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Biomedical subjects

M J Shepherd

Publications and source records attributed to M J Shepherd.

32 records · Page 2Linked to original sources
PubMed1986

Comparison and critical evaluation of six published extraction and clean-up procedures for aflatoxin M1 in liquid milk.

A practical evaluation has been carried out of six previously published extraction and clean-up methods for aflatoxin M1 in liquid milk. The procedures evaluated incorporated the most widely used stages of clean-up including solvent extraction and silica gel chromatographic clean-up, selective solvent extraction of the extracted residue, the use of deproteination prior to hydrophilic column liquid-liquid partition or solvent extraction and the use of pre-packed reversed-phase cartridges for the direct extraction of aflatoxin M1 from the milk. Analysis times for each method, recoveries and relative costs are reported together with fluorescence high-performance liquid chromatography chromatograms, obtained under identical conditions to compare the relative cleanliness of the final extracts produced by each method. A pre-packed reversed phase cartridge method was shown to be the most satisfactory in terms of speed, cost and cleanliness of the final residue.

Aflatoxin M1↗
PubMed1980

Gas chromatographic determination of vinylidene chloride monomer in packaging films and in foods.

Headspace electron-capture-gas chromatographic methods are described for the quantification of vinylidene chloride monomer in poly(vinylidene chloride) containing films and in film-packaged foodstuffs. Quantification of vinylidene chloride was possible at levels down to 0.001 mg/m2 in the films and 0.005 ppm in the foodstuffs. The results of a small survey of the amounts of this compound in packaging films and foodstuffs purchased from retail outlets are reported.

Chromatography, Gas↗
PubMedDate not supplied

A survey of the occurrence of aflatoxin M1 in UK-produced milk for the period 1981-1983.

A UK survey for the occurrence of aflatoxin M1 in bulked dried milks (totalling 277 samples) obtained at monthly intervals from a number of commercial creameries in the UK over a two-year period (1981-1983), showed 98% of the samples to have levels below 0.03 micrograms/kg. For liquid milks sampled from individual farms over the same period (totalling 409 samples), 94% of the samples had aflatoxin M1 levels below 0.01 micrograms/kg. All samples were initially screened by a two-dimensional thin layer chromatographic method and quantification of positive results was by reverse phase h.p.l.c. with fluorescence detection. The results of this survey show that UK milk is largely free of aflatoxin M1 contamination, the incidence and levels, where observed, being significantly lower than for other European countries, which demonstrates the effectiveness of UK legislative action controlling feedstuff contamination.

Aflatoxin M1↗
PubMedDate not supplied

An investigation of HPLC post-column iodination conditions for the enhancement of aflatoxin B1 fluorescence.

A systematic investigation was carried out of the conditions employed for the post-column iodination reaction used to enhance fluorescence sensitivity of aflatoxins B1 and G1 in reverse-phase HPLC. The effect of post-column reaction coil tubing dimensions, coil temperature, eluent and reagent flow rates and reagent concentration were examined and the optimum choice of each established. The maximum achievable sensitivity was shown to be 20 pg of B1 injected on column.

Aflatoxin B1↗
PubMedDate not supplied

A limited survey of retail apple and grape juices for the mycotoxin patulin.

A retail survey (38 samples) of apple, grape and other juice-based products for the mycotoxin patulin has been carried out using HPLC analysis. Positive results were confirmed by GC-MS of the TMS derivative using chemical ionization selected ion monitoring. No grape juice or mixed juice product contained detectable patulin (limit 5 micrograms/l), nor did the majority (58%) of the apple juices. Low levels of patulin (in the range 5-10 micrograms/l) were present in six apple juices and the remaining four positive samples contained 16, 18, 30 and 56 micrograms/l.

Beverages↗
PubMedDate not supplied

A survey of aflatoxins in peanut butters, nuts and nut confectionery products by HPLC with fluorescence detection.

