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Rice Starches
13
Rice Starches: Production and Properties Cheryl R. Mitchell Creative Research Management, Stockton, California, USA
I. Rice Production and Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Rice Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Rice Milling and Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II. Uses of Milled Rice and Rice By-products . . . . . . . . . . . . . . . . . . . . . . . . . 1. Milled Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. By-products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III. Preparation of Rice Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Traditional Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Mechanical Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV. Properties of Rice Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. General Properties Unique to Rice Starch . . . . . . . . . . . . . . . . . . . . . . . 2. Pasting Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Factors Affecting Rice Starch Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Rice Variety: Common Versus Waxy . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Protein Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Method of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI. Rice Starch Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
569 569 570 571 571 572 573 573 574 574 574 575 575 575 576 576 577 577 578
I. Rice Production and Composition 1. Rice Production Cultivated rice (Oryza sativa L.) is a major world food crop. Only wheat surpasses rice with regard to production and food use. About 90% of the world’s rice is produced and consumed in Asia.1 The production and consumption of rice in the United States, while not a staple food, increased more than 40% during the period from 1980 to 19952 and an additional 25% from 1995 to 2005.3 The price of rice in Starch: Chemistry and Technology, Third Edition ISBN: 978-0-12-746275-2
Copyright © 2009, Elsevier Inc. All rights reserved
570 Rice Starches: Production and Properties
Table 13.1 Typical amylose content (%) by grain length of commercial US rice varieties9 Long
Medium
Short
Waxy short
20–25
14–18
15–23
0–2
the United States showed an extraordinary increase during 2007, increasing by over 75% of its price during 2003. This increase was due to the increased demand for rice in the US and international markets, without an equivalent increase in production. Worldwide usage of milled rice in 2005 was reported to be 406 million metric tons (mmt), with the United States reportedly producing 10.2 mmt and using 5.7 mmt.4 Major rice producing areas include China, India, Indonesia, Bangladesh, Thailand, Burma, Japan, Korea, Vietnam and the Philippines. Other than Asia, major areas of rice production include Brazil, the United States, the Malagasy Republic, Egypt, Columbia, Nigeria and Italy.5 Major rice producing areas in the United States, in descending order of production, are Arkansas, California, Florida, Louisiana, Mississippi, Missouri and Texas.6 The US focus is on three grain types: short; medium; and long. Long grain represents approximately 70% of the total US rice production. Approximately 93% of the California rice crop is medium grain, while in the south about 84% of the rice grown is long grain and 16% is medium grain.7 In commercial crops grown in the US, the amylose content is to some extent associated with grain length, with long grain varieties having a higher amylose content than medium or short grain types (Table 13.1). Waxy rice currently cultivated in the US is a short grain type; long grain waxy rice varieties are available in the orient. Experimental rices having amylose contents of up to 40% (in 2% increments) have been reported, but are not commercially available. Rice varieties are distinguished by their amylose content. There are two basic types: common and waxy. Waxy rice has an amylose content of 0–2%. Common or regular rice varieties are referred to as having amylose contents that are low (9–20%), medium (20–25%) or high (25%) amylose. The availability of waxy rice is usually limited and large requirements for waxy rice are contracted in advance to ensure a supply. A typical variety of waxy rice produced in the US is Calmochi-101.9 Waxy rices are also referred to as ‘glutinous’ rices, due to their sticky cooking property, or as ‘sweet’ rices because of their use in Japanese ‘mochi’ cakes. Examples of lowamylose, medium-grain varieties are Calrose, Nato and Vista. Low-amylose, shortgrain varieties are Caloro, Colusa and Nortai. Intermediate-amylose, long-grain varieties are Belle Patna, Bluebelle, Labelle and Starbonnet.10
2. Rice Milling and Composition Harvested rice grain is composed of the outer hull, the bran layer and the inner white starchy endosperm. Rough rice, which is rice with the hull intact, is the form in which rice is stored for use throughout the year. Removal of the hull produces what is known as brown rice. Once the hull is removed, inadvertent scratching of the inner
II. Uses of Milled Rice and Rice By-products 571
Table 13.2 Typical mill yields and composition of products and by-products from rough rice13 Fraction
Yield from rough rice, %
Protein, N 5.95, %
Crude fat, %
Crude fiber, % d.b.
Crude ash, %
Nitrogen-free extract, %
Hull Brown rice Bran Polish Milled rice Head Seconds Brewers
18–28 72–82 4–5 3 64–74 56 9 3
2–4 7–15 12–17 13–16 6–13
0.4–0.8 2–4 15–22 9–15 0.3–0.6
48–53 1 9–16 2–5 0.1–0.6
15–20 1–12 9–16 5–9 0.3–0.7
26–34 79–90 40–49 54–71 84–93
bran layer releases lipases which effect lipolytic hydrolysis and oxidation of the kernel oil. The subsequent rancidity results in bitter, soapy, off-tastes. Normally, once the hull is removed the rice is sold immediately for use as brown rice or continues to the next step of milling, which is bran removal and polishing. Abrasive milling removes the outer bran layer to produce partially polished rice or, after polishing to remove the entire bran layer, white rice. Rice bran or polish may be subsequently stabilized by heat treatment to inactivate lipases. Stabilized rice bran has found use as an ingredient in human-grade processed foods. After removal of the bran layer and polishing to the desired degree, the residual milled rice is divided into several fractions depending on size. Total milled rice contains head rice (whole unbroken kernels and kernels that are at least three-fourths of an unbroken kernel) and broken rice. Further screening of the total milled rice separates the head rice from second heads (largest of the broken kernels, usually between onehalf and three-fourths of an unbroken kernel) and brewers rice (broken kernels that are about one-fourth of an unbroken kernel). The relative amounts in each category are a function of rice variety, growing conditions, harvesting, drying, handling and the type of milling operation. Typical mill yields and their compositions are given in Table 13.2.
