Analysis of the distribution of adenosine and guanosine on fermented soybean cryosections by MALDI-MSI

Bioactive compounds in fermented soybeans (Natto) may reduce cardiovascular disease risk because of their relatively high concentration of vitamin K but may also increase purine levels, thereby increasing the risk of gout. To investigate purine distribution, we overcame the challenges associated with plant cryosection quality by using a conductive adhesive film technique to produce high-quality cryosections suitable for matrix-assisted laser desorption/ionization mass spectrometry imaging. Sections from dried, soaked, and Natto revealed that adenosine and guanosine were widely distributed, whereas purines were localized mainly in the extracellular γ-polyglutamate (γ-PGA)-rich matrix of Natto. HPLC confirmed higher nucleotide levels in Natto. Moreover, our findings indicate that purines accumulate specifically in the γ-PGA-rich region, suggesting that consuming this portion may increase dietary purine intake. These results provide new spatial insights into purine distribution during soybean fermentation and suggest that avoiding the matrix portion of Natto could reduce the risk of gout and related conditions.