The brown substance belongs to a class of compounds called
melanoidin. They have varying molecular weights but are brown in
color. Maillard reaction (non-enzymatic browning) consists of many
steps which includes strecker degradation and other reactions which
result in formation of aromatic compounds (ketones, aldehydes,
etc). Maillard reaction is also responsible for the 'wok hei' in
some cooked food. Ya, the brown substance is formed from Maillard
reaction. For more information, you can search food chemistry books
from the library or try the net.. 