Acacia Ramírez

High-performance thin-layer chromatography–bioautography for multiple antibiotic residues in cow’s milk

An analytical method to identify and quantify multiple antibiotic residues (chloramphenicol, ampicillin, benzylpenicillin, dicloxacillin and erythromycin) in cows milk by high-performance thin-layer chromatography (HPTLC) combined with bioautography was developed. The test microorganism used for bioautography was Bacillus subtilis ATCC 6633. Antibiotic residues were extracted with acetonitrile, fat eliminated with petroleum ether and residues isolated with dichloromethane The sensitivity of the method guarantees the detection of the above-mentioned antibiotics at levels below maximum residue limits (MRL) allowed for milk. Percentage recoveries ranged between 90 and 100%, with coefficients of variation between 7.2 and 21.3%. Some advantages of this methodology over thin-layer chromatography (TLC)/bioautography are also discussed.

Detection of non-milk fat in milk fat by gas chromatography and linear discriminant analysis.

Gas chromatography was utilized to determine triacylglycerol profiles in milk and non-milk fat. The values of triacylglycerol were subjected to linear discriminant analysis to detect and quantify non-milk fat in milk fat. Two groups of milk fat were analyzed: A) raw milk fat from the central region of Mexico (n = 216) and B) ultrapasteurized milk fat from 3 industries (n = 36), as well as pork lard (n = 2), bovine tallow (n = 2), fish oil (n = 2), peanut (n = 2), corn (n = 2), olive (n = 2), and soy (n = 2). The samples of raw milk fat were adulterated with non-milk fats in proportions of 0, 5, 10, 15, and 20% to form 5 groups. The first function obtained from the linear discriminant analysis allowed the correct classification of 94.4% of the samples with levels <10% of adulteration. The triacylglycerol values of the ultrapasteurized milk fats were evaluated with the discriminant function, demonstrating that one industry added non-milk fat to its product in 80% of the samples analyzed.

Residuos de plaguicidas organoclorados en leche pasteurizada comercializada en Ciudad de México

Los residuos de algunos plaguicidas organo-clorados presentes en lasmuestras de leche pasteurizada analizadas representan un riesgo para lasalud de los consumidores. Se determino el contenido de plaguicidas organoclorados en 96 muestras de leche pasteurizada, por cromatografia gas liquido. Las muestras fueron colectadas quincenalmente y durante un ano en la Ciudad de Mexico, de cuatro marcas comerciales.En las muestras analizadas se determino el valor promedio X en µg/gbase grasa, la razon X/LMR y el porcentaje de muestras que sobrepaso el valor LMR. Los valores encontrados fueron los siguientes, respectivamente:(a + b)-HCH, 0.22 µg/g, 2.21 y 47.9%, Lindano, 0.07 µg/g, 0.38 y 8.3%, Aldrin + Dieldrin,0.25 µg/g, 1.67 y 39.5%, Heptacloro + heptacloroepoxido, 0.15µg/g, 1.00 y 23.9%, Endrin, 0.05 µg/g, 2.70 y 37.5% y DDT + metabolitos, 0.12 µg/g, 0.10 y 0.0%. Es altamente recomendable mantener un seguimiento en el control de algunos pesticidas organoclorados presentes en la leche pasteurizada de la Ciudad de Mexico.