Browsing by Author "Silva, C. L. M."
Now showing 1 - 10 of 18
Results Per Page
Sort Options
- Alicyclobacillus acidoterrestris spores as a target for Cupuacu (Theobroma grandiflorum) nectar thermal processing: kinetic parameters and experimental methodsPublication . Vieira, Margarida; Teixeira, A. A.; Silva, F. M.; Gaspar, N.; Silva, C. L. M.The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuaca (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 I (z = 7.8 +/- 2.6 degreesC, D-95 (degreesC) = 5.29 +/- 0.96 min), Experiment 2 (z = 22 +/- 5 degreesC, D-95 (degreesC) = 5.99 +/- 0.63 min), and Experiment 3 (z = 29 +/- 10 degreesC, D-95 degreesC = 3.82 +/- 0.48 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 = 31 +/- 6 degreesC, D-95 (degreesC) = 5.5 +/- 1.2 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 Cupuacu nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 degreesC only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 degreesC 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 the 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. (C) 2002 Elsevier Science B.V. All rights reserved.
- Biochemical and colour changes of watercress (Nasturtium officinale R. Br.) during freezing and frozen storagePublication . Gonçalves, E. M.; Cruz, R. M. S.; Abreu, M.; Brandao, T. R. S.; Silva, C. L. M.The effects of water blanching, freezing, and frozen storage during 400 days at three different temperatures (-7, - 15 and -30 degrees 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 (L(H) . a(H) . b(H), -a(H)/b(H,) L(H) . a(H)/b(H), L(H)/a(H) and hue (h(H)(0))) 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. (C) 2008 Elsevier Ltd. All rights reserved.
- Effect of cold chain temperature abuses on the quality of frozen watercress (Nasturtium officinale R. Br.)Publication . Cruz, R. M. S.; Vieira, M. M. C.; Silva, C. L. M.The objective of this work was to study the effect of temperature abuses on the colour and vitamin C content of a new frozen vegetable, watercress (Nasturtium officinale R. Br.). The vitamin C content, expressed as ascorbic (AA) and dehydroascorbic (DHAA) acids, and colour, expressed in the Hunter Lab parameters, were evaluated along a plan of temperature abuses, based on a real situation for a four month frozen storage period. A comparison between the hue angle and AA experimental data and prediction models, using kinetic parameters determined under isothermal conditions, was also run. The colour showed some variation, namely on the parameters L, a, TCD (Total Colour Difference) and hue angle. Although, during the temperature abuses, some fluctuation was observed, no vitamin C degradation or major colour changes occurred. A zero-order and a first-order prediction models fitted well the experimental data for the hue angle and AA behaviour with temperature abuses, respectively. In general, the frozen watercress colour and vitamin C content were not impaired by the imposed temperature abuses. This work will help to predict and understand the sensory and nutritional quality changes of frozen watercress that might occur during frozen storage and distribution in the cold chain under the used conditions.
- Effect of heat and thermosonication treatments on peroxidase inactivation kinetics in watercress (Nasturtium officinale)Publication . Cruz, R. M. S.; Vieira, M. M. C.; Silva, C. L. M.The effect of heat and the combined heat/ultrasound (thermosonication) treatment on the inactivation kinetics of peroxidase in watercress (Nasturtium officinale) was studied in the temperature range of 40-92.5 degrees C. In the heat blanching processes, the enzyme kinetics showed a first-order biphasic inactivation model. The activation energies and the rates of the reaction at a reference temperature for both the heat-labile and heat-resistant fractions were, respectively, E(a1) = 421 +/- 115 kJmol(-1) and E(a2) = 352 +/- 81 kJmol(-1), k(184.6 degrees C) = 18 +/- 14min(-1) and k(284.6 degrees C) = 0.24 +/- 0.14min(-1). The initial relative specific activity for both isoenzyme fractions were also estimated, being C(01) = 0.5 +/- 0.08 mu mol min(-1)mg protein(-1) and C(02) = 0.5 +/- 0.06 mu mol min(-1)mg protein(-1), respectively. The application of thermosonication was studied to enable less severe thermal treatments and, therefore, improving the quality of the blanched product. In this treatment the enzyme kinetics showed a first-order model. The activation energy, the rate of reaction at a reference temperature and the initial relative specific activity were, respectively, E(a3) = 496 +/- 65 kJmol(-1), k(387.5 degrees C) = 10 +/- 2min(-1) and C(03) = 1 +/- 0.05 mu mol min(-1)mg protein(-1), proving that the enzyme became more heat labile. The present findings will help to design the blanching conditions for the production of a new and healthy frozen product, watercress (Nasturtium officinale), with minimized colour or flavour changes along its shelf life. (c) 2004 Elsevier Ltd. All rights reserved.
