Going With the Grain - Part One
What's with Wheat
Rice is Nice
Feelin' your Oats
Grain-based ingredients play an integral role in many snack foods by enhancing flavor, texture and appearance, and increasing a healthful image. Taste and nutrition represent the two most important reasons consumers choose a particular food item, according to a 1997 Food Marketing Institute report, and snacks formulated with grains provide these essential elements.
Many popular snack foods are corn-based: tortilla chips, corn chips, extruded curls and balls. Formulations typically incorporate dry corn masa flour and snack meal. In addition, potential new uses exist for corn bran. Corn is dry-milled to produce products ranging from flaking grits to corn flour. "The corn kernel is first tempered to loosen the bran," explains Brian Anderson, plant manager, ConAgra Corn Processing, Atchison, KS. "The kernel is then split in half, and the germ and pericarp (bran) are removed. The degermed kernel is then ground and sized into flaking grits, brewer's grit, snack meal and corn flour." Most U.S. corn is degermed prior to grinding, since its oil content limits the storage life and flavor stability of non-degermed products.
Corn masa is a primary ingredient in taco shells, tortillas and tortilla chips. "Corn masa is traditionally made by steeping the corn in lime," Anderson says. "The alkaline environment breaks down the pericarp and disturbs the cell walls so that water penetrates the kernel. The water containing the pericarp is drained off. The corn is then ground on stones into a dough. Today, corn masa is made by a similar, but faster process." The alkaline treatment also generates a unique flavor characteristic associated with corn and tortilla chips.
Dry corn masa flour enjoys increasing popularity among snack manufacturers. Corn is processed into masa, dried and then milled into different granulations. The end-user mixes water with the flour to form a dough. Corn masa flour offers many advantages: consistent corn supply, no capital investment or floor-space allotment for corn-masa production equipment, and no waste-water treatment problem.
Choice of masa flour granulation depends on the desired end product. "Taco shells are made with coarse, ground flour," Anderson explains. "A fine flour is used for fresh tortillas, while tortilla chips are commonly made with a medium granulation. The finer the flour, the more water that can be added to a formulation. This will affect fat absorption during frying." When the starch in a grain is cooked in water, the granules swell or gelatinize. Pre-gelatinized flours absorb water and form a dough. Flour or meal made from raw grain is not water-soluble. "Since corn masa flour has been cooked, there is partial starch gelatinization," Anderson says. "The flour will absorb water during mixing, and form a dough that can be sheeted. Coarsely ground flour, however, makes sheeting difficult. Larger particles inhibit the matrix that holds the sheet together." Corn meal, which is made from raw grain, has application in extruded snacks, where the ingredient is cooked during processing.
With extruded snack foods, corn ingredient selection depends upon the type of snack and the type of extruder. A fine granulation of corn meal produces a fine texture and cell structure with a softer bite. A snack with a crunchy texture and a slightly larger cell structure is achieved with a more coarse granulation of corn meal. Extruded snacks most frequently use degermed corn because it expands better than whole corn. Expansion can be increased with a waxy corn ingredient. This is due to the type of starch present: Waxy corn is high in amylopectin, with very little amylose while normal corn contains 25% to 35% amylose.
"Direct-expanded snacks, like corn curls, are commonly made with a single-screw extruder," says Eric Sevatson, food technologist, Wenger Manufacturing Inc., Sabetha, KS. "This type of extruder is limited to a specific range of particle size. A twin-screw extruder is more expensive, but has greater processing flexibility. A wide range of particle sizes can be used. The equipment can better handle variations in raw materials. A variety of end products are possible: corn balls, multi-grain chips and third-generation half products."
Corn bran is the pericarp of the corn kernel. It contains 86% to 90% total dietary fiber (TDF), and has potential use in low-calorie, high-fiber products. "Corn bran is being looked at for use with masa flour for functional reasons," Anderson notes. "There is some indication that corn fiber helps strengthen the final product, like taco shells. It may also lower oil absorption."
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Wheat encompasses a broad spectrum of varieties and styles: hard and soft wheat, white flour, whole-meal flour, bran, cracked wheat and bulgur. While wheat flour dominates the baking industry, a wide range of wheat-based ingredients have application in snack foods. Wheat contains 8% to 15% protein; hard wheat has a higher protein content than soft wheat. Semolina has coarse particles and is usually produced from hard wheat. The higher the protein content, the crisper the bite. Snack foods made with all-semolina have a very crisp texture, according to the American Institute of Baking, Manhattan, KS.
Wheat starch contains 20% to 25% amylose. This gives good expansion during extrusion cooking. The amount of gluten in high-protein wheat, however, can suppress expansion. Typically, 1% to 2% added wheat gluten (on a flour weight basis) is used in snacks. The gluten provides nutritional value, crispness and desired texture to extruded products. Expanded snacks made with soft wheat (lower gluten levels) have a more tender texture.
White flour is made by removing the bran, germ and aleurone from wheat, and then grinding the remaining endosperm into a fine flour. Whole-meal, or whole-wheat, flour is produced by grinding the entire wheat kernel. Whole-meal flour contains more minerals, vitamins and dietary fiber than white flour. Though it also contains about 1% more protein, this additional protein isn't gluten, which can limit expansion in extruded snacks.
Wheat bran is high in fiber, and can be used to produce expanded snacks with high nutritional and fiber value. The phenolic compounds in bran contribute a slightly bitter flavor as well as color. A darker bran from a hard red wheat has a stronger flavor than a lighter colored bran made from a white wheat. "We ran an extruded snack made with soft, white wheat bran and whole-wheat flour, plus some sugars," Sevatson says. "The end product had a sweet, 'grahamy' flavor. The more bran that is used, the less the expansion. Starch is the expanding agent in extruded snacks. As bran replaces starch, expansion declines."
