ATLANTA — Officials on Tuesday were still trying to determine how food safety and security procedures failed to prevent tampered-with sandwiches from being served on Delta flights this weekend, 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.

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.

“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.”

FBI Atlanta is conducting a criminal investigation and leading criminal investigative efforts in the United States, while coordinating with the FBI’s legal attache in Amsterdam. Dutch police and the Netherlands Food and Consumer Product Safety Authority also are investigating.

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.