Margarida A. Ferreira

Métodos para avaliação do grau de oxidação lipídica e da capacidade antioxidante

In this work several methods for evaluation of the degree of lipid oxidation and antioxidant activity are reviewed. Some aspects related to the recent advances mentioned in the literature are also reported.

Quality evaluation of Portuguese honey

Abstract The present work was conducted to evaluate the quality of 25 brands of honey commercially available on the Portuguese market, in a total of 50 samples. The brands included unifloral and multifloral honeys, which were studied and botanically typified. Carbohydrate composition was determined by HPLC-RI to evaluate the contents of monosaccharides fructose and glucose; the disaccharides saccharose, maltose and trehalose and of the trisaccharide melizitose. 5-Hydroxymethyl-2-furfuraldehyde (HMF) was quantified by HPLC-UV and other physicochemical quality parameters were also carried out according to the European (Directive 74/409/EC) and Portuguese Regulations (Decreto-lei No. 131/85, 1985) in order to determine moisture, ash content, diastase activity, free acidity, free acidity and water-insoluble solids. All samples were organoleptically and microscopically examined. Only 13 brands were found to meet all major national and international specifications, the remaining 12 did not agree with one or more of the analysed parameters (HMF, diastase activity, or carbohydrate composition); such observations may reflect an inadequate manufacturing or storing process and a certain ageing of these honeys.

Combined ion-pair extraction and gas chromatography-mass spectrometry for the simultaneous determination of diamines, polyamines and aromatic amines in Port wine and grape juice.

An accurate and very sensitive method which allows for the simultaneous determination of the diamines (1,3-diaminopropane, putrescine and cadaverine), of the polyamines (spermidine and spermine), and of the aromatic amines (beta-phenylethylamine and tyramine) found in Port wines and corresponding grape juices is presented. Sample clean-up consisted of the extraction of the amines with the ion-pairing reagent bis-2-ethylhexylphosphate dissolved in chloroform followed by a back-extraction with 0.1 M HCl. The hydrochloric extract obtained was dried and the amines were further derivatized with heptafluorobutyric anhydride and analyzed by GC-MS in the selected ion-monitoring mode, with a total run time of 18 min. Under the adopted conditions, the extraction of all the studied compounds was almost complete and the obtained extracts were free of potential interferents present in the samples, namely sugars, and most of the amino acids and polyphenols. Via the use of a set of five selected internal standards (amphetamine, [2H8]putrescine, 1,7-diaminoheptane, norspermidine and norspermine), the data obtained from the linearity, repeatability and recovery experiments were very good for all the compounds assayed. The corresponding limits of detection were invariably below 10 microg l(-1). The method was successfully applied to measure the content of biogenic amines in twelve young and five aged Port wine samples, eleven grape juice samples as well as in ten Portuguese red and white table wines. Results are presented and briefly discussed.

Effect of temperature on evolution of free amino acid and biogenic amine contents during storage of Azeitão cheese

Abstract A study on the evolution of free amino acids and biogenic amines in Azeitao cheese during 4 weeks at different temperatures of storage (4 and 25°C) was performed. Free amino acids and biogenic amines were determined by RP-HPLC with visible detection, following extraction from the cheese and derivatization with dabsyl chloride. The method presented a linear relation between peak area and concentration from 2–200 mg/l. The detection limit value was less than 1.5 mg/l. The average repeatability was less than 4%. The major free amino acids were proline, valine, isoleucine and leucine and the major amines were tyramine, cadaverine and histamine. Room temperature (25°C) promoted a significant increase of the contents of valine, leucine, tyramine and putrescine, expressed as g/kg of dry matter. These two free amino acids and two biogenic amines may serve as indicators of temperatures changes in ripened cheese.

HPLC/diode-array applied to the thermal degradation of trigonelline, nicotinic acid and caffeine in coffee

Abstract A simultaneous determination of trigonelline, nicotinic acid and caffeine was performed in samples of arabica and robusta coffees, before and after roasting at either different temperatures (160–240°C) or different periods of time exposures, in order to study their thermal degradation. A reverse-phase HPLC/Diode-array detector method was used. The results were compared with a model dry system roast of the compounds under study, individually and in mixture. The loss of trigonelline was strongly dependent upon the degree of roast and was associated with the formation of nicotinic acid. A slight decrease in caffeine was verified in both species. This study showed diversified behavior of the compounds when in their native form or in an artificial mixture, eliciting the chemical environmental influence. Rate constants for the chemical reactions at 240°C were determined.

