Determination of heterocyclic aromatic amines (HAs) content in samples of household-prepared meat dishes.

Aminoazaarene content was investigated in 10 meat samples (including pork, beef, turey and chicken) thermally processed at home according to common recipes used by residents of Upper Silesia region in Poland. The clean-up procedure included tandem solid-phase extraction (SPE) using Extrelut-type columns filled with diatomaceous earth, propylsulphonic acid and chemically bounded phase-C18. Identification and quantitative analysis of HAs fraction was carried out using a HPLC system with DAD-type detector. Separation was achieved using TSK-gel ODS 80-TM column and a mixture of 5% acetonitrile and 95% triethylamine phosphate buffer (pH 3.3) as a mobile phase. The results of qualitative determinations were confirmed by GC-MS method. To achieve this, HAs fractions were derivatized to pentafluoropropionic acid (PFPA) amide derivatives. The summary content of five aminoazaarenes determined in investigated meat samples, i.e. 2-amino-3-methylimidazo [4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) falls within the range of 1.9-77.4 ng/g of sample. The calculated values of theoretically daily human exposure to five determined HAs were in the range of 0.2-7.7 microg per day per person.

Interaction of cAMP receptor protein from Escherichia coli with cAMP and DNA studied by dynamic light scattering and time-resolved fluorescence anisotropy methods.

Cyclic AMP receptor protein (CRP) regulates the expression of more than 100 genes in Escherichia coli when complexed with cyclic AMP. Dynamic light scattering (DLS) and fluorescence decay anisotropy measurements of CRP were performed in solution, in the absence and presence of cAMP. We have also measured the effect of DNA sequences, including lac and gal promoter sequences, on the shape of CRP-DNA complexes. DLS measurements show that upon cAMP binding at low nucleotide concentration, the Stokes radius decreases from the value of 2.8 nm for apo-CRP to the value of 2.7 nm. At higher cAMP concentration, only a very small further decrease was detected. Fluorescence anisotropy decay measurements, with the use of CRP labeled at Cys-178 with 1,5-I-AENS, indicate that apo-CRP exhibits two rotational correlation times. The longer time, theta1 = 23.3 ns, corresponds to the overall motion of the protein, and the shorter time, theta2 = 1.4 ns, exhibits segmental mobility of the C-terminal domain of CRP. Binding of cAMP into CRP induced substantial increase of theta1 to the value of 30.7 ns, whereas theta2 remained unchanged. The DLS measurements indicate that the binding of CRP into a fragment of DNA possessing a sequence of lac promoter induces a larger increase in the Stokes radius of lac-CRP complex than in case of gal-CRP complex. Similarly, a higher change was detected in rotational correlation time, theta1, in the case of lac-CRP complex than in case of gal-CRP. Because the lac and gal promoters are characteristic for the two different classes of CRP-dependent promoters, one can expect that the observed differences in lac-CRP and gal-CRP complexes are important in activation of transcription in Escherichia coli.

Clean-up procedures for the analysis of heterocyclic aromatic amines (aminoazaarenes) from heat-treated meat samples.

The purpose of the study was to determine optimum conditions for the isolation and quantitation of five most biologically active aminoazaarenes [2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)]. Some multistep procedures based on ultrasonic extraction, Soxhlet extraction, liquid-liquid extraction and solid-phase extraction (SPE) were tested in order to choose the optimum isolation conditions for aminoazaarenes from fried meat samples spiked with known amounts of standards. According to the tested methods the qualitative-quantitative analysis was performed on the unspiked sample of pork roasted in typical household conditions. The qualitative-quantitative analysis of the aminoazaarenes was performed by a HPLC method. A HPLC Hewlett-Packard HP 1090 liquid chromatograph equipped with a UV diode array detector (DAD) was used. Chemically bonded HPLC columns C8 and TSK-gel ODS 80-T(M) were used under gradient elution conditions. A two-component mixture containing triethylamine-phosphate buffer (pH 3.2 and 3.3) and acetonitrile was used as a mobile phase. The results of the studies showed that a solid-phase extraction procedure using diatomaceous earth (Extrelut, 20 ml), propylsulphonic acid (PRS, 500 mg) and octadecylsilane (C18, 500 mg) columns was the quickest and simplest one. Recoveries of the aminoazaarenes, spiked and isolated from meat samples by the chosen SPE procedure, were as follows: IQ 85%, MeIQ 50%, MeIQx 46%, 4,8-DiMeIQx 62%, PhIP 50%.