A spokeswoman from Gate Gourmet, the Dutch caterer used by Delta, has said that the company is cooperating fully with investigators. Christina Ulosevich added that "details of this matter must remain confidential".
Gate Gourmet is a subsidiary of Swiss-based gategroup Holding AG, one of the largest independent global providers of airline passenger products and services.
More top news
Sleet, snow & spring sunshine
Fitbit has said it is investigating its Flex 2 fitness tracker after a US woman claimed she suffered second-degree burns while reading.
North and South Korea have held live-fire training exercises from the land, sea and air involving thousands of military troops.