A preliminary survey in 1982 of aflatoxin levels in peanut butters indicated that 31 out of 32 samples of major national brand-named products examined contained less than 10 micrograms/kg aflatoxin B1 and that 59% of these were below the limit of detection (2 micrograms/kg). In contrast, of 25 peanut butters from specialist 'Health Food' outlets, 64% contained less than 10 micrograms/kg aflatoxin B1, the remainder ranging from 16 to 318 micrograms/kg, with one sample having a total aflatoxin concentration of 345 micrograms/kg. Subsequent surveys in 1983 and 1984 of 'Health Food' products confirmed that these manufacturers were still experiencing some difficulty in complying with the 30 micrograms/kg total aflatoxin voluntary guideline limit. A further survey in 1984 was carried out of 228 retail samples of nuts and nut confectionery products comprising peanuts (shelled, unshelled, roasted and salted), mixed nuts, almonds (both unblanched and ground), brazils (in shell), hazelnuts (in shell), chocolate-coated peanuts, peanut brittle and coconut ice. The results showed that 74% of the samples contained less than 0.5 microgram/kg of aflatoxin B1 with 3.1% exceeding the guideline tolerance of 30 micrograms/kg total aflatoxins, these being predominantly peanuts and brazils. The highest total levels of aflatoxins observed were in unshelled peanuts containing 4920 micrograms/kg and in a composite sample of visibly moulded brazils containing 17 926 micrograms/kg.

Aflatoxin B1↗
PubMedDate not supplied

A survey of trialkyl and triaryl phosphates in United Kingdom total diet samples.

Composite total diet samples, representative of 15 different commodity types overall encompassing an average complete adult diet, from each of eight regions in the UK, were analysed for the presence of trialkyl- and triarylphosphates. The analytical method consisted of solvent extraction, size exclusion clean-up and determination of individual phosphates by gas chromatography using phosphorus specific detection (alkali flame or flame photometric detection). Of the food groups offal, other animal products and nuts consistently contained the highest levels of trialkyl/triaryl phosphates, but there was variation in the incidence of individual compounds between different groups. Total phosphate intake was estimated to be between 0.07 and 0.1 mg per person per day.

Chromatography, Gas↗
PubMedDate not supplied

A survey of the occurrence of aflatoxin B1 in peanut butters by enzyme-linked immunosorbent assay.

A survey was carried out in 1986 for the occurrence of aflatoxin B1 in peanut butters (129 samples) obtained from specialist Health Food outlets. The results showed that 6.2% of the samples exceeded 10 micrograms/kg of aflatoxin, 8% contained between 2.5 and 10 micrograms/kg, and in the remainder (86%) aflatoxin could not be detected at a limit of 2.5 micrograms/kg. These results show a lower contamination by aflatoxin than found in these products in previous surveys (1982-1984). An aflatoxin B1-specific enzyme-linked immunosorbent assay (ELISA) was employed for the first time in these analyses; and to make an assessment of its performance positive aflatoxin results, together with a random selection of those below the ELISA limit of detection, were additionally analysed by conventional extraction and clean-up followed by HPLC. The ELISA technique offered a significant improvement in speed of analysis over conventional approaches, enabling a six-fold increase in sample throughput compared to that required for conventional analysis, together with other advantages.

Aflatoxin B1↗
PubMedDate not supplied

Enzyme-linked immunosorbent (ELISA) determination of aflatoxin B1 in peanut butter: collaborative trial.

Fourteen laboratories in the United Kingdom participated in a collaborative trial of a commercially available ELISA test kit for the determination of aflatoxin B1 in peanut butter. Each laboratory carried out six replicate analyses of each of six individual samples. Collaborators received a control, uncontaminated sample, together with samples prepared by blending naturally-contaminated and control material to give target levels of 8 micrograms/kg, 25 micrograms/kg and 75 micrograms/kg. Two of these samples (8 micrograms/kg and 25 micrograms/kg) were supplied as undisclosed duplicates. The repeatabilities of the assay ranged from 6.2 to 16.7 micrograms/kg. The reproducibilities for aflatoxin B1 concentrations in naturally-contaminated samples ranged from 3.6 to 18.7 micrograms/kg using uncontaminated peanut butter as a reference blank. Modifications to the format of the commercial kit were recommended as a result of the collaborative trial.

Aflatoxin B1↗