When roaches contaminate food the food should really be thrown out and not eaten.
Although heating of the food that the roaches contaminated should kill the germs from the roaches as long as you heat the food hot enough it's still not worth the risk to your health to eat the food that the roaches have been on.
When roaches contaminate food it's best to throw it out.
You could still become sick from eating the food that the roaches contaminated especially if you haven't heated up the food hot enough.
Heating the food up to 400 to 500 degrees or more should kill the germs that the roaches left on the food but still it's not a good idea to eat the roach contaminated food.
There could also be some dead roaches or dead roach eggs in the food even though you may not be able to see the roaches or roach eggs.
If you have a roach infestation I would recommend hiring an exterminator to kill the roaches.