Brining can make the meat more tender, which can be important to those who care about the texture of the foods they eat.
There are three ways you can brine the meat: with enzyme, with acidity, or with saltwater.
When you brine with enzyme (pineapple or kiwi) or with acidity (lemon juice) prior to slow cooking, make sure to be extra careful. If you don’t wash them off properly, then enzyme and acidity will continue its work to the point that the meals turn bitter.
It is because enzyme and acidity cause chemical breakdown of protein molecules where some byproducts can taste bitter. On the other hand, saltwater causes only physical changes (making the meat hold more water via osmosis) so it won’t introduce bitterness.
For slow cooking, saltwater brining is an easier option and my personal recommendation to prevent accidental bitterness.