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- Modelling colour and chlorophyll losses of frozen green beans (Phaseolus vulgaris, L.)Publication . Martins, R.C.; Silva, C. L. M.Colour changes and chlorophyll degradation of frozen green beans (Phaseolus vulgaris, L., variety bencanta) were studied during 250 days of storage at 7, 15 and 30 C. Chlorophyll a and b losses and colour Hunter a and b coordinates and total colour difference (TCDH) changes were successfully described by first order and reversible first order models, respectively. The temperature effect was described by the Arrhenius law. Disagreement between the colour co-ordinates and chlorophyll content was obtained. Therefore, chlorophyll content is not a good colour index of frozen green beans. The results emphasise that colour is a more important parameter to assess frozen green beans visual quality. # 2002 Elsevier Science Ltd and IIR. All rights reserved.
- Kinetics of frozen stored green beans (Phaseolus vulgaris, l.) quality changes: vitamin C, reduced sugars and starchPublication . Martins, R.C.; Silva, C. L. M.
- Accelerated life testing of frozen green beans (Phaseolus vulgaris, L.) quality loss kinetics: colour and starchPublication . Martins, R. C.; Lopes, I. C.; Silva, C. L. M.This study uses the information derived from a computational research for the design of accelerated life testing (ALT) to implement experimentally the step stress methodology for the quantification of frozen green beans (Phaseolus vulgaris, L.) colour and starch degradation kinetics. Colour loss and starch degradation were successfully modelled, respectively, by a first-order reversible and apparent first-order kinetics, under dynamic temperature fluctuations. Results show that the step stress produces models with lower regression standard errors than the conventional isothermal methodology, increasing the accuracy of the estimated kinetic parameters. The ALT methodology, produces however, higher confidence intervals for the estimated kinetic parameters, than the isothermal methodology (e.g. colour b-coordinate by the: (i) isothermal methodology: k₋₁₅ ºC=22.189±0.349 day⁻¹·10⁻³; and (ii) ALT methodology: k₋₁₅ ºC=22.189±0.349 day⁻¹·10⁻³). Furthermore, as expected, higher Arrhenius activation energies (Ea) were estimated by the ALT step-stress methodology, than by the isothermal methodology (e.g. Hunter total colour difference (TCDH): (i) isothermal methodology: Ea=106.272±18.67 kJmol⁻¹; and (ii) ALT methodology: Ea=140.344±18.670 kJmol⁻¹). Accelerated tests are valuable tools, that can aid the study of quality losses in frozen foods. Although ALT tests increase the complexity of data analysis, they produce satisfactory results, when applied to frozen green beans kinetics of starch and colour losses.
- Genomic and transcriptomic analysis of Saccharomyces cerevisiae isolates with focus in succinic acid productionPublication . Franco-Duarte, Ricardo; Bessa, Daniela; Gonçalves, Filipa; Martins, Rosa; Silva-Ferreira, António César; Schuller, Dorit; Sampaio, Paula; Pais, CéliaSuccinic acid is a platform chemical that plays an important role as precursor for the synthesis of many valuable bio-based chemicals. Its microbial production from renewable resources has seen great developments, specially exploring the use of yeasts to overcome the limitations of using bacteria. The objective of the present work was to screen for succinate-producing isolates, using a yeast collection with different origins and characteristics. Four strains were chosen, two as promising succinic acid producers, in comparison with two low producers. Genome of these isolates was analysed, and differences were found mainly in genes SDH1, SDH3, MDH1 and the transcription factor HAP4, regarding the number of single nucleotide polymorphisms and the gene copy-number profile. Real-time PCR was used to study gene expression of 10 selected genes involved in the metabolic pathway of succinic acid production. Results show that for the non-producing strain, higher expression of genes SDH1, SDH2, ADH1, ADH3, IDH1 and HAP4 was detected, together with lower expression of ADR1 transcription factor, in comparison with the best producer strain. This is the first study showing the capacity of natural yeast isolates to produce high amounts of succinic acid, together with the understanding of the key factors associated, giving clues for strain improvement.
- Facing the complexity of grape quality management and delivering an highthroughput device: VinePATPublication . Martins, R. C.; Lopes, V. V.; Ferreira, A. C. SilvaThe physiological response of plants to external perturbation is complex and occurs at different levels of their metabolism. This is a multivariate and multi-scale phenomena, therefore high-throughput methodologies are required to extract relevant information. The nonexistence of a device with such characteristics constitutes a barrier to the interpretation of the consequences of external inputs. Spectroscopy is a multivariate methodology with greatest interest for metabolic studies in biological systems. In fact, this technique provides detailed information on the molecular structure and reaction mechanisms. Moreover due to its non-destructive character, this methodology is currently used to characterize proteins, peptides, lipids, membranes, carbohydrates in pharmaceuticals and food products as well as plants and animal tissues. VinePAT is a vineyard management system based in the Process Analytical Technologies (PAT) methodologies to provide winemakers with state-of-the-art metabolic images of vineyards for precision winemaking by using UV-VIS-SWNIR spectroscopy techniques. The system hardware is based on miniaturized fiber-optics spectrometer adapted for grape and leaves measurements and suited for outdoor data acquisition. Combining these georeferenced outdoor measurements collected at the vineyard with state-of-the-art spectroscopy signal processing, the winemaker will be able to observe vine metabolism by using a non-destructive 'in-vivo' methodology, as well as, the global-picture of the vineyard for implementing precision winemaking technologies based on process analytical technology. Here we demonstrate the potential of the VinePAT technology for grape-growers by presenting: i) spectroscopy equipment in action; ii) the variance imaging and zone diagnostics; iii) metabolic imaging with especial incidence in key metabolites for grape maturation; iv) how to use multivariate control charts; and v) the full potential of the technology deployed by process analytical technology.
