Changes in the volatile fraction composition of port wines during aging: a mechanistic approach

A food product during shelf life suffers chemical changes, caused by sets of reactions regulated by thermodynamics principles forming several mechanisms. In food processing, Maillard reaction is probably the most described. The knowledge of the different mechanism and their possible interconnections is central to understand and consequently monitor food quality. It is within this context, that the motivation of this thesis arose: to provide insights about the inter- connections between the Maillard reaction and oxidation during Port wine aging and how these mechanisms will be affected by technological parameters such as temperature and oxygen. Conclusively know how they can be controlled and thus provide ways to manage the aging process and consequently the quality of the product. In this context wines used were aged for 63 days under different conditions of temperature and oxygen and wines of different ages were analyzed by gas chromatography coupled to a flame ionization detector and to mass spectrometry. Marker compounds of Maillard reaction, oxidation and from a possible mechanism that outcomes from the previous ones which leads to sotolon were quantified and was calculated the respective kinetic parameters, these were used for through Monte Carlo simulations predict the composition of wine stored in different conditions of oxygen and temperature. The chromatographic profiles (vectors of intensity vs. retention times) were used as chemical fingerprints to find out more markers related with the process. A new approach for chromatographic data visualization was created consisting in a network of connections (Pearson correlations) between retention times (compounds). The kinetic parameters have shown that the formation of sotolon is highly dependent upon oxygen and temperature. Kinetics models with Monte Carlo simulations where applied and on the basis of the modeling predictions, it would seem that the temperature of a cellar would have a more significant impact on the Port wines stored in containers where the oxygen intake is higher (barrels) when compared to containers with low oxygen permeability (bottles with cork stoppers). The use of chromatographic profiles as samples fingerprints allows classifying samples of different ages and finding more markers related to the process. The network reconstruction provides considerably more information in an effort to understand the probable kinetic contexts of the molecules represented by peaks in each chromatogram. The technology developed in the study allows the modulation of the Port sensory profiles and consequently contributes to quality improvement. This knowledge has high value for the industry because it allows the management of the quality and therefore the increment of the product value.