While your question is quite unusual for us, I don't think it will be a problem when it comes to site scope. We do answer questions on food safety, nutrient-composition, and food chemistry, so I guess we could stretch it to the chemical composition of decaying food.
The problem is that you will likely run afoul of the rules that the question has to be suitable for a Stack Exchange site. Your current wording requires book-length answers, which is not feasible. You would have to really focus your question, probably by picking a single food type and a single decay mechanism for the question. In fact, from an engineering perspective, it is probably much easier to tackle and solve a single problem before generalizing to everything.
The tricky part is that, for picking what you focus on, you will have to do so much preliminary research, that you might soon know more than we do. Picking at random may lead you to a bad choice - to take one clear-cut example, you probably don't want to start with the detection of moldy fruit, because 1) normal air mold loads differ between kitchens, and in each kitchen with time of season, and 2) you may a different sensor for detecting airborne mold particles than for gas molecules. But then again, until you know enough about each decay mechanism to decide which ones are worth starting with, you probably won't need to ask the question.
It is also a problem to ask "which one is optimal to start with", because it is likely that there are many optimal ones, making it a big-list question without a single objective answer, which is again not a SE-suitable question.
If you can think of other formulations or options, you can still run them here by us, or in chat, and we can see if one fits.