Slowing down digestion

by Jeff Gelski
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Starch may play a role — or be a roadblock — in developing processed foods that provide consumers with satiety, or a feeling of fullness. While resistant starch has made news in such applications, research also has focused on the differences between slowly and rapidly digestible starch and how processing techniques may slow the carbohydrate’s digestive rate.

Besides providing a feeling of satiety, a slower digestion rate may flatten the glycemic response and thus help prevent blood sugar spikes, said Bruce Hamaker, professor and director of the Whistler Center for Carbohydrate Research in the Department of Food Science at Purdue University in West Lafayette, Ind.

"Research has been done that at least supports those ideas — the benefits of slowly digestible starches over rapidly digestible starches," he said.

Human enzymes in the digestive system may chew rapidly digestible starch in 30 to 45 minutes after consumption, Mr. Hamaker said. High heat, a large amount of water and a long cooking time may quicken the digestive rate, he added.

In contrast, slowly digestible starch may take longer than 3 hours to digest. Pasta, because of its density and protein matrix, is digested slowly, he said.

Manipulating starch digestion

Different approaches may manipulate the rate of starch digestion, Mr. Hamaker said. He is scheduled to participate in a presentation that will examine such approaches on July 31 at the Institute of Food Technologists Annual Meeting and Food Expo at Chicago’s McCormick Place.

Supramolecular structure, such as raw cereal starch, may be a slowly digestible starch. Other examples include densely packed starch such as

polymer-entrapped starch, special molecular structures such as amylopectin from certain maize mutants, and enzyme-modified starches.

Research involving Mr. Hamaker and Purdue University along with Kasetsart University in Bangkok, Thailand, involved increasing the amount of slowly digestible starch and resistant starch in waxy rice starches. Researchers debranched the starch with an enzyme and cooled it to create a retrograded form.

Enzyme concentration, the hydrolysis period and the cooling temperature all affected the amount of resistant starch and slowly digestible starch. The retrograded, debranched starch had slightly higher amounts of slowly digestible starch and resistant starch than native starch and much higher amounts than cooked starches.

When food, including starch, is digested at a slower rate, blood sugar spikes may be avoided. The rate of digestion also has an effect on satiety, but more research is needed to prove satiety’s relationship to obesity, Mr. Hamaker said.

"I’m hesitant to say the relationship is that well established," he said.

Some scientific reports support the theory that a lower glycemic profile is beneficial to overcoming obesity while other reports do not support it, Mr. Hamaker said.

Mr. Hamaker is involved in a three-year project funded in part by a grant from the U.S. Department of Agriculture and will examine the development of starchy foods and the physiological consequences in the rate of starch digestion.

Resistant starches at I.F.T.

Resistant starch is named for its ability to resist digestion. More than 200 studies published in technical journals indicate natural resistant starch products from high-amylose corn resist digestion in the small intestine and ferment in the large intestine, according to National Starch Food Innovation, Bridgewater, N.J. The studies also have revealed a link between consumption of resistant starch and physiological benefits in areas such as weight management, glycemic management, energy management and digestive health. National Starch, which offers Hi-maize resistant starch, will exhibit at booth No. 9402 during the I.F.T. event in Chicago.

London-based Tate & Lyle, at booth No. 140, will have information on its new resistant starch ingredient that will be marketed under its Promitor brand of dietary fibers. Doris Dougherty, a senior food scientist with Tate & Lyle, will give a presentation on Promitor resistant starch on July 29 at the pavilion for poster sessions.

MGP Ingredients, Inc., Atchison, Kas., will exhibit at booth No. 4739. The company recently changed the name of its resistant starch to Fiberysym RW from Fibersym 70. Fibersym RW contains 85% fiber on a dry basis, said Steve Ham, director of marketing for MGP Ingredients.

Tate & Lyle to sell European starch operations

LONDON — Tate & Lyle, P.L.C. has agreed to sell its starch facilities in the United Kingdom, Belgium, France, Spain and Italy to Syral SAS, a subsidiary of Tereos of France. When the deal is completed, which could come as early as September, London-based Tate & Lyle will receive £209 million ($429 million) subject to closing adjustments relating to cash, debt, working capital and capital expenditure. Tate & Lyle plans to use the proceeds of the sale as part of a share buy-back program.

"The sale of these starch facilities marks another important step in focusing Tate & Lyle’s business on its value-added strategy and reduces the impact of our exposure to volatile markets and to the E.U. sugar regime," said Iain Ferguson, chief executive for Tate & Lyle, when the deal was announced July 18.

The starch business recorded sales of £520 million in the year ended March 31 and a profit before interest and exceptional items of £38 million. On March 31 the business had gross assets of £253 million and net operating assets of £184 million. The disposal is expected to result in an exceptional loss of about £20 million after restructuring costs.

This article can also be found in the digital edition of Food Business News, July 24, 2007, starting on Page 73. Click here to search that archive.

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