Melanoidin
Japanese: メラノイジン
Brown macromolecular pigments formed in the final stages of the Maillard reaction. They determine miso's color and also possess antioxidant properties.
Melanoidins are brown macromolecular substances produced in the later stages of the Maillard reaction. The reddish-brown color of aged miso is the result of accumulated melanoidins.
Short-aged white miso contains few melanoidins; red miso aged over two years contains many. The color difference between miso varieties is essentially a difference in melanoidin accumulation. Darker doesn't mean better—each color corresponds to its own flavor character.
Melanoidins are also known to possess antioxidant properties. Some health benefits of fermented foods may derive from these pigments. Functionality hidden within visual change—one example of fermentation's depth.