Browsing by Author "Nunes, Cláudia"
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- Amino acid profile and Maillard compounds of sun-dried pears. Relation with the reddish brown colour of the dried fruitsPublication . Coimbra, Manuel; Nunes, Cláudia; Cunha, Pedro; Guiné, RaquelThe sun-dried pear of S. Bartolomeu (Pyrus communis L. var. S. Bartolomeu) is a traditional sweet food product of unique elastic properties and reddish brown colour. Alternative drying methodologies to replace the traditional open air sun-drying procedure are under devel- opment, namely the use of greenhouses with and without air convection and a hot air tunnel. To test whether the Maillard reactions can contribute to the colour of this tra- ditional product, the profiles of free and bound amino acids constituents of the pulp of fresh pears as well as pears processed according to different drying methodologies were evaluated. Also, the occurrence of furosine, car- boxymethyllysine (CML) and carboxyethyllysine (CEL), indicative of Maillard reaction, was diagnosed and quan- tified. The drying of the pears affects the free amino acid profile, increasing proline content and decreasing aspartic and glutamic acids. Although the proteic amino acid profile was not significantly modified with the drying process, a loss of the relative content of Lys was observed. This loss was related with the increase in the amount of furosine, CML and CEL formed during the drying of the fruits. Although all drying methods tested promoted the increase in the amount of CML, CEL and furosine, this increase was higher in the case of the traditional sun-drying and green- house processing, where the fruits presented reddish brown colour, and lower for the hot air tunnel processing, where the fruits became less intense. These results allow affirming that the drying process promotes the occurrence of Mail- lard reaction, contributing to the characteristic reddish brown colour of the final product.
- Evaluation of phenolic compounds composition, antioxidant activity and bioavailability of phenols in dried thistle flowerPublication . Guiné, Raquel; Pedro, Ana; Matos, Joana; Barracosa, Paulo; Nunes, Cláudia; Gonçalves, FernandoThe objective of this work was to characterize the thistle flower in relation to the composition of phenolic compounds and antioxidant activity, as well as the evalua- tion of the stability of the phenols along the digestive tract. In addition, the effect of drying temperature was evaluated and the composition in polysaccharides was also studied. For this, samples of thistle flower were lyophilized and dried at 40, 50 and 60 C. Methanol:acetic acid (98:2 v/v) and ace- tone:water (60:40 v/v) extracts were obtained and analysed for antioxidant activity, phenolic compounds, ortho-diphe- nols, flavonoids, phenolic acids and polysaccharides, using colorimetric methods, HPLC and GC-FID. The results showed that the phenolic compounds and antioxidant activity with ABTS or DPPH methods on thistle flower decreased by 20, 34 and 72 %, respectively, with increasing temperature from 40 to 60 C. The amount of compounds available for intestinal absorption decreased along the gas- trointestinal system, by 15–50 %. The presence of sugars constituent of pectic polysaccharides was observed (101.6–222.0 mg/g) as well as of hydroxybenzoic (0.19–1.26 mg/g) and hydroxycinnamic acids (1.57–5.59 mg/g). As a conclusion it was found that thistle flower is rich in bioactive compounds with potential importance for the human health.
- Isolamento e caracterização estrutural de polissacarídeos pécticos da pêra passa de Viseu.Publication . Silva, Lizete; Nunes, Cláudia; Domingues, Maria do Rosário; Guiné, Raquel; Coimbra, Manuelpolissacarídeos constituídos, essencialmente, por uma longa cadeia de resíduos de ácido galacturónico (GalA). Estes compostos podem ser encontrados nas paredes celulares primárias dos frutos e vegetais, apresentando um papel importante na determinação da força e flexibilidade dos tecidos. Os polissacarídeos das paredes celulares da pêra de S. Bartolomeu obtida em fresco e das peras secadas foram fraccionados e caracterizados quanto à sua constituição em açúcares. Algumas fracções ricas em polissacarídeos pécticos foram seleccionadas para uma análise estrutural mais detalhada, nomeadamente o sobrenadante do resíduo celulósico da pêra fresca (SnCR). Estes polissacarídeos pécticos foram hidrolisados com uma endo- poligalacturonase (PG), uma hidrolase específica para os resíduos de ácido poligalacturónico em ligação w-(1 4). Os oligossacarídeos obtidos foram separados por tamanho utilizando uma cromatografia de exclusão molecular. As fracções de menor peso molecular foram analisadas por espectrometria de massa com ionização por electrospray (ESI-MS e ESI-MS/MS). Para comparação das características estruturais dos polissacarídeos das peras com a de outros frutos, estudou-se ainda uma pectina comercial proveniente de citrinos.
- Structural characterization of pectic polysaccharides by ESI-MS. Occurrence of hexoses directly linked to the galacturonic acid backbone.Publication . Silva, Lizete; Nunes, Cláudia; Domingues, Maria do Rosário; Guiné, Raquel; Coimbra, ManuelPectic polysaccharides include a large family of related polysaccharides based on a galacturonan-rich backbone. These polysaccharides are key components of the primary cell walls of fruits and vegetables, being important in determining tissues strength and flexibility. They can be viewed as multiblock components composed by four structural domains: homogalacturonan (HG), rhamnogalacturonan I (RG-I), which includes the arabinogalactan and arabinan side chains, the complex RG-II domain, and the xylogalacturonan (XGA). HG is a linear and partially 6-O methylated polymer constituted only by -(1→4)-D-galacturonic acid residues [→4)--D-GalpA-(1→]n, which can be 2-O and 3-O acetylated. The repeating units of the disaccharide [→4)--D-GalpA-(1→2)--L-Rhap-(1→] form the backbone of RG-I that comprises also branched at O-4 of Rha residues with Gal and/or Ara side chains. RG-II is described as a very complex heteropolysaccharide with a galacturonan backbone of around 30 residues substituted by side chains containing sugars such as 2-O-methyl-L-fucose and D-keto-3-deoxy-D-manno-2-octulosonic acid (KDO). In XGA, a HG chain is substituted on C-3 with D-Xyl. The high sensitivity and capacity for the analysis of mixtures provided by mass spectrometry led to a re-emergence for oligosaccharides structural characterization in recent years. In this study, we revisited the structures of pectic polysaccharides from commercial sources of citrus, as well as from plum and pear. The oligosaccharides from these pectic polysaccharide sources were generated by the selective hydrolysis of the GalA backbone with endo-polygalacturonase, followed by its partial separation on a Biogel size exclusion chromatography. The resultant fractions with lower molecular weight were analyzed by ESI-MS. Beyond uronic acid monomers (attributed to GalA) and the oligosaccharides characteristic of degraded HG such as GalAndHexq n=1,3; q= 1,3 (GalA-Rha series) and XGA, namely, GalAnPentp n= 2,3; p=1, it was also observed oligosaccharides bearing hexose residues linked to uronic acids (GalAnHexm n= 2,3 m= 1,2). The direct linkage of hexoses to the main galacturonan backbone is a structural feature of plant pectic polysaccharides that, until now, has been neglected but that should be included in the future structural models.