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
Even if you're having a tough day in the office, it's unlikely to be as difficult as the one facing the director of the US Secret Service.
The first behind-the-scenes photographs of George Clooney and Amal Alamuddin's Venice wedding have been published in a celebrity magazine.
The US Secret Service chief faces questions from politicians today over the latest in a series of worrying White House security breaches.