Loading...
46 results
Search Results
Now showing 1 - 10 of 46
- Thermal and non-thermal Cantaloupe melon juice pasteurization: Assessment of the impact of ozone exposure on microbiological, physicochemical and bioactive characteristicsPublication . Sroy, Sengly; Fundo, Joana F.; Miller, Fátima A.; Brandão, Teresa R.S.; Silva, Cristina 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.
- Impact of ozone processing on microbiological, physicochemical, and bioactive characteristics of refrigerated stored Cantaloupe melon juicePublication . Sroy, Sengly; Fundo, Joana F.; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.The objective of this study was to evaluate the impact of ozone treatment on microbiological decontamination (intrinsic microflora and inoculated Listeria innocua) and some physicochemical characteristics and bioactive compounds of Cantaloupe melon juice, also during refrigerated storage. To determine adequate ozone exposure, the survival curve of L. innocua was previously assessed. A thermal treatment was also performed seeking comparison with ozone treatment impact. After ozone exposure, L. innocua was not detected in juice samples, while thermal pasteurization allowed a reduction of 5.2 ± 0.2 log cycles. Although ozone reduced the intrinsic microflora loads, this reduction was higher for heat‐treated samples. Vitamin C was highly retained in ozone‐treated juices (68%), when compared with the pasteurized ones (39%). After 13 days of storage, ozone allowed the retention of the most quality parameters analyzed and, therefore, it can be considered as a promising alternative to traditional pasteurization of Cantaloupe melon juice. Practical applications The actual consumers' demand for high‐quality food standards has launched research to alternative and milder nonthermal processes, which have gained increasing attention and importance in the fruit juice industries. Ideally, preservation and/or processing of foods should involve technologies that prevent undesirable microbial survival and minimize quality attributes changes and nutrient losses. Thermal treatments are conventionally used to attain such targets; however, the content and the biological activity of the most health‐related compounds are dramatically reduced. In this context, and particularly in the beverages industries, ozone has been exploited due to its potential for inactivating spoilage and pathogenic microorganisms, while being effective in overall quality retention of the products.
- Application of optimal experimental design concept to improve the estimation of model parameters in microbial thermal inactivation kineticsPublication . Gil, Maria M.; Miller, Fátima A.; Silva, Cristina L.M.; Brandão, Teresa R. S.The estimation of model parameters with high precision is of major importance in mathematical predictions. If a mathematical model is properly chosen and if the primary objective is to improve parameter estimation, underlying statistical theories can be applied. Precision increases with the number of experimental points. However, and in many situations,maximum precision is attained when sampling consists of replicates of specific experimental points. Experimental conditions can be optimized using the Doptimal design concept based on minimization of the generalized variance of the parameter estimates. The objective of this work was to use this methodology for the design of experiments for microbial inactivation processes described by a Gompertz-based model under isothermal and non-isothermal conditions. The application of D-optimal design concept considerably improved parameters precision, when compared to the commonly used heuristic designs.
- Combined effects of temperature, pH and water activity on predictive ability of microbial kinetic inactivation modelPublication . Gil, Maria M.; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.It is well known that temperature is the key factor controlling the microbial survival/inactivation. However, the interactive effects of further stressing environmental conditions may influence microbial inactivation behaviour. The objective of this work was to include, in the inactivation model, temperature, pH and water activity effects using a black box polynomial model, aiming at accurate prediction. Experimental data of Listeria innocua obtained within the temperature range of 52.5 and 65.0 °C, pH of 4.5, 6.0 and 7.5, and water activity of 0.95 and 0.99 were used for model assessment. A Gompertz-inspired model for microbial inactivation was used, with shoulder period, maximum inactivation rate and tail as parameters. The relations of such parameters with temperature, water activity and pH were purely empirical and assumed to be polynomials. When these mathematical relationships were included in the primary kinetic model, accurate predictions of the inactivation data were attained, thus validating the predictive ability of the model expressed in terms of the stressing environmental factors studied. © 2015 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of Department of Food Science, Faculty of Food Engineering, University of Campinas.
