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

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.

Novel Blotting Method for Mass Spectrometry Imaging of Metabolites in Strawberry Fruit by Desorption/Ionization Using Through Hole Alumina Membrane

“…anthocyanidin-glycosides, which are referred to as anthocyanins, in plants. Detection of pelargonidin in our previous study [14] was considered to be caused by the detachment of sugar moieties from the pelargonidin-glycosides by in-source fragmentation [15], suggesting that the degree of in-source fragmentation of metabolites is higher in the DIUTHAME-MSI than in MALDI-MSI. DIUTHAME may be a harder ionization method than MALDI under the experimental conditions used in this study.…”

“…The optical image of DIUTHAME chip after blotting of metabolites on the cross-section of strawberry fruit is shown in Figure 2b. MSI measurements obtained in positive and negative ion modes are shown in Figure 2c and d. Although the detection intensities appeared to be lower than those in MALDI-MSI analysis [14,15], numerous signal peaks were detected in the m/z range from 100 to 500. In the m/z range from 500 to 800, peaks were hardly detected.…”

“…The predominant sugars are glucose, fructose, and sucrose, whereas the predominant organic acids are citric and malic acids [20]. In our previous study, major polyphenols, namely anthocyanins, such as pelargonidin-glycosides and flavan-3-ols, or sugars, and organic acids were visualized, using MALDI-MSI, in whole cross sections of strawberry fruit [14,15]. However, strawberry fruits larger in size than a single glass slide could not be analyzed because thin sections could not be prepared from the crumbling and fracturing tissues.…”

“…MSI has been used to separate various metabolites based on their mass-to-charge ratio (m/z) and to visualize their distribution in tissues. Recently, MSI was adapted for analysis of metabolites in foods and was successfully used for visualization using soft ionization techniques, such as matrix-assisted laser desorption/ionization (MALDI) [9][10][11][12][13][14][15][16][17] or desorption ESI [18,19]. These techniques generally require preparation of thin sections (usually 10-20 µm) of the samples using a cryomicrotome.…”

Unique Distribution of Diacyl-, Alkylacyl-, and Alkenylacyl-Phosphatidylcholine Species Visualized in Pork Chop Tissues by Matrix-Assisted Laser Desorption/Ionization–Mass Spectrometry Imaging

“…These techniques are useful for the qualitative and quantitative analysis of phospholipids and for investigating their spatial distribution by dividing samples into different tissues; however, the spatial resolution is dependent on the fineness of tissue differentiation. To resolve this problem, an emerging technique, mass spectrometry imaging (MSI), can be used to simultaneously investigate the content and spatial distribution of metabolites at microscopic resolution without the need for antibodies, staining, or complicated preliminary procedures [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. MSI has been successfully used to separate multiple lipids according to their mass-to-charge ratio (m/z) and visualize the tissue distribution of each molecule [14,23,[31][32][33].…”