It is not uncommon these days to pick up a vacuum packaged brisket at a grocery store and see a discolored edge on it.  This discoloration may be subtle or it may be quite distinct and is usually gray or brown, which contrasts with the purple color of the meat in the vacuum package (the meat will turn red when removed from the package and exposed to oxygen). The reason for this discoloration is that this edge of the brisket is exposed when the carcass is split into sides, and these sides have various antimicrobial treatments applied to them such as organic acids (lactic  acid is the most common), hot water, and/or steam pasteurization to destroy potential pathogens.  The application of these acids and/or heat will denatured the color pigments in the meat causing this graying or browning appearance to develop.  Application of antimicrobial treatments to beef carcasses is not new and has been used by the meat industry since the early 1990s to reduce the risk of E. coli O157:H7 and Salmonella on beef.

Trimming this discolored area from the briskets before barbecuing is a personal preference, but there is nothing wrong with leaving it on, seasoning and putting the briskets on to smoke.  The bark that develops on the surface of the barbecued briskets greatly affects the appearance and taste of the finished product, and the discolored area soon disappears.