Browsing by Author "Cruz, R. M. S."
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- 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 antioxidant and optimal antimicrobial mixtures of carvacrol, grape seed extract and chitosan on different spoilage microorganisms and their application as coatings on different food matricesPublication . Rubilar, Javiera F.; Cruz, R. M. S.; Khmelinskii, Igor; Vieira, M. M. C.There is growing interest in the use of natural agents with antimicrobial (AM) and antioxidant (AOX) properties. Optimization of the AM capacity for mixtures containing carvacrol, grape seed extract (GSE) and chitosan, against gram-negative (Pseudomonas aeruginosa), gram-positive bacteria (Staphylococcus aureus, Listeria innocua and Enterococcus faecalis) and yeast (Saccharomyces cerevisiae) at 106 cfu mL−1 was studied. To observe the synergistic or antagonistic effect and find optimal combinations between the three agents, a simplex centroid mixture design was run for each microorganism, combining carvacrol (0-300 ppm, X1)X, GSE (0-2000 ppm, X2) and chitosan (0-2% w/v, X3). Results of the response surface analysis showed several synergistic effects for all microorganisms. Combinations of 60 ppm-400 ppm-1.2% w/v (carvacrol-GSE-chitosan; optimal AM combination 1, OAMC-1); 9.6 ppm-684 ppm-1.25% w/v (OAMC-2); 90 ppm-160 ppm-1.24% w/v (OAMC-3) were found to be the optimal mixtures for all microorganisms. Radical scavenging activity (RSA) of the same agents was then compared with a standard AOX (butylated hydroxytoluene; BHT) at different concentrations (25, 50 and 100 ppm; as well as the optimal AM concentrations) by the 1,1-diphenyl-2- picrylhydrazyl (DPPH) method. RSA increased in the following order: chitosan< carvacrol< BHT< GSE and for the OAMC: OAMC-2< OAMC-1< OAMC-3. The best RSA (OAMC-3) was applied as a coating in two different food matrices (strawberries and salmon). For strawberries, P. aeruginosa was more sensitive to the action of OAMC-3 than S. cerevisiae. For salmon, S. aureus was more resistant to the action of OAMC-3 than E. faecalis and L. innocua.
- 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.
- 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.
- Modeling the kinetics of peroxidase inactivation, colour and texture changes of Portuguese cabbage (Brassica oleracea L. var. costata DC) during UV-C light and heat blanchingPublication . Cruz, R. M. S.; Godinho, Ana; Aslan, Dilek; Koçab, Necip; Vieira, M. M. C.The e ects of heat blanching and UV-C light followed by heat on Portuguese cabbage peroxidase (POD), colour and texture were studied in the temperature range of 80-95 °C. POD inactivation, lightness (L) and yellowness (b) colour changes were described by a rst-order reaction model. The greenness (a) colour and texture ( rmness) changes followed a two fraction kinetic model behaviour. The temperature e ect was well described by the Arrhenius law. At lower temperatures the combined treatment showed higher POD inactivation. Colour and texture parameters did not show signi cant di erences between treatments. Long processing times turned the leaves slightly darker, decreased greenness, yellowness and rmness. Short processing times increased the rmness and greenness of the leaves. The treatment at 80 °C for 90 seconds reduced 90% of POD, retaining 98% of lightness and 92% of yellowness and improved the green colour (130%) and rmness (125%). At 80 °C the heat blanching required 7.4 min to inactivate 90% of the enzyme activity, reducing lightness, greenness, yellowness and rmness to 92%, 68%, 62% and 61%, respectively. The present ndings will help to optimize the Portuguese cabbage blanching conditions.
- Modelling kinetics of watercress (Nasturtium officinale) colour changes due to heat and thermosonication treatmentsPublication . Cruz, R. M. S.; Vieira, M. M. C.; Silva, C. L. M.Watercress (Nasturtium officinale) colour changes due to blanching by heat and a combined treatment of heat/ultrasound (thermosonication) were studied in thetemperature range of 82.5 to 92.5 °C. The application of thermosonication was intended to enable less severe blanching treatments and, therefore, improve the quality of the blanched product. The thermosonication blanching processes promoted changes of the green colour (an parameter) at a higher rate (P < 0.05), when compared with the heat blanching processes. No significant differences (P > 0.05) were detected between heat and thermosonication blanching processes in terms of the colour parameters Ln, bn and TCD changes.In both treatments, a fractional first order model fitted well the experimental data for Ln, an and bn (RH2 = 0.99; RTs2 = 0.99) and TCD (RH2 = 0.92; RTs2 = 0.96) colour parameters. The chlorophylls content showed no significant differences (P > 0.05) between thermally treated and thermosonicated watercress samples. The present findings will help to evaluate the effectiveness of thermosonication as a novel process to replace the classical heat treatment.
- Physico-mechanical properties of chitosan films with carvacrol and grape seed extractPublication . Rubilar, Javiera F.; Cruz, R. M. S.; Silva, Hélder D.; Vicente, António A.; Khmelinskii, Igor; Vieira, M. M. C.The physico-mechanical properties of 3 films composed by carvacrol, grape seed extract (GSE) and chitosan in different proportions were studied. The films, prepared by solvent casting technique with the following compositions of the casting solutions in carvacrol, GSE and chitosan: film-1: 9.6 ppm–684 ppm–1.25% w/v, film-2: 60 ppm–400 ppm–1.2% w/v and film-3: 90 ppm–160 ppm–1.24% w/v and were compared to a control (1.25% w/v chitosan) film. Mechanical, structural, barrier and colour properties of the films were evaluated. Film-3 presented the lowest water vapour and carbon dioxide permeabilities (WVP and CO2P) and tensile strength (TS) values and the highest oxygen permeability (O2P), whereas film-1 presented the highest water content and the lowest crystallinity, CO2P, TS and luminosity. These results suggest that in the range studied, carvacrol and GSE affect the film structure and its mechanical properties due to hydrophilic (GSE) and hydrophobic (carvacrol) compounds. This work will help the development of edible films, based on physico-mechanical properties, contributing to food preservation and shelf-life extension.