II. Uses of Milled Rice and Rice By-products 1. Milled Rice Milled rice is comprised of head rice, second heads and brewers’ rice. Unlike most grains, the primary use of rice is its direct consumption as a table food. The two other major uses are in processed foods and to make beer. Head rice is the only rice that is used for table consumption and represents 82% of the milled rice. Broken rice, which is comprised of second heads and brewers’ rice, is considered to be a byproduct of milling and represents 18% of the milled rice. Broken rice generally has a lower market value than head rice. Due to the relatively high cost of head rice compared with other grains, lower cost by-products of head rice production are preferred for use in processed foods and beer production. In 2004–2005, the USDA estimated that the principle outlets for milled rice in the US included 52% for direct food use,
Free sugars, %
1.3–1.5 6.4–6.5 0.2–0.5
572 Rice Starches: Production and Properties
29% for use in processed foods and 17% for use as a beer adjunct.13 While use in beer has remained rather constant, use in processed foods grew 38% during 1985– 1995, with the fastest growing product categories being pet foods and rice ingredients.14 Obviously, an imbalance exists between the availability of milling by-products (18%) and use in processed foods (29%). Increase in demand for second heads and brewers rice by processed food manufacturers has resulted in a shortage of these by-products. Additionally, more and more rough and brown rice is being exported, thereby limiting even more the supply of milling by-products in the US. It is obvious that, as more and more processed food products are developed, that mill run rice (milled rice that has not been size separated) will have to be used. The cost of mill run rice is typically 2–3 times that of corn. Because of the economic disadvantage of rice over other grains, future use of rice or rice ingredients (including starch) in processed foods will be dependent on unique characteristics and nutritional aspects that rice products or ingredients contribute to processed food products. In 2006, the USDA advocated the consumption of at least six servings of grains per day, of which three should be wholegrain. The latter prompted an increase in the use of wholegrains in food products. Development of novel wholegrain rice products was catalyzed by the development of wholegrain brown rice ingredients, such as RiceLife®, which made it possible to make wholegrain beverages, frozen desserts and even wholegrain non-dairy yogurts. Other brown rice ingredients, such as brown rice or brown ricemilk syrup, and their resulting products have greatly expanded the use of brown rice throughout the food and beverage industry. Many processed foods, such as cereals, packaged mixes, pet foods, rice cakes and baby foods, were developed and incorporate broken rice, meal or flour. However, in recent years ingredients derived from milled rice, and now brown rice, have not only greatly extended the use of rice in processed foods, but have also been the basis for the development of novel food products. Commercially available rice ingredients mimic those products available from the corn wet-milling industry. Rice starch, rice proteins, rice syrups, rice dextrins and rice hydrolyzates are finding increased use. All these ingredients are uniquely different from their corn-derived counterparts. Products based entirely on rice starch-based ingredients, such as vinegars, oral rehydration solutions, non-dairy beverages, frozen desserts and puddings, are stable commodities in the marketplace, often taking the lead in sales over their corn or soy counterparts in natural foods and conventional marketing segments. Whole brown rice, while still in its developmental infancy, has great potential for growth as a processed food ingredient, due to its unique characteristics. Rice starch from white rice or brown rice exhibits unique properties as functional ingredients in many food categories.
2. By-products Hulls A major fraction of paddy rice is the hull. The hull is non-digestible, fibrous and abrasive in character, and has a low bulk density and a high ash content. It is used only in limited, low-value applications, such as in animal feed, in chicken litter, as a juice pressing aid and as fuel.15
III. Preparation of Rice Starch 573
Bran
Unstabilized bran and polish have been used almost exclusively for animal feed, due to the bitter flavor that develops from the lipolytic action of enzymes on the oil found in them. However, development of a thermal process that inactivates the lipases has resulted in a stabilized rice bran product that is suitable for the food industry. The impressive nutritional qualities of the oil, fiber, carbohydrate and proteins of rice bran have made it a valuable food material. Removal of fiber from the bran by physical16,17or enzymic18,19 processes produces a milk-like product having desirable nutritional and functional properties. The nutritional composition of the rice bran milk product described by California Natural Products has been shown to match the nutritional requirements of an infant formula. Originally, the anti-nutritional factor of the residual phytates was of concern. However, as of 2005, phytase enzymes are suitable for use to break down these phytates. Rice bran oil can be extracted from either stabilized or unstabilized bran. The by-product resulting from stabilized bran extraction is suitable for human food use. Stabilized rice bran is currently being used in baked goods, energy bars and protein fortification of powdered drink formulations.
III. Preparation of Rice Starch Rice starch is preferably prepared from broken rice for economic reasons, as discussed above. There are currently two commercial methods of rice starch isolation: traditional and mechanical. The traditional method involves alkali solubilization of rice protein, while the mechanical method releases starch via a wet-milling process. Worldwide production of rice starch amounts to about 25 000 metric tons.20 Approximately 75% of this was manufactured by the Belgium company Remy Industries, which has been manufacturing rice starch by the traditional alkali method for more than 100 years. Until 1990, rice starch prepared by the alkali process was the only commercially-available rice starch.
