Why are these cheese balls turning blue?

Mozzaralla balls made in Germany for Rome, Italy. 70,000 of these cheese balls have been confiscated, after Italian Police received numerous complaints that “the white balls turned blue when opened and exposed to the air”. several ball samples have been sent to a laboratory for tests. Question: did you know that Italy does not require a contents label on any sold dairy product, except milk? makes one wonder what’s really inside those tainted cheese balls. hidden drugs, maybe?

Source: Associated Press, 6–20-10