Browsing by Author "Ribeiro, Maria H. L."
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- Design of an immobilized enzyme system for naringin hydrolysis at high-pressurePublication . Pedro, Helder A. L.; Alfaia, Antonio J.; Marques, Joao; Vila-Real, Helder J.; Calado, Antonio; Ribeiro, Maria H. L.The effect of pressure was studied in an enzymatic reaction with an immobilized biocatalyst. Naringinase immobilized by entrapment in calcium alginate beads was the biocatalyst used to catalyze, at high-pressure, the hydrolysis of naringin to naringenin. These molecules have great potential in the pharmaceutical industry due to their recognized anti-oxidant, anti-inflammatory, anti-carcinogenic, anti-hypertensive and hypocholesterolemic effects. At high-pressure, the influence of relevant parameters on naringinase catalytic activity such as temperature, substrate concentration, and biocatalyst reuse was studied. At 160 MPa, naringinase entrapped in Ca-alginate beads displayed higher activity, namely in the range of 35-40 degrees C, whereas the optimum, at atmospheric pressure, was 35 degrees C. The immobilized naringinase presented a Michaelis-Menten kinetic, with a 65% higher maximum initial rate (V-max(ap) = 0.069 mM min(-1)), and a 70% lower K-M(ap) (0.097 mM) at 160 MPa, as compared to kinetic parameters, at atmospheric pressure (V-max(ap) = 0.042 mM min-1 and K-M(ap) = 0.303 mM). A positive effect of pressure on naringin hydrolysis by immobilized naringinase, in MCa-alginate beads was confirmed with a negative activation volume (Delta V-not equal) of -9 mL mol(-1). The stability of immobilized naringinase was also evaluated at high-pressure. (c) 2006 Elsevier Inc. All rights reserved.
- 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.
- Evaluation of the effect of high pressure on naringin hydrolysis in grapefruit juice with naringinase immobilised in calcium alginate beadsPublication . Ferreira, Luis; Afonso, Cristina; Vila-Real, Helder; Alfaia, Antonio; Ribeiro, Maria H. L.The reduction of bitterness in citrus juices would increase their acceptance by the consumer. This reduction in grapefruit juices can be achieved as a result of an enzymatic process, with improved commercial value and maintenance of health properties. The use of a cheap, simple and effective immobilisation method combined with high pressure can be a key asset in the debittering of citrus juices. The aim of this study is the debittering of grapefruit juice under high pressure, with naringinase immobilized in calcium alginate beads. Naringinase, an alpha-rhamnopyranosidase, hydrolyzes naringin (a flavanone glycoside and primary bitter component in grapefruit juice) to naringenin, which is tasteless. High pressure can activate or inhibit enzymatic activities depending on the proteins and conditions. The hydrolysis of naringin was first evaluated in model solution (acetate buffer 0.02 M, pH=4.0) and then in grapefruit juice. In model solution, at 160 MPa and 37 degrees C, a 50% increase in the concentration of reducing sugars was obtained when compared to the reaction at atmospheric pressure. The higher naringenin concentration (33 mg/L) was obtained at 54 degrees C under high pressure of 200 MPa, which corresponds to a naringin reduction of 72 % in model solution, while at atmospheric pressure (0.1 MPa), the naringin reduction was only 35 %. The decrease in naringin content can be directly correlated with the reduction in bitterness. From the concentration of residual naringin, the percentage of reduction in bitterness was evaluated. In grapefruit juice, a debittering of 75 % occurred with a pressure of 160 MPa at 37 degrees C for 20 minutes.
- High pressure and temperature combination with naringin hydrolysis by naringinase Ca-alginate beads in grapefruit juice processingPublication . Afonso, Cristina; Ferreira, Luis; Vila-Real, Heleer; Alfaia, Antonio J.; Ribeiro, Maria H. L.
- 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.
- Kinetic modelling of naringin hydrolysis using a bitter sweet alfa-rhamnopyranosidase immobilized in k-carrageenanPublication . Ribeiro, Isabel A. C.; Ribeiro, Maria H. L.Naringin. the principal bitter flavonone glycoside and the primary bitter component in grapefruit juice, can be hydrolysed by naringinase (with expressed activity in alfa-L-rhamnosidase and beta-D-glucosidase) into rhamnose and prunin (one-third bitterness ratio to naringin), which can be further hydrolysed into glucose and tasteless naringenin. The main goal of this work was the modelling and optimisation of the enzymatic activity of naringinase entrapped in k-carrageenan beads, in grapefruit juice. In order to attain these goals naringinase activity, naringin conversion and naringenin formation were evaluated. In this study response surface methodology was used for modelling the naringin hydrolysis by naringinase immobilized in k-carrageenan beads as a function of temperature (9-51 degrees C) and naringinase concentration (0.29-1.7 g L-1) in grapefruit juice. Experiments were carried out following a central composite rotatable design. Naringinase activity could be described by response surfaces that enabled to fit second-order polynomials to experimental data points. The high values of R-2 (0.996) and R-adj(2) (0.992) of the models show a close agreement between the experimental results and the theoretical values predicted by the models. The higher naringin conversion (95%) was attained with naringinase concentrations higher than 800 mg L-1 and temperatures higher than 30 degrees C. This is a promising result for a future application of enzymatic hydrolysis of naringin immobilized in k-carrageenan, in grapefruit juice industry, maintaining juice properties. (c) 2007 Elsevier B.V. All rights reserved.
