Browsing by Author "Torres, Duarte"
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- Adsorption equilibrium of fructose, glucose and sucrose for cationic resins in the sodium and potassium formPublication . Nobre, Clarisse; Santos, M.J.; Dominguez, Ana; Torres, Duarte; Peres, António M.; Rocha, Isabel; Ferreira, Eugénio C.; Rodrigues, Lígia R.; Teixeira, JoséSeparation of glucose from mixtures of fructose and sucrose in molasses is a major challenge in industrial sugar chromatographic separations. The efficiency of a chromatographic process is largely dependent on the adsorbent used. Sulfonated poly(styrene-co-divinylbenzene) (PS-DVB) ion exchange resins are the most frequently used for sugars separation, generally in a cationic form. The cation will complex with the hydroxyl group of the sugar leading to a selective adsorption according to the orientation of the hydroxyl group. Thus, the conformation of the sugar determines its relative affinity for the resin and its distribution coefficient. Consequently, fructose forms the more stable sugar-cation complex being preferentially adsorbed in the resin followed by glucose. Sucrose interacts very weakly with the cation and is partially or totally excluded from the resin matrix owing to its larger molecular size. The separation process is usually carried out at high temperatures. However, this implies high energy costs and an elevated level of hydrolysis. Adsorption isotherms of the sugars present in a mixture are a very important parameter for the selection of the adsorbent to be used in the chromatographic separation. Therefore, in this study, the adsorption isotherms of glucose, fructose and sucrose were determined for two resins of PS-DVB in the sodium and potassium forms. Potassium and sodium are the most recommended cations for the separation of sucrose, fructose and glucose. The sodium and potassium resins matrix used in this work consist in meshes of 500-600 μm and 290-350 μm, respectively. Solutions with single and multi-component mixtures of the three sugars were used at 25ºC and 40ºC. A static method was used to determine the equilibrium adsorptions: 3.5 mL of solutions with different sugar concentrations were added to a known amount of adsorvent. The mixture was held for 8h under agitation and a fixed temperature and a final concentration in equilibrium with resin was determined by HPLC. As expected, the results achieved showed that for all the conditions, fructose is the most adsorved sugar followed by glucose and sucrose. For both resins, the increase of temperature conducted to a decrease on the adsorption constant for all the sugars in the mono-component mixtures. Nevertheless, the adsorption in multi-component mixtures was not significantly affected by the temperature in the sodium resin, and regarding the potassium resin only a small increase in the adsorption was observed. Multi-component mixtures at 25 ºC showed a decrease in the adsorption as compared with mono-component mixtures. However, at 40ºC the adsorption observed for the multi-component mixtures was higher than the observed for the mono-component ones. The sugars that demonstrated lower selectivity values were fructose/glucose since these sugars have the same molecular weight. Sucrose/fructose selectivity showed a higher value when compared with sucrose/glucose because of the complex formed between fructose and the resin. This profile was found for both resins used, regardless of temperature. Selectivity of both resins decreased with the increase of the temperature values. Nevertheless, the selectivity obtained for the potassium resin was higher as compared to the selectivity obtained for the sodium resin. In sum, potassium resin appears to be the most suitable adsorvent and an operational temperature of 25 ºC showed the best results.
- Adsorption equilibrium of fructose, glucose, and sucrose for cationic resins in the sodium and potassium formPublication . Nobre, Clarisse; Santos, M.J.; Dominguez, Ana; Torres, Duarte; Peres, António M.; Rocha, Isabel; Ferreira, Eugénio C.; Rodrigues, Lígia R.; Teixeira, José
- Caracterização química de azeites da região de Trás-os-Montes com e sem Denominação de Origem Protegida (DOP).Publication . Silva, F.; Torres, Duarte; Lopes, I.; Pereira, J.A.; Oliveira, Beatriz
- Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resinsPublication . Nobre, Clarisse; Santos, M.J.; Dominguez, Ana; Torres, Duarte; Rocha, Orlando; Peres, António M.; Rocha, Isabel; Ferreira, Eugénio C.; Teixeira, José; Rodrigues, Lígia R.Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-codivinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K+) gel-type and sodium (Na+) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for monocomponent and multi-component sugar mixtures, at 25 and 40 ◦C, in a range of concentrations between 5 and 250 g L−1. All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na+ macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K+ gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 ºC, and a synergetic effect at 40 ºC. The temperature increase conducted to a decrease on the adsorption capacity for mono-component sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K+ gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25ºC.
