ATLANTA — Officials on Tuesday were trying to determine how food safety and security procedures failed to prevent tampered-with sandwiches from being served on Delta flights this weekend, including one to Seattle, but they said it doesn't appear to be a national-security issue.

The Transportation Security Administration said it conducts inspections to ensure airlines and contractors comply with security requirements for catering. And the website for Gate Gourmet said the in-flight catering company "conducts extensive monitoring and methodical food-safety checks thousands of times a day at all of our kitchens."

Yet, needles still ended up in sandwiches for business-class passengers on four Delta flights from Amsterdam — including two to Atlanta, one to Minneapolis and one to Seattle — and injured a passenger on the flight to Minneapolis.

TSA said it does not believe the incident represents a threat to national security.

"Obviously, there needs to be a review of their procedures," said California-based food-safety consultant Jeff Nelken.

Nelken said some large processing facilities have metal-detection equipment to scan boxes or trays of food to detect any metal that does not belong in the food.

He said he usually recommends that food-producing facilities get rid of pins used to hold up schedules or menus, "because the odds are these can pop out very easily, drop on the floor (and) become something to be used by someone disgruntled with management."

Gate Gourmet spokeswoman Christina Ulosevich said it "does not appear that this occurred at or after" the food was transferred to Delta, and the catering company is conducting its own investigation into the matter. Gate Gourmet is the world's largest independent airline-catering company. Its parent company, gategroup, has a safety and security operation called Gate Safe that handles airline catering inspection and monitoring.

FBI Atlanta is conducting a criminal investigation and leading criminal investigative efforts in the United States, while coordinating with the FBI's legal attaché in Amsterdam.

Dutch police and the Netherlands Food and Consumer Product Safety Authority also are investigating the incident.

In the short term, people likely will be "a little more tentative" and nervous about airline food, but it probably won't have much long-term effect, said Monique Turner, a professor of public health at George Washington University.

"People get more worried when these things are accidents, because accidents are hard to predict," Turner said.

Tjitte Mastenbroek, a spokesman for the Dutch government's Food and Consumer Product Safety Authority, said the agency also was investigating "from a food safety point of view." He said the agency would share its findings with the criminal investigation. He declined to give more detail.

Gate Gourmet's website calls the company "the world's largest independent provider of catering and provisioning services for airlines and railroads," with 122 flight kitchens serving 250 million meals each year and 9,700 flights per day. The company was founded in 1992 to cater Swissair flights and grew by taking over other airline caterers.