- Kinetic studies on selective adsorption of erythromycin onto new polymeric resinsPublication . Barroso, Gustavo; del Saza, Beatriz Rivas; Ribeiro, Maria H. L.
- Modelling of the high pressure-temperature effects on naringin hydrolysis based on response surface methodologyPublication . Marques, Joao; Vila-Real, Helder J.; Alfaia, Antonio J.; Ribeiro, Maria H. L.The aim of this study was the modelling, under high pressure, of naringin hydrolysis by naringinase. Response surface methodology (RSM) was used to compare the effects of the selected variables on the bioconversion under study. The combined action of temperature (13-61 degrees C) and pressure (80-216 MPa) on the catalytic activity of naringinase was investigated at pH 4.0 using naringin as the substrate. The choice of experimental domains resulted from preliminary studies. Naringinase activity, for naringin hydrolysis at pH 4.0, could be described by a convex surface with a maximum of 0.13 mM min(-1), at 41 degrees C and 158 MPa. After 1 h of reaction time, reducing sugars production could also be described by a convex surface, with a maximum reducing sugars concentration of 8 mM at 38 degrees C and 168 MPa. The interaction temperature-pressure had a significant effect on both naringinase activity and reducing sugar formation after 1 h. Under the optimized conditions, the naringin hydrolysis by naringinase was evaluated. (c) 2007 Elsevier Ltd. All rights reserved.
- Naringin and naringenin determination and control in grapefruit juice by a validated HPLC methodPublication . Ribeiro, Isabel A.; Ribeiro, Maria H. L.The main goal of this work was to develop and validate a fast, effective HPLC method for the simultaneous determination and control of naringin and naringenin, in several samples of citrus juices, namely, natural and commercial grapefruit and orange juices. The reason for developing this HPLC procedure is to control the debittering process using naringinase. A successful resolution and retention times were obtained with a C-18 reversed phase column, at a 1 mL min(-1) flow rate, with a gradient of acetonitrile:water and at the temperature of 25 degrees C. The method was linear in the working range of 55-95 mu g mL(-1) for naringin and 10-60 mu g mL(-1) for naringenin. Repeatability was determinate at three concentration levels obtaining a RSD (%) always lower than 2.5%, a limit of detection (LOD) and a limit of quantification (LOQ) of 2.83, 8.57 and 1.11, 3.37 pg mL(-1) for naringin and naringenin, respectively, were obtained. (c) 2007 Elsevier Ltd. All rights reserved.
- Response surface optimization of enzymatic hydrolysis of Cistus ladanifer and Cytisus striatus for bioethanol productionPublication . Ferreira, Susana; Duarte, Ana P.; Ribeiro, Maria H. L.; Queiroz, Joao A.; Domingues, Fernanda C.Current ethanol production processes using crops such as sugar cane and corn are well established: however, utilization of a cheaper substrate such as lignocellulose could make bioethanol more competitive with fossil fuel, without the ethical concerns associated with the use of potential food resources. The sequential configuration employed to obtain cellulosic ethanol implies that the solid fraction of pretreated lignocellulosic material undergoes hydrolysis. In this work, the enzymatic hydrolysis of pretreated Cistus ladanifer and Cytisus striatus was studied following an experimental design as a statistical problem solving approach. Plackett-Burman design was used in order to select the most important variables from the simultaneous study on influence of operating and reactional conditions, and central composite design to optimize the process of enzymatic hydrolysis. The optimization of enzymatic hydrolysis using the response surface methodology allowed a study on the influence of the variables (pH, temperature, cellulases concentration, polymer (PEG) concentration and incubation time) and variability due to the type of substrate (C ladanifer and C striatus) used. From the obtained results it can be concluded that the enzymatic hydrolysis was clearly enhanced by temperature, cellulase concentration, and incubation time. Model validation showed a good agreement between experimental results and the predicted responses. (C) 2009 Elsevier B.V. All rights reserved.. - Instituto de Financiamento e Apoio ao Desenvolvimento da Agricultura e das Pescas (IFADAP) [2006.09.001055.1]. - This research was supported by Instituto de Financiamento e Apoio ao Desenvolvimento da Agricultura e das Pescas (IFADAP) Project 2006.09.001055.1. We thank Univar Iberia, SA, Portugal, for supplying the enzymes.