A carregar...
123 resultados
Resultados da pesquisa
A mostrar 1 - 10 de 123
- Extraction of phenolic compounds from Juglans regia L. leaves using aqueous solutions of eutectic solventsPublication . Cordova, Isabella Weber; Oludemi, Taofiq; Vieira, Vanessa; Pires, Tânia C.S.P.; Pinho, Simão; Barros, Lillian; Ferreira, OlgaThe leaves of Juglans regia L. (walnut tree) are a rich source of bioactive phenolic compounds, particularly flavonoids and phenolic acids, which can be used in cosmetic applications due to their antioxidant properties. Conventionally, these compounds are extracted using volatile organic solvents. This study focuses on a more sustainable approach by designing a heat-assisted extraction process using aqueous solutions of eutectic solvents (ES) composed of cosmetic-compatible ingredients aiming for direct incorporation into cream formulations. In this context, aqueous solutions of the ES betaine + urea and betaine + 1,3-propanediol (PPD) were selected, considering their potential as cosmetic ingredients. The screening process targeted the maximum extraction yield of phenolic compounds (phenolic acids and flavonoids), quantified by HPLC-DAD. The selected variables were water content (25, 50 and 75 % in weight) and the molar proportion of the ES components. For comparison purposes, pure water was used as a reference solvent. The total phenolic content ranged between 5.5 and 14.6 mg/g of dry plant. Betaine:urea (2:1), betaine:PPD (1:2), betaine, and PPD, all with 50 % water mass percentage, were among those resulting in higher extraction yields and were further selected for bioactivity analysis. The system containing betaine presented the best antioxidant capacity, analysed through ferric reducing power, DPPH radical scavenging, and TBARS assays. The extracts obtained with PPD presented the highest antimicrobial activity against gram-positive and gram-negative bacteria, and yeast. The results show the potential of using binary aqueous mixtures of betaine, or 1,3-propanediol, which are simple ingredients in cosmetics formulations, to efficiently extract phenolic compounds from a natural matrix. Moreover, the bioactivity results, particularly in the antioxidant dimension, support using J. regia leaves as a source of natural antioxidants.
- E-Learning from nature: picking from nature the inspiration to teach and learn sciencePublication . Pereira, Ana I.; Ferreira, Olga; Barreiro, M.F.; Teixeira, Amílcar; Cortez, José Paulo; Aguiar, CarlosThis work aims to present the work done so far by he Polytechnic Institute of Bragança (IPB) within the projet E-learning form nature.
- Partial molar volumes of glycine and dl-alanine in aqueous ammonium sulfate solutions at 278.15, 288.15, 298.15 and 308.15 KPublication . Martins, Mónia A.R.; Ferreira, Olga; Hnědkovský, Lubomír; Cibulka, Ivan; Pinho, SimãoIn this work, the partial molar volumes of glycine and DL-alanine in aqueous solutions of ammonium sulfate at 0.0, 0.1, 0.3, 0.7, and 1.0 mol.kg(-1) are determined between 278.15 and 308.15 K. Transfer volumes were obtained, which are larger for glycine than DL-alanine. On the contrary, the hydration numbers are higher for DL-alanine than glycine, and dehydration of the amino acids is observed with increasing temperature or salt molality. The data suggest that interactions between ion and charged/hydrophilic groups are predominant and, by applying the methodology proposed by Friedman and Krishnan, it was concluded that they are mainly pairwise. A group-contribution scheme has been successfully applied to the pairwise volumetric interaction coefficient. Finally, the dehydration effect on glycine, alanine and serine in the presence of different electrolytes has been rationalized in terms of the charge density and a parameter accounting for the cation's hydration.
- Optimization of heat and ultrasound-assisted extraction of Eucalyptus globulus leaves reveals strong antioxidant and antimicrobial propertiesPublication . Lima, Laíres; Pereira, Ana I.; Vaz, Clara B.; Ferreira, Olga; Dias, Maria Inês; Heleno, Sandrina A.; Calhelha, Ricardo C.; Barros, Lillian; Carocho, MárcioThe extraction of phenolic compounds from eucalyptus leaves was optimized using heat and ultrasound-assisted techniques, and the bioactive potential of the resulting extract was assessed. The independent variables, including time (t), solvent concentration (S), and temperature (T) or power (P), were incorporated into a fivelevel central composite design combined with Response Surface Methodology. Phenolic content was determined by HPLC-DAD-ESI/MS and used as response criteria. The developed models were successfully fitted to the experimental data to identify the optimal extraction conditions. Heat-assisted extraction proved to be the most efficient method for phenolic recovery, yielding 27 ± 2 mg/g extract under optimal conditions (120 min, 76.5 ◦C, and 25 % ethanol, v/v). The extracts exhibited a high concentration of phenolic glycoside derivatives, including gallotannin, quercetin, and isorhamnetin. These findings suggest that the extracts hold promise as natural additives in food technology, owing to their moderate antimicrobial activity and strong antioxidant properties.
- Liquid phase stability via global optimizationPublication . Rodrigues, Vânia; Pereira, Ana I.; Ferreira, Olga; Pinho, Simão; Rodrigues, VâniaIn this work, the Penalty Stretched Simulated Annealing Method and the Multilocal Branch and Bound method were applied to identify the stationary points of the tangent plane distance function defined for the Gibbs energy. The classic excess Gibbs energy Non Random Two Liquid model was used for these studies in several multicomponent mixtures, for which specific numerical difficulties were shown. The preliminary results obtained by applying the methodology developed in this work were satisfactory.
