Determination of very low stable isotope enrichments of [(2)H(5)]-phenylalanine in chicken liver using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Stable isotope labeled amino acids are frequently used to examine nutritive effects on protein synthesis. This technique is characterized by tracing the incorporation of the label into newly synthesized proteins. In the present investigation, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of very low enrichment of protein-bound l-[(2)H(5)]-phenylalanine ([(2)H(5)]-phe) in chicken liver. The LC-MS/MS measurements were carried out in positive atmospheric pressure chemical ionization (APCI) mode. Two mass transitions each for [(2)H(5)]-phe (171.1/125.1 and 171.1/106.1) and l-phenylalanine (phe) (166.1/91.1 and 166.1/93.1) were chosen for quantification and qualification. Due to the high excesses of phe, less sensitive transitions were chosen in the case of phe. The separation was carried out on a phenyl-hexyl column using 0.1% formic acid as eluent A and methanol as eluent B. The method was calibrated with calibration standard solutions in the range of 0.01-0.5 mole percent excess (MPE). Linear regression analysis led to coefficients of determination (r(2)) greater than 0.9995. The method was applied on liver samples from experiments investigating nutritive effects on tissue protein synthesis in broiler chickens. These samples were analyzed with a gas chromatography-mass spectrometry (GC-MS) method and reanalyzed with the developed LC-MS/MS method one year later. Compared to GC-MS, the main advantages of the LC-MS/MS method are its higher selectivity as well as the elimination of the need to convert and derivatize the samples prior to measuring.

Effects of increasing concentrations of sodium metabisulphite (Na2S 2O 5, SBS) on deoxynivalenol (DON) concentration and microbial spoilage of triticale kernels preserved without and with propionic acid at various moisture contents.

Unground triticale kernels contaminated with 6.63 mg deoxynivalenol (DON) per kg dry matter were stored for up to 63 days at total moisture contents of 13 and 15% in order to study the time-dependent kinetics of DON concentration in dependence on graded levels of sodium metabisulfite [0, 1, 2, 3, 4 and 5 g Na2S2O5 (SBS) per kg], and in the absence and presence of 10 g propionic acid (PA) per kg. The DON concentration decreased with increasing amounts of supplemented SBS and with increasing duration of the preservation period in a bi-exponential fashion when SBS addition was ≥3 g/kg. Lower SBS concentrations yielded inconsistent results. The maximum measured DON reductions after adding 5 g SBS/kg were 3 and 4% of the initial DON concentration after 63 days in the absence and presence of PA at moisture contents of 15%, while the corresponding recovery for the variants preserved at 13% amounted to 21 and 11%, respectively. The 12 variants preserved without PA supplementation were more frequently contaminated by moulds and yeasts (n = 5) than the corresponding variants stored together with PA (n = 1). The overall results and regressive evaluations do suggest that the highest SBS addition of 5 g/kg triticale at a moisture content of 15% preserved for 63 days would be necessary for a maximum DON reduction. Although PA did not exert a direct decontaminating effect, an additional supplementation together with SBS seemed to be advantageous with regard to the prevention of yeast and mould contamination and favouring the decontamination reaction by the acid milieu.