For some reason this is most notable in Chinese dishes, but I had a plate of sliced pork last night at Sonny’s Real Pit BBQ, and it was a bit pink around the edges. Why does that happen?
In my experience, it’s part of the smoking process. The marinade - usually tomato/citrus/ vinegar - based- impregnates the upper layers of meat. And, as I said, I’ve only noticed this when I smoke food. From your description, you’re encountering the same thing.
I always thought it was some kind of saltpetre-based marinade used on smoked meats, but I learned recently that it was the smoke itself, in some kind of chemical reaction with the meat, that causes that ring of pinkness. Thus we see the reddish-colored ring in brisket and ribs.
However, I don’t know about the Chinese BBQ pork. Is it technically smoked? If not, perhaps nitrates are causing the color change, as they do in ham and bacon.
For BBQ, the pink smoke ring is caused by carbon monoxide. I’m not sure what the chemical process is, but I know that certain meat packers will treat their meat with carbon monoxide to retain its redness.
I looked it up. It’s myoglobic reacting with carbon monoxide to produce a stable pigment.
myoglobin