Browsing by Author "Silva, Cristina L.M."
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- Alicyclobacillus acidoterrestris spores as a target for Cupuaçu Theobroma grandiflorum) nectar thermal processing: Kinetic parameters and experimental methodsPublication . Vieira, Margarida C.; Teixeira, Arthur A.; Silva, Filipa M.; Gaspar, Nelma; Silva, Cristina L.M.The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuac u (Theobroma grandiflorum) pulp and 15% sugar] were determined by the isothermal method (IM), under batch heating, and by the paired equivalent isothermal exposures (PEIE) method, under non-isothermal continuous conditions. The isothermal experiments were repeated three times, every 4 months, with the same spore suspension kept frozen between experiments. The aging of spores, under frozen storage, seemed to produce a notorious increase in the z-value from experiment to experiment: Experiment 1 (z = 7.8F2.6 jC, D95 jC = 5.29F0.96 min), Experiment 2 (z=22F5 jC, D95 jC = 5.99F0.63 min), and Experiment 3 (z=29F10 jC, D95 jC = 3.82F0.48 min). The evaluation of the kinetic parameters by the PEIE method was carried out in parallel with Experiment 3, with the same aged spores, and the results (z=31F6 jC, D95 jC = 5.5F1.2 min) were close to the ones obtained in this experiment. From this work, it seems that the PEIE method can also be applied to evaluate the reduction parameters of a spore-forming microorganism, and in a more realistic way, since the continuous system eliminates the errors caused by come-up and cool-down times (CUT and CDT) that are unavoidable in isothermal experiments. Therefore, when designing a thermal process for a continuous system, the PEIE method should be used, or the chances are that the process would be underdesigned, risking that the desired level of spore inactivation would not be achieved. An optimization of the thermal processing conditions was next performed for Cupuac u nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 jC) only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 jC will ensure a safe product and retain 98.5% of the original ascorbic acid. Therefore, if A. acidoterrestris is considered as the target microorganism, the nectar should undergo an aseptic high temperature short time principle (HTST) process to achieve a 5D reduction in this acidophilus spore former. However, if the hot-fill-and-hold pasteurization process is preferred, the product should be fortified with ascorbic acid.
- 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.
- Assessment of the impact of hydrogen peroxide solutions on microbial loads and quality factors of red bell peppers, strawberries and watercressPublication . Alexandre, Elisabete M.C.; Brandão, Teresa R.S.; Silva, Cristina L.M.The impact of sodium hypochlorite and hydrogen peroxide (H2O2 at 1 and 5%) solutions on Listeria innocua in red bell peppers, total mesophiles in strawberries and total coliforms in watercress was studied. Quality attributes such as colour, firmness and pH were studied for all products; total anthocyanins content was determined for strawberries. Sensorial analyses were also carried out for all products. Results showed that H2O2 (5%) provided the highest reductions of microbial loads. Besides H2O2 (1%) had a lower impact, it was more effective than water-washings. Sodium hypochlorite solutions lead to microbial reductions comparable to water risings. In terms of quality, H2O2 (5%) was the solution with higher negative impact on products’ colour. For strawberries, such colour alterations were also detected by sensorial analyses. The anthocyanins content decreased significantly. Overall it was found that H2O2 (1%) was a good sanitizer solution, since microbial reduction was attained while quality factors did not suffer considerable alterations.
- Assessment of the impact of hydrogen peroxide soutions on microbial loads and quality factors of red bell peppers, strawberries and watercressPublication . Alexandre, Elisabete M.C.; Brandão, Teresa R.S.; Silva, Cristina L.M.The impact of sodium hypochlorite and hydrogen peroxide (H2O2 at 1 and 5%) solutions on Listeria innocua in red bell peppers, total mesophiles in strawberries and total coliforms in watercress was studied. Quality attributes such as colour, firmness and pH were studied for all products; total anthocyanins content was determined for strawberries. Sensorial analyses were also carried out for all products. Results showed that H2O2 (5%) provided the highest reductions of microbial loads. Besides H2O2 (1%) had a lower impact, it was more effective than water-washings. Sodium hypochlorite solutions lead to microbial reductions comparable to water risings. In terms of quality, H2O2 (5%) was the solution with higher negative impact on products’ colour. For strawberries, such colour alterations were also detected by sensorial analyses. The anthocyanins content decreased significantly. Overall it was found that H2O2 (1%) was a good sanitizer solution, since microbial reduction was attained while quality factors did not suffer considerable alterations.
- Avaliação e otimização da termossonicação como tratamento alternativo de pós-colheita de tomate fresco (Lycopersicum esculentum, cv. Zinac)Publication . Pinheiro, Joaquina; Alegria, C.; Abreu, Marta; Gonçalves, Elsa M.; Silva, Cristina L.M.
