Alberto Cepeda

Application of the assay of aflatoxins by liquid chromatography with fluorescence detection in food analysis

HPLC using fluorescence detection has already become the most accepted method for the determination of aflatoxins due to its several advantages over other analytical methods. Both normal- and reversed-phase HPLC can be used. However the reversed-phase HPLC methods are more popular. Liquid chromatographic determination of aflatoxins using fluorescence detection and its application in food analysis is reviewed in this article.

Inhibitory effects of eugenol and thymol on Penicillium citrinum strains in culture media and cheese

In the present work we studied the antifungal effect of eugenol and thymol on the growth and production of citrinin from Penicillium citrinum (NRRL 2274 and NRRL 2269) in culture media and in different Spanish cheeses (Arzúa-Ulloa, Cebreiro and San Simón). The rate of growth was assessed by measuring colony diameters and the production of citrinin was measured using a rapid semi-quantitative fluorometric technique confirmed by RP-HPLC. A stronger inhibitory effect of eugenol than thymol was evident. 200 microg/ml of eugenol in solid culture medium increased the lag time of growth up to 9 days, and decreased the rate of colony growth. In liquid medium, a complete inhibition of fungal growth was observed. By contrast, thymol in the liquid culture medium only affected the growth rate. In Arzúa-Ulloa cheese, 200 microg/ml of eugenol fully inhibited fungal growth, while in Cebreiro cheese no effect was observed for this compound. Regarding the capacity to inhibit mycotoxin production 100 microg/ml eugenol delayed citrinin production until the sixth day, after which a limiting effect persisted. In Arzúa-Ulloa cheese, no citrinin was detected at a concentration of 150 microg/ml of eugenol, but citrinin was detected after 5 days in the case of thymol at the same concentration. In Cebreiro cheese, neither eugenol nor thymol prevented the production of citrinin at the concentrations applied.

Determination of quinolones in animal tissues and eggs by high-performance liquid chromatography with photodiode-array detection

A rapid, specific reversed-phase HPLC method is described, with solid-phase extraction, for assaying five quinolones (ciprofloxacin, difloxacin, enrofloxacin, norfloxacin and marbofloxacin) with confirmative diode-array detection in samples of bovine kidney, muscle and eggs. The least efficient extraction was marbofloxacin from kidney tissue (64%). The lower detection limit for each quinolone was: enrofloxacin and ciprofloxacin, 1 ng; norfloxacin and difloxacin, 2 ng; marbofloxacin, 4 ng injected. The intra-day relative standard deviations were lower than 7.9% and lower than 8.6% for inter-day assays. These results indicate that the developed method had an acceptable precision.

New Additive for Culture Media for Rapid Identification of Aflatoxin-Producing Aspergillus Strains

ABSTRACT A new reliable, fast, and simple method for the detection of aflatoxigenic Aspergillus strains, consisting of the addition of a cyclodextrin (a methylated β-cyclodextrin derivative) to common media used for testing mycotoxin production ability, was developed. We propose the use of this compound as an additive for fungal culture media to enhance the natural fluorescence of aflatoxins. The production of aflatoxins coincided with the presence of a bright blue or blue-green fluorescent area surrounding colonies when observed under long-wavelength (365-nm) UV light after 3 days of incubation at 28°C. The presence of aflatoxins was confirmed by extracting the medium with chloroform and examining the extracts by high-pressure liquid chromatography with fluorescence detection.

Syntheses of molecularly imprinted polymers: Molecular recognition of cyproheptadine using original print molecules and azatadine as dummy templates

The use of custom-made polymeric materials with high selectivities as target molecules in solid-phase extraction (SPE), known as molecularly imprinted solid-phase extraction (MISPE), is becoming an increasingly important sample preparation technique. However, the potential risk of leakage of the imprinting molecules during the desorption phase has limited application. The use of a mimicking template, called a dummy molecular imprinting polymer (DMIP), that bears the structure of a related molecule and acts as a putative imprinting molecule may provide a useful solution to this problem. In the current study, cyproheptadine (CPH) and azatadine (AZA) were used as templates in the development of an MIP and DMIP for acrylic acid and methacrylic acid monomers. Our results indicate that DMIPs have equal recognition of CPH, avoiding the problem of leakage of original template during the desorption phase relative to MIPs synthesized in presence of the print molecule CPH. Examination of the surface structure of the two polymer products by SEM shows appreciable differences in structural morphology and function of the monomers employed. These results are well supplemented by data obtained for swelling ratios and solvent uptake. Molecular modelling of CPH and AZA suggests that both substrates are similar in shape and volume.