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One of the world's largest crops, rice is an underutilized ingredient in processed food. In the Western world, where rice isn't a staple, snacks often are corn-based. In Japan, snacks usually contain rice or rice flour.
Three rice varieties are commonly grown in the United States. "Long-grain rice grown in the South has about 22% amylose," explains Pete Vegas, president, Comet Rice Ingredients, Los Angeles. "This grain can give a harder crunch to a product. Medium-grain California rice contains about 18% amylose, and has a softer texture. Waxy rice is almost all amylopectin. It contains less than 1% amylose. Snacks made with waxy rice almost melt in your mouth, giving a perception of fat." The amylose-to-amylopectin ratio affects the gelatinization temperature: The higher the amylose content, the higher the temperature.
Snacks are formulated with puffed rice, crisped rice, rice bran and rice flour. Granola bars often use extruded crisped rice. Sheeted and extruded snacks might contain rice flour or rice bran.
Rice flour is typically made from broken rice kernels. In the milling process, the bran is removed and the cracked kernels are separated from the whole kernels. "With demand for rice flour exceeding the supply of broken kernels, it is sometimes necessary to grind whole, milled kernels," Vegas says. Rice flour granulation ranges traditionally from rice meal (coarsest) to rice starch (finest). The coarser the grind, the longer the cook.
Rice-ingredient selection is influenced by the other ingredients used in the formula and the processing equipment. If using rice flour with a wheat flour, for example, it's beneficial for both flours to have similar granulations. This enables the ingredients to hydrate and cook at comparable rates.
In an extrusion operation, some ingredients may require pre-conditioning. "Let's say a multi-grain product is being made with rice flour and wheat kernels," Sevatson suggests. "If all the ingredients are not cooked and hydrated evenly in the extruder, there can be hard spots in the finished product. It might be necessary to pre-cook and soften the whole-grain component before mixing it with the other ingredients in the extruder."
Sheeted snacks benefit from pre-gelatinized rice flour. Raw rice flour is ground, milled rice. Since it isn't cooked, no starch gelatinization occurs. Water tends to adhere to the flour's surface, but it isn't absorbed. It's difficult to achieve a dough that sheets well. The addition of pre-gelatinized or partially gelatinized rice flour encourages water absorption and provides more structure. A dough is formed, capable of being sheeted.
Brown rice has the bran left on the kernel. While it may be used to project a healthful image, rice bran also serves a functional purpose. "Rice bran contains about 20% fat," Vegas explains. "Brown rice would not be ground into flour, because it would go rancid quickly. Instead, the bran is removed from the kernel and stabilized. This process inactivates the lipase enzymes that cause fat rancidity. After stabilization, the bran can be added back to the rice flour in the same proportion it was removed to yield brown rice flour. Or, if the bran is to be used for functional purposes, it is added back at a 3% to 5% level. The oil in the bran seems to help sheeting and extrusion operations. Dough runs smoother through an extruder. It may help prevent dough from sticking to sheeting rolls."
Rice-based ingredients contribute many attributes to snack foods. Blending long-grain rice flour with wheat or corn increases the crispness of baked and fried snacks. Chips made with 100% rice flour absorb 20% to 30% less oil during frying. Pretzels formulated with rice have more crunchiness. Waxy rice flour can reduce product hardness and promote a melt-in-the-mouth texture, without added fat. Snacks made with rice as the major ingredient are bland, making them easy to flavor.
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Oats enjoy a positive consumer image for their nutrition and wholesomeness. Oat products contain about 17% protein and 10% TDF. Beta-glucan, the soluble fiber in oats, has proven health benefits. FDA ruled last year that foods containing 0.75 gram of beta-glucan from oats per reference amount qualify for a label declaration stating that the food may reduce the risk of heart disease when eaten as part of a diet low in saturated fats and cholesterol.
Oats are available in various forms: whole, dehulled grain; rolled oats; quick oat flakes; steel-cut oats; oat flour; oat bran; low-fat oat flour; and oat extract. Basic oat processing involves removing the hull and then stabilizing the groat with a heat-and-steam process. Oats contain 7% to 9% fat. Stabilization inactivates the enzymes that cause fat rancidity. The process also contributes to the toasted or nutty flavor and aroma of oat products.
Whole groats can be flaked or ground into flour. A steel-cut groat is cut into pieces, yielding nugget-like chips for topical application or flaking. Oat product choice depends on the texture and appearance desired in the finished product and the processing operation.
A coarser granulation requires more hydration time and keeps better visual identity in the finished product. "A thicker flake maintains its appearance in a sheeted, granola bar-type product," explains Bill Bonner, director, technical services, ConAgra Oat Processing, Omaha, NE. "A thin flake absorbs water more quickly than a thick one, which affects dough mixing. Adding oat flour to a multi-grain product puts a nutritious grain on the label statement." The fat content of regular oat flour suppresses the expansion of extruded snacks. Low-fat oat flour, which contains less than 1% fat, solves this problem. "An extruded product made with 100% low-fat oat flour exhibits good expansion," Bonner notes. "This snack provides the same quality and levels of oat protein and oat beta-glucan as if made with whole oat flour."
Free-lance technical writer Elaine Knehr holds a bachelor's degree in food technology and a master's degree in business. Her 10 years of experience in product development covers a wide range of food products.
Click here to read Going With the Grain - Part Two.
• Photo: ConAgra Oat Processing Co.
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