Browsing by Author "Martins, D."
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- Anthocyanin concentration of "Assaria" pomegranate fruits during different cold storage conditionsPublication . Miguel, Maria Graça; Fontes, C.; Antunes, Maria Dulce; Neves, Alcinda; Martins, D.The concentration of anthocyanins in fruits of "Assaria" pomegranate, a sweet Portuguese cultivar typically grown in Algarve (south Portugal), was monitored during storage under different conditions. The fruits were exposed to cold storage (5 degrees C) after the following treatments: spraying with wax; spraying with 1.5% CaCl2; spraying with wax and 1.5% CaCl2; covering boxes with 25 mu c thickness low-density polyethylene film. Untreated fruits were used as a control. The anthocyanin levels were quantified by either comparison with an external standard of cyanidin 3-rutinoside (based on the peak area) or individual calculation from the peak areas based on standard curves of each anthocyanin type. The storage time as well as the fruit treatment prior to storage influenced total anthocyanin content. The highest levels were observed at the end of the first month of storage, except for the fruits treated with CaCl2, where the maximal values were achieved at the end of the second month. The anthocyanin quantification method influenced the final result. When total anthocyanin was calculated as a sum of individual pigments quantified based on standard curves of each anthocyanin type, lower values were obtained.
- Ascorbic acid and flavanone glycosides in citrus: Relationship with antioxidant activityPublication . Miguel, Maria Graça; Duarte, Amílcar; Nunes, S.; Sustelo, V.; Martins, D.; Dandlen, S. A.The effects of cultivar and orchard on the content of ascorbic acid and flavanone glycosides as well as on the antioxidant activity of citrus juices were studied. Ascorbic acid and flavanone glycosides were determined using HPLC method. For antiradicalar activity evaluation, TAEC and ORAC methods were used. Citrus of 'Valencia late' from Faro and 'D. Joao' presented the highest levels of hesperidin in contrast to the citrus of 'Valencia late' from Silves with 0.4 mg/ml, a value closer to those of Navel oranges 'Navelate' and 'Lanelate'. Citrus of 'Valencia late' from Silves and 'D. Joao' presented the lowest levels of narirutin. 'Ortanique' and 'Encore' cultivars were poorer in ascorbic acid compared with the oranges. When the TEAC method was used for the determination of antioxidant activity, 'Valencia late' from Faro presented the best activity. A good relation was observed between antiradical activity measured through the TEAC method and the amount of ascorbic acids in samples. None relation was found between the levels of flavanones and antiradical activity. When the ORAC method was applied, the best activity was found for 'Navelate' and 'Encore' samples and practically none relation between this method and the amounts of ascorbic acid and flavanones was found.
- Effect of the essential volatile oils isolated from Thymbra capitata (L.) Cav. on olive and sunflower oilsPublication . Miguel, Maria Graça; Figueiredo, A. C.; Costa, M. M.; Martins, D.; Barroso, J. G.; Pedro, L. G.The chemical composition of the volatile constituents of the oils isolated from different parts of Thymbra capitata collected at different developmental stages were analysed by GC and GC/MS. The antioxidant ability of the oils isolated from T capitata was evaluated determining the peroxide values, on olive and sunflower oils, stored at 60 degreesC. These peroxide values were compared with those obtained when BHT, carvacrol and control (without adding antioxidants) were used and subjected to the same conditions. The best yield oil was obtained from the whole aerial part of T capitata collected during the flowering phase. The major component of the oils was carvacrol. Relative high amounts of p-cymene, gamma-terpinene and beta-caryophyllene were also found. BHT revealed to be the best antioxidant when the olive oil was used. On sunflower oil, the antioxidant ability of BHT was not so evident, being the carvacrol-rich essential oils of T capitata or carvacrol more important antioxidants.
