Joan King | 4/30/2005 2:20:24 AM
Researchers at the LSU AgCenter are working with a product that has the potential to provide several significant health benefits and add value to an important Louisiana commodity.
The product is rice with resistant starch – which resists digestion and absorption in the small intestine and passes through to the large intestine, where it acts just like dietary fiber. In addition, the starch’s calories and carbohydrates aren’t digested.
Dr. Joan King, a researcher in the LSU AgCenter’s Department of Food Science, is working with rice flour and pure rice starch to find a way to produce resistant starch. Dr. Jim Oard, a rice geneticist in the AgCenter’s Department of Agronomy and Environmental Management, is trying to develop new rice breeding lines with resistant starch.
Resistant rice is higher in amylose – the portion of rice that "clumps," King says. "Most rice varieties have about 25 percent amylose," she says.
Oard is looking for high-amylose lines to cross with proven high-yielding varieties to get high amylose naturally in a commercially viable rice line.
In the meantime, King is working in the laboratory to find ways to manipulate rice starch with enzymes to enhance resistance.
She’s working with both rice flour and pure rice starch, but the flour contains oils and proteins along with the starch.
"We’ve had better success with pure starch," King says.
LSU AgCenter experts say resistant starch can occur naturally in foods, including raw potatoes and bananas, or in processed foods and starches. Although some raw foods have resistant starch, cooking can destroy it, so it is important that the method used to process the starch makes it heat-stable.
While some resistant starch is present in all rice, much of what’s there is lost in cooking. To remedy this, King is using enzymes to modify the starch.
"We have to make it stable for cooking," she says.
Resistant starch acts like soluble fiber in the gastrointestinal tract, thus providing the health benefits of fiber. Resistant starch and soluble fiber ferment in the small intestine. Not surprisingly, resistant starch is in high demand as a functional food ingredient.
"Most resistant starches are used in baking, because they don’t thicken like regular starch," King says. But the resistant starches she’s developed in the laboratory have the same thickening properties and can be used in puddings, roux, gravies and similar applications.
King likens resistant starch to "carbohydrates without sugar."
"Putting resistant starch in baked goods is like whole grains versus white bread," she says.
"It’s good for people with diabetes," King adds. "Resistant starch has a low glycemic index because of the slow release of glucose. This may lower the insulin response by the body after eating resistant starch – helping people with diabetes normalize their blood sugar."
King has been working with resistant starch for more than 10 years, first with corn starch in private industry and now with rice starch at the LSU AgCenter. The market currently has high-amylose corn starch but not high-amylose rice starch.
King’s process to produce resistant-starch rice should save money commercially, because it removes a step in processing since starch doesn’t have to be heated to be converted.
The LSU AgCenter has applied for a patent on King’s process.