Proving food poisoning in law is vv difficult, the main vector for infection is people touching their mouth and face area with dirty hands by a long long way...but then when people get sick they will (understandably) default to the last dogyish thing they ate when the infection could have come from literally anywhere in the last few weeks. A friend is a senior chef in a major international hotel chain - food poisoning complaints are something that happens on a regular (if not too frequent) basis. They have a procedure and I imagine the airlines would do something similar. When there is a complaint they go into the kitchens and they take samples from the food, from the environment. Obviously if the complaint isn't quick enough they can't sample the food itself but you'll be amazed how much of what you eat hangs around in walk ins and deep freeze. These samples get sent to a lab and tested for everything under the sun.
He says when there is one complaint noone cares, the individual probably blamed them for something else and the tests have always proved him right. It's when multiple people at the same service get something they know they've got something serious to worry about. So you should complain OP but unless there were others who do likewise and you get backed up the labs, I wouldn't hold your breath for recompense. Trust you recover swiftly.