Browsing by Author "Martins, R. C."
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- 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.
- Colour and chlorophyll's degradation kinetics of frozen green beans (Phaseolus Vulgaris, L.)Publication . Martins, R. C.; Silva, C. L. M.Colour changes and chlorophyll's degradation of frozen green beans (Phaseolus vulgaris, L., variety bencanta) were studied during 250 days of storage at -7, -15 and -30°C. Chlorophyll's a and b losses were modelled by a first order reaction kinetics. Colour Hunter a and b coordinates and total colour difference were successfully described by a first order reversible model. The temperature effect was well mathematically described by the Arrhenius law, for both quality parameters.
- 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.
- 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.
- Frozen green beans (Phaseolus vulgaris, L.) quality profile evaluation during home storagePublication . Martins, R. C.; Silva, C. L. M.Home storage is at the end of the frozen foods distribution chain, and not much is known how it affects frozen vegetables quality. This research presents a computational evaluation of frozen green beans (Phaseolus vulgaris, L.) quality profile, in terms of ascorbic acid, starch content, chlorophylls a and b, colour (Hunter a and b co-ordinates and total colour difference) and flavour, at storage temperatures of +5, )6, )12 and )18 C, for respectively, 1, 4, 14, and 60 days. Simulations were set to access the impact of the preestablished after sale dates of the star dating’ system. Results demonstrate that green beans nutritional and sensory parameters are well retained at the storage temperatures of +5, )6 and )12 C. At )18 C, sensory parameters (e.g. colour and flavour) are well retained, but nutritional parameters, such as ascorbic acid and starch, degraded. The study concluded that the star dating’ system is a good after sale dating system for frozen green beans for the storage temperatures of +5, )6 and )12 C. The system fails to maintain a good balance between sensory and nutritional parameters at low storage temperatures (e.g. <)18 C).
- 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.
- Modelização dos abusos de temperatura em vegetais congelados : efeitos na qualidadePublication . Martins, R. C.; Silva, C. L. M.0 mercado dos alimentos congelados tem tido nos últimos anos uma rápida expansão, onde o consumidor cada vez mais exige alimentos com maior qualidade, quer sensorial quer nutricional. Esta nova consciência leva a que se espere dos produtores e distribuidores produtos congelados um elevado nivel de qualidade e segurança, durante todo o ciclo de vida do produto até ser consumido. Torna-se óbvio que os abusos de temperatura, que ocorrem durante a vida útil do produto congelado, é um factor de risco que é limitativo da qualidade e segurança. 0 presente trabalho pretende apresentar as razões e as vantagens de modelizar a cadeia de frio, por forma a compreender como os abusos de temperatura deterioram a qualidade dos produtos congelados.
- 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.