- UV-C radiation as an effective non-thermal process for ‘Cantaloupe’ melon juice decontaminationPublication . Mandro, Gabriela; Fundo, Joana F.; Miller, Fátima A.; Tremarin, Andréia; Brandão, Teresa R. S.; Silva, Cristina L. M.Thermal pasteurization has negative impacts on overall quality characteristics of foods. UV-C radiation has a germicidal effect and has been applied to eliminate undesirable microorganisms in food products. This technology is more effective in liquid foods, being an alternative non-thermal processing that can be applied to fruit juices.The objective of this study was to evaluate the effect of UV-C radiation on some quality characteristics and microbiological decontamination of cantaloupe melon (Cucumis meloL. var. reticulatus) juice, whichis an excellent source of antioxidant compounds, such as vitamins, phenolics and carotenoids. Cantaloupe melon juice was artificially inoculated with Alicyclobacillus acidoterrestrisspores (spoiler indicator) and Listeria innocua(non-pathogenic surrogate of L.monocytogenes), used as indicators of the UV-C treatment efficacy. The initial concentration of both microorganisms was around 107CFU/mL. Juice was exposed to UV-C radiation at an intensity of 13.44 W/m2, during 5 and 20 minutes. Some physic-chemical characteristics (pH, colour and soluble solids content), total phenolics and antioxidant capacity were evaluated before and after treatments. Exposure time affected significantly colour (very distinct alterations) and pH (slight increase from 6.3±0.1 in fresh, to 6.7±0.1 and 7.0±0.1 after 5 and 20 min of radiation; values are mean±margin of confidence interval at 95%). The remaining characteristics were not affected by the radiation and were similar to the ones observed in fresh/untreated juice. In terms of A. Acidoterrestris spores, reductions of 0.8±0.1 and 4.7±0.1log-cycles were observed after 5 and 20 minutes of radiation, respectively. For L. innocua, a reduction of 3.9±0.7 log-cycles was attained after 5 minutes and, for the highest exposure time, no cells were detected. Since UV-C was effective on microbial inactivation and was able to retain the most of quality parameters analysed, this technology can be considered as a promising alternative to traditional pasteurization of fruit juices.
- 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.
- Effect of non-thermal processing on the aromatic profile of Cantaloupe melon juicePublication . Georgiev, Radoslav; Pereira, Joel; Fundo, Joana F.; Miller, Fátima A.; Brandao, Teresa R.S.; Chalova, Vesela I.; Silva, Cristina L. M.
- On the use of the gompertz model to predict microbial thermal inactivation under isothermal and non-isothermal conditionsPublication . Gil, Maria M.; Miller, Fátima A.; Brandão, Teresa R. S.; Silva, Cristina L. M.Food processes should be designed to provide an adequate margin of safety against microbiological risk of food poisoning and food spoilage throughout shelf life. In this field, the use of mathematical models that describe the microorganisms’ kinetics in such conditions is an important tool for convenient design, control and optimization of efficient processes. If those models are accurate and precise, one can extract the best aiming at predictive purposes. The Gompertz equation is commonly applied to describe sigmoidal kinetics. Besides the proven adequacy of the model in those kinetics descriptions, most of the reported works do not use Gompertz equation in the most convenient form, and insightful information could be obtained with re-parameterized forms. This work aims at reviewing the use of the Gompertz model to describe inactivation, as well as re-parameterized forms that include parameters related to the survival curve features. Microbial survival often presents a shoulder prior to inactivation, followed by a linear phase (corresponding to a maximum inactivation rate) and a tail residual population. The versatility of the Gompertz model in describing kinetics with different shapes, varying from a log-linear tendency till a complete sigmoidal shape, makes it attractive for predictive purposes, both under static and dynamic temperature conditions. Drawbacks and critical features of the model, when it is applied to microbial responses, will be overview.