Mineral content of the honeys produced in Galicia (North-west Spain)

Abstract Sodium, potassium, calcium, magnesium, copper, iron, manganese, phosphorus (phosphate), chlorine (chloride), silicon (silica), sulphur (sulphate), and ash contents of 91 samples of raw honey from Galicia (NW Spain) were determined. The mean ash content was 0.408%. Potassium was the most abundant of the elements determined, with an average content of 1572 mg/kg (38.5% of the ash). All mineral contents showed high coefficients of variation, ranging from 0.34 (sodium, calcium, and sulphur) to 0.71 (iron). In general, the Galician honeys studied have high mineral contents in comparison with honeys reported in the literature.

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.

Magnetic solid phase extraction followed by high-performance liquid chromatography for the determination of sulphonamides in milk samples.

A simple and effective method based on magnetic solid-phase extraction combined with high performance liquid chromatography was used for the determination of nine sulphonamides in milk samples. The extraction and cleanup via silica-based magnetic adsorbent dispersion in milk samples followed by the magnetic isolation and desorption of the analytes using NaOH-methanol. Three different magnetic phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated for sulphonamides retention in terms of their pH and degree of hydrophobicity. The optimal conditions were a pH of 6.0 and a magnetic:sorbent ratio of 2:1. Under optimal conditions, limits of detection ranging from 7 to 14 μg L(-1) were obtained. The method was validated according with the European Commision Decision 2002/657/EC. The proposed method was applied to analyse sulphonamides in 27 milk samples of different brands. Thirteen samples tested were positive for the presence of sulphonamides.

Egg and Egg-Derived Foods: Effects on Human Health and Use as Functional Foods.

Eggs are sources of protein, fats and micronutrients that play an important role in basic nutrition. However, eggs are traditionally associated with adverse factors in human health, mainly due to their cholesterol content. Nowadays, however, it is known that the response of cholesterol in human serum levels to dietary cholesterol consumption depends on several factors, such as ethnicity, genetic makeup, hormonal factors and the nutritional status of the consumer. Additionally, in recent decades, there has been an increasing demand for functional foods, which is expected to continue to increase in the future, owing to their capacity to decrease the risks of some diseases and socio-demographic factors such as the increase in life expectancy. This work offers a brief overview of the advantages and disadvantages of egg consumption and the potential market of functional eggs, and it explores the possibilities of the development of functional eggs by technological methods.

Detection and quantification of spoilage and pathogenic Bacillus cereus, Bacillus subtilis and Bacillus licheniformis by real-time PCR

A new primer-probe set for the detection and quantification of Bacillus cereus, Bacillus licheniformis and Bacillus subtilis by real-time PCR (Rti-PCR) was developed. For it, forty-eight strains belonging to these species were considered. The DNA of these strains was isolated and a fragment of the 16S rRNA gene amplified. The amplicons were sequenced and the obtained sequences were aligned with reference sequences from the GenBank. For the development of the Real-Time PCR (RTi-PCR) methodology based on TaqMan probes, a primer pair and probe, specific for the studied Bacillus spp., were designed. To establish the quantification method, two RTi-PCR standard curves were constructed; one with DNA extracted from a serially-diluted B. cereus culture and a second curve with DNA extracted from a sterilised food product inoculated with serial dilutions of B. cereus. The curves exhibited R(2) values of 0.9969 and 0.9958 respectively. Linear correlations between the log(10) input DNA concentration and the threshold cycle (Ct) values were observed with a magnitude of linearity in the range of 1.65 × 10(1) CFU/mL to 1.65 × 10(6) CFU/mL for both standard curves. The specificity of the designed primers and probe was tested with DNA extracted from B. cereus, B. licheniformis and B. subtilis strains, which gave Ct values between 14 and 15, whereas non-specific amplifications of the DNA from other microbial species of food interest exhibited a Ct value above 28.5. To our knowledge, this method represents the first study about the quantification of spoilage and/or pathogenic B. cereus, B. licheniformis and B. subtilis in food products, with the aim to prevent the presence of these undesirable species in the food chain.