Recebido em 18/12/07; aceito em 25/2/08; publicado na web em 2/4/09The water content in seafoods is very important since it affects their sensorial quality, microbiological stability, physical characteristics and shelf life. In this study, thermoanalytical techniques were employed to develop a simple and accurate method to determine water content (moisture) by thermogravimetry (TG) and water activity from moisture content values and freezing point depression using differential scanning calorimetry (DSC). The precision of the results suggests that TG is a suitable technique to determine moisture content in biological samples. The average water content values for fish samples of Lutjanus synagris and Ocyurus chrysurus species were 76.4 ± 5.7% and 63.3 ± 3.9%, respectively, while that of Ulva lactuca marine algae species was 76.0 ± 4.4%. The method presented here was also successfully applied to determine water activity in two species of fish and six species of marine algae collected in the Atlantic coastal waters of Bahia, in Brazil. Water activity determined in fish samples ranged from 0.946 -0.960 and was consistent with values reported in the literature, i.e., 0.9 -1.0. The water activity values determined in marine algae samples lay within the interval of 0.974 -0.979.

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Recebido em 4/9/08; aceito em 13/5/09; publicado na web em 6/11/09 VALIDATION OF CHROMATOGRAPHIC METHODS-AN EXPERIMENT USING HPLC AND GREEN CHEMISTRY IN METHYLXANTHINES DETERMINATION. The validation of analytical methods is an important step in quality control. The main objective of this study is to propose an HPLC experiment to verify the parameters of validation of chromatographic methods, based on green chemistry principles, which can be used in experimental courses of chemistry and related areas.

Two ozonation procedures for sunflower oils at different applied ozone dosages were carried out. Ozone was obtained from medicinal oxygen and from air. Peroxide, acidity, and iodine indexes, along with density, viscosity and antimicrobial activity were determined. The fatty acid compositions of the samples were analyzed using GC. The content of oxygen was determined using an elemental analysis. Electronic Paramagnetic Resonance was used to measure the organic free radicals. The reactions were achieved up to peroxide index values of 658 and 675 mmolequiv kg^–1 using medicinal oxygen and air for 5 and 8 hours, respectively. The samples of ozonized sunflower oil did not present organic free radicals, which is a very important issue if these oils are to be used as drugs. The ozonation reaction is more rapid with medicinal oxygen (5 hours) than with air (8 hours). Ozonized sunflower oil with oxygen as an ozone source was obtained with high potential for antimicrobial activity.<br><br>Se ha aplicado dos procedimientos de ozonización a aceites de girasol a diferentes dosis de ozono, obteniendo el ozono a partir de oxígeno medicinal y de aire. Se han determinado los índices de peróxido, yodo y acidez conjuntamente con la densidad, viscosidad y la actividad antimicrobiana. La composición de ácidos grasos fue analizada mediante CG. El contenido de oxígeno fue determinado mediante Análisis Elemental. Se utilizó la resonancia paramagnética electrónica para medir los radicales libres orgánicos. Las reacciones fueron realizadas hasta valores de índice de peróxidos de 658 y 675 mmol-equiv kg^–1 usando oxígeno medicinal y aire durante 5 y 8 horas, respectivamente. Las muestras de aceite de girasol ozonizado no presentaron radicales libres orgánicos, lo cual es muy importante en el caso de que estos aceites sean utilizados en medicina. La reacción de ozonización es más rápida cuando se utiliza oxígeno medicinal (5 horas) que el aire (8 horas). El aceite de girasol ozonizado con oxígeno como fuente de ozono presentó mayor potencial de actividad antimicrobiana

a b s t r a c tCarotenoids are present in many foods. Due to their polyenic chains, they undergo oxidation reactions which may give several compounds. Ozone, a powerful antimicrobial agent, is applied in the food industry due to its high reactivity and penetrability. This work presents a chemical study of the degradation of b-carotene in solutions, under the influence of ozone. The experiments were carried out at ozone concentrations ranging from 0.8 to 2.5 ppm and the b-carotene solutions were sampled and analysed from zero to seven hours of reaction. The oxidation products were collected in C18 cartridges coated with dinitrophenylhydrazine and the hydrazones formed were analysed by LC-MS. The oxidation reaction was found to follow a zero order kinetic model and the b-carotene decay ranged between 17.2% and 99.8%. Fourteen oxidation products were tentatively identified, amongst them eight which had not been cited yet in the literature as oxidation products of b-carotene.Ó

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A new analytical method is reported for the determination of 11 volatile carbonyl compounds isolated at room temperature from the headspace of marine algae. This method is based on the conversion of the carbonyl compounds to their 2,4-dinitrophenylhydrazone derivatives followed by high-performance liquid chromatography analysis. Using this method, 11 carbonyl compounds are detected and identified from the dynamic headspace sampling of 10 species of marine algae. Eight compounds are quantitated and the three remaining are only identified. Under optimized conditions, all carbonyl compounds are separated in 32 min. The detection and quantitation limits of the high-performance liquid chromatography method are, respectively, in the range of 0.26-0.85 ng/g of algae (formaldehyde) to 13.77-45.90 ng/g of algae (E)-2-hexenal. The calibration curves are linear in the concentration range of 2.0-1000 microg/L of solution, corresponding to 0.34-170.00 ng/g of algae. Acetaldehyde and propanal are the most abundant carbonyl compounds identified, with concentrations as high as 980 and 790 ng/g, respectively. The present work, as far as we know, is the first analytical methodology that has been developed to determine low-molecular-weight carbonyl compounds in marine algae. Because many species of marine algae are used as human food, the reported method should be useful to investigators studying the nutritional value as well as oxidative spoilage of fresh and preserved marine algae that is destined for human consumption.