Annual Variation in Sterol Levels in Leaves of Taraxacum officinale Weber

Sterol levels in dandelion (Taraxacum officinale Weber) leaves were monitored over a period of 19 months. Sitosterol was the most abundant free sterol, followed by stigmasterol, then campesterol. Cholesterol could not be detected. With the exception of stigmasterol and campesterol, esters were present in greater quantities than were free forms, with 4,4-dimethyl sterol esters being the most abundant type. Glycosides occurred only sporadically. Free 4-demethyl sterols were maximal during the winter months; levels correlated negatively with sunshine and temperature, but proportions did not alter significantly. Sitosterol ester and cycloartenol ester (but not others) showed the opposite response, with levels correlating positively with sunshine and temperature. Relative amounts of 4-demethyl sterol esters remained reasonably constant, but those of cycloartenol ester and 24-methylene cycloartanol ester varied on an annual basis and were negatively correlated with each other.