Spatiotemporal Dynamics of Polyphenolic Compounds in <i>Musa</i> spp. during Ripening Revealed by Mass Spectrometry Imaging

Bananas (<i>Musa</i> spp.) are climacteric fruits that ripen after harvest and undergo further softening and browning, including the generation of melanin-derived black "sugar spots" on the peel via the reaction of polyphenolic compounds, such as L-DOPA, a tyrosine metabolite. Although polyphenol-related metabolite levels are altered in bananas, data visualizing localization changes while preserving spatial information have not been reported. In this study, we visualized polyphenol-related metabolites at each ripening stage using mass spectrometry imaging. We found that the L-DOPA content decreased with ripening, the dopamine content increased with banana sugar spot formation and then decreased, and tyrosine and dopaquinone contents were not related to the ripening stage. L-DOPA and dopamine were localized in the peel, whereas tyrosine and dopaquinone levels decreased in the pulp (center) and peel and increased in the outer pulp. These findings provide insights into the polyphenolic compounds underlying banana sugar spots and the melanin synthesis pathway.