Visualization of anthocyanin species in rabbiteye blueberry Vaccinium ashei by matrix-assisted laser desorption/ionization imaging mass spectrometry

Anthocyanins are naturally occurring compounds that impart color to fruits, vegetables, and plants, and are believed to have a number of beneficial health effects in both humans and animals. Because of these properties, pharmacokinetic analysis of anthocyanins in tissue has been performed to quantify and identify anthocyanin species although, currently, no methods exist for investigating tissue localization of anthocyanin species or for elucidating the mechanisms of anthocyanin activity. Imaging mass spectrometry (IMS) is powerful tool for determining and visualizing the distribution of a wide range of biomolecules. To investigate whether anthocyanin species could be identified and visualized by IMS, we performed matrix-assisted laser desorption/ionization (MALDI)–IMS analysis, by tandem mass spectrometry (MALDI–IMS–MS), of ten anthocyanin molecular species in rabbiteye blueberry (Vaccinium ashei). The distribution patterns of each anthocyanin species were different in the exocarp and endocarp of blueberry sections. Anthocyanin species composed of delphinidin and petunidin were localized mainly in the exocarp. In contrast, those species composed of cyanidin, peonidin, and malvidin were localized in both the exocarp and the endocarp. Moreover, MALDI–IMS analysis of anthocyanidins in a blueberry section indicated that the distribution patterns of each anthocyanidin species were nearly identical with those of the corresponding anthocyanins. These results suggested that the different distribution patterns of anthocyanin species in the exocarp and endocarp depended on the aglycone rather than on the sugar moieties. This study is the first to visualize anthocyanin molecular species in fruits.