- Ionic liquids as entrainers for terpenes fractionation and other relevant separation problemsPublication . Vilas-Boas, Sérgio M.; Teixeira, Gabriel; Rosini, Sabrina Barbosa; Martins, Mónia A.R.; Gaschi, Priscilla S.; Coutinho, João A.P.; Ferreira, Olga; Pinho, SimãoThis work discusses the potential of two phosphonium-based ionic liquids (ILs), [P6,6,6,14]Cl and [P6,6,6,14][(C8H17)2PO2], and one methylimidazolium-based IL, [C4mim][OAc], as entrainers in the fractionation of terpene mixtures, in the desulfurization and denitrification of fuel oils, and in the separation of aromatics from aliphatic hydrocarbons. To this aim, the activity coefficients at infinite dilution of 45 solutes were obtained by gas-chromatography in the temperature range (333.15–458.15) K. Selectivities and capacities were calculated showing that [P6,6,6,14]Cl is adequate for the fractionation of (−)-menthone/L-(−)-menthol mixture, being also a suitable option for the deterpenation of citrus essential oil, and the removal of thiophene and pyridine from aliphatic hydrocarbons. To complement the experimental measurements COSMO-RS model was tested, demonstrating good potential to screen separation agents and give insights for several important separation problems, including the removal of contaminants from fuels and the isolation, fractionation and purification of terpenes mixtures.
- Modelling of phase equilibria for associating mixtures using an equation of statePublication . Ferreira, Olga; Brignole, Esteban A.; Macedo, Maria E.In the present work, the group contribution with association equation of state (GCA-EoS) is extended to represent phase equilibria in mixtures containing acids, esters, and ketones, with water, alcohols, and any number of inert components. Association effects are represented by a group-contribution approach. Self- and cross-association between the associating groups present in these mixtures are considered. The GCA-EoS model is compared to the group-contribution method MHV2, which does not take into account explicitly association effects. The results obtained with the GCA-EoS model are, in general, more accurate when compared to the ones achieved by the MHV2 equation with less number of parameters. Model predictions are presented for binary self- and cross-associating mixtures.
- Solubility of hesperetin in mixed solventsPublication . Ferreira, Olga; Schröder, Bernd; Pinho, SimãoThe study of the solubility of important biomolecules such as flavonoids is essential to support the design of several separation processes in the food and pharmaceutical industries. Following our previous studies, new solubility data of hesperetin in the mixed solvents water + acetone, water + ethanol, and water + methanol were measured, at 298.2 K, by the isothermal shake-flask method. The results obtained show three solid−liquid phase diagrams with distinct features. Additionally, the solid crystals obtained from the solubility studies were analyzed by powder X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis indicating that, depending on the mixed solvents composition, two different crystal structures of hesperetin, already described in the literature, can be obtained, corresponding either to the anhydrous or the monohydrate forms.
- Evaluation of ionic liquids for the sustainable fractionation of essential oilsPublication . Vilas-Boas, Sérgio M.; Coelho, Aline Zambom; Martins, Mónia A. R.; Coutinho, João A.P.; Ferreira, Olga; Pinho, SimãoFractionation of terpenes from natural complex matrices is economically attractive due to the wide use of these compounds in the cosmetic, food, and pharmaceutical industries. In this study, the potentialities of ionic liquids (ILs), and their mixtures, as separation agents in the fractionation of essential oils, were assessed through experimental and modeling approaches. Inverse gas chromatography was used to investigate solute-solvent interactions, and the COSMO-RS predic t i v e model was applied to describe the experimental data and to search for other potential ILs by selecting the appropriate cation-anion combination. Both the experimental and predicted approaches demonstrate that chloride-based ILs are very good options for fractionating essential oi l s containing hydrogen-bond donor monoterpenoids. In particular, the experimental and COSMO-RS screenings suggest that [P6,6,6,14]Cl gives the best performance for the separation of the main components present in citrus, mentha, and basil essential oils. The results gathered herein allow a deep understanding of terpene-IL interactions, and support the prediction of the ILs performance in the extraction and separation of natural products, optimizing resources and promoting sustainability.
- Octanol–water partition coefficients and aqueous solubility data of monoterpenoids: experimental, modeling, and environmental distributionPublication . Vilas-Boas, Sérgio M.; Costa, Mariana C.; Coutinho, João A.P.; Ferreira, Olga; Pinho, SimãoTerpenes and terpenoids encompass one of the most extensive and valuable classes of secondary metabolites. Their ten-carbon-containing oxygenated representatives, monoterpenoids, are the main components of plant essential oils, being widely exploited in the cosmetic, pharmaceutical, and food industrial areas. Due to its widespread use, it is crucial to investigate their environmental distribution. Thus, new water solubility data were obtained for six monoterpenoids ((1R)-(+)-camphor, (S)-(+)-carvone, eucalyptol, (1R)- (−)-fenchone, L-(−)-menthol, and (−)-menthone) at 298.2 and 313.2 K. Furthermore, octanol−water partition coefficients of 12 monoterpenoids (the six mentioned above plus carvacrol, (±)-β-citronellol, eugenol, geraniol, linalool, and thymol) were measured at 298.2 K. The COSMO-RS thermodynamic model and other more empirical approaches were evaluated for the description of the solubilities and partition coefficients, showing reliable predictions. Lastly, the distribution of the monoterpenoids in the different environmental compartments was assessed through an intuitive two-dimensional chemical space diagram based on the physicochemical equilibrium information reported.