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1.
The effect of mint ( Mentha piperita ) essential oil (0·5, 1·0, 1·5 and 2·0%, v/w) on Salmonella enteritidis and Listeria monocytogenes in a culture medium and three model foods; tzatziki (pH 4·5), taramosalata (pH 5·0) and pâté (pH 6·8), inoculated at 107 cfu g-1 , at 4° and 10°C for ca 1 week was studied. In the culture medium supplemented with the essential oil, no growth was observed over 2 d at 30°C determined by a conductance method with a Malthus 2000 growth analyser. Salmonella enteritidis died in tzatziki in all treatments and declined in the other foods except for pâté at 10°C as judged with viable counts. Listeria monocytogenes populations showed a declining trend towards the end of the storage period but was increased in pâté. Mint essential oil antibacterial action depended mainly on its concentration, food pH, composition, storage temperature and the nature of the micro-organism. 相似文献
2.
Aims: To investigate the effect of pH, water activity ( a w ) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs.
Methods and Results: The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), aw (0·935–0·994) and temperature (10–45°C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol 23, 277–294). The effect of pH, a w and temperature on maximum specific growth rate (μmax ) were estimated by fitting a cardinal model. μmax under optimal conditions (pH = 6·6, a w = 0·994, T = 36·3°C) was estimated to be 0·93 h−1 . Minimum and maximum estimated pH and temperature for growth were 3·6 and 8·15, and 9·0°C and 47·8°C, respectively, while minimum a w was 0·918 (equivalent to 12·2% w/v NaCl).
Conclusions: Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study: This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations. 相似文献
Methods and Results: The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), a
Conclusions: Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study: This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations. 相似文献
3.
Scales were used for the determination of age with back-calculation of length. The oldest fish was VII + years old. Back-calculation did not exhibit Lee's phenomenon. The most rapid growth occurred in summer at water temperatures over 25°C. The growth in weight was c . 331 g year-1 after IV vears of life. Growth was well described by von Bertalanffy equation : ll - 91·0 [ l= 0·122 (l0·25) ] The length-weight relationship followed the cube law (b = 3·0601) Kn ranged from 0·74 to 1·18 with a mean value of 1·0. Spawning occurred in January, fecundity was 74 509 with a mean of 1157 eggs -1 body weight. Mean diameter of eggs was 1071 (pm). A developed ovary had ova of two sizes, immature oocytes and mature ova. The fish is a carnivorous feeder. 相似文献
4.
The von Bertalanffy growth parameters for common wolf–fish Anarhichas lupus in the North Sea were: male: L ∞=111·2 cm, t 0 =–0·43 and K =0·12; and female: L ∞=115·1 cm, t 0 =–0·39 and K =0·11, making this the fastest growing stock reported. Resting metabolic rates (RMR±S.E.) and maximum metabolic rates (MMR±S.E.) for six adult common wolf–fish (mean weight, 1·39 kg) at 5° C were 12·18±1·6 mg O2 kg–1 h–1 and 70·65±7·63 mg O2 kg–1 h–1 respectively, and at 10° C were 25·43±1·31 mg O2 kg–1 h–1 and 113·84±16·26 mg O2 kg–1 h–1 . Absolute metabolic scope was 53% greater at 10° C than at 5° C. The diet was dominated by Decapoda (39% overall by relative occurrence), Bivalvia (20%) and Gastropoda (12%). Sea urchins, typically of low energy value, occupied only 7% of the diet. The fast growth probably resulted from summer temperatures approximating to the optimum for food processing and growth, but may have been influenced by diet, and reduced competition following high fishing intensity. 相似文献
5.
Aims: The objective of this study is to develop kinetic models based on batch experiments describing the growth, CO2 consumption, and H2 production of Anabaena variabilis ATCC 29413-UTM as functions of irradiance and CO2 concentration.
Methods and Results: A parametric experimental study is performed for irradiances from 1120 to 16100 lux and for initial CO2 mole fractions from 0·03 to 0·20 in argon at pH 7·0 ± 0·4 with nitrate in the medium. Kinetic models are successfully developed based on the Monod model and on a novel scaling analysis employing the CO2 consumption half-time as the time scale.
