Peptide
Japanese: ペプチド
A short chain of 2 to several dozen amino acids. An intermediate product of protein breakdown, contributing to body and umami.
Peptides are molecules of several to dozens of amino acids linked together—intermediates born when enzymes break down proteins (hundreds to thousands of amino acids).
During miso aging, proteases first break proteins into peptides, then further into free amino acids. What's interesting is that peptides already influence taste at their stage: some impart bitterness, others enhance umami, still others create body.
Recently, health-functional peptides—ACE-inhibitory peptides that lower blood pressure, antioxidant peptides—have been discovered in fermented foods. The 'intermediate existence' before amino acids holds its own distinct value.