- Balsamic vinegar from Modena: an easy effective approach to reduce Listeria monocytogenes from lettucePublication . Ramos, Bárbara; Brandão, Teresa R. S.; Teixeira, Paula; Silva, Cristina L.M.The microbiological safety of fresh produce is a significant concern of consumers and industry. After applying at an inoculated level (6e7 log CFU/mL) of Listeria monocytogenes on Iceberg lettuce, the antilisterial properties of balsamic vinegar from Modena, white wine vinegar and acetic acid solutions were investigated. Different proportions of the vinegars, acetic acid (58.7 g/L), and deionized water were evaluated to determine the role of those solutions at the stage of washing Iceberg lettuce to remove L. monocytogenes. The maximum observed log reduction of L. monocytogenes was 2.15 0.04 for balsamic vinegar (50% (v/ v)), 1.18 0.06 for white wine vinegar ((50% (v/v)) and 1.13 0.06 for acetic acid ((50% (v/v)). Washing with water only reduces 0.05 0.04 log CFU/mL of L. monocytogenes numbers. Listeria reductions observed for balsamic vinegar are similar or higher than those of chlorine-based sanitizers evaluated in other studies with lettuce. In the case of balsamic vinegar solutions, Listeria inhibition followed a linear reduction according to the model: Log (N/N0) ¼ 4.09 balsamic vinegar proportion % (v/v) 0.13; R2 ¼ 0.95. Balsamic vinegar washings may be a promising method for reducing other foodborne pathogens present in produce or other foods, at home and retail environments.
- Biochemical and colour changes of watercress (Nasturtium officinale R. Br.) during freezing and frozen storagePublication . Gonçalves, E.M.; Cruz, R.M.S.; Abreu, M.; Brandão, Teresa R. S.; Silva, Cristina L.M.The effects of water blanching, freezing, and frozen storage during 400 days at three different temperatures ( 7, 15 and 30 C), on watercress (Nasturtium officinale R. Br.) colour Hunter Lab parameters,chlorophyll degradation, vitamin C content loss and peroxidase (POD) activity were evaluated. The blanching induced significant changes on colour values and chlorophylls and vitamin C contents. POD activity was reduced 85% from its initial value. Freezing did not affect chlorophylls and vitamin C levels, however, promoted significant differences in colour values and POD residual activity. During frozen storage, ascorbic acid (AA) and POD activity Degradations followed first-order kinetics, and colour parameters (LH aH bH, aH/bH, LH aH/bH, LH/aH bH and hue (h0 H)) were successfully described by zero-order kinetics. The storage temperature effect was successfully described by the Arrhenius law. Chlorophylls and dehydroascorbic acid (DHAA) contents were kept constant during frozen storage.
- 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 behaviour. The objective of this work was to include, in the inactivation model, temperature, pH and aw effects using a black box polynomial model, aiming at accurate prediction. 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 aw of 0.95 and 0.99 were used for model assessment. The relations of such parameters with temperature, aw and pH were assumed to be polynomials.
- Comparison of recovery methods for the enumeration of injured Listeria innocua cells under isothermal and non-isothermal treatmentsPublication . Miller, Fátima A.; Ramos, Bárbara; Brandão, Teresa R.S.; Teixeira, Paula; Silva, Cristina L.M.This study compares the feature of different media with the combination of selective with non-selective media in a TAL method for recovery of Listeria innocua cells exposed to thermal treatments. Experiments were conducted in broth at constant temperature (52.5 and 65.0 ºC) and pH (4.5 and 7.5) conditions, using NaCl or glycerol to adjust water activity to 0.95. Four different media were used in bacterial cell enumeration: (i) a non-selective medium e TSAYE, (ii) two selective media e TSAYE þ 5%NaCl and Palcam Agar and (iii) TAL medium (consisting of a layer of Palcam Agar overlaid with one of TSAYE). Two food products were used as case studies aiming at comparison of results obtained on selective and TAL media enumeration. Parsley samples were inoculated with L. innocua and subjected to posterior thermal treatments both under isothermal (52.5, 60.0 and 65.0 ºC) and non-isothermal (heating rate of 1.8 ºC/min from 20.0 to 65.0 ºC) conditions. The recovery capability of TAL method was also studied when a pre-cooked frozen food (i.e. meat pockets) was fried (oil temperature of w180 ºC). TAL method proved to be better than Palcam Agar in terms of capability to recover injured cells and was effective in L. innocua enumeration when non-sterile samples were analysed.
- Degradation kinetics of colour, vitamin C and drip loss in frozen broccoli (Brassica oleracea L. ssp. Italica) during storage at isothermal and non-isothermal conditionsPublication . Gonçalves, Elsa M.; Abreu, Marta; Brandão, Teresa R. S.; Silva, Cristina L.M.Studies were undertaken on colour CIE L*a*b* values, vitamin C (ascorbic acid) and drip loss alterations of frozen broccoli (Brassica oleracea L. ssp. Italica) stored at isothermal ( 7, 15, and 25 C) and non-isothermal (accelerated life testing with step-stress methodology; temperature range from 30 to 5 C) conditions. The storage temperatures were selected according to conditions that occur in the cold chain. Frozen storage at all regimes had significant impact on all quality parameters analysed. Significant alterations in broccoli green colour, vitamin C content and drip loss were observed. Experimental data of h* colour degradation and drip loss (%) at isothermal conditions and a =a0 at non-isothermal conditions could be modelled by zero order kinetics. A first order kinetic model was adequate for the remaining quality factors and temperature regimes. The effect of storage temperature on kinetic parameters was successfully described by the Arrhenius equation.