Mass Spectrometry Imaging of Fructooligosaccharides in Barley Seeds with the iMScope QT

Importance of the Topic

Barley is a nutrient-rich grain valued for its high fiber and prebiotic fructooligosaccharide (FOS) content, which support gut health and may mitigate chronic lifestyle diseases. Visualizing the spatial distribution of FOS within barley seeds enhances our understanding of varietal differences and guides breeding for improved nutritional quality.

Objectives and Study Overview

This study aimed to demonstrate the capabilities of the Shimadzu iMScope QT imaging mass microscope for high-resolution mass spectrometry imaging (MSI) of three FOS—kestose (m/z 503.16), nystose (m/z 665.21) and fructosyl-nystose (m/z 827.26)—in seed sections of three barley varieties: BARLEYmax, glutinous barley rice and Hindmarch. The goal was to compare FOS detection sensitivity and spatial mapping between the newer QT model and previous instrumentation.

Methodology

Seed sections were mounted on indium tin oxide (ITO) slides and coated with a uniform 0.9 µm layer of 9-aminoacridine matrix via the iMLayer vapor deposition system, reducing user variability. MALDI MSI was performed in negative ion mode over an m/z range of 500–835. Imaging conditions included a 25 µm pitch, 60% laser intensity, 1,000 Hz frequency and 50 laser shots per pixel. Total ion count (TIC) and individual FOS m/z channels were acquired for each sample.

Used Instrumentation

• iMScope QT Imaging Mass Microscope (Shimadzu)
• iMLayer Matrix Vapor Deposition System (Shimadzu)
• 9-Aminoacridine MALDI Matrix

Results and Discussion

All three target FOS were detected in each barley variety, with BARLEYmax showing the strongest signals for kestose, nystose and fructosyl-nystose. Spatial ion images revealed lower FOS concentration around the hypocotyl compared to the seed body in BARLEYmax, while lower overall signal intensities in glutinous barley rice and Hindmarch limited detailed mapping. Hindmarch exhibited localized kestose accumulation at the hypocotyl base despite weaker signals.

Benefits and Practical Applications

• Enables rapid, high-resolution visualization of prebiotic carbohydrates in cereal seeds.
• Supports comparative analysis of breeding lines for nutritional enhancement.
• Streamlines sample preparation and improves reproducibility using vapor deposition.

Future Trends and Applications

Advances in MSI instrument speed and resolution will allow routine screening of grain germplasm libraries for beneficial metabolites. Integration with quantitative imaging workflows and multimodal microscopy could further elucidate seed biochemistry. Expanding these approaches to other functional compounds will enhance crop quality research and functional food development.

Conclusion

The Shimadzu iMScope QT system successfully detected and imaged key FOS in barley seeds at high spatial resolution, confirming elevated levels in BARLEYmax. The combination of uniform matrix deposition and optimized imaging parameters offers a robust platform for comparative metabolic mapping in plant tissues.

References

1. Teijin (Biolier). 2023. BARLEYmax. Retrieved January 2023, from https://biolier.jp/en/barleymax
2. Tamiya T, et al. 2020. Mass spectrometry of BARLEYmax fructooligosaccharidides. Journal of Cereal Science, 95:103068