Miguel Palma

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.

Ultrasound assisted extraction of phenolic compounds from grapes

A new ultrasound-assisted extraction method was developed for the determination of phenolic compounds present in grapes. Several extraction variables including extraction temperature (0-75°C), output amplitude (20, 50 and 100%), duty cycle (0.2 s, 0.6 s and 1 s), the quantity of sample (0.5-2 g), and the total extraction time (3-15 min) were evaluated. One of the most widely used extraction methods of polyphenol extraction has been used as reference method. Three parameters were compared: total amount of phenolic compounds, total amount of anthocyanins and total amount of tannic components. The resulting method produced similar or higher recoveries for these three parameters; however a much shorter extraction time was needed: 6 min (ultrasound assisted extraction method) instead of 60 min (reference method). Analytical properties for the new method were established, including limit of detection, limit of quantification, repeatability and reproducibility. The developed method was applied to two different types of grapes in different ripening degree.

Extraction of polyphenolic compounds from grape seeds with near critical carbon dioxide

A new analytical method using near critical carbon dioxide to extract polyphenolic compounds from white grape seeds has been developed. Carbon dioxide density, organic modifier, percentage of modifier, and extraction temperature were optimized utilizing an experimental design. Gallic acid, catechin, and epicatechin were the main phenolic compounds detected in the HPLC chromatogram of each extract. Recovery and reproducibility of catechin from grape seed was calculated. Under optimized conditions recovery was estimated to be 79% with a RSD equal to 7.3%. Results from the supercritical fluid method were compared with results obtained via liquid-solid extraction using methanol-water.

Stability of phenolic compounds during extraction with superheated solvents

The stability of nine phenolic compounds in the extraction with superheated methanol at different temperatures (40, 50, 100 and 150 degrees C) has been tested. The evolution of the same compounds in boiling methanol (65 degrees C) in contact with air was also determined. All the assayed phenolic compounds were stable under the extraction conditions with the exception of catechin and epicatechin (recoveries: 87.4% for catechin and 86.0% for epicatechin at 150 degrees C and 94.1% for epicatechin at 100 degrees C). Phenolic compounds kept at the boiling point of methanol (65 degrees C) showed lower recoveries: gentisic acid (85.5%), syringic aldehyde (92.8%), catechin (63.7%) and epicatechin (63.4%). Extraction with superheated solvents was also applied to the extraction of phenolic compounds from solid wastes of the winemaking process.

Ultrasound-assisted extraction and determination of tartaric and malic acids from grapes and winemaking by-products

Abstract The optimization of an ultrasound-assisted extraction (UAE) method for tartaric and malic acids from grape derived samples is shown. A fractional factorial experimental design allowed for the determination of the effects of seven extraction variables. Relationships between all the variables were examined. By applying graphical analysis, the best extractions conditions were obtained. The most important variables were the extracting liquid and the extraction temperature. Later, a central composite design was applied for optimizing the temperature and the composition of the extracting liquid. The optimized method was applied to grapes and to winemaking by-products. The repeatability of the method was studied and the recovery of tartaric and malic acids was established. Organic acids quantification was done by liquid chromatography (LC) using a post-column buffer and a conductivity detector.

Ultrasound-assisted extraction of capsaicinoids from peppers

The development of a rapid, reproducible and simple method of extraction of the majority capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin) present in hot peppers by the employment of ultrasound-assisted extraction is reported. The study has covered four possible solvents for the extraction (acetonitrile, methanol, ethanol and water), the optimum temperature for extraction (10-60 degrees C), the extraction time (2-25 min), the quantity of sample (0.2-2 g), and the volume of solvent (15-50 mL). Under the optimum conditions of the method developed, methanol is employed as solvent, at a temperature of 50 degrees C and an extraction time of 10 min. The repeatability and reproducibility of the method (R.S.D.<3%) have been determined. The capsaicinoids extracted have been analysed by HPLC with fluorescence detection and using monolithic columns for the chromatographic separation. The method developed has been employed for the quantification of the various capsaicinoids present in different varieties of hot peppers cultivated in Spain.

Application of FT-IR spectroscopy to the characterisation and classification of wines, brandies and other distilled drinks.

FT-IR spectra were employed for the differentiation and classification of wines and brandies during their ageing process, as well as for the characterisation and differentiation of distilled drinks from several producing countries. The FT-IR spectra have enabled the differentiation of the six scales of ageing of sherry wine. A good linear regression fit (regression coefficient=0.995) has been obtained between ageing scale and the data of the FT-IR spectrum. In the case of Brandy of Jerez, it has been possible to differentiate the three degrees of ageing and to devise a system of classification by means of linear discriminant analysis, with a reliability of 83%. The application of the regression by partial least squares has allowed us to obtain a regression between the degree of ageing and the data of the FT-IR spectrum (correlation coefficient=0.986). Lastly, Spanish, French and South African brandies, as well as cognacs and armagnacs have been characterised, and a complete differentiation of the latter two types from the rest of the samples of distilled drinks has been obtained.

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.

Direct determination of organic acids in wine and wine-derived products by Fourier transform infrared (FT-IR) spectroscopy and chemometric techniques

FT-IR with partial least squares (PLS) was used to establish a full calibration model for tartaric acid, malic acid, lactic acid, succinic acid, citric acid and acetic acid in wines, vinegars and spirits. Sample pre-treatment was not required except for filtering. The PLS method was employed and FT-IR spectra were correlated with the results from a reference HPLC method. In the validation with an independent set of samples, a strong correlation with the reference values was demonstrated for the highest concentration range (>0.6 g L(-1)) in all acids but the correlation was much weaker in the lower range (<0.6 g L(-1)). In the case of acetic acid, however, good results were obtained in the low concentration range for both red and white wine and for spirit drinks. This finding explains the fact that calibration and validation of the FT-IR spectroscopy method depends very strongly on the composition of the sample set and on the quality of the reference analysis. It was not possible to obtain a single calibration for all of the analysed samples and in some cases individual calibrations for specific samples were required. This situation was due to the different matrixes in the studied samples: 12-15% ethanol (wines), 30-40% ethanol (spirits) and 6-10% acetic acid (vinegars). As a result, a calibration model was developed for each acid in red and white wine, tartaric acid, acetic acid and total acidity in vinegar, and acetic acid in spirit drinks.

Optimization of the ultrasound-assisted extraction of anthocyanins and total phenolic compounds in mulberry (Morus nigra) pulp.

New ultrasound-assisted extraction methods for the determination of anthocyanins and total phenolic compounds present in mulberries have been developed. Several extraction variables, including methanol composition (50-100%), temperature (10-70°C), ultrasound amplitude (30-70%), cycle (0.2-0.7s), solvent pH (3-7) and solvent-solid ratio (10:1.5-20:1.5) were optimized. A Box-Behnken design in conjunction with a response surface methodology was employed to optimize the conditions for the maximum response based on 54 different experiments. Two response variables were considered: total anthocyanins and total phenolic compounds. Extraction temperature and solvent composition were found to be the most influential parameters for anthocyanins (48°C and 76%) and phenolic compounds (64°C and 61%). The developed methods showed high reproducibility and repeatability (RSD<5%). Finally, the new methods were successfully applied to real samples in order to investigate the presence of anthocyanins and total phenolic compounds in several mulberry jams.