Biomedical subjects

Miguel Palma

Publications and source records attributed to Miguel Palma.

7 recordsLinked to original sources

PubMed2006

Investigation on phenolic compounds stability during microwave-assisted extraction.

The stability of 22 phenolic compounds of different families (benzoic acids, benzoic aldehydes, cinnamic acids, catechins, coumarins, stilbens and flavonols) has been studied under conditions of microwave-assisted extraction. The influence on the stability affected by the working temperature between 50 and 175 degrees C has been evaluated, and it has been concluded that all the compounds studied are stable up to 100 degrees C, whereas at 125 degrees C there is significant degradation of epicatechin, resveratrol and myricetin. Conclusions have been drawn on the relationship between the chemical structure and the stability of the compounds; it has been found that those that have a greater number of hydroxyl-type substituents are more easily degraded under the extraction conditions.

Chemical Fractionation↗

PubMed2006

Pressurized liquid extraction of capsaicinoids from peppers.

A method has been developed for the extraction of capsaicinoids from peppers by pressurized liquid extraction (PLE); these compounds are determined by reverse phase high-performance liquid chromatography (HPLC), with detection by fluorescence spectrophotometry and mass spectrometry (MS). The stability of capsaicin and dihydrocapsaicin has been studied at different temperatures (50-200 degrees C), and several extraction variables have been assayed: solvent (methanol, ethanol, and water), different percentages of water in the methanol (0-20%) and in the ethanol (0-20%), and the number of extraction cycles. The study has evaluated the repeatability (RSD < 7%) and the reproducibility (RSD < 7%) of the method. Finally, the PLE method developed has been applied to quantify the capsaicinoids present in three varieties of hot peppers cultivated in Spain, quantifying five capsaicinoids: nordihydrocapsaicin, capsaicin, dihydrocapsaicin, an isomer of dihydrocapsaicin, and homodihydrocapsaicin.

Capsaicin↗

PubMed2005

Solid-phase extraction of soy isoflavones.

An automated method using solid-phase extraction (SPE) for the concentration and clean-up of soy isoflavone extracts is proposed in this work. Using a standardized sample (0.1 g of a freeze dried soybean extract/25 mL of water); eight SPE cartridges with a wide range of sorbents (C18, divinylbenzene and modified divinylbenzene) from different suppliers were evaluated and compared. A large variation on SPE cartridges performance was observed, especially regarding retention and breakthrough volume of isoflavones during sample load and washing steps. The most effective cartridges were the divinylbenzene based cartridges, especially Strata X (from Phenomenex) and HLB oasis (from Waters). Using Strata X cartridges, several extraction parameters, such as sample loading flow (5-15 mL min(-1)), extracting solvent volume (2-6 mL of methanol), pH of the extracting solvent and the necessity of drying the sorbent before elution, were evaluated to provide a fast, specific, quantitative and reproducible SPE method. The optimized method consists of conditioning the cartridge with 10 mL of methanol and 10 mL of water (10 mL min(-1)), loading 25 mL of the standardized extract onto the cartridges (5 mL min(-1)), washing the cartridge with 10 mL of water (10 mL min(-1)) and finally eluting with 4 mL of methanol (10 mL min(-1)). Mean isoflavones recovery was 99.37% and mean intra- and inter-day reproducibility was higher than 98%. The developed sample clean-up/concentration (6.25:1) method takes less than 10 min and can be used in the analysis of isoflavones from soy extracts.

Chromatography, High Pressure Liquid↗

PubMed2005

Determination of the age of sherry wines by regression techniques using routine parameters and phenolic and volatile compounds.

This paper describes a study of the possibility of obtaining regression models by means of partial least squares (PLS) and multiple linear regression (MLR) that would enable us to correlate a series of parameters, such as the concentration of short-chain organic acids, higher alcohols, and phenolic compounds with the age of vintage Sherry wines or "anadas". The aim of this study is to characterize how these parameters evolve with aging. If this could be done, it would then be possible to guarantee the age of such wines using objective variables. A PLS regression model was established that allows the age to be predicted with a mean deviation of 1.6 years with respect to the age of the wines. In the case of the MLR, a model with 6 variables was obtained that gives a mean deviation of 3.3 years in the predictions.

Least-Squares Analysis↗

PubMed2004

Determination of catechins by means of extraction with pressurized liquids.

The technique of extraction with pressurized liquids is applied for extraction of catechin and epicatechin in tea leaves and in grape seeds. The extracts obtained are then analyzed by HPLC. A comparison has been made of the recoveries obtained employing extraction by magnetic stirring, ultrasound-assisted extraction, and extraction with pressurized liquids. In the three extraction systems, four different pure solvents were utilized, namely water, methanol, ethanol, and ethyl acetate. Methanol produced the best results. For this comparison, an initial step was to check the stability of catechins during the process of extraction using pressurized liquids at high temperature (100-200 degrees C). It has been confirmed that recoveries of these two compounds begin to fall, to below 95%, at 130 degrees C and above. Pressurized liquid extraction using methanol as solvent, produces results, in terms of recovery of catechin and of epicatechin, notably higher than any of the other conditions of extraction tested. The duration of the extraction cycle was also evaluated and re-extractions were performed to ensure the full recovery from the samples. It was found that, forcatechin, the R.S.D. of the method is 3.21%, and for epicatechin the R.S.D. was 2.96% (n = 5). The final optimized pressurized liquid extraction method allows for the determination of catechin and epicatechin in diverse types of samples with a rapid (10 min) and reproducible method.

Catechin↗

PubMed2003

Ultrasound-assisted extraction of soy isoflavones.

Efficiency in extracting four isoflavone derivatives (daidzin, glycitin, genistin and malonyl genistin) from freeze-dried ground soybeans was compared for mix-stirring extraction and ultrasound-assisted extraction, using different solvents and extraction temperatures with both. The efficiency of the extraction of soy isoflavones was improved by ultrasound but was dependent on the solvent employed. Optimization of the ratios of sample quantity to solvent volume and length of extraction time was also performed. Isoflavones can be quantitatively extracted from soybeans with 50% ethanol at 60 degrees C using ultrasound-assisted extraction in 20 min.

Chromatography, High Pressure Liquid↗

PubMed2002

In-line pressurized-fluid extraction-solid-phase extraction for determining phenolic compounds in grapes.

A new method of pressurized-fluid extraction coupled in-line with solid-phase extraction has been used for the extraction of phenolic compounds from grapes. The full extraction method is performed under an inert atmosphere. Five different solvents have been assayed using different extraction pressures and temperatures. Using two extraction stages with two different solvents, water and methanol, quantitative recovery for most of the assayed compounds has been found in the second extract. Only the most polar phenolic compound, gallic acid, was found distributed in both extracts. The application to real samples allows for a clean-up of the extracts. Cinnamic esters like caftaric acid, cis and trans-coutaric acids were found only in the methanolic extract. The reproducibility for the new method was measured using both an inert solid spiked with standards and grapes. Using between 202 and 424 microg of spiked standards, the resulting relative standard deviations were less than 5%, with the exception of gallic acid (RSD=13%). For grapes, the resulting RSD were 11% for trans-coutaric acid, 10% for caftaric acid and 6% for cis-coutaric acid.

Phenols↗