1. Traditional Method The traditional method of starch production involves alkali solubilization of the glutelin which constitutes approximately 80% of the protein in rice. This method has been described by Hogan,21 and is utilized in some form by almost every rice starch manufacturer (with the exception described below). It produces a starch containing 1% protein. The protein by-product of this process, while good-quality protein, has a distinct aftertaste (alkali, salt and amino acid), making it not easily acceptable as a food ingredient. In the alkali process, broken milled rice is steeped in 0.3–0.5% sodium hydroxide solution for up to 24 hours at temperatures that may vary from room temperature to 50ºC. This steeping process softens the grain and effects solubilization of the proteins. Wet-milling of the steeped grain, in the presence of sodium hydroxide solution, releases the starch, producing a starch slurry. The starch is kept in suspension and stored for
574 Rice Starches: Production and Properties
10–24 hours to further dissolve the proteins. The cell wall material is then removed by filtration, and the starch slurry is washed with water (to remove the protein), neutralized and dried. The commercial drying process, which necessarily involves initially low air temperatures to prevent gelatinization, has the potential for allowing high bacterial growth and, consequently, total plate counts must be carefully monitored. An advantage to the alkali process is the ease with which the alkali solution allows for modification of the starch, since most modification reactions are done at high pH values. A disadvantage is the alkali waste water that is produced and its ecological consequences. These two problems, along with the limited economic potential of rice starch, are the primary reasons why the alkali process has not been used in the US since 1943.22
2. Mechanical Method The mechanical method of rice starch production is a wet-milling process first used on milled rice that permits optional protein removal. Protein is not solubilized in this process, but rather is removed by physical separation after the starch granules and protein have been mechanically liberated from the starchy endosperm. The released starch granules exist in clumps or small aggregates of 10–20 m in diameter. Products containing from 0.25% to 7% protein may be produced by this commercial method. If the protein is removed, the resulting starch is similar in appearance to that produced via the traditional process. However, differences in pasting and functional characteristics (described below) exist. Unlike alkali-solubilized protein, the protein resulting from the mechanical process is a valuable by-product, having excellent taste qualities suitable for the food industry. A current patent pending variation of the mechanical method, as developed by this author and practiced by Creative Research Management, utilizes whole brown rice. The resulting whole brown rice starches are unique and contain both protein and rice bran oil. Both of these constituents of the whole brown rice impart novel physical properties to the starch-containing fraction. The advantage of the use of these types of starches is relatively new and is just now becoming available to the industry as an ingredient. The primary advantage of the mechanical process is the variety of starches of different protein and fat content that may be produced, and their respective unique functional properties. Also, the waste water from the mechanical process has no negative environmental impact and is quite suitable for land application.
IV. Properties of Rice Starch 1. General Properties Unique to Rice Starch Traditionally, there have been basic properties associated with rice starch that have given it advantages over other starches. These characteristics include hypoallergenicity, digestibility, consumer acceptance, bland flavor, small granules (2–10 m), white color, greater freeze–thaw stability of pastes, greater acid resistance and a wide range of amylase:amylopectin ratios.
V. Factors Affecting Rice Starch Properties 575
Rice is considered to be hypoallergenic, because it does not possess gliadins or parts of proteins that are normally associated with the allergenic responses, such as those that may be caused by wheat, barley or rye. Because of its extensive table use, consumers perceive rice as a balanced food, as indeed it is. Its better digestibility, as compared to other cereal grains, has led to its preferred use in infant and geriatric foods, to medical recommendations that rice be the first cereal grain given to infants, and to it being the preferred grain for recuperating patients. There is no specific scientific evidence to support why rice has this digestive advantage, only hundreds of years of anecdotal experience. However, research on the utilization of rice in oral rehydration solutions and in infant formulas is generating some understanding of the beneficial qualities unique to rice.23 The bland taste of rice starch, its whiteness and its small granule size have provided it with the advantages necessary in the manufacture of smooth gravies, sauces and puddings, having excellent mouthfeel and flavor profiles. Non-food uses of rice starch are also based on its small granule size; they include textile size, cosmetic and printing ink applications. A spray dried form of rice starch in which the individual starch granules are dried in aggregates has been developed by CNP. These porous starch spheres are advantageous with regard to their greatly improved dispersibility over other starches. The aggregates also have special properties associated with absorption of other solutes within the sphere structure and slow release for an improved distribution. Depending on the relative amylopectin:amylose ratio found in the rice, the starch can exhibit a variety of gelatinized textures and strengths, as well as resistance to acid. Overall, there are several basic factors that affect starch performance. These factors, which include rice variety, protein content, method of starch production and modification, are described below.
2. Pasting Properties The Rapid ViscoAmylograph (RVA) has been the preferred instrument for determining the pasting properties of rice flour and rice starches24,25 (see Chapter 8).
V. Factors Affecting Rice Starch Properties 1. Rice Variety: Common Versus Waxy The functionality of rice starch depends on the amylose:amylopectin ratio. Differences among rice starches made from long-, medium- or short-grain rice are insignificant relative to the amylose content. Rice starches made from common rice tend toward higher peak, cooked and cooled viscosities, as well as paste textures that are short and pasty. The texture of waxy rice starch pastes tends to be long and stringy (Table 13.3). Rice starch from common rice contains 0.3%–0.4% lipids, while waxy rice contains considerably less (0.03%). Complexes of these lipids are not easily removed from the starch, and are presumably responsible for the lack of paste clarity and the difficulty in clarification of starch hydrolyzates.