- Effect of the volatile constituents isolated from Thymus albicans, Th. mastichina, Th. carnosus and Thymbra capitata in sunflower oilPublication . Miguel, Maria Graça; Figueiredo, A. C.; Costa, M. M.; Martins, D.; Duarte, J.; Barroso, J. G.; Pedro, L. G.The composition of essential oils isolated from Thymus albicans and Thymbra capitata collected in Algarve (Portugal), Th. mastichina collected in Algarve and Estremadura (Portugal) and Th. carnosus also collected in Algarve, during the flowering phase, was analysed by gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS). The antioxidant capacity of the oils as well as some of their main components was determined by periodic evaluation of the peroxide values in sunflower oils stored at 60 degreesC. These peroxide values were compared to that of butylated hydroxytoluene (BHT) and control (without adding antioxidants) under the same experimental conditions. The oils of Th. albicans and Th. mastichina, collected in Algarve, were dominated by 1,8-cineole (68% and 45%, respectively), whereas linalool (52%) was the main component from the oils isolated from Th. mastichina collected in Estremadura. Carvacrol (68%) was the major component present in the oils of Thymbra capitata while borneol (18%), terpinen-4-ol (11%) and camphene (9%) were the major ones in the essential oil of Th. carnosus. The essential oils as well as some of their main components showed higher antioxidant capacity than that of the synthetic antioxidant BHT. At the end of the experiment (57 days), BHT showed a percentage of inhibition of 20%, while that of the essential oils ranged from 46% for Th. carnosus, to 59% for Th. mastichina collected in Estremadura.
- Effects of post-harvest treatment and storage time on the organic acid content in Assaria and Mollar pomegranate (Punica granatum L.) fruitPublication . Miguel, Maria Graça; Fontes, C.; Martins, D.; Neves, Alcinda; Antunes, Maria DulceThe effects of postharvest treatment and storage at 5 degrees C on changes in the organic acid content in the juice of 'Assaria' and 'Mollar' pomegranate were monitored. The fruit was chill stored after the following treatments: covering boxes with a 25-mu thick low-density polyethylene film and spraying with 1.5% CaCl2; untreated fruit was used as the control. The results showed that citric acid is the main organic acid in the 'Mollar' cultivar, followed by tartaric acid, whereas three organic acids were present at similar levels in 'Assaria' pomegranate: citric, oxalic and tartaric acids. Differences in the main organic acid contents were detected when fruit was submitted to different treatments prior to cold storage. The different pretreatments did not significantly interfere with the accumulation of organic acids in either cultivar. There were two exceptions. The ascorbic acid content was significantly higher in the 'Mollar' cultivar when the fruit was treated with calcium, while the pyruvic acid content was significantly higher in the 'Assaria' cultivar in the untreated fruit.
- The effect of two methods of pomegranate (Punica granatum L) juice extraction on quality during storage at 4 degrees CPublication . Miguel, Maria Graça; Dandlen, S. A.; Antunes, Maria Dulce; Neves, Alcinda; Martins, D.The effect of two extraction methods of pomegranate juice on its quality and stability was evaluated. The first method consisted of separation of the seeds from fruits and centrifugation. The second method consisted of squeezing fruit halves with an electric lemon squeezer. During a period of 72 hours of cold storage at 4 degrees C, the juices were evaluated for the presence of sugars, organic acids, and anthocyanins. Delphinidin 3-glucoside was identified to be the major anthocyanin present at the level of 45-69 mg/L. Among the organic acids, oxalic and tartaric acids dominated. The major sugars detected in pomegranate juice were glucose and sucrose. No significant differences in the content of sugars, organic acids, or anthocyanins in juices obtained through application of the two different extraction methods were detected, with the exception of the drastic decrease of cyanidin 3,5-diglucoside level in juice obtained by seed centrifugation. The pH did not show differences between treatments. Titrable acidity and the level of sugars expressed as degrees Brix decreased after 32 and 15 hours after extraction, respectively, when juice was obtained by centrifuging the seeds.