Effects of methionine-containing dipetides on αs1 casein gene expression were investigated in cultured bovine mammary epithelial cells. αs1Casein gene expression was higher in the culture added with methionylmethionine than in that with methionine. Addition of methionyllysine enhanced αs1 casein gene expression, compared with methionine plus lysine. These results indicated that mammary epithelial cells can utilize methionine-containing dipeptides for milk protein synthesis with a higher effi ciency than the respective amino acid.
A rapid and sensitive indirect competitive fluorescence-linked immunosorbent assay (icFLISA) method was developed for detection of melamine in milk based on secondary antibody (Ab 2 )-conjugated quantum dots (QDs). The sensitivity of icFLISA with a limit of detection (LOD) of melamine (3.88 ng mL À1 ) and 50% inhibition value (IC 50 ) (31.58 ng mL À1 ), was much higher than that of icELISA. As a proof of principle, recovery tests involving four fortification levels (150, 80, 40, and 20 ngmL À1 ) in blank samples were also performed. The recoveries ranged from 80.85 to 110.54% with coefficient of variations (CVs) of 2.82-8.82%. When challenged with authentic samples, these results of icFLISA were consistent with that of icELISA, immuno-chromatographic assay and gas chromatography-single quadruple mass spectrometry (GC-MS)method, indicating that icFLISA can be considered as a new screening method for detection of melamine in milk.
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