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- On the use of the Gompertz model to predict microbial inactivation behaviourPublication . Gil, Maria M.; Miller, F.; Quintas, M.; Brandão, Teresa R. S.; Silva, C. L. M.
- Recovery of heat-injured listeria innocuaPublication . Miller, Fátima A.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L.M.Listeria innocua was subjected to thermal inactivation and the extent of heat-injured cells was quantified. Cultures were heated in liquid medium for different times, using temperatures in the range of 52.5 to 65.0 °C, and plated on Tryptic Soy Agar with 0.6% yeast extract (TSAYE) used as non-selective medium and on TSAYE plus 5% NaCl (TSAYE+NaCl) and Palcam agar with selective supplement (Palcam agar) as selective media. The difference observed in counts in non-selective and in selective media gave an indication of cell injury during the heat treatment. D- and z- values were calculated for all conditions considered. For each temperature, D-values obtained using non-selective recovery procedures were higher than the ones obtained using the two selective media. When comparing the selective media, it can be concluded that Palcam agar allowed recovery and growth of thermally injured cells and so it was less inhibitor than TSAYE+NaCl. Another important result was the influence of temperature on the degree of cellular injury. As temperature increases, the degree of heat-injured cells also increases, and consequently concern has to be taken with the temperature and the counting medium used in food processing studies. The results of this work clearly demonstrated that selective media used for Listeria monocytogenes enumeration/detection might not be suitable for the recovery of heatinjured cells, which can dangerously underestimate the presence of this foodborne pathogen.
- Heat inactivation of Listeria innocua in broth and parsley under non-isothermal conditionsPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Effect of temperature, pH and type of acid on the inactivation of Listeria innocuaPublication . Miller, Fátima A.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Heat inactivation of Listeria innocua in broth and parsley under non-isothermal conditionsPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- On the assessment of an agar overlay method for the recovery of heat-injured Listeria innocua in parsleyPublication . Miller, Fátima A.; Ramos, Bárbara F.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.
- Mathematical models to predict thermal inactivation kinetics of Listeria innocua 10528Publication . Gil, M. M.; Miller, F. A.; Brandão, Teresa R. S.; Silva, C. L. M.
- A microbiologia preditiva como instrumento da garantia da segurança de produtos alimentaresPublication . Miller, Fátima A.; Gil, Maria Manuel; Brandão, Teresa R. S.; Silva, Cristina L. M.The quality and safety of products is of great importance to food industry. In terms of public health, the appropriate control of growth and/or inactivatiton of microorganisms is crucial. No contamination by micraorganisms responsible for degradation is as well important to assure food quality along the distribution chain. The train microorganisms responsible for foodborn diseases are: Campylobacter spp, Escherichia coli, Listeria monocytogenes and Salmonella spp. Studies on the effect of several factors, such as process time-temperature, pH and water activity, on microbial behaviour are fundamental to attain the appropriate control of foods' quality. The development of mathematical models (predictive microbiology) that describe the microorganisms' inactivation is therefore important and it is a relatively new researching field. In this work a review on inactivation kinetics of microorganisms and mathematical models commonly used to describe this behaviour (primary, secondary and tertiary) is presented. Based on a critical analysis of available information, new research lines are suggested.
- Sigmoidal thermal inactivation kinetics of listeria innocua in broth: Influence of strain and growth phasePublication . Miller, Fátima A.; Gil, Maria M.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L.M.Listeria innocua inactivation was studied within the temperature range 52.5–65.0 ºC, comparing two different strains (10528 and 2030c) and two growth phases (exponential and stationary). Survival curves may present a sigmoidal behaviour, with an initial shoulder (L), followed by a maximum inactivation rate (kmax) period and a final tailing tendency. A Gompertz-inspired model was used to fit experimental data, and kinetic parameters (L, kmax and tail) were estimated by non-linear regression analysis. The influence of temperature, growth phase and strain on kinetic parameters was studied using a 23 factorial experimental design. Results showed that temperature and growth phase were the most significant variables affecting the kinetic parameters. Listeria thermal inactivation varied from a log-linear tendency till a pronounced sigmoidal behaviour, depending on the studied factors.
- Recovery of heat-injured Listeria innocuaPublication . Miller, Fátima A.; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L. M.