A cost-effective and environmentally friendly process for extracting rice starch — by breaking down milled rice into its starch and protein fractions — has proved elusive. For nearly 60 years, the processing of rice starch has hardly changed, relying always on the action of a corrosive alkali, sodium hydroxide, to slowly dissolve rice protein and release the starch.
But this procedure, and the copious amounts of salt waste it generates, could soon be replaced with a more benign and efficient separation method.
Harmeet Guraya, a food technologist with the U.S. Department of Agriculture’s Agricultural Research Service (ARS) Southern Regional Research Center in New Orleans, Louisiana, U.S., believes his approach could help rebuild the rice starch and protein production industries in the U.S., which now imports about $40 million worth of rice starch each year.
The technology, which could be commercially available by 2006, 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.
VALUABLE AND VERSATILE
Rice is valued both as a staple and for the versatility of its components.
Rice starch — with its tiny granule size, neutral taste and soft mouthfeel — can be found in a wide range of foodstuffs. It is 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. It can also be found in more unexpected consumables, like frozen foods, meat products, and thanks to rice starch’s hypoallergenic nature, pharmaceuticals and cosmetics.
Long-, medium- and short-grain rice contains 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 ap
plications in industry. For instance, starch from waxy rice exhibits high freeze-thaw stability. "Because this starch holds water well, a food product won’t lose valuable moisture or juices when it’s frozen and then thawed," said 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.
Rice bran too 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, said 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."
HIGH PRESSURE HOMOGENIZATION PROCESS
Processes that separate and extract bound-up rice fractions can however, alter the nutritional qualities of starch and protein and are often not cost effective.
Milled rice contains agglomerates 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. That degrades the protein, leaving it bittertasting and unfit for human consumption. Salts and other potentially harmful waste products are also generated.
Guraya’s approach, which has been under development for four years, instead relies on very high pressure, supplied by 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 homo
geneously dispersed in a watery matrix. The starch and protein components can then be separated by traditional densitybased separation processes.
Guraya’s technology preserves valuable rice protein. "The protein from our processing has higher integrity and functionality," he said. "It hasn’t been degraded with pH adjustments and washings."
Guraya, established a cooperative research and development agreement with Sage V Foods, a rice-based products company, in 1999. Based in Los Angeles, California, U.S., with facilities in Freeport, Texas, U.S., 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 said. "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. "So far, the results from our tests are very encouraging," said Pete Vegas, president of Sage V Foods. "While there’s still some uncertainty about the costs related to the process, we’re very hopeful." WG
This research is part of Quality and Utilization of Agricultural Products, an ARS National Program. More information can be found on the website: