Anonymous Modernist 5247

I am having trouble with oxidation of my bananas. I sous vide them at 88C for 12 minutes and they still turn grey while I sieve them. I looked online for some help and found other people had success with 20-30 minutes, that didn't work for me. I successfully completed the gel and it tasted great, but the color was not yellow. It ended up a grey/brown color. I tried bananas that had just turned yellow, still a little green on the stem and also tried slightly over ripe bananas. I tried apple bananas (bad idea) they get hard and starchy when you sous vide them. Any help that could be provided would be great, thanks in advance for your help.