Conclusions: Monod models predict the growth, CO2 consumption and O2 production within 30%. Moreover, the CO2 consumption half-time is an appropriate time scale for analysing all experimental data. In addition, the optimum initial CO2 mole fraction is 0·05 for maximum growth and CO2 consumption rates. Finally, the saturation irradiance is determined to be 5170 lux for CO2 consumption and growth whereas, the maximum H2 production rate occurs around 10 000 lux.
Significance and Impact of the Study: The study presents kinetic models predicting the growth, CO2 consumption and H2 production of A. variabilis . The experimental and scaling analysis methods can be generalized to other micro-organisms. 相似文献
Methods and Results: A parametric experimental study is performed for irradiances from 1120 to 16100 lux and for initial CO
Conclusions: Monod models predict the growth, CO
Significance and Impact of the Study: The study presents kinetic models predicting the growth, CO
6.
Carvacrol, a natural plant constituent occurring in oregano and thyme, was investigated for its bactericidal effect towards the food-borne pathogen Bacillus cereus . Carvacrol showed a dose-related growth inhibition of B. cereus . At concentrations of 0·75 mmol l−1 and above, total inhibition of the growth was observed. Below this concentration, carvacrol extended the lag-phase, reduced the specific growth rate and reduced the maximum population density. Incubation for 40 min in the presence of 0·75–3 mmol l−1 carvacrol decreased the number of viable cells of B. cereus exponentially. Spores were found to be approximately 2·3-fold less sensitive to carvacrol than vegetative cells. Bacillus cereus cells showed reduced susceptibility towards carvacrol at pH 7·0 compared with different values between pH 4·5 and 8·5. The culture and exposure temperatures had a significant influence on the survival of vegetative cells. The highest death rate of cells was observed at an exposure temperature of 30 °C. Membrane fluidity was found to be an important factor influencing the bactericidal activity of carvacrol. 相似文献
7.
Inhibition of the tempe mould, Rhizopus oligosporus, by ammonia 总被引:1,自引:0,他引:1
The hyphal extension rate of Rhizopus oligosporus NRRL 2710 was slowed in the presence of 0·42 and 0·84 mmol NH3 l−1 and inhibited by 1·3 mmol l−1 . Sporulation was prevented at NH3 concentrations of 0·42 mmol l−1 andabove. There was no evidence of toxicity due to NH+ 4 at concentrations up to 300 mmol l−1 .Independent of the concentrations of NH3 or NH+ 4 , the lower the pH value, in therange 6·0–9·0, the higher was the rate of hyphal extension. It is suggested that accumulationof toxic levels of NH3 could be responsible for the cessation of mould growth in tempe. 相似文献
8.
9.
The use of a surface adhesion immunofluorescent (SAIF) method for the rapid detection of Yersinia enterocolitica serotype O:3 in meat 总被引:1,自引:1,他引:0
J. J. Sheridan C. M. Logue D. A. McDowell I. S. Blair T. Hegarty P. Toivanen 《Journal of applied microbiology》1998,85(4):737-745
This study examined the attachment kinetics of Yersinia enterocolitica serotype O:3 to determine the optimum conditions for its isolation from meat enrichment systems using a novel surface adhesion technique. Minced beef was inoculated with Y. enterocolitica at an initial level of 10 cfu g−1 and incubated at 25 °C in an enrichment broth. Yersinia was recovered from enriched samples on polycarbonate membranes by surface adhesion and enumerated using immunofluorescence microscopy. The surface adhesion immunofluorescence technique (SAIF) had a minimum detection limit of approximately 4·0–4·5 log10 cfu ml−1 and provided good correlation between the estimation of the numbers of Yersinia in the enrichment broth derived from plate counts on Yersinia Selective agar (CIN) and those determined by SAIF ( r 2 = 0·94; rsd = ± 0·21). A derived regression equation of the SAIF count vs plate counts was used to predict Y. enterocolitica numbers in spiked meat samples stored at 0 °C for up to 20 d. The numbers as predicted by the SAIF method showed good correlation with counts derived by plating techniques ( r 2 = 0·78; rsd = ± 0·42). The application of the SAIF technique for the rapid detection of Y. enterocolitica serotype O:3 from meat is discussed. 相似文献
10.
