Validation of a Method for Quantification of Lutein in Spinach Using High-Performance Liquid Chromatography: Interlaboratory Study.

BACKGROUND: Lutein is gaining attention as a strong antioxidant contained in foods. It accumulates in the human blood and retina, and is considered to play an important role in the body, especially in the eyes. OBJECTIVE: A method to determine the lutein content of raw spinach (Spinacia oleracea L.) was developed with the aim of its enactment as a Japanese agricultural standard (JAS) measurement method for components beneficial to human health. METHODS: An interlaboratory study was conducted to evaluate an analytical method for the determination of lutein in spinach. The detection limit and quantification limit of lutein for this method were 0.2 and 0.7 mg/kg, respectively. Twelve participating laboratories independently analyzed test samples (five pairs of blind duplicates) using high-performance liquid chromatography (HPLC). RESULTS: After removal of a few outliers, the repeatability relative standard deviation (RSDr), reproducibility (RSDR), and predicted RSDR of the evaluated method were 3.4-7.5, 4.6-13, and 7.5-8.5%, respectively, in a concentration range from 64.9-150 mg/kg. CONCLUSIONS: The HorRat values (RSDR/predicted RSDR) of the lutein concentration were calculated to be 0.61-1.6. HIGHLIGHTS: The study results indicate the acceptable precision of this method.

FXYD6, a Na,K-ATPase regulator, is expressed in type II taste cells.

Taste buds contain three types of taste cells. Each type can respond to taste stimulation, and type II and III taste cells are electrically excitable. However, there are differences between the properties of type II and III taste cells. In this study, we found that Fxyd6, an Na,K-ATPase regulator gene, is expressed in type II taste cells in the taste buds of mice. Double-labeled in situ hybridization analysis showed that Fxyd6 was coexpressed with transient receptor potential cation channel, subfamily M, member 5 (Trpm5), a critical component of the sweet, bitter, and umami taste signal transduction pathways and that it was specifically expressed in type II taste cells. We also found that taste cells frequently coexpressed Fxyd6 and Na,K-ATPase ß1. These results indicate the presence of an inherent mechanism that regulated transmembrane Na(+) dynamics in type II taste cells.