576 Rice Starches: Production and Properties
Table 13.3 Ranges of physicochemical properties of common and waxy rice starchesa,16
Amylose:amylopectin Bound lipid, % Initial paste temperature, ºC Peak temperature, ºC Brabender ViscoAmylograph, BU Peak Cooked Cooled Texture
Common
Waxy
20:80 0.2–0.4 65–74 91–95
2:98 0.02–0.03 61–64 69–71
560–1020 260–480 490–785 short
670–685 280–425 320–675 long
a
Prepared from US rice varieties by the mechanical method
2. Protein Content Residual protein can greatly affect the pasting and functional properties of rice starch. The higher protein content of alkali-processed rice starches appears to reduce the pasting curve viscosity. However, among mechanically processed rice starches, this is not the case. Mechanically produced rice starches with a relatively high protein content, in most cases, give higher pasting curve viscosities than those starches with a lower protein content. This relationship is particularly dramatized in the case of a waxy rice starch having a protein content of 4.1% versus one containing 0.7% protein. Increasing protein content among mechanically produced rice starches also significantly improves functional properties such as dispersibility, gel smoothness, stability during ultra-high-temperature (UHT) processing, acid resistance and freeze–thaw stability. It was found that freeze–thaw stability in common rice starch containing at least 2% protein is equivalent to that normally associated with waxy rice starch. Some of these functional advantages may be attributed to the unique sphere aggregates that are formed in the mechanical process on spray drying of the rice starch in the presence of the protein. After spray drying, rice starch containing 0.5% protein is present as clusters of 10–20 m. At 1.5% and again at 6.0% protein, increased formation of spheres of 30–70 m is observed. The presence of these spheres is responsible for improved dispersibility and gel smoothness.26 It has also been suggested that the unique absorption properties of the sphere aggregates may have application in holding and dispersement of flavor material or pharmaceuticals.27
3. Method of Preparation RVA curves compare commercial rice starch prepared by traditional alkali methods and rice starches prepared by the mechanical method. In the case of common rice starches, the onset of pasting appears to occur earlier (at lower temperature) and the final cooled viscosity appears to be lower for the starches prepared using alkaline conditions. The latter differences may be due to either rice type or the effect of alkali on granules. In the case of waxy rice starches, mechanically produced starches, in
VI. Rice Starch Applications 577
general, have both higher paste and cooled viscosities as compared to those prepared by the alkali method.
4. Modification Properties of rice starches are changed by chemical modification in the same way as the properties of other starches (see Chapter 18). Starches prepared via the alkali method have been modified to provide additional pH and shear stability. In general, hypochlorite-oxidized rice starch has a lower gelatinization temperature and lower maximum paste viscosity producing a softer, clearer gel. Hydroxypropylated rice starches have lower gelatinization temperatures, whereas crosslinked rice starch has an increased gelatinization temperature, increased shear resistance and acid stability.
VI. Rice Starch Applications Rice starch applications are normally discussed in terms of common and waxy types and are specified that way in Table 13.4. A 10% solution of a common rice starch, when sheered and gelatinized simultaneously, produces a product that resembles a solid shortening in texture. The waxy rice starches do not produce this same texture; however, they too have been used very effectively for fat replacement due to a fat-like mouthfeel when blended with other food products. Waxy rice starches also tend to resist oil uptake when used in batters for fried foods. Most applications of rice starch may be attributed to one or more of the characteristics already discussed that are unique to rice starch. Table 13.4 Rice starch applications16 Common
Waxy
Binder Confectioneries Dairy products Infant foods Processed meats Puddings/custards Sauces/soups Dusting agent Confectioneries Pharmaceuticals
Fat-mimetic Coatings for deep-fat frying Dairy products Pastries Processed meats Sauces/soups
Miscellaneous Cosmetics Laundry products Pet foods Photographic
Binder Canned foods Infant foods Rapid cook (microwaveable) foods Ready-to-eat meals Crispness agent Breakfast cereals Extruded snacks
Frozen foods Low-fat ice cream Non-fat sauces Source: reference 29
578 Rice Starches: Production and Properties
VII. References 1. Marshall WE, Wadsworth JI. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:5. 2. Newman R. Rice Forecast: What’s in Store for 1995 and Beyond. Rice Utilization Workshop. Houston, TX: USA Rice Federation; 1995:33. 3. USA Rice Federation Report. www.USARice.com; June 2007. 4. USDA. Economic Research Services. www.ers.usda.gov. Rice Outlook/RCS-05F/ June 15. 5. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press; 1984:507. 6. USDA. Rice Market News. 1992;73:8. 7. Marshall WE, Wadsworth JI. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:10–11. 8. McKenzie KS. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:91. 9. McKenzie KS. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:98. 10. Webb BD. Texas Agr. Expt. Sta. Res. Monograph. 1975;4:97 [Beaumont, TX]. 11. Houston, TX: USA Rice Federation. 12. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press; 1984:511. 13. US Rice Federation, Domestic Usage Report, MY 2004–2005. 14. Meyers R. Current Domestic Markets for Rice. In: Rice Utilization Workshop. Houston, TX: USA Rice Federation; 1995:44. 15. Luh BS. In: Luh BS, ed. Rice Utilization. Vol. II. New York, NY: Van Nostrand Reinhold; 1991:269. 16. Lathrop, CA: Courtesy of California Natural Products. 17. Patty Mayhew, Food Extrusion Inc., El Dorado Hills, California, Personal Communication. 18. Hammond NA. US Patent 5 292 537; 1995. 19. Ribus, Inc., St. Louis, MO, personal communication. 20. Orthoefer F. Riceland Foods, Inc., Stuttgart, Arkansas; 1995, personal communication. 21. Hogan JT. In: Whistler RL, Paschall EF, eds. Starch: Chemistry and Technology, vol. II, New York: Academic Press; 65. 22. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press, Inc. 1984:513. 23. Khin-Maung-U, Greenough WB. J. Pediatrics. 1991:118. 24. Welsh LA, Blakeney AB, Bannon DR. Modified R.V.A. for Rice Flour Viscometry [unpublished method]. Australia: Yanco Agricultural Institute, NSW; 1983. 25. Deffenbaugh LB, Walker CE. Cereal Chem. 1989;66:493. 26. Courtesy of Hall J. California Natural Products, Lathrop, California. 27. Zhao J, Whistler RL. Food Technol. July 1994;104.