Alicia Ragout Faustino Siñeriz H. Diekmann Graciela Font de Valdez 《Journal of applied microbiology》1994,77(4):388-391
The influence of environmental pH on the regulation of glucose catabolism by Lactobacillus reuteri was examined in anaerobic batch cultures. Under acidic conditions both glucose consumption and end-products formation were low. Maximum biomass was reached at pH 5·0, with a specific growth rate of µ= 0·78 h-1 . The shift in pH values from 4.3 to 6.5 reflected an increase in glucose uptake as well as in the yield ( Y p/x ) of acetate, lactate and ethanol after 12 h of incubation. Ethanol was the major metabolite produced at all pH values assayed. 相似文献
11.
Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels 总被引:1,自引:0,他引:1
Juvenile (12–152 g) shortfinned eels Anguilla australis and longfinned eels A. dieffenbachia caught in New Zealand streams were fed squid mantle Nototodarus spp. 4 days per week in laboratory experiments. A linear multiple regression equation showed the amount of food eaten (0–2·7% w day−1 ) explained 77·7% of the variation in specific growth rates (–0·60 to +1·07% w day−1 ) among individual eels, while previous growth rates, water temperature (10·0–20·6°C), and eel weight (12–152 g) explained a further 5·6, 1·4 and 0·8%, respectively. Growth in length ranged from –0·3 to +0·9 mm day−1 . Eels which were starved and then given high rations grew substantially faster than expected. Once growth rates were adjusted for differences in ration and other factors, there were no significant differences in growth rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water temperatures and ceased below 9·0°C. Growth rates in the wild were substantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild. 相似文献
12.
The genus Pectinatus has been often reported in beer spoilage with off-flavours. The bacteria are strictly anaerobic, Gram-negative rods. Propionate and acetate are the main fermentation products from glucose in the two species belonging to the genus, P. cerevisiiphilus and P. frisingensis. Amino acids routinely present at a high level in beer were not growth substrates for both species, and a significant accumulation of succinate was observed with lactate as growth substrate. Both Pectinatus ssp. showed almost identical fermentation balances on glucose. Growth kinetics of both glucose-grown species were unchanged under a N2 , H2 or 20% CO2 -containing atmosphere. Combinations of culture medium pH values from pH 3·9 to pH 7·2, of glucose levels between 5 and 55 mmol l-1 , and of lactate concentrations varied from 4 to 40 mmol l-1 demonstrated that biomass and volatile fatty acids production were proportional to glucose concentration for both Pectinatus species. A significant increase of volatile fatty acid production was measured for both species at the lowest pH values with a lactate or a glucose concentration increase. The maximum biomass production was observed at pH 6·2 for P. cerevisiiphilus , and between pH 4·5 and pH 4·9 for P. frisingensis. Glucose and lactate or pH value were dependent with regard to propionate and acetate production in P. frisingensis. On the other hand, the variations of these three parameters were independent with regard to biomass production for both strains, and to volatile fatty acids production for P. cerevisiiphilus. Addition of ethanol to glucose-grown cultures completely inhibited growth at 1·3 mol l-1 ethanol for P. cerevisiiphilus , and at 1·8 mol l-1 for P. frisingensis. 相似文献
13.
Factors affecting the production of hydrogen sulphide by Lactobacillus sake L13 growing on vacuum-packaged beef 总被引:3,自引:3,他引:0
Lactobacillus sake L13 produced hydrogen sulphide during growth at 0°C on vacuum-packaged beef of normal pH (5·6–5·8) when the packaging films used had oxygen permeabilities as high as 200 ml/m2 /24 h/atm (measured at 25°C and 98% relative humidity. No hydrogen sulphide was detected when the film permeability was 300 ml/m2 /24 h/atm. Sulphmyoglobin was formed whenever hydrogen sulphide was present except when the film permeability was very low (1 ml of oxygen/m2 /24 h/atm). Lactobacillus sake L13 also produced hydrogen sulphide when grown on beef under anaerobic conditions at 5°C. When meat pH was high (6·4–6·6) hydrogen sulphide was first detected after incubation for 9 d. When 250 μg of glucose was added to each g of high pH meat, or when meat pH was normal (5·6–5·8), hydrogen sulphide was first detected after incubation for 18 d. The spoilage of beef by hydrogen sulphide-producing lactobacilli is more rapid when the pH of the meat is high because high-pH meat contains less glucose. Sulphmyoglobin formation and greening can be prevented by the use of packaging films of very low oxygen permeability. 相似文献
14.
