The mechanism of melanosis development
starts with the enzymatic action of polyphenol oxidase, which
oxidizes naturally occurring phenols from amino acids into quinones.
Subsequent non-enzymatic polymerization of the colorless
quinones causes a build-up of high-molecular-weight black pigments
(Ramirez, Whitaker, Virador, Voragen, & Wong, 2003), and
the appearance of black spots devalues the shrimp