Chemical composition, in vitro color reconstruction, and bee vision modeling regarding anthocyanins and other phenolics from the flowers of Petrea macrostachya and Petrea volubilis

Abstract Delphinidin 3-O-[6-(4-O-(6-(4-O-β-glucopyranosylvanilloyl)-β-glucopyranosyl)-vanilloyl)-β-glucopyranoside]-5-O-β-glucopyranoside (petreadelphin), a novel anthocyanin, and β-(3,4-dihydroxyphenyl)ethyl 4-E-caffeoyl-3,6-di-β-xylopyranosylglucopyranose (petreathanoside), a novel phenylethanoid, were respectively isolated from the violet petals and sepals of Petrea macrostachya (Verbenaceae). In addition, nine known phenolic compounds were also isolated from the tepals of P. macrostachya.The pH of the petals and sepals was shown to be 5.7 and 5.6, respectively. In vitro color reconstruction experiments using two anthocyanins, namely, petreadelphin from the petals and delphinidin 3-O-(6-caffeoylglucoside)-5-O-glucoside from the sepals, revealed that their absorption spectra closely match those of the corresponding floral tissues. We also found that these anthocyanins are primarily responsible for the coloration of the petals and sepals.Stability assays showed that the sepal anthocyanin faded rapidly after 15 min in the buffer solution, whereas petreadelphin retained its color for at least 24 hours. This is attributed to the greater structural stability of petreadelphin conferred by its polyacylation.In addition, bee color vision modeling using the reflectance spectra indicated that the petals have significantly higher color intensity than sepals. These findings suggest that the type and number of acyl groups in anthocyanin may enhance pigment stability and light absorption, thereby contributing to increased intensity and potentially improving floral detectability by bees.