Anthranoid contents of rhubarb (Rheum undulatum L.) and other Rheum species and their toxicological relevance
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Extracts of different parts of rhubarb (Rheum undulatum L.) were investigated for their total content of anthranoids. After oxidation and hydrolyzation the anthranoid derivatives emodin, chrysophanol and physcion were detected in rhubarb leaves. The highest amount of anthranoids occurred in the lamina (0.06% of dry weight) of plants harvested in April. The lowest amounts were present in the part of the petiole proximal to the roots (0.001%), whereas the upper parts of the petioles contained up to 0.004% of hydroxyanthracene derivatives. With respect to the season, the highest anthranoid contents were always observed in leaves cut in the springtime (April) followed by a continuous decrease during the summer. The lowest anthranoid amounts were evident in the plants harvested in the late summer (September). Ethanolic extracts of different Rheum species were also compared with respect to their mutagenicity in the Salmonella/microsome assay. Positive effects were observed for the laminal parts of the leaves of Rh. undulatum in S. typhimurium 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 the use of rhubarb as a food.
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