Author: Ronald C. Deis, Ph.D.
Rice is the number one food crop in the world. Although it is consumed mainly in the familiar whole kernel form, rice can also serve as the base material for a wide variety of ingredients.
In general, rice has enjoyed a rapid growth rate in processed foods despite its cost disadvantage versus other grains. Rice is considered a staple in the United States, where 85% of households have one or more packages of a rice product in their pantry. Health-conscious individuals perceive rice as very nutritious as does the U.S. Department of Agriculture Food Guide Pyramid, recommending 6 to 11 servings per day of rice, bread, cereal or pasta.
Containing little to no fat, no cholesterol, and minimal sodium, rice contains all eight essential amino acids, and is a good source of B-complex vitamins and essential minerals. Importantly, it is also non-allergenic and gluten-free. These factors combined make rice ingredients well-accepted by the consumer.
Varieties and milling products
Use of rice derivatives demands careful consideration of both the variety of rice crops available in the United States, and those steps involved in the milling of rice grain. The southern states are the primary producers of long grain rice (115.8 MM cwt.), while medium and short grain varieties (60.2 million cwt.) are grown primarily in California. California also produces some waxy, or sweet, and high-amylose types, as well as aromatic rices.
The cooking characteristics produced by the different varieties are due mainly to the amylose:amylopectin ratio of the starchy endosperm. This starch ratio can also affect the functionality of many rice ingredients derived from a particular variety. Amylose content ranges from 0% to 2% in waxy rice, 5% to 12% for short grain, 12% to 20% for medium grain, 20% to 25% for long grain, with a high amylose variety at 25% to 33%. Gelatinization temperature of the starch increases from 55°C to 80°C as the amylose content rises. (The general cooking characteristics of these varieties, as well as their physical differences are discussed in the December 1995, Food Product Design article “Truth of Grain: Formulating with Rice.”)
Rice enters the mill as rough or paddy rice. These are rice kernels still encased within the hull. The milling process then produces a number of rice forms.
In the first step of milling, the hull is removed. This gives the rice a brown appearance and a nutty flavor. Because the bran layer remains intact during this initial phase, the kernel maintains its nutritional content. This form is called brown rice. Further abrasion removes the bran layer, resulting in regular-milled white rice, also called milled or polished rice. This is often enriched with additional vitamins, minerals and fiber to provide nutritional values similar to those of brown rice.
Rice can also be parboiled using a steam pressure process that soaks, steams and dries the paddy rice prior to milling. This ensures a firmer, more separate grain that produces higher yields of whole kernels, or “head rice,” while improving the nutritional content.
Finished rice can also be pre-cooked (instantized, pregelatinized) and dried to decrease preparation time of the whole kernel. Final yields of the milling process are 55% whole kernels, 20% hulls, 15% broken kernels, and 10% rice bran and polish.
The majority of whole rice kernels, especially Grade #1, are used as is with the exception of special crops. This leaves the derivatives, which are the focus of the remainder of this article.
The rice hulls are inedible, but can be used in various non-food applications. They contain primarily cellulose, ash (mostly silica), pentosans, lignin, and trace amounts of protein and fat. These are used as fuel and mulch, in abrasives, and in bedding and litter.
The broken kernels, or “second heads,” are those considered less than three-fourths of a kernel. These are primarily used for blending and making rice flour. Brewers rice, the smallest broken fragments, are used primarily for brewing and as a carbohydrate source in pet foods.
Nutritional value of bran
The composition of rice bran, like the kernels, varies based on the source and the milling process. On average, rice bran has approximately 3.2 kcal/gram, contains 8% moisture, and 20% to 30% total dietary fiber, mostly insoluble. It also acts as an excellent source of B vitamins and minerals.
The protein content of rice bran ranges from 12% to 20%, depending on pre-treatment. Protein digestibility and nutritional value are high, with a protein efficiency ratio (PER) of 1.6 versus 2.5 for casein.
Comprised of 16% to 22% fat, the fatty acid composition of rice bran is roughly 19% saturates (primarily palmitic), 41% monounsaturates (primarily oleic acid), and 36% polyunsaturates (primarily linoleic acid).
While the majority of rice bran from milling is used in rice mill feed, recognition of rice bran’s significant health benefits has increased its use in a range of foods beyond its current health store supplement status.
Research from a number of sources, including the USDA, the University of Minnesota, and the University of Massachusetts at Lowell, has shown the positive effects of rice bran on laxation, cholesterol reduction, and renal calcium reduction. Isolation of an antitumor polysaccharide has also been reported.
