"Tonkatsu" pork cutlet with sous vide pork 低温調理のトンカツ

We like tonkatsu トンカツ and make it occasionally. Although in Japan, serving undercooked pork is not unusual especially when using SPF pork from specific named-producers (although it does not specifically say it is cysticercus free, I am sure the risk is extremely low). I am sure American pork is relatively safe as well but I, just to be safe, make sure I cook pork completely. In the Weber grill, I roast pork using indirect heat to the inner temperature of 145F as per USDA standard. (Actually, I start going down to the grill when it reads 142F, by the time I am ready to remove the pork from the grill, the temperature will reach 145F). I previously posted sous vide pork tenderloin at 140F for 3 hours which appears to be safe for both bacteria and cysticercus. Going back to tonkatsu, I usually insert an instant digital thermometer in the center of the meat until it registers 140F but it is not easy to get it right. Many times,  the pork is a bit overcooked (since I err on the side of overcooking). To eliminate this anxiety of under or over cooking, I decided to try making tonkatsu from sous vide cooked pork tenderloin. This is what it looks like. I only deep fried it for a total of 1 minute  since the meat itself was precooked. As you can see the center looks slightly pink. It tasted great with a nice fried bread crust. So why is the center is pink?

I sous vide cooked pork tenderloin seasoned with salt and pepper at 140F for 4 hours which is more than enough to completely cook the pork and render it safe. I soaked the vacuum packages after completion of cooking in ice water for 30 minutes to quick cool down before moving them to the meat drawer of the refrigerator for future use. Just before making it into tonkatsu, I sliced it and the cut surfaces were totally homogenous and gray (see below).

So, the only explanation I can come up with is the oxygen exposure. The pork was cooked in a vacuum but after it was breaded and deep fried, oxygen may have bound to myoglobin to make a slightly pink color. This was an  interesting experiment and  proof of concept. I am not sure I will do this as a regular way to cook tonkatsu, though.