Percorrer por autor "Pereira, David M."
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- Brassica oleracea var. costata: comparative study on organic acids and biomass production with other cabbage varietiesPublication . Sousa, Carla; Pereira, David M.; Taveira, Marcos; Dopico-García, Sonia; Valentão, Patrícia; Pereira, J.A.; Bento, Albino; Andrade, Paula B.BACKGROUND: A study was undertaken to evaluate the effect of agronomic practices, harvesting time and leaf age on the organic acid composition and biomass production of Brassica oleracea L. var. costata DC (tronchuda cabbage). Samples were cultivated under eight different fertilisation regimes (two levels each of nitrogen, boron and sulfur, an organic fertiliser and no fertiliser) and collected at three different times. RESULTS: Principal component analysis of the data indicated significant differences. Three principal components with an eigenvalue higher than one accounted for 79.0% of the total variance of the data set. Samples obtained with conventional fertilisation were characterised by the highest values of fresh weight. External leaves showed higher total organic acid and malic acid contents than internal leaves,while the latterwere characterised by higher proportions of citric acid. For consecutive harvests, total organic acid concentration decreased in both external and internal leaves. CONCLUSION: The use of a conventional fertilisation regime (nitrogen, boron or sulfur) improved the growth of B. oleracea var. costata without affecting its organic acid profile. However, for consecutive harvests, total organic acid concentration was observed to decrease independently of the agronomic practices tested. Leaf age influenced the quantitative composition of organic acids.
- Free amino acids of Tronchuda Cabbage (Brassica oleracea L. Var. costata DC): influence of leaf position (internal or external) and collection timePublication . Oliveira, Andreia P.; Pereira, David M.; Andrade, Paula B.; Valentão, Patrícia; Sousa, Carla; Pereira, J.A.; Bento, Albino; Rodrigues, M.A.; Seabra, Rosa M.; Silva, Branca M.The free amino acid profile of 18 samples of tronchuda cabbage (Brassica oleracea L. var. costata DC) leaves, harvested at three different months, was determined by HPLC/UV−vis. The tronchuda cabbage leaves total free amino acid content varied from 3.3 to 14.4 g/kg fresh weight. Generally, arginine was the major compound, followed by proline, threonine, glutamine, cysteine, and glutamic acid. This study indicates that free amino acids are not similarly distributed: in external leaves, proline and arginine were the major free amino acids, while in internal ones, arginine was the main free amino acid, followed by threonine, glutamine, and cysteine. Significant differences were observed for valine, proline, arginine, leucine, cysteine, lysine, histidine, and tyrosine contents. The levels of some free amino acids were significantly affected by the collection period. In external leaves, this occurred with glutamic acid, serine, valine, leucine, cysteine, and ornithine contents, while in internal leaves, it occurred with aspartic acid, arginine, and total contents.
- Headspace solid-phase microextraction and gas chromatography/ion trap-mass spectrometry applied to a living system: Pieris brassicae fed with kalePublication . Fernandes, Fátima; Pereira, David M.; Pinho, P. Guedes de; Valentão, Patrícia; Pereira, J.A.; Bento, Albino; Andrade, Paula B.The influence of Pieris brassicae feeding on kale was monitored, by evaluating its effect on the volatiles released by the plant through time. This is the first study applying headspace solid-phase microextraction (HS-SPME) and gas chromatography/ion trap-mass spectrometry to an isolated insect, as most studies analyse the insect–plant system as a whole, being unable to evaluate the contribution of the insect itself. Substantial differences were noticed between the volatiles composition of kale before and after the insect’s attack. More than 60 compounds were found, including terpenes, lipoxygenase pathway by-products, ketones, norisoprenoids, etc. After insect attack, l-camphor, sabinene and a-thujene were found and limonene and eucalyptol suffered a noticeable increase. A considerable rise in (Z)-3-hexenyl acetate was also observed. In vivo accumulation of limonene and camphor by the insect was detected. The findings contribute to the knowledge of the ecological interactions between the two species.
- In vitro cultures of Brassica oleracea L. var. costata DC: potential plant bioreactor for antioxidant phenolic compoundsPublication . Taveira, Marcos; Pereira, David M.; Sousa, Carla; Ferreres, Frederico; Andrade, Paula B.; Martins, Anabela; Pereira, J.A.; Valentão, PatríciaIn this work were studied the phenolic composition of in vitro material (shoots, calli, and roots) of Brassica oleracea var. costata and its antioxidant capacity. Samples were obtained in different culture medium, with distinct supplementations to verify their influence on those parameters. Phenolic determination was achieved by HPLC-DAD. Antioxidant activity was assessed against DPPH•. In calli and roots no phenolic compound was identified. In shoots was verified the presence of 36 compounds, which included hydroxycinnamic acids, flavonoids (kaempferol and quercetin derivatives), and hydroxycinnamic acyl glycosides (with a predominance of synapoyl gentiobiosides). MS liquid medium supplemented with 2 mg/L benzylaminopurine (BAP) and 0.1 mg/L naphthaleneacetic acid (NAA) revealed to be the best in vitro condition to produce shoot material with highest phenolic compound contents and stronger antioxidant potential, thus with a possible increase of health benefits.