Research at the University of Massachusetts indicates that rice bran and rice bran oil reduce low-density lipoproteins (LDL), often referred to as the “bad cholesterol.” According to one USDA study, conducted by Kahlon and coworkers, individuals with moderate hypercholesterolemia given a diet supplemented with 35.5 grams of full-fat rice bran per day for 18 days, reported a 4% to 10% reduction in LDL cholesterol. Thirty grams per day of defatted rice bran did not promote the same effect.
Rice wax, oryzanols and sitosterol - all components of rice bran - have been shown to lower serum cholesterol. Oryzanol, a mixture of ferulic acid esters and triterpenoid alcohols, represents 20% to 30% of the unsaponifiable matter of the oil, or 1.1% to 2.6% of the total oil.
Rice has also been used significantly for its hypoallergenic properties. Since rice does not contain gluten, gluten-intolerant individuals can safely digest it. Patients with celiac sprue disease can generally tolerate rice and corn, but must avoid gluten-containing wheat, oats, barley, rye, and triticale.
Preserving the integrity of rice bran
In the past, storage of rice bran has presented a problem due to the presence of a powerful lipase enzyme. In 1985, however, the USDA developed a rice bran stabilization method based on dry heat extrusion, which destroys the enzyme immediately after milling.
A joint venture (Calbran, Redondo Beach, CA) was formed between Comet Rice and extruder manufacturer Brady International to take advantage of this process. This company offers several rice bran products which vary in total dietary fiber and oil content. These include a stabilized natural rice bran (18% to 22% oil), a low-fat natural rice bran (6% to 9% oil), and a defatted version (0.5% to 1.5% oil).
Ribus, Inc. of St. Louis, MO, has also developed a patented non-heat inactivation method of stabilization. A protease enzyme destroys the lipase, resulting in less heat denaturation of the stabilized rice bran. According to Ribus’ president Steve Peirce, the stabilized bran can then be separated into a number of soluble and insoluble fractions with a wide array of functional properties. These products include a natural emulsifier containing 16% protein, 18% fat and 12% carbohydrate; a vitamin/mineral concentrate; a rice bran fiber; and a dough conditioner.
The dough conditioner, which contains protein, lipids, and pentosans from rice bran, is designed to improve machinability, leavening, and retard staling in breads and cakes. It has also been used in cookies, pies, and tortillas.
“The emulsifier, which can be labeled ‘rice extract,’ already has applications in several crackers, baked goods, and salad dressings, and is currently being evaluated in several extruded snack food items, such as rice and cereal products,” says Peirce. “Its ability to replace mono- and di-glycerides in the production of pasta, reduces extruder wear and tear, decreases torque, and improves quality.”
According to Peirce, North Dakota State University has also seen positive results using this emulsifier in the production of pasta made from semolina. Other applications include granola bars, icings, natural foods, cosmetics and pharmaceuticals.
Extracting the oil
Rice bran oil, a popular cooking oil in Japan, is noted for its nutrition and delicate flavor. The demand for rice oil in Japan exceeds the country’s production capability, which has been estimated at about 100,000 metric tons annually. In 1993, a partnership was formed between Riceland Foods, Inc., Little Rock, AR, the worlds largest miller of rice, and Itochu Corporation, a leading global trading company, to produce and market rice bran oil. The result was Rito, the only U.S. source of rice bran oil, according to Don McCaskill, director of research and development at Riceland.
Rice bran is collected at Riceland’s mills, where it is then heat-stabilized and pressed into pellets. These are transported to Stuttgart, AR, where oil is extracted and refined. This crude rice bran oil contains 90% to 96% saponifiable lipids and 4.2% unsaponifiable lipids, including those components noted for the reduction of LDLs. Fatty acid composition is given below:
- Palmitic 16:0 - 4.0%
- Stearic 18:0 - 2.0%
- Oleic 18:1 - 45.0%
- Linoleic 18:2 - 34.0%
- Linolenic 18:3 - 1.5%
Oryzanol, which seems to have the greatest effect on lowering serum cholesterol, is highest in crude rice bran oil. Alkali refining and bleaching lower the level of oryzanol, so minimal refining results in the highest nutritional value.
Refining the endosperm
Products derived from rice endosperm have enjoyed growing popularity over the last several years. According to Dr. Eugene Sander, president of Zumbro, Inc., Hayfield, MN, this is due to a number of factors:
- User-friendly label recognition; broad ethnic appeal.
