α-starch and glycyrrhizin denature the acrid raphides of Pinellia tuber in traditional processing

Objective: Pinellia tuber, the dried tuber of Pinellia ternata, causes severe acrid irritation in the mouth and throat when swallowed in its raw form. Based on the theory of traditional Chinese medicine, this acridity is reduced by heating or processing using ginger, licorice, alum, or lime. Although these detoxification methods have been known since ancient times, only little is known about the mechanisms by which they detoxify Pinellia tubers. In the present study, we aimed to reveal the effectiveness of α-starch, and glycyrrhizin in licorice for the detoxification of Pinellia tubers. Methods: Previously, we found that intact raphides of raw Pinellia tuber have a lipophilic character, and denaturation of the raphides reduced their lipophilicity and acridity. Accordingly, we developed a raphide denaturation assay (RDA) to quantify the degree of denaturation of raphides by measuring the absorbance of the petroleum ether (PE) layer comprising the raphides. The effect of α-starch or the decoction of licorice (the root and stolon of Glycyrrhiza uralensis) on raphide denaturation was then determined using this assay. Results: The treatment of raphides with α-starch markedly enhanced heat denaturation of the raphides. Licorice decoction, glycyrrhizin, and glycyrrhetinic acid significantly denatured raphides in a calcium-dependent manner at high pH. Glycyrrhizin and glycyrrhetinic acid are also attached to the denatured raphides. Conclusions: α-starch in Pinellia tubers contributes to detoxification by heating. In the traditional processing method for Pinellia tubers using licorice and lime, glycyrrhizin in licorice and calcium ions play important roles in denaturing raphides. Graphical abstract: http://links.lww.com/AHM/A42.