Distribution of Flavan-3-ol Species in Ripe Strawberry Fruit Revealed by Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging

Molecules. 2019 Dec 26;25(1):103. doi: 10.3390/molecules25010103.

Abstract

Flavan-3-ols, which comprise proanthocyanidins and their monomers, are major flavonoids in strawberries, and they have a wide range of biological activities and health benefits. However, their spatial distribution in strawberry fruit remains poorly understood. Therefore, we performed matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI), to visualize flavan-3-ols in ripe strawberry fruit. Peaks matching the m/z values of flavan-3-ols [M - H]- ions were detected in the negative ion mode using 1,5-diaminonaphthalene as matrix. Catechin and/or epicatechin, three B-type procyanidins, and two B-type propelargonidins were identified by MALDI-tandem MS. These flavan-3-ols were mainly distributed in the calyx, in and around the vascular bundles, and in the skin. In-source fragmentation of proanthocyanidins was determined using their standards, suggesting their distribution was mixed ion images of themselves, and fragment ions generated from those had a higher degree of polymerization. B-type procyanidins were predominantly distributed in the vascular bundles than in the skin, whereas B-type propelargonidins were almost equally distributed between the vascular bundles and skin, suggesting that their distribution patterns are different from the type of their flavan-3-ol monomers. Flavan-3-ols, especially B-type procyanidins, may help prevent pathogen infection not only in the skin but also in and around the vascular bundles.

Keywords: flavan-3-ols; mass spectrometry imaging (MSI); matrix-assisted laser desorption/ionization (MALDI); proanthocyanidins; procyanidins; propelargonidins; strawberry.

MeSH terms

  • Flavonoids / chemistry
  • Flavonoids / isolation & purification*
  • Fragaria / chemistry*
  • Molecular Structure
  • Plant Extracts / chemistry
  • Plant Extracts / isolation & purification
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
  • Tissue Distribution

Substances

  • Flavonoids
  • Plant Extracts
  • flavan-3-ol