- Hypoallergenicity - based both on the consumer’s low sensitivity to rice protein, and its processing, which omits sulfur dioxide, a necessary process aide in the corn wet-milling industry.
- The fact that they can easily be certified organic and natural, and are heavily favored by the health food industry.
- The fact that micro and macro structures of the kernel make component separation and further processing simpler, thus eliminating the need for chemical processes.
Rice starches have also been a popular ingredient in fat-reduced products, partially due to the above characteristics, but also due to the physical characteristics of rice starch. Rice starch granules are very small relative to other starches. The granules are polygonal in shape and are about 2 to 8 microns in diameter. In comparison, corn averages about 15 microns, tapioca about 20 microns, and potato ranges from 15 to 100 microns.
When used in an ungelatinized form, these naturally small particles can produce a smooth texture. Rice starch gels tend to be smooth, creamy and spreadable, with a clean flavor.
“Rice starches have an excellent natural heat and freeze/thaw stability,” says Gil Bakal, director of marketing for A&B Ingredients, Inc., Fairfield, NJ. “They also have lower gelatinization temperatures than cornstarch. In addition, we can provide cross-linked, modified versions for more shear and acid resistance.”
The potential exists for a wide variety of rice derivatives based on the variety of grain, which influences amylose:amylopectin ratios, granulation, and type of milling. Starches or, more readily, flours could be prepared from parboiled or instantized rice. These processes influence the rate of granule swelling as well as resistance to shear. Required properties can be discussed with starch suppliers or flour millers.
Remy Industries, a Belgian company, produces about 70% of the world’s rice starch supply, and is represented in the United States by A&B Ingredients, Inc. Their business in Europe has grown largely from the use of rice products developed for the pharmaceutical industry. Here in the United States, according to Bakal, much of their business is based on a waxy rice starch which is 99+% amylopectin, and a starch with an 80:20 amylopectin:amylose ratio. Modified waxy rice starches are available for additional acid and shear stability.
In addition to physical properties, one must bear in mind chemical attributes when looking for rice starch or flour products. Due to their pharmaceutical origins, these starches are high in carbohydrate purity. Fat, ash and protein contents are minimized. Moisture content is approximately 15%. Pregelatinized versions, a waxy rice flour, and a protein concentrate are also available.
According to Joseph Hall, technical manager, California Natural Products (CNP), Lathrop, CA, the use of rice starches has grown primarily in response to health foods, the hypoallergenic sector, and the organic sector. Another fast-growth area for rice-based ingredients, says Hall, is the oral rehydration products industry - products that prevent dehydration caused by dysentery, plague and cholera.
The company’s business has grown through customized production, resulting in a wide range of rice starches, maltodextrins, syrups, flours, pregelled flours and starches, and rice protein concentrate. Hall notes that these rice starches are produced without alkali and retain some native protein, resulting in better dispersion and unique gel properties.
These starches contain from 2.5% protein (considered “low protein”) to 6% protein, and typically have less than 5% moisture. According to Hall, the waxy variety starches provide excellent freeze/thaw stability with no modification.
Rice flour is available from a number of sources. Flour can be custom-milled from waxy rice, short-, medium- or long-grain rice to produce flours which contribute different levels of crispness, tackiness or crunchiness to a food. Brown rice flour is desirable for the nutritional value of the bran and/or, for its more natural appearance.
Different granulations are available - from white or brown rice meal through rice flour with its very fine granulation. Brown rice flour is produced by blending white rice with stabilized rice bran, which prevents the flour from becoming rancid. Then the combination is co-milled. Flour from organically grown rice is also available.
Rice flour can be used to produce gluten-free rice bread for gluten-sensitive individuals, but hydroxypropyl methylcellulose is required for proper leavening. These breads tend to stale very rapidly, limiting their distribution. Rice flours, syrups, and starches can be used to provide a number of gluten-free baked products. This is a very small industry, but very necessary for individuals with celiac disease. Further information about the use of rice flour in baking can be found in an American Institute of Baking Research Department Technical Bulletin (Volume XVIII, Issue 3, March 1996), authored by Hall.
A healthy alternative
Rice syrups, syrup solids and maltodextrins are also available, but differ according to source and the method of processing. These vary by supplier.
According to Sander, Zumbro’s process starts with a mixture of flour and water which is thermally processed in the presence of an amylase enzyme to hydrate and open up the starch granule. A second amylase enzyme treatment, called saccharification, breaks the partially hydrolyzed starch granule into lower molecular weight fractions. The length of the saccharification step results in the generation of maltodextrins with a dextrose equivalence (DE) up to 20 or syrups with 20 DE.