- Estimated dietary flavonoid intake and major food contributors in the Portuguese population: results from the national food, nutrition and physical activity survey (IAN-AF 2015–2016)Publication . Martins, Sofia; Meireles, Manuela; Caetano, Estela; Correia, Daniela; Carvalho, Catarina; Silva, Catarina Campos; Magalhães, Vânia; Vilela, Sofia; Lopes, Carla; Torres, DuarteFlavonoids are a key class of polyphenols, i.e., phytochemical compounds present in foods and beverages, which have been described as having health benefits in preventing several chronic diseases. Estimating flavonoid intake has already been conducted in several countries but has yet to be performed in Portugal. This study included 5005 participants aged 3–84 years and aimed to estimate dietary flavonoid intake in the Portuguese population, using data from the National Food and Physical Activity Survey 2015–2016, providing information on intake, main food contributors and the socio-demographic factors associated with the intake. Food intake data from the survey was converted to flavonoid intake using a database built to include the most updated USDA databases on flavonoids, isoflavones and proanthocyanidins and the Phenol-Explorer database. The rationale for combining food consumption data and different flavonoid databases using the FoodEx2 classification system was established. Linear regressions assessed the associations between socio-demographic factors and dietary flavonoid intake. The total flavonoid intake of the Portuguese population was estimated to be 107·3 mg/d. Flavanols were the most representative subclass, followed by flavonols, anthocyanidins, flavanones, flavones and isoflavones. Fruits and vegetables were the primary food contributors, providing 31·5 % and 12·4 % of the total flavonoid intake. Adolescents had the lowest total flavonoid intake, and older adults had the highest. This study provides information on the Portuguese population’s dietary flavonoids, allowing for international comparisons. It can also streamline forthcoming investigations into the link between flavonoid consumption and its impact on health, contributing to the future establishment of dietary reference values.
- New improved method for fructooligosaccharides production by Aureobasidium pullulansPublication . Dominguez, Ana; Nobre, Clarisse; Rodrigues, Lígia R.; Peres, António M.; Torres, Duarte; Rocha, Isabel; Lima, Nelson; Teixeira, JoséFructooligosaccharides are prebiotics with numerous health benefits within which the improvement of gut microbiota balance can be highlighted, playing a key role in individual health. In this study, an integrated one-stage method for FOS production via sucrose fermentation by Aureobasidium pullulans was developed and optimized using experimental design tools. Optimization of temperature and agitation speed for maximizing the FOS production was performed using response surface methodology. Temperature was found to be the most significant parameter. The optimum fermentation conditions were found to be 32 ◦C and 385 rpm. Under these conditions, the model predicted a total FOS production yield of 64.7 gFOS/gsucrose. The model was validated at optimal conditions in order to check its adequacy and accuracy and an experimental yield of 64.1 (±0.0) gFOS/gsucrose was obtained. A significant improvement of the total FOS production yields by A. pullulans using a one-stage process was obtained.
- Simultaneous determination of tocopherols and tocotrienols in hazelnuts by a normal phase liquid chromatographic method.Publication . Amaral, Joana S.; Casal, Susana; Torres, Duarte; Seabra, Rosa M.; Oliveira, BeatrizA normal-phase high-performance liquid chromatography (NP-HPLC) method for the determination of tocopherols and tocotrienols in hazelnuts is reported. Three extraction procedures (with and without saponification) were assayed, being the best results obtained with a simple solid-liquid extraction procedure. Chromatographic separation was achieved using an Inertsil 5 SI column using isocratic elution with n-hexane/1,4-dioxane (95.5:4.5, v/v) at a flow rate of 0.7 mL/min. The effluent was monitored by a series arrangement of a diode-array followed by a fluorescence detector. All compounds were separated in a short period of time (17 min). The method proved to be rapid, sensitive, reproducible and accurate, allowing the simultaneous determination of all vitamin E isomers.
- UV spectrophotometry method for the monitoring of galacto-oligosaccharides productionPublication . Dias, L.G.; Veloso, Ana C.A.; Correia, Daniela M.; Rocha, Orlando; Torres, Duarte; Rocha, Isabel; Rodrigues, Lígia R.; Peres, António M.Monitoring the industrial production of galacto-oligosaccharides (GOS) requires a fast and accurate methodology able to quantify, in real time, the substrate level and the product yield. In this work, a simple, fast and inexpensive UV spectrophotometric method, together with partial least squares regression (PLS) and artificial neural networks (ANN), was applied to simultaneously estimate the products (GOS) and the substrate (lactose) concentrations in fermentation samples. The selected multiple models were trained and their prediction abilities evaluated by cross-validation and external validation being the results obtained compared with HPLC measurements. ANN models, generated from absorbance spectra data of the fermentation samples, gave, in general, the best performance being able to accurately and precisely predict lactose and total GOS levels, with standard error of prediction lower than 13 g kg-1 and coefficient of determination for the external validation set of 0.93–0.94, showing residual predictive deviations higher than five, whereas lower precision was obtained with the multiple model generated with PLS. The results obtained show that UV spectrophotometry allowed an accurate and non-destructive determination of sugars in fermentation samples and could be used as a fast alternative method for monitoring GOS production.