72-Hour Short Ribs Green Discoloration

sjelms

I've done boneless short ribs before at 62 °C / 144 °F for 72 hours and they were great. 

I've just pulled a new batch from the bath done at 58 °C / 136 °F for 72 hours as recommended in Modernist Cuisine at Home.

I did three batches packed in pairs and vacuum sealed and double bagged (which is my practice for long cook times). I didn't add anything to the meat before bagging it.

When they were done the au jus looked a lovely dark color but the surface of the meat had a green tint with a lovely pink center (see photo). I couldn't detect the slightest hint of a bad oder.

I took a blowtorch to the surface and after the maillard reaction everything looked fine. 

Should I be concerned?   

sjelms

Do you have any idea what would cause this so that I can avoid it happening again? Green meat is rather off putting. 

Thanks.