- Effect of heat and thermosonication treatments on watercress (Nasturtium officinale) vitamin C degradation kineticsPublication . Cruz, R. M. S.; Vieira, M. M. C.; Silva, C. L. M.The use of ultrasound in food processing creates novel and interesting methodologies, which are often complementary to classical techniques. In this work, the effect of heat and the combined treatment heat/ultrasound (thermosonication) on the thermal degradation kinetics of vitamin C in watercress (Nasturtium officinale) was studied in the temperature range of 82.5 to 92.5 °C. First order reaction kinetics adequately described the vitamin C losses during both blanching processes. The activation energies and the reaction rates at 87.5 °C for heat (H) and thermosonication (Ts) treatments were, respectively, EavitCH = 150.47 ± 42.81 kJ mol− 1 and EavitCTs = 136.20 ± 60.97 kJ mol− 1, and k87.5 °CvitCH = 0.75 ± 0.10 min− 1 and k87.5 °CvitCTs = 0.58 ± 0.11 min− 1. No significant differences (P > 0.05) were detected between both treatments. The thermosonication treatment was found to be a better blanching process, since it inactivates watercress peroxidase at less severe blanching conditions and consequently retains vitamin C content at higher levels. The present findings will help to optimise the blanching conditions for the production of a new and healthy frozen product, watercress, with heat and a new blanching process methodology.
- Enterococcus faecalis and Pseudomonas aeruginosa behaviour in frozen watercress (Nasturtium officinale) submitted to temperature abusesPublication . Oliveira, S. R.; Cruz, R. M. S.; Vieira, M. M. C.; Silva, C. L. M.; Gaspar, M. N.Watercress is an herb traditionally consumed fresh. If frozen, would be readily available to consumers. However, pathogenics resistant to frozen storage are a safety concern in this new product. in this study watercress was artificially contaminated with Pseudomonas aeruginosa ATCC 27853 and Enterococcus faecalis ATCC 29212. Their survival was evaluated after blanching, frozen storage and temperature fluctuations of the frozen product. The blanching caused a reduction of about 2 log cfu per gram of product of total viable count (TVC) and about 1.7 and 1.3 log cfu per gram of product of P. aeruginosa and E. faecalis, respectively. P. aeruginosa seemed to be more sensitive to temperature abuses than E. faecalis. After 3 months, TVC was still observed with a reduction of about 3 log cfu per gram of product. At the end of the study, exposure to freeze-thaw cycles resulted in death or injury of the microorganisms. These findings on the behaviour of two microorganisms of concern in frozen watercress will help improving the safety and cold chain settings for this product. (C) 2008 Elsevier Ltd and IIR. All rights reserved.
- Heat treatment evaluation on quality and safety of whole tomato (lycopersicum esculentum l.) fruitsPublication . Pinheiro, Joaquina; Alegria, Carla; Abreu, Marta; Fernandes, Isabel; Gonçalves, Elsa M.; Silva, C. L. M.; Nunes, CarlaQuality and safety attributes, like colour (CIELab parameters), texture (Maximum force – MF), total phenolics content (TPC), peroxidase activity (POD), microbial count and moulds & yeasts (Log10 cfu g-1) were determined on heat treated mature-green tomatoes at temperature ranging of 40 to 50 ºC and different times. Heat treatments (HT) did not affect significantly (p>0.05) the tomatoes colour. In terms of texture, a reduction of 10% MF was observed at 50 ºC_15min...
