Compartmentalization. Company A produces mix containing ingredients 1, 3 and 5. Company B produces mix containing ingredients 2, 4 and 6. Only a handful of people at Coca-Cola even know the details of what companies A and B produce, and everyone below just knows "we combine the two mixes we receive"
Also, good lawyers + good contracts. Its way more profitable for those companies to be quiet about what their mix is than risk the wrath of a $233B beverage company.