Rice Starches: Production and Properties Cheryl R. Mitchell Creative Research Management, Stockton, California, USA
I. Rice Production and Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Rice Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Rice Milling and Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II. Uses of Milled Rice and Rice By-products . . . . . . . . . . . . . . . . . . . . . . . . . 1. Milled Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. By-products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III. Preparation of Rice Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Traditional Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Mechanical Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV. Properties of Rice Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. General Properties Unique to Rice Starch . . . . . . . . . . . . . . . . . . . . . . . 2. Pasting Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V. Factors Affecting Rice Starch Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Rice Variety: Common Versus Waxy . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Protein Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Method of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI. Rice Starch Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
569 569 570 571 571 572 573 573 574 574 574 575 575 575 576 576 577 577 578
I. Rice Production and Composition 1. Rice Production Cultivated rice (Oryza sativa L.) is a major world food crop. Only wheat surpasses rice with regard to production and food use. About 90% of the world’s rice is produced and consumed in Asia.1 The production and consumption of rice in the United States, while not a staple food, increased more than 40% during the period from 1980 to 19952 and an additional 25% from 1995 to 2005.3 The price of rice in Starch: Chemistry and Technology, Third Edition ISBN: 978-0-12-746275-2
Copyright © 2009, Elsevier Inc. All rights reserved
570 Rice Starches: Production and Properties
Table 13.1 Typical amylose content (%) by grain length of commercial US rice varieties9 Long
Medium
Short
Waxy short
20–25
14–18
15–23
0–2
the United States showed an extraordinary increase during 2007, increasing by over 75% of its price during 2003. This increase was due to the increased demand for rice in the US and international markets, without an equivalent increase in production. Worldwide usage of milled rice in 2005 was reported to be 406 million metric tons (mmt), with the United States reportedly producing 10.2 mmt and using 5.7 mmt.4 Major rice producing areas include China, India, Indonesia, Bangladesh, Thailand, Burma, Japan, Korea, Vietnam and the Philippines. Other than Asia, major areas of rice production include Brazil, the United States, the Malagasy Republic, Egypt, Columbia, Nigeria and Italy.5 Major rice producing areas in the United States, in descending order of production, are Arkansas, California, Florida, Louisiana, Mississippi, Missouri and Texas.6 The US focus is on three grain types: short; medium; and long. Long grain represents approximately 70% of the total US rice production. Approximately 93% of the California rice crop is medium grain, while in the south about 84% of the rice grown is long grain and 16% is medium grain.7 In commercial crops grown in the US, the amylose content is to some extent associated with grain length, with long grain varieties having a higher amylose content than medium or short grain types (Table 13.1). Waxy rice currently cultivated in the US is a short grain type; long grain waxy rice varieties are available in the orient. Experimental rices having amylose contents of up to 40% (in 2% increments) have been reported, but are not commercially available. Rice varieties are distinguished by their amylose content. There are two basic types: common and waxy. Waxy rice has an amylose content of 0–2%. Common or regular rice varieties are referred to as having amylose contents that are low (9–20%), medium (20–25%) or high (25%) amylose. The availability of waxy rice is usually limited and large requirements for waxy rice are contracted in advance to ensure a supply. A typical variety of waxy rice produced in the US is Calmochi-101.9 Waxy rices are also referred to as ‘glutinous’ rices, due to their sticky cooking property, or as ‘sweet’ rices because of their use in Japanese ‘mochi’ cakes. Examples of lowamylose, medium-grain varieties are Calrose, Nato and Vista. Low-amylose, shortgrain varieties are Caloro, Colusa and Nortai. Intermediate-amylose, long-grain varieties are Belle Patna, Bluebelle, Labelle and Starbonnet.10
2. Rice Milling and Composition Harvested rice grain is composed of the outer hull, the bran layer and the inner white starchy endosperm. Rough rice, which is rice with the hull intact, is the form in which rice is stored for use throughout the year. Removal of the hull produces what is known as brown rice. Once the hull is removed, inadvertent scratching of the inner
II. Uses of Milled Rice and Rice By-products 571
Table 13.2 Typical mill yields and composition of products and by-products from rough rice13 Fraction
Yield from rough rice, %
Protein, N 5.95, %
Crude fat, %
Crude fiber, % d.b.
Crude ash, %
Nitrogen-free extract, %
Hull Brown rice Bran Polish Milled rice Head Seconds Brewers
18–28 72–82 4–5 3 64–74 56 9 3
2–4 7–15 12–17 13–16 6–13
0.4–0.8 2–4 15–22 9–15 0.3–0.6
48–53 1 9–16 2–5 0.1–0.6
15–20 1–12 9–16 5–9 0.3–0.7
26–34 79–90 40–49 54–71 84–93
bran layer releases lipases which effect lipolytic hydrolysis and oxidation of the kernel oil. The subsequent rancidity results in bitter, soapy, off-tastes. Normally, once the hull is removed the rice is sold immediately for use as brown rice or continues to the next step of milling, which is bran removal and polishing. Abrasive milling removes the outer bran layer to produce partially polished rice or, after polishing to remove the entire bran layer, white rice. Rice bran or polish may be subsequently stabilized by heat treatment to inactivate lipases. Stabilized rice bran has found use as an ingredient in human-grade processed foods. After removal of the bran layer and polishing to the desired degree, the residual milled rice is divided into several fractions depending on size. Total milled rice contains head rice (whole unbroken kernels and kernels that are at least three-fourths of an unbroken kernel) and broken rice. Further screening of the total milled rice separates the head rice from second heads (largest of the broken kernels, usually between onehalf and three-fourths of an unbroken kernel) and brewers rice (broken kernels that are about one-fourth of an unbroken kernel). The relative amounts in each category are a function of rice variety, growing conditions, harvesting, drying, handling and the type of milling operation. Typical mill yields and their compositions are given in Table 13.2.
