in dairy products outside of pasteurized fluid milk and cheese. The goal of this study was to (1) provide information on the survival of a diverse set of bacterial hygiene indicators in the low pH environment of Greek yogurt, (2) compare traditional and alternative detection methods for their ability to detect bacterial hygiene indicators in Greek yogurt, and (3) offer insight into optimal hygiene indicator groups for use in low-pH fermented dairy products. To this end, we screened 64 bacterial isolates, representing 24 dairy-relevant genera, for survival and detection in Greek yogurt using 5 testing methods. Before testing, isolates were inoculated into plain, 0% fat Greek yogurt (pH 4.35 to 4.65), followed by a 12-h hold period at 4 ± 1°C. Yogurts were subsequently tested using Coliform Petrifilm (3M, St. Paul, MN) to detect coliforms; Enterobacteriaceae Petrifilm (3M), violet red bile glucose agar and the D-Count (bioMérieux, Marcy-l'Étoile, France) to detect EB; and crystal violet tetrazolium agar (CVTA) to detect total gram-negative bacteria. Overall, the non-EB gram-negative isolates showed significantly larger log reductions 12 h after inoculation into Greek yogurt (based on bacterial numbers recovered on CVTA) compared with the coliform and noncoliform EB isolates tested. The methods evaluated varied in their ability to detect different microbial hygiene indicators in Greek yogurt. Crystal violet tetrazolium agar detected the highest portion of coliforms, whereas EB Petrifilm detected the highest portion of EB, as well as highest portion of total gram-negative bacteria. Additionally, the D-Count method allowed for faster detection of EB in yogurt by generating results in approximately 13 h rather than the 24 h required when using EB Petrifilm and violet red bile glucose agar. Results from this study indicate that the coliform and EB groups encompass a broad range of dairy-relevant gram-negative bacteria with the ability to survive in Greek yogurt, supporting their use as microbial hygiene indicator groups in low-pH fermented dairy products.
The American journal of clinical nutrition, 1991
Lactose in yogurt with live bacteria is better tolerated than lactose in other dairy foods, partly because of the activity of microbial beta-galactosidase (beta-gal), which digests lactose in vivo. To evaluate the ability of different strains and species of lactic acid bacteria to digest lactose in vivo, yogurts (containing mixtures of strains of Streptococcus salivarius subsp thermophilus and Lactobacillus delbrueckii subsp bulgaricus) and fermented milks (containing individual species of S thermophilus, L bulgaricus, L acidophilus, or Bifidobacterium bifidus) that varied in microbial beta-gal activity were produced. Selected products were fed to healthy people who cannot digest lactose, and breath hydrogen production was monitored. All yogurts dramatically and similarly improved lactose digestion, regardless of their total or specific beta-gal activity. The response to fermented milks varied from marginal improvement with B bifidus milk to nearly complete lactose digestion with L ...
International Journal of Food Engineering and Technology
E. coli and L. monocytogenes are all dairy product related pathogens. The presence of these pathogens can lead to contamination. To increase the shelf life of yogurt we have to monitor the temperature at which it is stored, the change in microbial counts, pH, acidity, sensory attributes and percentage of free whey. Adaptation Test Acid demonstrates that the microorganisms such as Salmonella spp., E. coli, and L. monocytogenes are frequently identified to have a higher survival rate in meals when compared with non-adopted ones. When they are exposed to unfavorable growth circumstances such as severely acidic environments. In this study, we evaluated the survival of wild and adapted L. monocytogenes strains, inoculated at the same concentration around 4 log cfu/g; a slow decrease in the loads was observed until d 28 in unflavored inoculated with the wild strain. Three different experiments are performed on yogurt to evaluate the difference between flavored and unflavored yogurt, shelf life of them at different temperatures and to determine the role of E. coli and Listeria monocytogenes and see what changes it brings to the composition of yogurt. First trial is performed at three different temperatures. These are at 4, 8 and 20°C. Both flavored and unflavored yogurt sample showed low viable counts at 4°C until the end of trial. While performing this trial at 4°C the loads are lower in strawberry yogurts as compared to that of unflavored yogurt because potassium sorbate is present in fruit pure and anti-microbial activity is exerted by that. In second trial, E. coli and Listeria monocytogenes are added to the yogurt sample at two concentrations which 2 and 5 log cfu/g which will show a rapid decrease in acidic conditions in both flavored and unflavored yogurt samples. Listeria monocytogenes is very resistant in this case and presence of it can always be seen until the end period. In the third trial, the adaption of the yogurt sample is monitored after the inoculation of microorganisms in it. Between the wild acid adapted strains of L. monocytogenes no statistically significant difference is detected and that must be because to the quick adaption after the inoculation. Pasteurization is one of the main processes which are used to make the dairy products pathogen free and the basic functioning of it is through temperature and discussed in the paper.
This study aimed to isolate Lactobacillus species from yoghurt and to evaluate its antimicrobial activity against enterohemorrhagic Escherichia coli O157:H7. After incubation of different yoghurt samples in MRS (de Man, Rogosa and Sharpe) agar at 37C under anaerobic conditions, four Lactobacillus species, L. casei, L. acidophilus, L. helveticus and L. delbrueckii ssp. bulgaricus were identified. Standard growth curves of E. coli O157:H7 in proximity with lactobacilli test strains were obtained. The antibacterial effects of lactobacilli cell debris and culture superna-tant against E. coli O157:H7 were determined. The results showed that the anti-bacterial effects of culture supernatant were stable at different temperature conditions (56–100C) for 30 and 60 min; also, it was stable at pH 3–10. With regard to the antibacterial effect of the lactobacilli strains in this study, they may help in the treatment of E. coli O157:H7-associated diseases and can be applied as a biological preservative in the food industry.
Journal of Dairy Science, 2015
In addition to its nutritional and therapeutic properties, camel milk has the ability to suppress the growth of a wide range of foodborne pathogens, but there is a lack of information regarding the behavior of these pathogens in products such as yogurt produced from camel milk. The objective of the current study was to investigate the behavior of Listeria monocytogenes and Escherichia coli O157:H7 during manufacture and storage of camel yogurt. Camel milk inoculated with L. monocytogenes and E. coli O157:H7 was fermented at 43°C for 5 h using freeze-dried lactic acid bacteria (LAB) starter cultures (Streptococcus thermophilus and Lactobacillus bulgaricus) and stored at 4 or 10°C for 14 d. Camel milk inoculated with L. monocytogenes and E. coli O157:H7 without starter culture was also prepared. During fermentation, the numbers of L. monocytogenes and E. coli O157:H7 increased 0.3 and 1.6 log cfu/mL, respectively, in the presence of LAB, and by 0.3 and 2.7 log cfu/mL in the absence of LAB. During storage at 4 or 10°C, L. monocytogenes increased 0.8 to 1.2 log cfu/mL by 14 d in camel milk without LAB, but in the presence of LAB, the numbers of L. monocytogenes were reduced by 1.2 to 1.7 log cfu/mL by 14 d. Further, E. coli O157:H7 numbers in camel milk were reduced by 3.4 to 3.5 log cfu/mL in the absence of LAB, but E. coli O157:H7 was not detected (6.3 log cfu/mL reduction) by 7 d in camel yogurt made with LAB and stored at either temperature. Although camel milk contains high concentrations of natural antimicrobials, L. monocytogenes was able to tolerate these compounds in camel yogurt stored at refrigerator temperatures. Therefore, appropriate care should be taken during production of yogurt from camel milk to minimize the potential for postprocess contamination by this and other foodborne pathogens.