Metabolic Visualization Reveals the Distinct Distribution of Sugars and Amino Acids in Rice Koji.

The compounds inside rice koji have been thoroughly investigated as an essential material in making many food-related products, including sake. However, these studies focused only on quantitative aspects, leaving features that can still be uncovered if seen from a new perspective. Visualization of the metabolites inside rice koji may as well be the new angle needed to retrieve more information regarding rice koji making. Here we utilized mass spectrometry imaging (MSI) to visualize the distribution of sugars, sugar alcohols, and amino acids inside rice koji. Imaging results revealed that several sugars alcohols and amino acids were shown to have characteristic distribution near the edges or surface of rice koji. Furthermore, the distribution appears to be correlated with the different structure of rice koji. This study is the first report of using MSI to visualize sugars, sugar alcohols, and amino acids in rice koji.