Going With the Grain

ARS scientist finds a more natural way to separate rice's valuable starch and protein.

It's the creamy component in some ice creams and yogurts, a satisfying alternative to fat in reduced-fat foods, and a thickener that adds a smooth finish to soups and sauces. While many consumers aren't able to detect it, rice starch—with its tiny granule size, neutral taste, and soft mouthfeel—can be found in a wide range of foodstuffs.

This list also includes more unexpected consumables, like frozen foods, meat products, and—thanks to rice starch's hypoallergenic nature—even pharmaceuticals and cosmetics.

But a cost-effective and environmentally friendly process for accessing rice starch—by breaking down milled rice into its starch and protein fractions—has been elusive. For nearly 60 years, the processing of this starch has hardly changed, relying always on the action of a corrosive alkali, sodium hydroxide, to slowly dissolve rice protein and release the starch.

This procedure, and the copious amounts of salt waste it generates, could soon be replaced with a more benign and efficient separation method developed by food technologist Harmeet Guraya. Guraya, who works at ARS's Southern Regional Research Center in New Orleans, Louisiana, believes his approach could help rebuild the rice starch and protein production industries in the United States, which now imports about $40 million worth of rice starch each year.

The technology—perhaps in commercial use by next year—could also increase the bottom line for U.S. rice farmers and millers, who have historically lost out on valuable rice derivatives because of a lack of cost-effective processing.

Why Rice?

Whether it's long-grain, sticky, or a specialty type like aromatic, rice is fast becoming a popular grain. And its components—starch, protein, and bran—are equally desirable.

Long-, medium-, and short-grain rices contain varying ratios of the two starch components, amylose and amylopectin. Amylopectin is found in highest concentrations in short-grain (also called "sticky" or "waxy") rice. Amylose is highest in long-grain rice—enabling these grains to be separate and fluffy when cooked.

Each possessing its own unique chemistry, these rice starches have different applications in industry. "With cosmetics and tableting, the kind of starch used is not necessarily important," explains Guraya, "but with foods, starch type does matter."

For instance, starch from waxy rice exhibits high freeze-thaw stability. "Because this starch holds water well, a food product—say Buffalo wings—won't lose valuable moisture or juices when it's frozen and then thawed," says Guraya.

Rice protein is valued for its easy digestibility. Baby foods and formula and special dietary goods rely on a steady stream of this protein, since some children and adults are sensitive to the proteins in other grains.

And the bran, which sits just under rice's outer hull, is getting increasing acclaim for biologically active compounds that may act as powerful, cell-protecting antioxidants. High in dietary fiber, too, bran can impart a hearty flavor to breads and other baked goods.

Despite its potential, says Guraya, "most of the rice bran produced in the United States is a byproduct of milling and is used for animal feed or simply discarded."

While it seems a treasure trove of nutritional, food, and sensory possibilities, a grain of rice doesn't easily give away its valued parts. Processes that separate and extract bound-up rice fractions can alter the nutritional qualities of starch and protein and are often not cost effective.

Without a Grain of Salt

Milled rice contains agglomerates, or clumps, of starch and protein. Typically, rice is steeped in sodium hydroxide for several hours to dissolve the protein and let the starch molecules break free. But that degrades the protein, leaving it bitter-tasting and unfit for human consumption. Salts and other potentially harmful waste products are also generated.

Guraya's approach instead relies on very high pressure, supplied by a special homogenizer known as a microfluidizer, to physically split apart the starch-protein agglomerates. A single pass through this piece of equipment yields many small, individual particles of starch and protein homogeneously dispersed in a watery matrix. The starch and protein components can then be separated by traditional density-based separation processes.

And Guraya's technology preserves valuable rice protein. "The protein from our processing hashigher integrity and functionality," he says. "It hasn't been degraded with pH adjustments and washings."

Guraya, who's been developing his rice starch separation process for about 4 years, established a cooperative research and development agreement with Sage V Foods, a rice-based products company, in 1999. Based in Los Angeles, with facilities in Freeport, Texas, Sage V Foods produces rice-based ingredients that are sold to major U.S. food companies.

An important part of their collaboration has been trying out a scaled-up version of Guraya's technology. "Being able to produce rice starch in the lab is not enough," he says. "We have to show that it can be done in a large-scale, continuous process."

A complete production line was set up in March 2004, and thousands of pounds of rice starch were generated. The samples, from different kinds of rice, are currently being analyzed by Sage V Foods.

"So far, the results from our tests are very encouraging," says Pete Vegas, president of Sage V Foods. "While there's still some uncertainty about the costs related to the process, we're very hopeful."

Guraya continues to offer technical advice to Sage V Foods, but he's moved on to another project that's an ideal complement to his rice starch technology. "It's a method for extracting protein from rice bran," he says, "and could ultimately make use of bran's other fractions—oil and starch—which are currently being underused."—By Erin K. Peabody, Agricultural Research Service Information Staff.

This research is part of Quality and Utilization of Agricultural Products, an ARS National Program (#306) described on the World Wide Web at www.nps.ars.usda.gov.

Harmeet Guraya is with the USDA-ARS Food Processing and Sensory Quality Research Laboratory, 1100 Robert E. Lee Blvd., New Orleans, LA 70124-4305; phone (504) 286-4258, fax (504) 286-4419.

"Going With the Grain" was published in the February 2005 issue of Agricultural Research magazine.