R Gutiérrez

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.

Presence of Polycyclic Aromatic Hydrocarbons (PAHs) in Semi-Rural Environment in Mexico City

The quality of the environment in big cities depends on its population and their domestic, transport, and industrial activities. In some places agricultural land use coexists with urban areas and as a result of this urbanization and the presence of infrastructure for services like water, electricity, drainage, and the use of fossil fuels etc, contamination problems in the atmosphere, soil and water (Wilcke, 2000), that lately lead some ills on organisms such as respiratory malaises, liver-lung-skin cancer, irritation on eyes and others discomforts. The growth of urban environments presents a major challenge. However, Mexico City as center of economic growth, education, technological advancement, and culture, large city also offer opportunities to manage the growing population in a sustainable way.

Fatty acid profile of goat milk in diets supplemented with chia seed (Salvia hispanica L.)

Chia seed (Salvia hispanica L.) is the greatest known plant source of n-3 α-linolenic acid. The present study evaluated the effects of 3 inclusion levels of chia seed [zero (control); low, 2.7% (CLow); and high, 5.5% (CHigh)] in diets of dairy goats on milk yield and fatty acid profile. Nine Saanen dairy goats in the last third of lactation period, live weight 38 ± 8.7 kg, housed in metabolic cages, were fed iso-proteic and iso-energetic (160 g of crude protein/d and 11 MJ of metabolizable energy/d) diets. Gas chromatography was used to analyze fatty acid profile and total conjugated linoleic acid (CLA). Silver ion HPLC was used to analyze the isomeric profile of CLA. The results were subjected to variance analysis using a Latin square design repeated 3 × 3. The CHigh treatment was higher for dry matter, neutral detergent fiber, and acid detergent fiber intake compared with CLow and control diets. Digestibility was not affected by the inclusion of chia seeds. The CHigh diet improved N intake with respect to the control and CLow diet. Milk yield and chemical composition were not affected by the treatment. The milk fatty acid profile of C18:0, C18:1, C18:2, and C:20 was higher for CHigh than the other treatments. The in vitro gas production (mL of gas/g of dry matter) was lower in CHigh than the control diet. In conclusion, the addition of chia seeds at the CHigh level in dairy goat diets negatively affected in vitro rumen fermentation, but increased the milk fatty acid profile of C18:0, C18:1n-9 cis, and C:20, monounsaturated fatty acids, and polyunsaturated fatty acids. The total CLA content increased from 0.33 to 0.73% with the supplementation of chia to the diet, as well as the isomers cis-9,trans-11, trans-7,cis-9, trans-11,cis-13, and trans-12,trans-14.

Polychlorinated biphenyls (PCBs) residues in milk from an agroindustrial zone of Tuxpan, Veracruz, Mexico.

The coasts of the Gulf of Mexico are zones exposed to the exploration and exploitation of petroleum sources, and the products generated in agricultural zones may become contaminated by persistent organic pollutants (POPs). The objective of the present study was to evaluate the presence of polychlorinated biphenyl compounds (PCBs) in milk from dairy production units near sources of environmental pollutants. It was confirmed that the seven congeners of nondioxin-like PCBs (NDL-PCBs) are present in milk where compounds PCB101, PCB118, PCB153 and PCB180 appear in 100% of the samples analyzed, the rank of concentration for the sum of the seven congeners fluctuating between 2.6 and 26 ng g(-1) with a median of 6 ng g(-1). None of the samples surpassed the provisional value established by the EU of 40 ng g(-1) of milk fat for the sum of the seven congeners, indicator that was not affected by the season of the year (p<0.05), whose median of 8.6 ng g(-1) and 6.3 ng g(-1) for rain and drought respectively. The concentrations of NDL-PCBs found in milk do not represent a problem for human health; however, they alert the existence of spontaneously generated, uncontrolled sources that may represent a potential danger for human and animal health.

Residues levels of organochlorine pesticide in cow's milk from industrial farms in Hidalgo, Mexico

A survey was carried out from 2008 to 2010 to determine the concentrations of 16 organochlorine pesticide residues (OPRs) from Tizayuca, Hidalgo, Mexico. Organochlorine residue determinations were made from milk fat, using chromatographic cleanup and analysis by gas chromatography with an electron capture detector. The OPR concentrations found were from below the detection limit (DL) to 0.91 ng g−1 in 2008, DL to 0.38 ng g−1 in 2009 and DL to 0.59 ng g−1 in 2010. In general concentrations of organochlorine pesticides were higher in the wet season (3.37 ng g−1 and 4.79 ng g−1) than the dry season (1.92 ng g−1 and 2.71 ng g−1) for 2009 and 2010, due to control of pests in the pasture and sheds. According to Codex Alimentarius regulations, individual pesticides did not exceed the permissible limits, which for example were 10 μg kg−1 for alpha hexachlorocyclohexane (HCH) and endosulfan I, 20 μg kg−1 for p,p’-DDT, and 6 μg kg−1 for dieldrin, endrin and heptachlor. A reduction of organochlorine pesticide concentrations in cows milk was noted, indicating that the Mexican government has achieved reduction or elimination of some organochlorine pesticides in response to global agreements on persistent organic pollutants.