A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme  If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme
Ttherefore, what destroys the enzyme is not heat but microwaves, which generate heat
Heating any liquid by microwave creates small zones within it that are much hotter than the overall temperature that the liquid will ultimately reach.