I haven't necessarily heard anything about this (either positive or negative) but I think that some of the bad bacteria from the mom's mouth isn't good for the baby - heck, many of the bacteria in the mouth isn't even good for the mom (I've heard that humans have one of the dirtiest mouths in nature, no pun intended). However, as I said, I've never heard about the bacteria issue before so I can't say.
As for the enzymes, I do know that the baby already has the enzymes that it needs to digest his own food. There are certain foods that babies shouldn't have before 1 year old because their bodies can't digest it properly but those enzymes are found in the stomach and intestines, not the mouth/saliva, so chewing the food beforehand won't do any good for the baby.
Also, I say good for your wife for continuing to breastfeed your baby since she's able to! :-) That is very good for him.