I understand that when lipid molecules - triacylglycerol - are hydrolysed, the fatty acids 'break' off from the glycerol backbone. And when fatty acids oxidise, these in turn can break into smaller end products. Does hydrolysis always happen first? I have made this image - would it be a fair representation of what happens when oils turn rancid?
I am currently finishing my Ph.D. in rancidity, and therefore I know quite a bit about it. The picture is not a fair representation of what happens, since free fatty acids should be present, though you just show the triacylglycerols. Which rancidity happens first will depend on the matrix and on the storage condition of the oil. Usually, but not always, oxidative rancidity happens first.