Perfecting Sweet Potato Chips

Treating sweet potato slices with a particular blend of enzymes may help chip makers create better sweet potato chips, research from the U.S. Department of Agriculture’s (USDA) Agricultural Research Service (ARS) suggests.

The research was a project of the USDA-ARS Food Science and Market Quality and Handling Research Unit in Raleigh, N.C., says research associate and food technologist Matthew Allan. Allan, whose research focus is sweet potato processing and chemistry, looks to find new uses and value-added products for off-grade sweet potatoes. Sweet potatoes are one of North Carolina’s top 10 agricultural commodities.

Allan is part of a team interested in the chemistry that influences the texture and fat content of sweet potato chips. While it’s known that dry matter and starch content are the primary factors, team members noticed that there are still differences in texture features when chips are made from sweet potatoes with similar starch content or dry matter content. They hypothesized that the cell wall polymers also play a role in texture and fat content and wanted to explore what happens when the cell wall polymers are changed.

The researchers used Covington sweet potatoes, a variety often chosen for sweet potato snacks. Sliced potatoes were treated with a range of food grade enzymes—cellulase, hemicellulase, pectinase, pectin methyl esterase, protease, and a blend—before they were fried. Each of the enzymes had a specific function; one broke down pectin, one strengthened it, one broke down proteins, another broke down hemicellulose, and a different one broke down cellulose. The enzyme blend was designed to “wreak havoc [and] destroy multiple cell walls,” says Allan. As a control, no enzyme was used. The potato slices were exposed to the enzymes for ½ hr, 1 hr, and 2 hr. Then the fat content, sugars, color, and other chip properties were analyzed.

Because of COVID restrictions, the researchers couldn’t use human sensory evaluators, so they used a tool in the lab that measures the amount of force needed to break a chip. “[It] targeted changes for different timelines,” explains Allan. “How does that affect texture, and how did that affect breaking force?”

The research team found that the enzyme blend that broke multiple cell wall polymers lowered fat content the most, which was a surprise, Allan says. Also, the protease, which Allan thought would have no effect at all, reduced the chip’s breaking force. “My speculation is that these proteases are breaking down those structural proteins in the cell wall, and that’s why we saw a decrease in breaking force,” he says.

Generally, the enzyme blend and the protease both reduced the breaking force, and pectin methyl esterase, which strengthens the pectin, produced harder chips. “That confirmed our hypothesis that the cell wall polymers do, in fact, affect chip textures, and possibly their fat content, too,” says Allan.

Suitable Sweet Potatoes

This research can help guide snack makers in their potato and processing choices. “Processing schemes or sweet potato selections can be more educated,” Allan says.

The researchers are planning to do a follow-up study with human taste testers. Additionally, Allan is now working on similar research but centering on sweet potato french fries, which represents a bigger market than chips. In that case, says Allan, a sensory study will be a must. Fries are complicated because of their varying textures, while chips are very uniform.

“Our goal is to understand what is driving sweet potato chip texture and french fries’ texture,” says Allan. “Because some people like soft, but other people are interested in crispy. Can we get a crispier sweet potato fry is kind of a question we’re chasing.”

The market for sweet potato snacks is no longer niche, Allan says, which he attributes to sweet potatoes’ nutritional profile. “U.S. consumers are wanting more sweet potato products because of [their] beta-carotene and health benefits,” he says.