Joan M. King
Finding new uses for sweet potato components, such as starch, would increase the demand for sweet potatoes and save processors money by finding a use for the waste produced during cutting and canning.
The United States produces approximately 600,000 tons of sweet potatoes annually, making it the world’s 10th leading producer. About 24 percent of the nation’s sweet potatoes are grown in Louisiana, accounting for more than half of the state’s vegetable cash income and contributing $100 million to the state’s economy.
Sweet potato roots grown in Louisiana are used for processing, mainly canning. During the season, the canning process produces 600,000 pounds of sweet potato waste per day. At least half goes directly into lagoons, creating an environmental waste issue. Much of this waste is from cutting sweet potatoes for canning, and the byproduct is mainly starchy sweet potato flesh.
Increasingly stringent environmental regulations drive the need for innovative methods to remediate sweet potato waste. Creating high-value products from sweet potato by-products using value-added processing can minimize the waste stream, as well as provide a new source of income from high-value products manufactured from this waste.
Resistant starch is a type of starch that acts like fiber in the human body and thus provides the health benefits of fiber. Resistant starch is in high demand as a food ingredient. Research with resistant starch is exciting because of so many possible health benefits. They include improved glucose regulation and better weight control, reduced constipation, reduced colon cancer risk and reduced blood cholesterol and triglycerides.
Resistant starch has a low glycemic index. This may lower insulin demand by the body and benefit diabetics as they try to regulate their blood glucose within a normal range. Resistant starch can occur naturally in such foods as raw potatoes and bananas or in processed foods and starches.
Research at the LSU AgCenter involves testing of the effects on resistant starch levels by adding amino acids to starch from two types of sweet potatoes. White-fleshed sweet potato starch has significantly more resistant starch than the orange-fleshed starch in both cooked and uncooked forms. Research shows adding the amino acid lysine enhanced the level of resistant starch by 20 percent in cooked orange-fleshed sweet potato starch.
Further research is planned to increase the amount of resistant starch. This research will target reducing environmental waste for the sweet potato industry, as well as providing a new source of income from high-value products manufactured from this waste.
The sweet potato industry will realize additional and significant economic impact as a result of this work.
Joan M. King, Associate Professor, Department of Food Science, LSU AgCenter, Baton Rouge, La.
(This article was published in the spring 2009 issue of Louisiana Agriculture.)