Resistant Starch from Rice, A New Source of ‘Fiber’

Linda Benedict  |  5/6/2005 1:58:17 AM

Joan M. King, Maren Hegsted and Carol E. O’Neil

Resistant starch is chemically not a fiber; however, there is an effort to have it declared so because it 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—conferring their health effects. Not surprisingly, resistant starch is in high demand as a functional food ingredient. LSU AgCenter researchers are conducting a variety of studies on resistant starch, including the effect it has on properties of rice and rice flour, which will add value to this Louisiana commodity, and the effect it has on weight gain and body fat in rats, with the goal of understanding the role resistant starch plays in obesity.

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. One way to enhance resistant starch in a food product is to heat the starch to a gel and cool it quickly. This process is called retrogradation and is what happens to bread when it cools after cooking—the process is accelerated by storing bread in the refrigerator.

Another way to increase the level of resistant starch in foods is to modify the starch by the addition of fats, which bind inside the spiral of the starch molecule to stabilize it and make it resistant to attack by enzymes. LSU AgCenter researchers are conducting studies on the use of enzymes and additives on rice flour and starch to enhance resistant starch content.

The modification of corn starch to produce functional food ingredients has resulted in driving the selling price of native corn starch from 20 cents per pound to $2.50 per pound for modified corn starch. There is a potential of a 10-fold increase in the value of rice flour, from the development of rice starch-based ingredients, such as resistant starch, through the same technology. The low protein content makes rice hypoallergenic; thus, it is often a better choice for people with allergies to wheat or other cereal grains.

Broken rice kernels, which make up 15 percent of milled rice in the United States, can be used to produce value-added food ingredients. Rice varieties that may have excellent agronomic traits but may lack acceptability by consumers because of negative cooking or other characteristics may also be used for value-added food ingredient development. This research will benefit everyone in the rice industry by providing an expanded use of rice and an increased demand for rice and rice products, as well as providing a healthy choice for consumers.

Clinical health research with resistant starch is exciting because there are so many potential health benefits associated with its use. These include:

1) improved glucose regulation and better weight control,
2) reduced constipation,
3) reduced colon cancer risk,
4) and reduced blood cholesterol and triglycerides.

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, thus helping people with diabetes normalize their blood sugar. The better blood sugar levels can be controlled, the fewer the long-term complications of diabetes that may occur. The lowered insulin response may also reduce the subsequent drop in blood sugar that triggers hunger for the next meal. This could result in a lower energy intake at the following meal and better body weight regulation. In a study using rats as a model for human obesity, AgCenter researchers found that when they replaced regular starch with high amylose cornstarch (60 percent resistant starch), it reduced body fat in rapidly growing male and female rats. Blood insulin levels were also lower in the rats fed resistant starch.

Resistant starch can also help improve colon health. As resistant starch moves through the intestinal tract, it decreases constipation by increasing fecal moisture, bulk and transit time. The non-digested starch in the large intestine is fermented by bacteria producing short chain fatty acids, primarily acetate, butyrate and propionate. Butyrate is the preferred energy source for colon cells, resulting in healthier colon cells. Resistant starch encourages the growth of beneficial bacteria in the large intestine and lowers the pH of the intestinal contents, all of which may reduce the development of colon cancer. Diets high in resistant starch can reduce blood cholesterol and triglyceride levels because of higher excretion rates of cholesterol and bile acids.

Overall, increasing resistant starch content in the diet has the potential to provide several significant health benefits and add value to rice, an important Louisiana commodity.

Joan M. King, Assistant Professor, Department of Food Science; Maren Hegsted, Professor, and Carol E. O’Neil, Associate Professor, School of Human Ecology, LSU AgCenter, Baton Rouge, La.

(This article appeared in the fall 2002 issue of Louisiana Agriculture.

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