When I bake chicken breast, some unsavory white gunk comes out. It is a perfectly edible protein, but not pleasant to eat. And when I cook the chicken with vegetables in a pressure cooker, the gunk gets all over the vegetables. What is the best way prevent the gunk from coming out or keep it separate?
When I bake chicken I usually use, depending on how and what for I cook it, a deep tray with grill/baking/cooling rack. That way all juice fall onto the tray. This chicken is very dry so I usally cook it wrapped in tin foil and for chicken with dairy made marinate. Or I use tray with a concave in the middle where all the juices (and proteins) gather. I've also seen ones that have a canal around the bottom to gather juices.
When cooking there are two schools. One, practiced by my grandmothers is to cook chicken soup (or chicken in any liquid) on very low heat for a very long time. That' way the proteins don't get out (they call them noise).
The other way is to have more liquid than it's needed, that way the foam will form on the surface while all the veggies and chicken will fall to the bottom. Then you just filter it with a slotted spoon. I learned that you can only do this once (and it's beest to do when foam is kinda grayish from protein. As otherwise you will break the proteins and they will mix with the liquid. Then you need to use colander with big holes to filter solids and then rinse them. And filter luqid through very small holes (cloth) to remove proteins.
I suspect you're overcooking the chicken. This will happen with fish as well if you overcook it. The proteins are being pushed out of the meat along with water because they are shrinking too much.
I cook chicken breast to about 150°F for three minutes (dark meat should be cooked to a higher temp in order to break down the sinew). When everyone tells you 165° that's because that's the temperature that kills most bacteria (to a 7 log10 reduction, or 1/10M). Cooking to 150° for three minutes does the same and the chicken is much moister, not stringy and dry. It's easy to test temperature in an oven but trickier in a pressure cooker. How are your vegetables coming out? Mushy and overcooked or just tender?
If you cook sous vide you can cook at a lower temperature for much longer without negative effects. But I have found dark meat easier to get right with sous vide, and if I have the time I cook thighs and legs for eight hours at 158°F (but at least three or four).
Here's an article on temp and chicken that you may find helpful. I'd also suggest reading Kenji López-Alt's book.