Determination of 9-cis β-carotene and ζ-carotene in biological samples

Concentrations of 9-cis β-carotene (9-cis βC) and ζ-carotene (ζC) in biological samples may provide crucial information on the biological activities of these carotenoids. However, in high-performance liquid chromatography (HPLC) these carotenoids are often co-eluted. Therefore, there is an urgent need to develop a method for 9-cis βC and ζC quantitation. Both 9-cis βC and ζC have peak absorbance at 400 and 450 nm, respectively, whereas only 9-cis βC has peak absorbance at 475 nm. We developed a HPLC method to quantitate 9-cis βC and ζC by using peak absorbance ratios. The 9-cis βC/ζC peak area was monitored at 475, 450 and 400 nm. The 9-cis βC was quantified by using absorbance value at 475 nm; ζC was then calculated from the 9-cis βC/ζC peak at 400 nm by subtracting 9-cis βC contribution at 400 nm using the 400-nm/475-nm peak absorbance ratio of 9-cis βC (0.39). This method was applied to determine 9-cis βC and ζC concentrations in serum and breast milk samples (n=12) from American lactating women and serum and breast adipose tissue samples (n=16) from Korean women with either benign or malignant breast tumors. 9-cis βC concentrations in serum and breast milk of American women, and serum and adipose tissue of Korean women were 7.1±0.8 and 1.1±0.2 nM, and 15.6±1.1 nM and 0.2±0.1 nmol/g, respectively. ζC concentrations in the above samples were 54.2±7.2 and 8.3±1.8 nM, and 49.0±3.9 nM and 0.3±0.1 nmol/g, respectively.