By Lisa Sigell

CARSON (CBSLA.com) — The U.S. Department of Homeland Security is partnered with the FDA to anticipate potential threats to an issue of national security: the food supply.

According to federal statistics, 15 percent of the nation’s food supply is imported from overseas.

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CBS2 was recently given access inside a tightly monitored plant in Carson, where FDA officers were busy inspecting foreign-made foods and spices, like black pepper from Vietnam, with the goal of intercepting any danger.

“We’re doing a random sampling of black pepper from Vietnam, specifically for Salmonella,” said Pamela Lee, an FDA inspector.

Dan Solis, the FDA Director of Import Operations, says they’ve seen problems with spices before.

“A lot of it is what we call filth. Bug parts. Hair. Rat feces,” he said.

In addition to the black pepper, FDA inspectors also took a closer look at Japanese red peppers from China, canola oil from China and a shipment of anchovies from Korea.

The anchovies came from a manufacturer already on a government watch list.

“These shipments have been refused by the FDA and are now being exported back to the country of origin,” said Solis.

The inspection site is just one facility in Southern California.

At another secure facility, a shipment of cucumbers with banned pesticides had to be destroyed along with Russian soft drinks tainted with potentially dangerous dyes.

Across the country, though, the same issue is emerging at inspection sites. For instance, in Boston, federal inspectors recently intercepted dangerous jam.

“In strawberry preserves, we’ve seen unsafe food dyes,” said Sean Smith of the U.S. Customs and Border Patrol.

But some products are misrepresented more often than others.

In fact, a recent study at UC Davis found that 70 percent of olive oils aren’t what the label says they are.

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“Sometimes, it’s mixed with nut oils and then there’s allergens involved,” said Patrick Vardaro, an olive oil seller.

As CBS2’s Lisa Sigell reports, olive oil is a target because it’s expensive.

“There’s a lot of fraud in the industry, and it’s obviously for monetary gain,” Vardaro said.

Amy Kircher is with the National Center for Food Protection and Defense, which is a University of Minnesota lab set up to protect the nation’s food supply.

“Anything made in bulk or produced or shipped in bulk is something that we’re always very careful with,” Kircher said.

Honey is often sent through multiple countries to cover the trail of pesticides and antibiotics banned in the United States.

And species substitution, which occurs when cheaper breeds are passed off as expensive ones, is a growing problem with fish.

“Substituting escolar for tuna. Tuna is more expensive. Escolar, on the other hand, just naturally causes some gastrointestinal problems in people,” Kircher said.

With so many imports and relatively few inspectors, federal officials say they’re faced with an uphill battle.

But here and elsewhere, food watchdogs are doing their best to protect the food supply and say the greatest risk of food fraud arises when purchasing from a vendor consumers don’t know well.

They say the labels and products consumers purchase should look familiar.

For more information on food safety, visit the FDA’s website.

For information on the White House’s efforts to address food fraud, click here.

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The following segment was produced by CBS 2 Medical Producer Gerri Shaftel Constant.