Temperature and pH conditions that prevail during fermentation of sausages are optimal for production of the antilisterial bacteriocin sakacin K.
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Sakacin K is an antilisterial bacteriocin produced by Lactobacillus sake CTC 494, a strain isolated from Spanish dry fermented sausages. The biokinetics of cell growth and bacteriocin production of L. sake CTC 494 in vitro during laboratory fermentations were investigated by making use of MRS broth. The data obtained from the fermentations was used to set up a predictive model to describe the influence of the physical factors temperature and pH on microbial behavior. The model was validated successfully for all components. However, the specific bacteriocin production rate seemed to have an upper limit. Both cell growth and bacteriocin activity were very much influenced by changes in temperature and pH. The production of biomass was closely related to bacteriocin activity, indicating primary metabolite kinetics, but was not the only factor of importance. Acidity dramatically influenced both the production and the inactivation of sakacin K; the optimal pH for cell growth did not correspond to the pH for maximal sakacin K activity. Furthermore, cells grew well at 35 degrees C but no bacteriocin production could be detected at this temperature. L. sake CTC 494 shows special promise for implementation as a novel bacteriocin-producing sausage starter culture with antilisterial properties, considering the fact that the temperature and acidity conditions that prevail during the fermentation process of dry fermented sausages are optimal for the production of sakacin K. (+info)
Organization of the gene cluster for biosynthesis of penicillin in Penicillium nalgiovense and antibiotic production in cured dry sausages.
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Several fungal isolates obtained from two cured meat products from Spain were identified as Penicillium nalgiovense by their morphological features and by DNA fingerprinting. All P. nalgiovense isolates showed antibiotic activity in agar diffusion assays, and their penicillin production in liquid complex medium ranged from 6 to 38 microgram. ml-1. We constructed a restriction map of the penicillin gene cluster of P. nalgiovense and found that the organization of the penicillin biosynthetic genes (pcbAB, pcbC, and penDE) is the same as in Penicillium chrysogenum and Aspergillus nidulans. The pcbAB gene is located in an orientation opposite that of the pcbC and penDE genes in all three species. Significant amounts of penicillin were found in situ in the casing and the outer layer of salami meat during early stages of the curing process, coinciding with fungal colonization, but no penicillin was detected in the cured salami. The antibiotic produced in situ was sensitive to penicillinase. (+info)
Augmentation of killing of Escherichia coli O157 by combinations of lactate, ethanol, and low-pH conditions.
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The acid tolerance of Escherichia coli O157:H7 strains can be overcome by addition of lactate, ethanol, or a combination of the two agents. Killing can be increased by as much as 4 log units in the first 5 min of incubation at pH 3 even for the most acid-tolerant isolates. Exponential-phase, habituated, and stationary-phase cells are all sensitive to incubation with lactate and ethanol. Killing correlates with disruption of the capacity for pH homeostasis. Habituated and stationary-phase cells can partially offset the effects of the lowering of cytoplasmic pH. (+info)
Variation in resistance of natural isolates of Escherichia coli O157 to high hydrostatic pressure, mild heat, and other stresses.
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Strains of Escherichia coli O157 isolated from patients with clinical cases of food-borne illness and other sources exhibited wide differences in resistance to high hydrostatic pressure. The most pressure-resistant strains were also more resistant to mild heat than other strains. Strain C9490, a representative pressure-resistant strain, was also more resistant to acid, oxidative, and osmotic stresses than the pressure-sensitive strain NCTC 12079. Most of these differences in resistance were observed only in stationary-phase cells, the only exception being acid resistance, where differences were also apparent in the exponential phase. Membrane damage in pressure-treated cells was revealed by increased uptake of the fluorescent dyes ethidium bromide and propidium iodide. When strains were exposed to the same pressure for different lengths of time, the pressure-sensitive strains took up stain sooner than the more resistant strain, which suggested that the differences in resistance may be related to susceptibility to membrane damage. Our results emphasize the importance of including stress-resistant strains of E. coli O157 when the efficacy of a novel or mild food preservation treatment is tested. (+info)
A large outbreak of hemolytic uremic syndrome caused by an unusual sorbitol-fermenting strain of Escherichia coli O157:H-.
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Escherichia coli O157:H7 does not ferment sorbitol, a factor used to differentiate it from other E. coli. From December 1995 to March 1996, 28 children with hemolytic uremic syndrome in Bavaria, Germany, were identified; many had a sorbitol-fermenting (sf) E. coli O157:H- cultured. A case-control study showed a dose-response relationship between sausage consumption and illness. A second case-control study showed a relationship between mortadella and teewurst consumption and illness, particularly during December (mortadella odds ratio [OR], 10.5, P=.004; teewurst OR, 6.2, P=.02). Twelve sf O157:H- were characterized to determine clonality and virulence traits. The strains possessed the Stx2, eae, and EHEC-hlyA genes but were nonhemolytic on blood agar plates. The O157:H- isolates belonged to phage type 88 and had identical pulsed-field gel electrophoresis patterns. This outbreak was caused by sf E. coli O157:H-, which is not detectable by culture on sorbitol MacConkey's agar. Consumption of two sausages, including a raw beef-containing sausage, was statistically related to illness. (+info)
Beef customer satisfaction: cooking method and degree of doneness effects on the top loin steak.
