Browsing by Author "Calado, Antonio R. T."
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- Development of co-solvent systems in the bioconversion of naringin to naringenin by naringinasePublication . Vila-Real, Helder; Alfaia, Antonio J.; Calado, Antonio R. T.; Ribeiro, Maria H. L.
- Gemini Surfactant-Protein InteractionsPublication . Faustino, Celia M. C.; Calado, Antonio R. T.; Garcia-Rio, LuisThe interactions between bovine serum albumin (BSA) and gemini surfactants derived from cystine have been investigated and were compared with the conventional single-chain surfactant derived from cysteine. The influence of the stereochemistry of the gemini surfactant on its behavior toward BSA was also investigated, as well as the effects of pH and temperature. Electrical conductivity and surface tension measurements were used to obtain important system parameters such as critical aggregation concentration (cac), polymer saturation point (psp), degree of ionization (alpha), and the amount of surfactant binding to protein (M). Stereochemistry was found to influence the surface properties of the surfactants studied and their interaction with BSA but not their micellar properties in solution.
- High pressure-temperature effects on enzymatic activityPublication . Real, Helder J. Vila; Alfaia, Antonio J.; Calado, Antonio R. T.; Ribeiro, Maria H. L.Initially exploited in chemistry and physics, high-pressure technology has gained importance in various fields. Flavonoids, namely naringin and naringenin, from citrus, are functional chemicals with important properties in the fields of healthcare, food and agriculture. Naringin, the principal bitter flavonone glycoside and the primary bitter component in grapefruit juice, can be hydrolysed by naringinase into tasteless naringenin. The temperature of 303 K was ideal for maximizing the activity of the naringinase at 160 MPa when compared to atmospheric pressure. The pressure had a positive effect on the reaction rate, with a value of - 15.0 1.8 cm(3) mol(-1) for the activation volume. Kinetic parameters, k(m) and V-max for naringinase were evaluated, the maximum initial rate at 160 MPa (V-max = 2.7 mM min(-1)) was higher than that at atmospheric pressure (V-max = 0.06 mM min(-1)). This is a promising result for future application of enzymatic hydrolysis of naringin at high pressure, in the citrus juice industry. @ 2006 Elsevier Ltd. All rights reserved.
- New Urea-Based Surfactants Derived from alpha,omega-Amino AcidsPublication . Faustino, Celia M. C.; Calado, Antonio R. T.; Garcia-Rio, LuisNew anionic urea-based surfactants derived from alpha,omega-amino acids and in particular from beta-alanine were synthesized and their solution properties characterized by electrical conductivity, equilibrium surface tension, and steady-state fluorescence spectroscopy techniques. Double-chain surfactants and the single-chain surfactant containing a sulfate head group exhibited the lowest critical micelle concentration (cmc) values and superior efficiency in lowering surface tension. All surfactants promoted adsorption relative to micellization, and micellar parameters were sensitive to the hydrophobicity of the amino acid residue. The polarity of the interfacial region, measured with the solvatochromic probe E-T(30) (Reichardt's betaine dye), was similar to sodium dodecyl sulfate (SDS) micelles.