Protein synthesis, nitrogen excretion and long-term growth of juvenile Pleuronectes flesus 总被引:3,自引:0,他引:3
This study aimed to measure protein synthesis using a stable isotope method, investigate protein-nitrogen flux in a flatfish Pleuronectes flesus , and use the data to test the hypothesis that individual differences in growth efficiency were related to individual differences in protein-nitrogen flux mediated through differences in protein synthesis and degradation. Three measurements of protein-nitrogen flux via consumption, protein synthesis and nitrogenous excretion were made for individual flounder during a 212-day period and fractional rates of protein-nitrogen flux were scaled for a 50–g flounder to provide mean values for protein consumption (2·11 ± 0·21% day−1 ), protein synthesis (2·08±0·23% day−1 ), protein growth (0·71±0·06% day−1 ) and protein degradation (1·37±0·24% day−1 ). Mean rates of nitrogenous excretion were 0·142 mg N g−1 day−1 and 0·047 mg N g−1 day−1 for ammonia and urea, respectively. Individual flounder had different protein growth efficiencies and this was correlated negatively and significantly with mean rates of protein synthesis ( r - 0·70; P <0·05) and degradation ( r - 0·67; P < 0·05) and correlated positively and significantly with the efficiency of retaining synthesized protein ( r +0·63, P <0·05). This supported the proposed hypothesis that flounder which grow more efficiently achieve this through adopting a low protein turnover strategy. 相似文献
15.
The effect of chlorine on β- D- galactosidase activity of sewage bacteria and Escherichia coli was studied. β- D- galactosidase activity of sewage was more resistant to chlorine than faecal coliform cultivability. At low initial dosage (0·05 mg Cl2 l−1 ) neither cultivability (colony-forming units (cfu)), nor enzyme activity of E. coli suspensions were severely impaired. When initial chlorine concentration was increased to 0·1 mg Cl2 l−1 , the cfu number decreased whereas enzyme activity remained high, i.e. the enzyme activity calculated cfu−1 increased. At higher chlorine doses both cfu and enzyme activity were reduced, but non-cultivable cells retained assayable activity after chlorination. Mean values of the enzyme activity calculated cfu−1 decreased when the chlorine dosage was increased from 0·1 to 0·5 mg Cl2 l−1 , but were not significantly different ( P > 0·05) for dosages of 0·2–0·7 mg Cl2 l−1 . After chlorination, β- D- galactosidase activity of E. coli was less reduced than cfu and direct viable count numbers, but more reduced than 5-cyano-2-3, ditolyl tetrazolium chloride and total cell counts, and the enzyme activity represented an alternative activity parameter of chlorinated samples. 相似文献
16.
Modelling the surface conductance of a broad-leaf canopy: effects of partial decoupling from the atmosphere 总被引:2,自引:0,他引:2
F. Magnani S. Leonardi R. Tognetti J. Grace & M. Borghetti 《Plant, cell & environment》1998,21(8):867-879
The transpiration of a mature beech ( Fagus sylvatica L.) forest was measured over a whole season by the heat pulse velocity technique and the results analysed in terms of a new analytical canopy conductance model, which takes into account the effects of partial decoupling from the atmosphere on the local humidity environment experienced by the canopy. Stand daily transpiration ranged from 0·62 to 2·97 mm d–1 , with a seasonal mean value of 1·97 mm d–1 . Maximum canopy conductance was 18·5 mm s–1 , with a mean estimated value of 5·0 mm s–1 ; computed values were little affected by the assumption of neutral atmospheric conditions. The decoupling coefficient Ω varied greatly on a daily and seasonal basis, with an average value of 0·28. As a result of partial decoupling, the estimated vapour pressure deficit at the notional canopy surface exceeded the values measured above the canopy by 380 Pa on average. When correctly expressed in terms of humidity at the canopy surface, the model explained 80% of the variance in half-hourly transpiration measurements. Upon cross-validation it still explained 72% of the variance, as compared to only 40% when correction for partial decoupling was not introduced. A baseline canopy conductance of 0·7 mm s–1 , not modulated by the environment, was estimated. The implications of the model are discussed for the representation of canopy conductance and transpiration of broad-leaf forests. 相似文献
17.
