There probably isn't a surface area on your flight that would meet your personal standard of cleanliness, but Canadian researchers have found tray tables to be among the dirtiest areas on an airplane.
It can't be easy deep-cleaning an airplane, as you have people coming in and out, multiples times a day, but you would think there'd be some extra care put into the area where food is placed.
The CBC's "Marketplace" TV show put out a study where researchers went on 18 flights on three different airlines and started collecting samples throughout the planes.
In those samples, they found several types of bacteria, from yeast to E. coli.
You will be happy to know that those tray tables weren't the absolute dirtiest spots, as those distinctions belong to the headrests, followed by seat belts. Tray tables were in the top five, though.
Obviously attendants do their best to clean out the planes, but the study also concluded that attendants are just in too much of a hurry to really get into the nooks and crannies.
If you want to feel a little better about your flight, you can remind yourself that this was done in Canada, and give any other country's flights the benefit of the doubt.