- In vitro cultures of Brassica oleracea L. Var. Costata DC: potential plant bioreactor for antioxidant phenolic compoundsPublication . Taveira, Marcos; Pereira, David M.; Andrade, Paula B.; Sousa, Carla; Ferreres, Frederico; Martins, Anabela; Pereira, J.A.; Seabra, Rosa M.; Valentão, Patrícia
- Influence of different fertilization regimes on the amounts of organic acids of Brassica oleracea L. var. costata DC.Publication . Ribeiro, Bárbara; Sousa, Carla; Lopes, Graciliana; Pereira, David M.; Taveira, Marcos; Dopico-García, Sonia; Pereira, J.A.; Bento, Albino; Rodrigues, M.A.; Valentão, Patrícia; Seabra, Rosa M.; Andrade, Paula B.
- Leucopaxillus giganteus mycelium: effect of nitrogen source on organic acids and alkaloidsPublication . Pereira, David M.; Ribeiro, Bárbara; Andrade, Paula B.; Baptista, Paula; Barros, Lillian; Ferreira, Isabel C.F.R.; Seabra, Rosa M.; Valentão, Patrícialn order to study the influence 01 lour inorganic nitrogen sources (NH4N03, NaN02, KN03 and (NH4)2HP04) on the chemical composition 01 Leucopaxillus giganteus mushroom mycelium, its organic acids profile was determined by HPLC-UV and total alkaloids content was assessed by a spectrophotometric method, alter precipitation by Dragendorlf's reagent. lhe results showed that L. giganteus presented an organic acids profile composed by oxalicis-aconitic, citric and lumaric acids, being citric acid the major one.
- Metabolic fate of dietary volatile compounds in Pieris brassicaePublication . Fernandes, Fátima; Pereira, David M.; Pinho, P. Guedes de; Valentão, Patrícia; Pereira, J.A.; Bento, Albino; Andrade, Paula B.In this work, the evolution of the qualitative and quantitative profile of the volatile fraction of Pieris brassicae after feeding on Brassica oleracea var. acephala (kale) was monitored through time. HS-SPME/GC-MS was applied to both the host plant and the living insect and its excrements. A total of seventy seven compounds (lipoxygenase pathway by-products, nitrogen compounds, norisoprenoids, sulphur compounds, terpenes, among others) were identified. Thirty eight compounds were identified in insect after 2 h of starvation and forty eight compounds in excrements. Qualitative and quantitative changes were detected along time. Dimethyldisulfide, dimethyltrisulfide, limonene and eugenol were major compounds for all analysed times in both matrices, being limonene an important compound in insect after starvation. The accumulation by P. brassicae of some compounds, such as limonene, was verified, suggesting a mechanism by which the insect can take benefit from bioactive constituents from the diet. Along with accumulation, complete excretion of some compounds, including nitrogen bearing compounds, by-products of glucosinolates was detected. These results reflect one of the strategies used to overcome plant barriers, namely detoxification of toxic compounds. The findings contribute to the knowledge of the metabolization of the volatile compounds in insects and contribute to the body of knowledge of this ecologic system.
- Multivariate analysis of Tronchuda Cabbage (Brassica oleracea L. var. costata DC) phenolics: influence of fertilizersPublication . Sousa, Carla; Pereira, David M.; Pereira, J.A.; Rodrigues, M.A.; Bento, Albino; Dopico-García, Sonia; Lopes, Graciliana; Valentão, Patrícia; Seabra, Rosa M.; Andrade, Paula B.A field experiment was carried out to investigate the effect of fertilization level on the phenolic composition of tronchuda cabbage (Brassica oleracea L. var. costata DC) external and internal leaves. Eight different plots were constituted: a control without fertilization, one with organic matter, and six experiments with conventional fertilizers (nitrogen, boron, and sulfur, two levels each). The phenolic compounds were analyzed by reversed-phase HPLC-DAD. External and internal leaves revealed distinct qualitative composition. In the internal leaves were found 15 phenolics (5 kaempferol and 10 cinnamic acid derivatives), whereas the external leaves presented 3-p-coumaroylquinic acid and 13 kaempferol derivatives. Principal component analysis (PCA) was applied to assess the relationships between phenolic compounds, agronomical practices, and harvesting time. Samples obtained with conventional practices were quite effectively separated from organic samples, for both types of leaves. In general, samples developed without any fertilization presented the highest phenolics amounts: external and internal leaves contained 1.4- and 4.6-fold more phenolic compounds than the ones that received conventional fertilizer, respectively, and the internal leaves presented 2.4 times more phenolics than the ones grown with organic amendment. Additionally, samples from organic production exhibited higher total phenolics content than those from conventional practices, collected at the same time. Samples harvested first were revealed to be distinct from the ones collected later. The results show that it is possible to grow tronchuda cabbage without excess fertilizers, with highest amounts of phenolics and reduced environment contamination.
- Phenolic compounds in Brassica oleracea L. var. costata DC: effect of fertilization conditionsPublication . Dopico-García, Sonia; Sousa, Carla; Lopes, Graciliana; Pereira, David M.; Pereira, J.A.; Bento, Albino; Rodrigues, M.A.; Valentão, Patrícia; Seabra, Rosa M.; Andrade, Paula B.