- Impact of thermal blanching and thermosonication treatments on watercress (Nasturtium officinale) quality: thermosonication process optimisation and microstructure evaluationPublication . Cruz, R. M. S.; Vieira, M. M. C.; Fonseca, Susana C.; Silva, C. L. M.The objectives of the present work were to optimise watercress heat and thermosonication blanching conditions, in order to obtain a product with better quality for further freezing, and to evaluate the effects of thermosonication on the microstructure of watercress leaves. In a chart of optimal time–temperature conditions for a 90% peroxidase inactivation (imposed constraint), vitamin C (objective function) and a-value (improvement toward green) were mathematically predicted for both heat and thermosonication blanching treatments. Two optimal thermosonication combinations were selected: 92°C and 2 s, retaining 95% of vitamin C content and 5% a-value improvement, and a better condition in terms of practical feasibility, 86°C and 30 s, allowing a 75% vitamin C retention and 8% a-value improvement. The experimental values, for each thermosonication optimal time–temperature zone, were in good agreement with the models' predicted responses. In terms of microstructure, thermosonicated watercress at 86 and 92°C showed similar loss of turgor and release of chloroplasts. The proposed optimal thermosonication blanching conditions allow the improvement of the blanched watercress quality and consequently contribute for the development of a high-quality new frozen product. However, a suitable scale-up is mandatory for industrial implementation.
- Inactivation kinetics of peroxidase in zucchini (Cucurbita pepo L.) by heat and UV-C radiationPublication . Neves, Filipa I. G.; Vieira, M. M. C.; Silva, C. L. M.The effect of traditional thermal water blanching, or its combination with a UV-C radiation pre-treatment (11 J/m2), on the inactivation kinetics of peroxidase in zucchini (Cucurbita pepo L.) was carried out in the temperature range of 80 to 98 °C, and up to 3 min of processing time. Peroxidase inactivation started being noticed only at temperatures around 85 °C. For both treatments, the inactivation kinetics followed a first order reaction with the Arrhenius model describing the temperature dependence of the reaction rate. The obtained kinetic parameters (kHeat 89.6 °C = 7.37 × 10− 7 ± 3.47 × 10− 7 min− 1 and Ea Heat = 925 ± 69 kJ mol− 1; kHeat 89.6 °C + UV-C = 2.42 × 10− 5 ± 6.58 × 10− 6 min− 1 and Ea Heat + UV-C = 596 ± 48.8 kJ mol− 1) showed that UV-C radiation had a significant contribution to increase the peroxidase degradation rate. These results will help to design new pre-processing conditions for the production of frozen zucchini, using less severe thermal treatments and attempt to minimize quality losses.
- Kinetic parameters estimation for ascorbic acid degradation in fruit nectar using the partial equivalent isothermal exposures (PEIE) method under non-isothermal continuous heating conditionsPublication . Vieira, M. M. C.; Teixeira, A. A.; Silva, C. L. M.With the purpose of testing the Paired Equivalent Isothermal Exposures (PEIE) method to determine reaction kinetic parameters under non-isothermal conditions, continuous pasteurizations were carried out with a tropical fruit nectar [25% cupuacu (Theobroma grandiflorum) pulp and 15% sugar] to estimate the ascorbic acid thermal degradation kinetic parameters. Fifteen continuous thermal exposures were studied, with seven being cycled. The experimental ascorbic acid thermal degradation kinetic parameters were estimated by the PEIE method (E-a = 73 +/- 9 kJ/mol, k(80 degreesC) = 0.017 +/- 0.001 min(-1)). These values compared very well to the previously determined values for the same product under isothermal conditions (E-a = 73 +/- 7 kJ/mol, k(80 degreesC) = 0.020 +/- 0.001 min(-1)). The predicted extents of reaction presented a good fit to the experimental data, although the cycled thermal treatments presented some deviation. In addition to being easier and faster than the Isothermal method, the PEIE method can be a more reliable method to estimate first-order reaction kinetic parameters when continuous heating is considered.