Browsing by Author "Martins, Sara I. F. S."
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- Phenylacetaldehyde real-time release kinetics in wine like model solutionsPublication . Monforte, Ana Rita; Martins, Sara I. F. S.; Ferreira, António César SilvaThe present work shows key possibilities in modelling the kinetics of phenylacetaldehyde formation as a function of sugar, phenolic compounds, metals and sulphur dioxide. The release kinetics were measured online by proton transfer reaction-mass spectrometry (PTR-MS). Phenylacetaldehyde formation was fitted using Weibull models and an activation energy of 73 kJ/mol estimated. Also, a confirmation that glucose can inhibit the aldehyde formation was demonstrated, and the sequential additions in real time showed that the inhibition level was dependent on metal ions presence. Moreover, for the first time it was observed in real time the capacity of SO2 to bind with phenylacetaldehyde, and by trapping it, lowering its release. Finally, the impact of pH and temperature in the stability of the formed adducts and underling release mechanism is also elucidated.
- Response surface methodology: a tool to minimize aldehydes formation andoxygen consumption in wine model systemPublication . Monforte, Ana Rita; Oliveira, Carla; Martins, Sara I. F. S.; Ferreira, António César SilvaA response surface methodology was applied to study the effect of precursors on o-quinone and phenylacetaldehyde formation in wine model systems stored at 40 °C during 24 h. The results confirmed that glucose plays an important role in reducing aldehyde formation by inhibiting the formation of o-quinone. The regression equations showed that oxygen consumption followed a 2nd polynomial equation whereas phenylacetaldehyde and o-quinone were best fit with a polynomial function containing quadratic terms. These behaviors indicate that different pathways are involved in the respective aldehyde formation and oxygen consumption. RSM has been shown to be a powerful tool to better understand key chemical reactions. By considering a number of factors, individually and in combinations, the derived equations predicted that the best combination to minimize phenylacetaldehyde was achieved for high glucose levels and low amounts of gallic acid and metals. This is valuable information when trying to improve wines sensorial properties during shelf-life.
- Strecker aldehyde formation in wine: new insights into the role of gallic acid, glucose, and metals in phenylacetaldehyde formationPublication . Monforte, Ana Rita; Martins, Sara I. F. S.; Ferreira, António C. SilvaStrecker degradation (SD) leading to the formation of phenylacetaldehyde (PA) was studied in wine systems. New insights were gained by using two full factorial designs focusing on the effects of (1) pH and (2) temperature. In each design of experiments (DoE) three factors, glucose, gallic acid, and metals at two levels (present or absence), were varied while phenylalanine was kept constant. The obtained results gave a clear indication, with statistical significance, that in wine conditions, the SD occurs in the presence of metals preferentially via the phenolic oxidation independent of the temperature (40 or 80 °C). The reaction of the amino acid with the o-quinone formed by the oxidation of the gallic acid seems to be favored when compared with the SD promoted by the reaction with α-dicarbonyls formed by MR between glucose and phenylalanine. In fact, kinetics results showed that the presence of glucose had an inhibitory effect on PA rate of formation. PA formation was 4 times higher in the control wine when compared to the same wine with 10 g/L glucose added. By gallic acid quinone quantitation it is shown that glucose affects directly the concentration of the quinone. decreasing the rate of quinone formation. This highlights the role of sugar in o-quinone concentration and consequently in the impact on Strecker aldehyde formation, a promising new perspective regarding wine shelf-life understanding.