II. Uses of Milled Rice and Rice By-products 1. Milled Rice Milled rice is comprised of head rice, second heads and brewers’ rice. Unlike most grains, the primary use of rice is its direct consumption as a table food. The two other major uses are in processed foods and to make beer. Head rice is the only rice that is used for table consumption and represents 82% of the milled rice. Broken rice, which is comprised of second heads and brewers’ rice, is considered to be a byproduct of milling and represents 18% of the milled rice. Broken rice generally has a lower market value than head rice. Due to the relatively high cost of head rice compared with other grains, lower cost by-products of head rice production are preferred for use in processed foods and beer production. In 2004–2005, the USDA estimated that the principle outlets for milled rice in the US included 52% for direct food use,
Free sugars, %
1.3–1.5 6.4–6.5 0.2–0.5
572 Rice Starches: Production and Properties
29% for use in processed foods and 17% for use as a beer adjunct.13 While use in beer has remained rather constant, use in processed foods grew 38% during 1985– 1995, with the fastest growing product categories being pet foods and rice ingredients.14 Obviously, an imbalance exists between the availability of milling by-products (18%) and use in processed foods (29%). Increase in demand for second heads and brewers rice by processed food manufacturers has resulted in a shortage of these by-products. Additionally, more and more rough and brown rice is being exported, thereby limiting even more the supply of milling by-products in the US. It is obvious that, as more and more processed food products are developed, that mill run rice (milled rice that has not been size separated) will have to be used. The cost of mill run rice is typically 2–3 times that of corn. Because of the economic disadvantage of rice over other grains, future use of rice or rice ingredients (including starch) in processed foods will be dependent on unique characteristics and nutritional aspects that rice products or ingredients contribute to processed food products. In 2006, the USDA advocated the consumption of at least six servings of grains per day, of which three should be wholegrain. The latter prompted an increase in the use of wholegrains in food products. Development of novel wholegrain rice products was catalyzed by the development of wholegrain brown rice ingredients, such as RiceLife®, which made it possible to make wholegrain beverages, frozen desserts and even wholegrain non-dairy yogurts. Other brown rice ingredients, such as brown rice or brown ricemilk syrup, and their resulting products have greatly expanded the use of brown rice throughout the food and beverage industry. Many processed foods, such as cereals, packaged mixes, pet foods, rice cakes and baby foods, were developed and incorporate broken rice, meal or flour. However, in recent years ingredients derived from milled rice, and now brown rice, have not only greatly extended the use of rice in processed foods, but have also been the basis for the development of novel food products. Commercially available rice ingredients mimic those products available from the corn wet-milling industry. Rice starch, rice proteins, rice syrups, rice dextrins and rice hydrolyzates are finding increased use. All these ingredients are uniquely different from their corn-derived counterparts. Products based entirely on rice starch-based ingredients, such as vinegars, oral rehydration solutions, non-dairy beverages, frozen desserts and puddings, are stable commodities in the marketplace, often taking the lead in sales over their corn or soy counterparts in natural foods and conventional marketing segments. Whole brown rice, while still in its developmental infancy, has great potential for growth as a processed food ingredient, due to its unique characteristics. Rice starch from white rice or brown rice exhibits unique properties as functional ingredients in many food categories.
2. By-products Hulls A major fraction of paddy rice is the hull. The hull is non-digestible, fibrous and abrasive in character, and has a low bulk density and a high ash content. It is used only in limited, low-value applications, such as in animal feed, in chicken litter, as a juice pressing aid and as fuel.15
III. Preparation of Rice Starch 573
Bran
Unstabilized bran and polish have been used almost exclusively for animal feed, due to the bitter flavor that develops from the lipolytic action of enzymes on the oil found in them. However, development of a thermal process that inactivates the lipases has resulted in a stabilized rice bran product that is suitable for the food industry. The impressive nutritional qualities of the oil, fiber, carbohydrate and proteins of rice bran have made it a valuable food material. Removal of fiber from the bran by physical16,17or enzymic18,19 processes produces a milk-like product having desirable nutritional and functional properties. The nutritional composition of the rice bran milk product described by California Natural Products has been shown to match the nutritional requirements of an infant formula. Originally, the anti-nutritional factor of the residual phytates was of concern. However, as of 2005, phytase enzymes are suitable for use to break down these phytates. Rice bran oil can be extracted from either stabilized or unstabilized bran. The by-product resulting from stabilized bran extraction is suitable for human food use. Stabilized rice bran is currently being used in baked goods, energy bars and protein fortification of powdered drink formulations.
III. Preparation of Rice Starch Rice starch is preferably prepared from broken rice for economic reasons, as discussed above. There are currently two commercial methods of rice starch isolation: traditional and mechanical. The traditional method involves alkali solubilization of rice protein, while the mechanical method releases starch via a wet-milling process. Worldwide production of rice starch amounts to about 25 000 metric tons.20 Approximately 75% of this was manufactured by the Belgium company Remy Industries, which has been manufacturing rice starch by the traditional alkali method for more than 100 years. Until 1990, rice starch prepared by the alkali process was the only commercially-available rice starch.
