Pulvinic Acid Derivative Pigments in Lanmaoa asiatica and L. macrocarpa

Lanmaoa asiatica G. Wu & Zhu L. Yang and L. macrocarpa N. K. Zeng, H. Chai & S. Jiang are two important gourmet bolete in China, and locally named "Jian Shou Qing" meaning their fruiting bodies turn blue after bruising. The genus represents a distinct lineage in Boletaceae. The pigment(s) associated with the discoloration in Lanmaoa has not been identified. The aim of this study was to determine the pigment(s) underpinning the bluing reaction of L. asiatica and L. macrocarpa when bruised. Potential compounds were isolated by HPLC and identified by LC-HRMS and NMR. In total five to six pigments of hydroxylated pulvinic acid derivatives were detected with similar distribution patterns in both L. asiatica and L. macrocarpa, which by abundance were variegatic acid, variegatorubin, xerocomic acid (and/or isoxerocomic acid), xerocomorubin, and atromentic acid. Variegatic acid, the most abundant pigment, was isolated by HPLC, and the structure was further characterized by NMR. The amount of variegatic acid increased after regular cooking, which may suggest its enhanced health benefit as human diet. The types of pigments that cause bluing reactions often differ among families of Boletales. Our results showed that the pigments in Lanmaoa belong to the category of hydroxylated pulvinic acid derivatives, the major bluing compounds in Boletaceae.