Ammonium ion affecting tylosin production by Streptomyces fradiae NRRL 2702 in continuous culture 总被引:1,自引:0,他引:1
S.H. Lee 《Letters in applied microbiology》1997,25(5):349-352
Nitrogen regulation in tylosin production by Streptomyces fradiae NRRL 2702 was studied in chemostat culture using a soluble synthetic medium. The maximum value of specific tylosin formation rate ( q TYL ) was 1·13 mg g−1 h−1 at the specific growth rate (μ) of 0·05 h−1 , and q TYL decreased with increasing levels of the specific growth rate after reaching a rate of 0·1 h−1 . The optimum conditions for tylosin formation were that the specific ammonium ion uptake rate ( q N ) and μ were 0·13 mmol g−1 h−1 and 0·05 h−1 , respectively. The specific formation rates of threonine dehydratase (TDT) and tylosin were repressed by high levels of specific ammonium ion uptake rate. This study showed the adaptation to chemostat cultures of the nitrogen regulation of tylosin fermentations. 相似文献
18.
Rapid selective enumeration of bacteria in foods using a microcolony epifluorescence microscopy technique 总被引:1,自引:0,他引:1
The growth patterns of macrocolonies of 59 different pure cultures were studied on eight selective solid media. A method of growing microcolonies on the surface of polycarbonate membrane filters, placed on the selective agar media, followed by staining and examination by epifluorescent microscopy was developed. The patterns of growth of the pure cultures as microcolonies were studied on the eight selective media. Only four media proved to be reliable for this purpose and the relationship between the microcolony count and plate count was studied on these media together with nutrient agar. Microcolony counts using three of these media (enriched lauryl sulphate aniline blue, pseudomonas selective agar (C-F-C) and Baird-Parker medium) were capable of giving reliable estimates of coliforms (r = 0·89), pseudomonads (r = 0·93) and staphylococci (r = 0·92) after incubation at 30°C for 3 or 6 h (staphylococci) at contamination levels of above 103 bacteria/g in a variety of foods. The results are available within a working day and should allow the more efficient management of food supplies. 相似文献
19.
M. Schubert V. Dengler S. Mourad F.W.M.R. Schwarze 《Journal of applied microbiology》2009,106(5):1734-1742
Aim: To evaluate the influence of water activity ( a w ), temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete was used in the biotechnological process of bioincising.
Methods and Results: Radial growth was monitored for 20 days on malt extract agar medium. Five levels of aw (0·998, 0·982, 0·955, 0·928, 0·892) were combined with three incubation temperatures (10, 15, 20°C) and three pH values (4, 5, 6). Data analyses showed a highly significant effect of a w and temperature ( P < 0·0001) and a significant effect of pH ( P < 0·05). The radial growth rate and lag phase of P. vitreus were very sensitive to a w reduction. Although P. vitreus was able to grow at all the selected temperatures and pH values, the lag phase increased with decreasing a w and growth became inhibited at a w = 0·955. Optimal conditions for growth of P. vitreus were a w = 0·998, 20°C and pH 5. The response surface model provided reliable estimates of these growth parameters and confirmed a greater dependence on a w than on temperature or pH under in vitro conditions.
Conclusions: Low levels of aw can prevent growth of P. vitreus , so wood moisture content should be adjusted accordingly.
Significance and Impact of the Study: Implementation of these results should contribute towards the optimization and efficiency of bioincising. 相似文献
Methods and Results: Radial growth was monitored for 20 days on malt extract agar medium. Five levels of a
Conclusions: Low levels of a
Significance and Impact of the Study: Implementation of these results should contribute towards the optimization and efficiency of bioincising. 相似文献
20.
M. W. Aprahamian 《Journal of fish biology》2000,56(1):223-227
The growth rate of 1980 eel Anguilla anguilla from 15 sites in the Severn system varied between 16·4 and 27·9 mm year-1 , density from 0·12 to 1·14 m-2 and biomass from 2·56 to 25·24 g m-2 . There was no significant relationship between growth rate and density or biomass ( P > 0·05). 相似文献