1. Traditional Method The traditional method of starch production involves alkali solubilization of the glutelin which constitutes approximately 80% of the protein in rice. This method has been described by Hogan,21 and is utilized in some form by almost every rice starch manufacturer (with the exception described below). It produces a starch containing 1% protein. The protein by-product of this process, while good-quality protein, has a distinct aftertaste (alkali, salt and amino acid), making it not easily acceptable as a food ingredient. In the alkali process, broken milled rice is steeped in 0.3–0.5% sodium hydroxide solution for up to 24 hours at temperatures that may vary from room temperature to 50ºC. This steeping process softens the grain and effects solubilization of the proteins. Wet-milling of the steeped grain, in the presence of sodium hydroxide solution, releases the starch, producing a starch slurry. The starch is kept in suspension and stored for
574 Rice Starches: Production and Properties
10–24 hours to further dissolve the proteins. The cell wall material is then removed by filtration, and the starch slurry is washed with water (to remove the protein), neutralized and dried. The commercial drying process, which necessarily involves initially low air temperatures to prevent gelatinization, has the potential for allowing high bacterial growth and, consequently, total plate counts must be carefully monitored. An advantage to the alkali process is the ease with which the alkali solution allows for modification of the starch, since most modification reactions are done at high pH values. A disadvantage is the alkali waste water that is produced and its ecological consequences. These two problems, along with the limited economic potential of rice starch, are the primary reasons why the alkali process has not been used in the US since 1943.22
2. Mechanical Method The mechanical method of rice starch production is a wet-milling process first used on milled rice that permits optional protein removal. Protein is not solubilized in this process, but rather is removed by physical separation after the starch granules and protein have been mechanically liberated from the starchy endosperm. The released starch granules exist in clumps or small aggregates of 10–20 m in diameter. Products containing from 0.25% to 7% protein may be produced by this commercial method. If the protein is removed, the resulting starch is similar in appearance to that produced via the traditional process. However, differences in pasting and functional characteristics (described below) exist. Unlike alkali-solubilized protein, the protein resulting from the mechanical process is a valuable by-product, having excellent taste qualities suitable for the food industry. A current patent pending variation of the mechanical method, as developed by this author and practiced by Creative Research Management, utilizes whole brown rice. The resulting whole brown rice starches are unique and contain both protein and rice bran oil. Both of these constituents of the whole brown rice impart novel physical properties to the starch-containing fraction. The advantage of the use of these types of starches is relatively new and is just now becoming available to the industry as an ingredient. The primary advantage of the mechanical process is the variety of starches of different protein and fat content that may be produced, and their respective unique functional properties. Also, the waste water from the mechanical process has no negative environmental impact and is quite suitable for land application.
IV. Properties of Rice Starch 1. General Properties Unique to Rice Starch Traditionally, there have been basic properties associated with rice starch that have given it advantages over other starches. These characteristics include hypoallergenicity, digestibility, consumer acceptance, bland flavor, small granules (2–10 m), white color, greater freeze–thaw stability of pastes, greater acid resistance and a wide range of amylase:amylopectin ratios.
V. Factors Affecting Rice Starch Properties 575
Rice is considered to be hypoallergenic, because it does not possess gliadins or parts of proteins that are normally associated with the allergenic responses, such as those that may be caused by wheat, barley or rye. Because of its extensive table use, consumers perceive rice as a balanced food, as indeed it is. Its better digestibility, as compared to other cereal grains, has led to its preferred use in infant and geriatric foods, to medical recommendations that rice be the first cereal grain given to infants, and to it being the preferred grain for recuperating patients. There is no specific scientific evidence to support why rice has this digestive advantage, only hundreds of years of anecdotal experience. However, research on the utilization of rice in oral rehydration solutions and in infant formulas is generating some understanding of the beneficial qualities unique to rice.23 The bland taste of rice starch, its whiteness and its small granule size have provided it with the advantages necessary in the manufacture of smooth gravies, sauces and puddings, having excellent mouthfeel and flavor profiles. Non-food uses of rice starch are also based on its small granule size; they include textile size, cosmetic and printing ink applications. A spray dried form of rice starch in which the individual starch granules are dried in aggregates has been developed by CNP. These porous starch spheres are advantageous with regard to their greatly improved dispersibility over other starches. The aggregates also have special properties associated with absorption of other solutes within the sphere structure and slow release for an improved distribution. Depending on the relative amylopectin:amylose ratio found in the rice, the starch can exhibit a variety of gelatinized textures and strengths, as well as resistance to acid. Overall, there are several basic factors that affect starch performance. These factors, which include rice variety, protein content, method of starch production and modification, are described below.
2. Pasting Properties The Rapid ViscoAmylograph (RVA) has been the preferred instrument for determining the pasting properties of rice flour and rice starches24,25 (see Chapter 8).
V. Factors Affecting Rice Starch Properties 1. Rice Variety: Common Versus Waxy The functionality of rice starch depends on the amylose:amylopectin ratio. Differences among rice starches made from long-, medium- or short-grain rice are insignificant relative to the amylose content. Rice starches made from common rice tend toward higher peak, cooked and cooled viscosities, as well as paste textures that are short and pasty. The texture of waxy rice starch pastes tends to be long and stringy (Table 13.3). Rice starch from common rice contains 0.3%–0.4% lipids, while waxy rice contains considerably less (0.03%). Complexes of these lipids are not easily removed from the starch, and are presumably responsible for the lack of paste clarity and the difficulty in clarification of starch hydrolyzates.