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The objective of this research was to evaluate the consumer-controlled factors of cooking method and degree of doneness on Top Choice, Low Choice, High Select, and Low Select top loin steaks. The in-home product test was conducted in Chicago, Houston, Philadelphia, and San Francisco. Consumers (n = 2,212) evaluated each top loin steak for overall like (OLIKE), tenderness (TEND), juiciness (JUIC), flavor desirability (DFLAV), and flavor intensity (IFLAV) using 23-point hedonic scales. Respondents in San Francisco and Philadelphia cooked their top loin steaks to lower degrees of doneness than those in Chicago and Houston. Outdoor grilling was the most common method of cookery for top loin steaks in all cities. Consumers had the highest preference for Top Choice steaks (P < .05) and the lowest preference for Low Select steaks (P < .05). Consumer OLIKE scores were the highest (P < .05) for steaks cooked to a medium rare or lesser degree of doneness. Consumers preferred (P < .05) medium and well done or more degrees of doneness over medium well. The interaction of city x cooking method was significant for all steak palatability attributes. The differences in consumer preparation techniques among cities present challenges for the beef industry to develop market-specific promotional campaigns. (+info)
Beef customer satisfaction: cooking method and degree of doneness effects on the top sirloin steak.
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The objective of this research was to evaluate the consumer-controlled factors of cooking method and degree of doneness on Top Choice, Low Choice, High Select, and Low Select top sirloin steaks. The in-home product test was conducted in Chicago, Houston, Philadelphia, and San Francisco. Consumers (n = 2,212) evaluated each top sirloin steak for overall like (OLIKE), tenderness (TEND), juiciness (JUIC), flavor desirability (DFLAV), and flavor intensity (IFLAV) using 23-point hedonic scales. Top sirloin steaks, regardless of city, were consistently cooked to well done or higher degrees of doneness. Dry-heat methods such as outdoor grilling, broiling, and indoor grilling were the most frequent cooking methods used. Four significant interactions existed for OLIKE: USDA quality grade x cooking method (P = .02), city x cooking method (P = .0001), city x degree of doneness (P = .01), and cooking method x degree of doneness (P = .009). Greater differences were found between cooking methods within USDA quality grade than between USDA quality grades within cooking method. Consumers in Houston rated steaks cooked by outdoor grilling higher than those from the other cities, and steaks cooked by indoor grilling were rated the highest among all cooking methods by consumers in Chicago. In Chicago, steaks cooked to more advanced degrees of doneness tended to receive higher ratings, but few differences between degrees of doneness in the other three cities were detected. For outdoor grilling, broiling, and pan-frying, the trend was for OLIKE ratings to decline as degree of doneness increased. The lowest customer satisfaction ratings tended to be given to top sirloin steaks cooked to more advanced degrees of doneness, and consumers most frequently cooked steaks to at least the well done stage. Consumer information programs or the development of postmortem techniques that would ensure acceptable palatability of top sirloin steaks may need to be developed. (+info)
Beef customer satisfaction: cooking method and degree of doneness effects on the top round steak.
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The objective of this research was to evaluate the consumer-controlled factors of cooking method and degree of doneness on Top Choice, Low Choice, High Select, and Low Select top round steaks. The in-home product test was conducted in Chicago, Houston, Philadelphia, and San Francisco. Consumers (n = 2,212) evaluated each top round steak for overall like (OLIKE), tenderness (TEND), juiciness (JUIC), flavor desirability (DFLAV), and flavor intensity (IFLAV) using 23-point hedonic scales. Stir-frying, braising, and simmering and stewing consistently produced higher consumer attribute ratings. There were clear OLIKE rating differences (P = .0001) for top round steaks among the four cities. The highest ratings were given by consumers in Houston, and the lowest ratings were given by consumers in Philadelphia (P < .05). There were two interactions for OLIKE: USDA quality grade x degree of doneness (P = .002) and degree of doneness x cooking method (P = .02). Higher ratings generally were given to steaks cooked to medium rare or less or to very well degrees of doneness. Stir-frying, braising, and simmering and stewing were preferred at lower degrees of doneness. Customer satisfaction with the top round steak is very dependent on how it is cooked and by whom it is consumed. (+info)