Anthranoid contents of rhubarb (Rheum undulatum L.) and other Rheum species and their toxicological relevance

Extracts of different parts of rhubarb (Rheum undulatum L.) were investigat ed for their total content of anthranoids. After oxidation and hydrolyzatio n the anthranoid derivatives emodin, chrysophanol and physcion were detecte d in rhubarb leaves. The highest amount of anthranoids occurred in the lami na (0.06% of dry weight) of plants harvested in April. The lowest amounts w ere present in the part of the petiole proximal to the roots (0.001%), wher eas the upper parts of the petioles contained up to 0.004% of hydroxyanthra cene derivatives. With respect to the season, the highest anthranoid conten ts were always observed in leaves cut in the springtime (April) followed by a continuous decrease during the summer. The lowest anthranoid amounts wer e evident in the plants harvested in the late summer (September). Ethanolic extracts of different Rheum species were also compared with respect to the ir mutagenicity in the Salmonella/microsome assay. Positive effects were ob served for the laminal parts of the leaves of Rh. undulatum in S, typhimuri um strain TA 1537, whereas no evidence of mutagenicity could be detected in the edible parts of rhubarb (i.e. the petioles). The root extracts of Rh. officinale and Rh, rhaponticum, which are used for medicinal purposes, were clearly mutagenic in this assay. From these data it can be concluded that in contrast to Rheum species used in medicine, no risk is associated with t he use of rhubarb as a food.