Recently we have started suspecting that one of our children has hypolactasia (lactose intolerance), and so accordingly I have had my first exposure to lactose-free dairy- and dairy-like products. In addition to soy milk and almond milk, we have recently purchased actual dairy milk that was labeled lactose-free. This gave me the impression that they had used some process to remove the lactose, but looking at the ingredients more closely, it seems that they simply added lactase enzyme to the milk to assist breaking down the sugars.
My question is this: when is the lactase enzyme active? Does the lactase activity begin right as it is added to the milk, or will it not become active until ingested?
Essentially, I'm wondering if this type of milk can/should be used in cooking or baking. High temperatures will certainly denature the lactase enzymes in the milk, but if the lactose has already been broken down, this shouldn't be a problem.