SIMULTANEOUS DETERMINATION OF BENZOIC AND SORBIC ACIDS IN QUINCE JAM BY HPLC

Abstract An isocratic HPLC technique is described for the determination of benzoic acid and sorbic acid in industrial quince jam. The preparation procedure was optimized. Precipitation of proteins and fat by the addition of methanol, followed by centrifugation and/or filtration provided an extract suitable for chromatographic analysis. The chromatographic separation was achieved with a C18 column and acetate buffer (pH=4.4) - methanol (65:35) as the mobile phase. The effluent was monitored at 235 nm. Effective separation and quantification was achieved in less than 7 min. Specificity of the method was checked against common food additives added to industrial quince jam, such as l -ascorbic acid and citric acid. Diode array detection was used for confirmation of the preservatives. Mean recoveries of 95–104% were obtained with a precision less than 2.6%, detection limits of 25 and 6.25 mg/kg were obtained for benzoic and sorbic acids, respectively. Results were in good agreement with the reference methods. The presence of benzoic and sorbic acids in quince jams available on the Portuguese market, was also determined. Eleven commercial brands of quince jam were analysed. All contained benzoic acid. The concentration ranged from 413.9±10.4 to 1501±4.2 mg of benzoic acid/kg of quince jam. Only two brands also contained sorbic acid. The concentrations were 515.0±7.0 and 908.3±5.3 mg of sorbic acid/kg of quince jam.

Composition of Quince (Cydonia oblonga Miller) seeds: phenolics, organic acids and free amino acids

Phenolic compounds, organic acids and free amino acids of quince seeds were determined by HPLC/DAD, HPLC/UV and GC/FID, respectively. Quince seeds presented a phenolic profile composed of 3-O-caffeoylquinic, 4-O-caffeoylquinic, 5-O-caffeoylquinic and 3,5-dicaffeoylquinic acids, lucenin-2, vicenin-2, stellarin-2, isoschaftoside, schaftoside, 6-C-pentosyl-8-C-glucosyl chrysoeriol and 6-C-glucosyl-8-C-pentosyl chrysoeriol. Six identified organic acids constituted the organic acid profile of quince seeds: citric, ascorbic, malic, quinic, shikimic and fumaric acids. The free amino acid profile was composed of 21 identified free amino acids and the three most abundant were glutamic and aspartic acids and asparagine.

Gas chromatographic quantification of amino acid enantiomers in food matrices by their N(O,S)-ethoxycarbonyl heptafluorobutyl ester derivatives

Several amino acid enantiomer derivatives were prepared with different chloroformates and analysed by gas chromatography (GC) on a Chirasil-L-Val GC column, at a temperature below 200 degrees C. Among them the N(O,S)-ethoxycarbonyl heptafluorobutyl esters presented the best compromise between short retention times, high yield responses and good resolution for almost all the tested amino acids. These derivatives proved to be suited for quantification of amino acids in aqueous media, with L-p-chlorophenylalanine as internal standard. The developed procedure was applied to several food samples for determination of their free amino acid profiles.

Phenolic profile in the evaluation of commercial quince jellies authenticity

Abstract The phenolic profiles of 12 samples of Portuguese commercial and one home-made quince jelly were determined by reversed-phase HPLC/DAD, in order to evaluate their authenticity. Two different extraction methods were needed for the complete definition of quince jelly profile, one of them including an Amberlite XAD-2 cleaning step. These analyses showed that all samples presented a similar profile composed of at least eight identified phenolic compounds. None of the samples were fraudulently adulterated by the addition of pear or apple, since they did not contain arbutin, the characteristic compound of pear, nor phloretin 2′-xylosylglucoside and phloretin 2′-glucoside, considered the chemical markers of apple. All samples exhibited 5-HMF, a sugar derivative, as the major compound.

Gas chromatographic-mass spectrometric determination of 4-(5) methylimidazole in ammonia caramel colour using ion-pair extraction and derivatization with isobutylchloroformate

Abstract A procedure for the gas chromatographic-mass spectrometric quantification of 4-(5-)methylimidazole in ammonia caramel colours by using isobutylchloroformate as dervitizing reagent has been developed. The use of this reagent coupled to a previous ion-pair extraction of the compound with Bis-2-ethylhexylphosphate enabled routine determination of 4-(5) methylimidazole with several advantages compared to others methods previously described. Examples of the analysis of some samples are presented as well as data on linearity, recovery and repeatability. Under the adopted conditions the limit of detection and the limit of quantification were 0.250 mg kg −1 and 1 mg kg −1 , respectively.