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- Unveiling the evolution of Madeira Wine key metabolites: a three-year follow-up studyPublication . Pereira, Vanda; Leça, João M.; Freitas, Ana I.; Pereira, Ana C.; Pontes, Marisela; Albuquerque, Francisco; Marques, José C.Madeira wine (MW) encompasses an unusual oxidative ageing process that makes it distinc tive. Several metabolites have been related to its quality and safety, such as 5-hydroxymethylfurfural (HMF), furfural, sotolon, and ethyl carbamate (EC). These compounds were quantified over a three year period to assess their formation rate according to the ageing procedure used: canteiro vs. estufagem. Estufagem, which includes thermal processing of young MWs, promoted greater HMF, furfural, and sotolon accumulation, especially in sweet wines, in which sotolon contributed significantly to aroma (odour active values up to 17.5). Tinta Negra revealed a higher predisposition to form EC while Malvasia and Sercial were less prone to its formation. The formation of furfural, HMF, and EC strongly correlated with the ageing time. Sotolon had a strong correlation with the ageing time in canteiro (r = 0.79) and a moderate correlation in estufagem (r = 0.65). In both ageing procedures, sotolon, furfural, and HMF formation trends strongly correlated with each other (r = 0.74–0.90). In turn, EC also correlated with all furans (r = 0.51–0.85). Yellow tones (b*) correlated with these metabolites only when wines undergo estufagem. This study provides valuable insights to improve MW quality and safety management procedures.
- Micro-oxygenation in Madeira WinePublication . Freitas, Ana Isabel Camacho de; Marques, José Carlos Antunes; Pereira, Vanda Nulita GomesA micro-oxigenação consiste na adição deliberada e controlada de pequenas quantidades de oxigénio durante o processo de vinificação, com o intuito de melhorar as características organoléticas do vinho. Tendo em conta o carácter oxidativo do processo de envelhecimento do vinho Madeira, avaliou-se o impacto de três tratamentos de microoxigenação (t1- 66 mg/L por mês, antes da estufagem; t2 - 66 mg/L por mês, durante a estufagem; t3 – oxigénio dissolvido acima de 7 mg/L, durante a estufagem) no conteúdo de oxigénio dissolvido, parâmetros enológicos básicos, cor, polifenóis, furanos, composição volátil e características sensoriais. Em geral, a adição de um fluxo padrão de oxigénio não teve um impacto notável na cor, na composição polifenólica, nos furanos ou no perfil volátil, favorecendo, no entanto, o desenvolvimento de sotolon (até 97%) e de acetais heterocíclicos (até 95% para o trans-dioxolano). Já as condições de sobreoxigenação (t3) diminuíram consideravelmente a intensidade da cor (cerca de 41%) e o conteúdo polifenólico (até 29% durante a estufagem). Adicionalmente, este tratamento desacelerou a formação de furanos e de sotolon até cerca de 36%, comparativamente ao controlo. Para tal, foi desenvolvida uma metodologia para a determinação simultânea de sotolon e acetais heterocíclicos (cis- e trans-dioxano e cis- e trans-dioxolano), tendo por base a miniaturização da extração líquido-líquido e análise por GC-MS/SIM. Após otimização, o procedimento de extração foi validado relativamente ao sotolon, demonstrando ter boa sensibilidade (LOD e LOQ de 2,3 e 6,8 μg/L, respetivamente), linearidade (R2 de 0,999), precisão (desvios padrão para repetibilidade e reprodutibilidade inferiores a 8% e 10%, respetivamente) e exatidão (recuperação média de 105,4%), recorrendo a uma abordagem ecológica, rápida e de baixo custo. Relativamente aos acetais heterocíclicos, a metodologia foi avaliada em termos de precisão, com desvios padrão inferiores a 13% para a repetibilidade e a 17% para a reprodutibilidade.
- Profiling of passion fruit volatiles: an effective tool to discriminate between species and varietiesPublication . Porto-Figueira, Priscilla; Freitas, Ana; Cruz, Catarina J.; Figueira, José; Câmara, José S.The aim of this work was to gain insights on the volatile composition of nine passion fruits grown at Madeira Island (Portugal) – Yellow, Purple, Lemon, Orange, Pineapple, Peach, Melon, Banana and Tomato – and discriminate between them. The volatile composition of these fruits has been investigated using the same analytical technique, HS–SPME/GC–MS and multivariate analysis (MVA). The selected SPME methodology (DVB/CAR/PDMS fiber at 40 ± 1 °C for 30 min and 10% (w/w) of NaCl under stirring mode (47 × g)) was applied in the profiling of nine different passion fruit samples by GC–MS, allowing the identification of up to 169 volatile compounds belonging to different chemical groups, namely linear and branched esters, terpenes, alcohols and others. Esters were found to be the dominant metabolites regardless of passion fruit sample, with hexyl hexanoate (ranging from 6 to 31%), methyl hexanoate (14–75%) ethyl hexanoate (12–53%) and hexyl butanoate (11–26%) being the principal volatile compounds found, followed by cis-β-ocimene (from 8 to 55%), (E)-2-hexenal (4 to 10% for Banana and Tomato passion fruit samples) and eucalyptol (18% for Tomato passion fruit). The results revealed that the differences in the volatile profile among the studied passion fruits were essentially qualitative, with only 7 common volatiles found in all samples, in different abundance. Advanced statistical techniques (PCA and PLS-DA) were used to explore data. Characteristic markers were successively identified using the NIST library, thus showing that the volatile profile was able to differentiate all nine species and varieties. Profiling of passion fruit volatile metabolites can provide an effective tool to characterize the product and to extract useful information concerning its quality or geographic origin.