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
Billionaire Microsoft co-founder Paul Allen has claimed discovery of the Japanese battleship Musashi that was sunk by the US Navy in 1945.
Friday will be mostly dry with sunny spells for much of the UK. Temperatures will be mild across the country.
Some famous Liberal Democrat names will be fighting for their political lives in the election, now just over two months away.