Browsing by Author "Martins, Rui C."
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- Design and optimization of hot-filling pasteurization conditionsPublication . Silva, Filipa V. M.; Martins, Rui C.; Silva, Cristina L. M.Cupuacüu (Theobroma grandiflorum) is an Amazonian tropical fruit with a great economic potential. Pasteurization, by a hot-filling technique, was suggested for the preservation of this fruit pulp at room temperature. The process was implemented with local communities in Brazil. The process was modeled, and a computer program was written in Turbo Pascal. The relative importance among the pasteurization process variables (initial product temperature, heating rate, holding temperature and time, container volume and shape, cooling medium type and temperature) on the microbial target and quality was investigated, by performing simulations according to a screening factorial design. Afterward, simulations of the different processing conditions were carried out. The holding temperature (TF) and time (thold) affected pasteurization value (P), and the container volume (V) influenced largely the quality parameters. The process was optimized for retail (1 L) and industrial (100 L) size containers, by maximizing volume average quality in terms of color lightness and sensory “fresh notes” and minimizing volume average total color difference and sensory “cooked notes”. Equivalent processes were designed and simulated (P91°C ) 4.6 min on Alicyclobacillus acidoterrestris spores) and final quality (color, flavor, and aroma attributes) was evaluated. Color was slightly affected by the pasteurization processes, and few differences were observed between the six equivalent treatments designed (TF between 80 and 97 °C). TF g 91 °C minimized “cooked notes” and maximized “fresh notes” of cupuacüu pulp aroma and flavor for 1 L container. Concerning the 100 L size, the “cooked notes” development can be minimized with TF g 91 °C, but overall the quality was greatly degraded as a result of the long cooling times. A more efficient method to speed up the cooling phase was recommended, especially for the industrial size of containers.
- Oxidation management of white wines using cyclic voltammetry and multivariate process monitoringPublication . Martins, Rui C.; Oliveira, Raquel; Bento, Fatima; Geraldo, Dulce; Lopes, Vitor V.; Pinho, Paula Guedes de; Oliveira, Carla M.; Ferreira, António C. SilvaThe development of a fingerprinting strategy capable to evaluate the “oxidation status” of white wines based on cyclic voltammetry is proposed here. It is known that the levels of specific antioxidants and redox mechanisms may be evaluated by cyclic voltammetry. This electrochemical technique was applied on two sets of samples. One group was composed of normal aged white wines and a second group obtained from a white wine forced aging protocol with different oxygen, SO2, pH, and temperature regimens. A study of antioxidant additions, namely ascorbic acid, was also made in order to establish a statistical link between voltammogram fingerprints and chemical antioxidant substances. It was observed that the oxidation curve presented typical features, which enables sample discrimination according to age, oxygen consumption, and antioxidant additions. In fact, it was possible to place the results into four significant orthogonal directions, compressing 99.8% of nonrandom features. Attempts were made to make voltammogram fingerprinting a tool for monitoring oxidation management. For this purpose, a supervised multivariate control chart was developed using a control sample as reference. When white wines are plotted onto the chart, it is possible to monitor the oxidation status and to diagnose the effects of oxygen regimes and antioxidant activity. Finally, quantification of substances implicated in the oxidation process as reagents (antioxidants) and products (off-flavors)was tried using a supervised algorithmic the partial least square regression analysis. Good correlations (r > 0.93) were observed for ascorbic acid, Folin-Ciocalteu index, total SO2, methional, and phenylacetaldehyde. These results show that cyclic voltammetry fingerprinting can be used to monitor and diagnose the effects of wine oxidation.
- Saccharomyces cerevisiae oxidative response by cyclic voltammetry and GC-MSPublication . Oliveira, Carla Maria; Castro, Cristiana C.; Gunning, Caitriona; Couto, José A.; Teixeira, José A.; Martins, Rui C.; Silva Ferreira, António César
- Saccharomyces cerevisiae oxidative response evaluation by cyclic voltammetry and gas chromatography−mass spectrometryPublication . Castro, Cristiana C.; Gunning, Caitriona; Oliveira, Carla M.; Couto, José A.; Teixeira, José A.; Martins, Rui C.; Ferreira, António C. SilvaThis study is focused on the evaluation of the impact of Saccharomyces cerevisiae metabolism in the profile of compounds with antioxidant capacity in a synthetic wine during fermentation. A bioanalytical pipeline, which allows for biological systems fingerprinting and sample classification by combining electrochemical features with biochemical background, is proposed. To achieve this objective, alcoholic fermentations of a minimal medium supplemented with phenolic acids were evaluated daily during 11 days, for electrochemical profile, phenolic acids, and the volatile fermentation fraction, using cyclic voltametry, high-performance liquid chromatography−diode array detection, and headspace/solid-phase microextraction/gas chromatography−mass spectrometry (target and nontarget approaches), respectively. It was found that acetic acid, 2- phenylethanol, and isoamyl acetate are compounds with a significative contribution for samples metabolic variability, and the electrochemical features demonstrated redox-potential changes throughout the alcoholic fermentations, showing at the end a similar pattern to normal wines. Moreover, S. cerevisiae had the capacity of producing chlorogenic acid in the supplemented medium fermentation from simple precursors present in the minimal medium.
- The X-windows high-throughput mass spectroscopy pipelinePublication . Martins, Rui C.; Castro, C. C.; Teixeira, J. A; Ferreira, J. A. C Silva