- Green beans (Phaseolus vulgaris, L.) quality loss upon thawingPublication . Martins, R.C.; Silva, C. L. M.Frozen green beans (Phaseolus vulgaris, L.) thawing is one of the operations that compromises significantly quality. The present research aims at studying the effects of thawing, at environmental and refrigeration temperatures, on the quality profile of a frozen green beans package. Quality losses were computationally evaluated, using a simulation system based on object-oriented technologies. Simulations show that sensory parameters, such as flavour and colour, are more sensitive to thawing at environmental temperatures, than nutritional parameters, such as vitamin C and starch contents. The study demonstrates that green beans quality retention is also influenced by packaging materials, with different degrees of thermal insulation, and environmental conditions, such as temperature and surface heat convection coefficients. Important conclusions are discussed on shelf-life limiting quality parameters during thawing and temperature abuses, as well as on thawing green vegetables to maximise their quality profile. Results emphasise that the principle of high-temperature–short-times is not directly applicable to frozen green beans thawing. Furthermore, simulations lead to the conclusion that overall quality profile is maximised by thawing under refrigeration temperatures.
- Oxidation Management of White Wines Using Cyclic Voltammetry and Multivariate Process MonitoringPublication . Martins, R.; Bento, F.; Geraldo, D.; Lopes, V.; Lopes, T. I. M. S.; Oliveira, C.; Ferreira, A. C. Silva
- Influence of temperature abuses on the quality of frozen broad beansPublication . Martins, R. C.; Despré, B.; Molinari, A. F.; Silva, C. L. M.The main objective of this study was to evaluate the impact of temperature abuses on the quality of frozen broad beans. Test samples suffered the application of three types of abuses, simulating the pack in the outermost corner of a pallet when placed at room temperature, defrosting in a display cabinet and home transport. Control samples were kept at -18±2°C. Several quality parameters were analysed along storage. No significant difference in acidity, pH, moisture and sugars was detected, and no regeneration of peroxidase was observed. However, a significant difference was found for colour coordinates. Sensory evaluation lead to the conclusion that there is a significant difference in terms of colour, flavour intensity and firmness, but there was no preference for any of the samples. Frozen broad beans are sensitive to temperature abuses, therefore special care must be taken to keep a constant storage temperature.
- Texture losses of green beans along frozen storagePublication . Martins, R. C.; Silva, C. L. M.The texture loss of frozen green beans ( Phaseolus vulgaris, L., variety Bencanta) was macroscopically evaluated by a puncture test, using the INSTRON (Universal Testing Machine, model 4500) with a 4,85 mm diameter plunger, along 250 days of isothermal storage at -7, -15 and -30°C. The force deformation curves were recorded for data analysis of: i) Energy - the area below the force deformation curve, as a measurement of the resistance to compression by the plunger, ii) Stress at the failure point - pressure at the failure point, as an index of firmness and iii) Stiffness -Stress / Strain, both at the failure point. The force deformation curves exhibit a decrease in the resistance to compression, with storage time at all studied temperatures. For longer periods of storage, the well-defined failure point, that is a characteristic of fresh green beans, decreases in Stress magnitude and increases in Strain, corresponding to the softening of green beans initia texture.The softening of the green beans tissues was assessed by the decrease in Energy, Stress and Stiffness along storage time and at the three studied temperatures. This texture loss has an exponential behaviour, with a residual value of texture that is maintained for a long period of storage. Thus, the softening process was modelled with a first reversible order kinetics. The kinetic parameters were estimated by nonlinear regression to all data, maximising the likelihood function and solving the normal equations by the Gauss-Newton algorithm. Although the high biological variability observed in the texture of green beans influence the precision of the estimated kinetic parameters, the temperature effec was well described by an Arrhenius behaviour. This research work lead to the conclusion that the softening of frozen stored green beans, is an irreversible degradation of texture, and is an important quality attribute, that can be macroscopically described.
- Computational design of accelerated life testing applied to frozen green beansPublication . Martins, R. C.; Silva, C. L. M.Three different accelerated life tests (ALT) were designed by computer simulation to investigate their practical applicability to quantify kinetics of quality loss in frozen stored foods. Heat transfer and quality degradation inside a green bean were simulated, using a spectral finite element method (SFEM), to develop pseudo-experimental data. Temperature fluctuations inside a refrigerator were simulated, by a piecewise linear stochastic differential equation, and integrated into the SFEM program. Thereafter, the simulated data was treated by non-linear regression analysis to estimate the kinetic parameters. The different ALT tests were then compared in terms of precision and accuracy. This study shows that temperature fluctuations, inside a refrigerator, influence the accuracy of the kinetic estimates, and if the temperature spectrum is used to derive kinetic estimates, it is possible to apply accurately ALT methodologies to frozen foods.
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