“The choice of amylase enzymes used can control the final carbohydrate profile of the finished maltodextrin or syrup,” Sander notes. “Typically, specific amylases are used to generate maltodextrins and syrups up to 42 DE, with carbohydrate profiles similar to their recognized, corn-based counterparts. Hence, these rice maltodextrins and syrups have similar chemical and physical characteristics, and can be used as replacements for these counterparts.”
Zumbro has developed a 90 DE dry rice syrup that can be used alone or blended with other maltodextrins and syrups to create specific profiles. A water-gelling fat replacer and adhesive was also developed by leaving the rice protein with a maltodextrin or syrup, then microparticulating the mixture prior to spray-drying. These can be custom-blended. The company is also able to produce organically certified products for specific needs.
According to Hall, “CNP syrups are enzymatically produced from USDA #2 rice kernels selected from a variety of rice sources. These are typically white rice, brown rice or partially polished brown rice.”
The rice syrup contains protein as well as residual fat and, unlike corn syrup, rice syrups are free of sulfites.
“Our rice syrups are converted to specific profiles within a 26 to 70 DE range, and are offered in two clarity stages - lightly filtered and clarified,” continues Hall. “Clarified syrups contain less protein and fat than the lightly filtered versions. A high-maltose 42 DE rice syrup (white or brown) is also available, and all DEs and clarity-types can be obtained organically certified.” The CNP process also yields a 5 DE and an 8 DE rice maltodextrin and a range of 26 to 50 DE syrup solids.
Since rice products are roughly three times the cost of corn, these syrups and maltodextrins cannot compete economically, but they do fill specific nutritional and functional needs, Hall notes. For instance, lightly filtered rice syrups offset the beany note in soy milks more effectively than corn syrup. Brown syrups are heavily favored in granola products, and rice products have a much higher acceptability in health and nutraceutical markets.
Overall, the rice ingredient industry has been inhibited by the importance of rice as a world food staple, which has kept its economic value high. The growth of the health food industry and growing consumer interest in nutrition has generated a largely custom industry, which has resulted in a diverse range of ingredient possibilities. The food product developer benefits from the range of selections, but needs to remain aware of the chemical/functional differences between the many ingredients available.
The Value in the Grain
The world harvest of rice in 1995 was 525 million metric tons. Wheat and corn are close in harvest tonnage, but 20% of wheat and 65% of corn go to feed livestock. Rice is a daily staple for 2.7 billion Asians, and comprises 25% to 80% of their caloric intake.
Thirty-six percent of the world crop is grown in China, but only 8% of that is exported. Most of the world crop is consumed where it is grown. According to USDA data, the leading 1996 exporters of rice are Thailand, India, Vietnam and the United States. Leading importers are Indonesia, Brazil, China, Japan and Iran.
The U.S. rice crop is grown on about three million acres in seven states - Arkansas, which accounts for 40% of U.S. production, California, Florida, Louisiana, Mississippi, Missouri and Texas. Over 90% of the rice consumed in the United States is grown here; 40% of U.S.-grown rice is exported. The United States supplies about 17% of the rice exported world-wide.
The USDA October 1996 projection for the U.S. rice crop was 176.1 million hundredweight (cwt.), and the projected season average farm price was $8.50 to $9.50 per cwt. There continues to be a strong domestic and export demand for rice.
A $1.5-billion category in the United States in 1994, the sale of rice and rice products is expected to exceed $2 billion by the year 2000. Due to the high value of rice grain, rice derivatives are a small percentage of this. Because grain prices are high, ingredient prices remain high and must compete on the basis of unique nutritional and functional attributes.
Per capita consumption of rice has tripled over the past 30 years, outstripping population growth 220% in the past three years - the average American now consumes 25 pounds of rice per year. Fifty-four percent of the rice consumed in the United States is for direct food use. Twenty-seven percent (nearly double the 1980-81 rate) is used in processed foods, and 19% is used in the production of beer.
In terms of food categories, which are the heaviest users?
According to USDA data, the cereal industry uses nearly six million cwt. per year (includes all grains, plus flour), packaged mixes use approximately 3.2 million cwt. per year (specialty; long, medium grains), and pet foods use about 4.4 million cwt. per year (primarily brokens and flour). After that, the other fast-growing categories are crackers and snacks, rice cakes, frozen dinners, baby foods, candy and soups. Beer remains relatively stable at 11 million cwt. of rice used per year.