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A Cepeda

Publications and source records attributed to A Cepeda.

11 recordsLinked to original sources
PubMed1998

Interaction between cyclodextrins and aflatoxins Q1, M1 and P1. Fluorescence and chromatographic studies.

The fluorescence properties of the aflatoxins M1, Q1, P1 in solution and the effect of various cyclodextrins (alpha-, beta-, gamma-, hydroxypropyl-beta- and alpha-beta-heptakis-di-O-methyl-beta-) on their fluorescence emission were studied. Among the aflatoxins, a substantial enhancement of the fluorescence emission of aflatoxin Q1 in the presence of aqueous solutions of alpha-, beta-, hydroxypropyl-beta, and alpha-beta-heptakis-di-O-methyl-beta-cyclodextrin, was observed. On the contrary, gamma-cyclodextrin proved to be inefficient to enhance the fluorescence properties of this compound. No important fluorescence enhancement was found for aflatoxins P1 or M1 for any of the cyclodextrin derivatives tested. The complex formation constant (Kf) of these compounds with beta-cyclodextrin was chromatographically determined, and from the results obtained, we can conclude that Kf cannot be used alone to explain the fluorescence increase. Thermodynamic studies showed that delta-H and delta-S parameters, associated with the partition of aflatoxins in RP-HPLC, increased when beta-cyclodextrin was added to the eluent.

Aflatoxin M1↗
PubMed1998

The legal importation of prescription drugs into the United States from Mexico: a study of Customs declaration forms.

The nature and magnitude of the problem of the diversion of prescription drugs from legal to illegal markets have been identified as a high priority by the federal government. This study was based on a random sample (2,005) of declaration forms of persons declaring Mexican prescription drugs at the US Customs office in Laredo, Texas. Of the 75 different types of drugs, the most frequently declared drugs were Valium (71%), Rohypnol (46%), and Tafil (25%), drugs highly associated with nonmedicinal use among United States teenagers and young adults. These data reinforce a documented need for more transnational cooperative efforts between the United States and Mexico.

Adult↗
PubMed1997

Determination of residues of the beta-agonist clenbuterol in liver of medicated farm animals by gas chromatography-mass spectrometry using diphasic dialysis as an extraction procedure.

A method has been developed for the rapid confirmation of clenbuterol in cow liver using gas chromatography coupled with detection by mass spectrometry of the trimethylsilyl derivatives of clenbuterol. The technique used for the extraction was diphasic dialysis. It was observed that the best suitable solution to homogenize the liver the barium hydroxide-barium chloride buffer, the optimal extraction solvent was tert.-butylmethyl ether at an extraction temperature of 37 degrees C, and stirring should be applied at 150 rpm for 4 h. This extraction method improves clenbuterol recovery up to values of 99.3%. With the use of the barium buffer, derivatization is performed more efficiently and the detection and quantification limits can be decreased to values close to 250 ppt and 500 ppt, respectively.

Adrenergic beta-Agonists↗
PubMed1997

Incidence of toxigenic Escherichia coli in soft cheese made with raw or pasteurized milk.

Soft cheeses made with raw (221 samples) or pasteurized (75) cow's milk were collected. Enterotoxigenic, verotoxigenic and necrotoxigenic Escherichia coli strains were studied. Three raw milk cheeses were positive for toxigenic E. coli (1.4%): the first with toxin CNF2 and serogroup O5 (40% of colonies studied with typical E. coli morphology); the second with VT and O2 (10%); and the third with LT and O51 (10%). Toxigenic E. coli of bovine origin can pass to the milk destined to make cheese, and survive. Soft cheese should be considered as a possible vehicle of infection in future investigations.

Animals↗
PubMed1997

Rapid semi-quantitative fluorimetric determination of citrinin in fungal cultures isolated from cheese and cheese factories.

A new rapid semi-quantitative fluorimetric assay for citrinin production testing in mould cultures has been developed. The chemical structure of the citrinin makes it a weak native fluorophore. This fluorescence can be strongly enhanced in an acidic environment. A standard curve where the concentration of HCl needed to show the yellow fluorescence signal of different concentrations of citrinin was established, thus providing a semi-quantitative method to prove the capacity of toxin production of fungal cultures. Two Penicillium strains from the Spanish National Collection of Type Cultures, were studied for the toxin production on YES broth at 25 degrees C for 21 d. The culture was assayed daily for the presence/absence and quantification of citrinin by adding the HCl concentration set, and also quantified by RP-HPLC as a confirmation procedure. Experiments demonstrate that 5 d are necessary to show the presence of citrinin. As an illustration, a total of 48 strains of Penicillium isolated from cheese and cheese factories were analysed with the proposed method.

Cheese↗
PubMed1996

Simple and sensitive high-performance liquid chromatography--fluorescence method for the determination of citrinin application to the analysis of fungal cultures and cheese extracts.

A new and highly sensitive method for the detection of the important mycotoxin, citrinin, has been developed. Spectroscopic studies demonstrate that the fluorescence of this metabolite is influenced by the pH of the environment. This fact was exploited in the chromatographic determination of citrinin with fluorescence detection. The proposed method, based on the addition of 1 M hydrochloric acid as an acidic post-column reagent, has a limit of detection of 0.9 center dot 10(-7) M. Analytical validation shows that linearity can be assumed from 2 center dot 10(-7) to 10(-4) M citrinin. The repeatability and reproducibility are satisfactory, with R.S.D. = 5.1% (n = 9, c = 10(-5) M) and R.S.D. = 7.2% (n = 9, c = 10(-5) M). The method was also applied to the determination of this mycotoxin produced by mould cultures isolated from soft cheese and also from soft cheese and also from cheese extracts spiked with citrinin. The specificity of the method is demonstrated and the necessity for post-column acidification is illustrated on real samples.

Cheese↗
PubMed1996

Postcolumn excitation of aflatoxins using cyclodextrins in liquid chromatography for food analysis.

Measurement of fluorescence increase was used for the comparative quantification of the effect that several cyclodextrins (alpha-, beta-, heptakis-2,6-beta-omicron-dimethyl- and gamma-) produce on the fluorescent response of aflatoxins B1 and G1. This constitutes a new chromatographic method with stability of the mobile phase, and shows general improvements in the chromatographic conditions with respect to other methods (especially those using an iodine reservoir as a postcolumn reactor). A C18-type column was used, with methanol-water (60:40, v/v) as the mobile phase. The excitation phase of the natural fluorescence of aflatoxins, a 10(-2) M solution of each cyclodextrin, was introduced postcolumn. The determination of the elution order aflatoxin G2 > G1 > B2 > B1 was performed for each phase in less than 15 min. As expected using an aqueous-alcoholic medium, an increase in the fluorescence response of aflatoxins with an unsaturated furanic ring was found to occur with all the cyclodextrins studied, except gamma-cyclodextrin. The observed increase was larger for heptakis-2,6-beta-omicron-dimethyl- than for beta-cyclodextrin (to our knowledge, the only cyclodextrin previously described in the literature to serve for the determination of aflatoxins). The difference is of the order of 70.1-fold in the case of aflatoxin G1 and 45.2-fold in the case of aflatoxin B1. The detection limit in the mobile phase used was determined (for aflatoxin B1) for beta-cyclodextrin and 2,6-beta-omicron-dimethylcyclodextrin (signal-to-noise ratio 1:3) to be 4 and 9 mg 1(-1), respectively.

Aflatoxin B1↗
PubMed1995

Silicon, phosphorus, sulphur, chlorine and ash contents of Spanish commercial honeys.

Silicon, phosphorus, sulphur, chlorine and ash contents were determined in samples of 24 Spanish commercial honeys. Mean contents (mg/kg of honey) were 3.2 for silicon, 78 for phosphorus, 45 for sulphur and 262 for chlorine. The values for phosphorus and chlorine are high with respect to honeys from other regions. Mean ash content was 0.19%. In all cases there were high coefficients of variation, ranging from 0.43 for silicon to 0.58 for phosphorus.

Chlorides↗
PubMed1994

Effects of central muscarinic blockade on passive avoidance: anterograde amnesia, state dependency, or both?

It was recently reported that administration of relatively high intensities of footshock (overreinforcement) during training of passive avoidance protected animals against the amnesic effect of scopolamine, injected 5 min after training. This was interpreted in terms of a lesser involvement of acetylcholine in memory consolidation. An alternative explanation was that overreinforcement accelerated the consolidation process, which could have taken place before the injection of scopolamine. To test for this possibility, male Wistar rats were injected with 4, 8, or 12 mg/kg of scopolamine, 5 min before training with low or high levels of footshock and then tested for retention of the task. Scopolamine induced the expected memory deficit after the low-intensity footshock; after overreinforcement the higher doses of scopolamine induced state dependency, while no deficits were produced with the lower dose. It was concluded that: (a) acetylcholine is indeed involved in memory consolidation of passive avoidance; (b) scopolamine interacts with high footshock levels to produce state dependency; and (c) when relatively low doses of scopolamine are used in conditions of overreinforcement, protection against scopolamine-induced amnesia becomes evident.

Amnesia↗
PubMedDate not supplied

Determination of fat, protein, and total solids in cheese by near-infrared reflectance spectroscopy.

Near-infrared reflectance (NIR) spectroscopy was used to analyze fat, protein, and total solids in cheese without any sample treatment. A set of 92 samples of cow's milk cheese was used for instrument calibration by principal components analysis and modified partial least-square regression. The following statistical values were obtained: standard error of calibration (SEC) = 0.388 and squared correlation coefficient (R2) = 0.99 for fat, SEC = 0.397 and R2 = 0.98 for protein, and SEC = 0.412 and R2 = 0.99 for total solids. To validate the calibration, an independent set of 25 cheese samples of the same type was used. Standard errors of validation were 0.47, 0.50, and 0.61 for fat, protein, and total solids, respectively, and R2 for the regression of measurements by reference methods versus measurements by NIR spectroscopy was 0.98 for the 3 components.

Calibration↗