576 Rice Starches: Production and Properties
Table 13.3 Ranges of physicochemical properties of common and waxy rice starchesa,16
Amylose:amylopectin Bound lipid, % Initial paste temperature, ºC Peak temperature, ºC Brabender ViscoAmylograph, BU Peak Cooked Cooled Texture
Common
Waxy
20:80 0.2–0.4 65–74 91–95
2:98 0.02–0.03 61–64 69–71
560–1020 260–480 490–785 short
670–685 280–425 320–675 long
a
Prepared from US rice varieties by the mechanical method
2. Protein Content Residual protein can greatly affect the pasting and functional properties of rice starch. The higher protein content of alkali-processed rice starches appears to reduce the pasting curve viscosity. However, among mechanically processed rice starches, this is not the case. Mechanically produced rice starches with a relatively high protein content, in most cases, give higher pasting curve viscosities than those starches with a lower protein content. This relationship is particularly dramatized in the case of a waxy rice starch having a protein content of 4.1% versus one containing 0.7% protein. Increasing protein content among mechanically produced rice starches also significantly improves functional properties such as dispersibility, gel smoothness, stability during ultra-high-temperature (UHT) processing, acid resistance and freeze–thaw stability. It was found that freeze–thaw stability in common rice starch containing at least 2% protein is equivalent to that normally associated with waxy rice starch. Some of these functional advantages may be attributed to the unique sphere aggregates that are formed in the mechanical process on spray drying of the rice starch in the presence of the protein. After spray drying, rice starch containing 0.5% protein is present as clusters of 10–20 m. At 1.5% and again at 6.0% protein, increased formation of spheres of 30–70 m is observed. The presence of these spheres is responsible for improved dispersibility and gel smoothness.26 It has also been suggested that the unique absorption properties of the sphere aggregates may have application in holding and dispersement of flavor material or pharmaceuticals.27
3. Method of Preparation RVA curves compare commercial rice starch prepared by traditional alkali methods and rice starches prepared by the mechanical method. In the case of common rice starches, the onset of pasting appears to occur earlier (at lower temperature) and the final cooled viscosity appears to be lower for the starches prepared using alkaline conditions. The latter differences may be due to either rice type or the effect of alkali on granules. In the case of waxy rice starches, mechanically produced starches, in
VI. Rice Starch Applications 577
general, have both higher paste and cooled viscosities as compared to those prepared by the alkali method.
4. Modification Properties of rice starches are changed by chemical modification in the same way as the properties of other starches (see Chapter 18). Starches prepared via the alkali method have been modified to provide additional pH and shear stability. In general, hypochlorite-oxidized rice starch has a lower gelatinization temperature and lower maximum paste viscosity producing a softer, clearer gel. Hydroxypropylated rice starches have lower gelatinization temperatures, whereas crosslinked rice starch has an increased gelatinization temperature, increased shear resistance and acid stability.
VI. Rice Starch Applications Rice starch applications are normally discussed in terms of common and waxy types and are specified that way in Table 13.4. A 10% solution of a common rice starch, when sheered and gelatinized simultaneously, produces a product that resembles a solid shortening in texture. The waxy rice starches do not produce this same texture; however, they too have been used very effectively for fat replacement due to a fat-like mouthfeel when blended with other food products. Waxy rice starches also tend to resist oil uptake when used in batters for fried foods. Most applications of rice starch may be attributed to one or more of the characteristics already discussed that are unique to rice starch. Table 13.4 Rice starch applications16 Common
Waxy
Binder Confectioneries Dairy products Infant foods Processed meats Puddings/custards Sauces/soups Dusting agent Confectioneries Pharmaceuticals
Fat-mimetic Coatings for deep-fat frying Dairy products Pastries Processed meats Sauces/soups
Miscellaneous Cosmetics Laundry products Pet foods Photographic
Binder Canned foods Infant foods Rapid cook (microwaveable) foods Ready-to-eat meals Crispness agent Breakfast cereals Extruded snacks
Frozen foods Low-fat ice cream Non-fat sauces Source: reference 29
578 Rice Starches: Production and Properties
VII. References 1. Marshall WE, Wadsworth JI. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:5. 2. Newman R. Rice Forecast: What’s in Store for 1995 and Beyond. Rice Utilization Workshop. Houston, TX: USA Rice Federation; 1995:33. 3. USA Rice Federation Report. www.USARice.com; June 2007. 4. USDA. Economic Research Services. www.ers.usda.gov. Rice Outlook/RCS-05F/ June 15. 5. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press; 1984:507. 6. USDA. Rice Market News. 1992;73:8. 7. Marshall WE, Wadsworth JI. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:10–11. 8. McKenzie KS. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:91. 9. McKenzie KS. In: Marshall WE, Wadsworth JI, eds. Rice Science and Technology. New York, NY: Marcel Dekker; 1993:98. 10. Webb BD. Texas Agr. Expt. Sta. Res. Monograph. 1975;4:97 [Beaumont, TX]. 11. Houston, TX: USA Rice Federation. 12. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press; 1984:511. 13. US Rice Federation, Domestic Usage Report, MY 2004–2005. 14. Meyers R. Current Domestic Markets for Rice. In: Rice Utilization Workshop. Houston, TX: USA Rice Federation; 1995:44. 15. Luh BS. In: Luh BS, ed. Rice Utilization. Vol. II. New York, NY: Van Nostrand Reinhold; 1991:269. 16. Lathrop, CA: Courtesy of California Natural Products. 17. Patty Mayhew, Food Extrusion Inc., El Dorado Hills, California, Personal Communication. 18. Hammond NA. US Patent 5 292 537; 1995. 19. Ribus, Inc., St. Louis, MO, personal communication. 20. Orthoefer F. Riceland Foods, Inc., Stuttgart, Arkansas; 1995, personal communication. 21. Hogan JT. In: Whistler RL, Paschall EF, eds. Starch: Chemistry and Technology, vol. II, New York: Academic Press; 65. 22. Juliano BO. In: Whistler RL, BeMiller JN, Paschall EF, eds. Starch: Chemistry and Technology. Orlando, FL: Academic Press, Inc. 1984:513. 23. Khin-Maung-U, Greenough WB. J. Pediatrics. 1991:118. 24. Welsh LA, Blakeney AB, Bannon DR. Modified R.V.A. for Rice Flour Viscometry [unpublished method]. Australia: Yanco Agricultural Institute, NSW; 1983. 25. Deffenbaugh LB, Walker CE. Cereal Chem. 1989;66:493. 26. Courtesy of Hall J. California Natural Products, Lathrop, California. 27. Zhao J, Whistler RL. Food Technol. July 1994;104.