I have very thin mattress so i place three old heavy comforter on my mattress i deep clean every 6 month when i remove comforter there was some food particles in one last comforter my 9 month old suddenly eat it what can i do now?

Be patient and monitor the situation. The average 9-15 month old sticks their dirty fingers or other objects in their mouth constantly. An estimate of 100 germ challenges/d occur in these infants. Thankfully their immune system has a robust response & protects them in most instances. If the kid "acts sick" deal with it as you would any other time. I doubt it will trigger a problem.