Rice, Corn, and Cereals

Introduction to Grains and Cereals

• Global Nutritional Importance: The World Health Organization (WHO) and various countries, including the United States, emphasize the nutritional importance of grains as the foundation of a healthy diet.

• Rising Popularity: Grain consumption has seen a substantial increase in popularity. This trend is attributed to consumers making more nutritious food selections.

• General Definition: A cereal is defined as a cultivated grass that produces an edible seed. This term encompasses all cereal products prepared from grain.

Structure of a Wheat Kernel

• The Germ (Embryo):     * Location: The inner portion of the kernel, situated on the lower end.     * Protein Content: Contains approximately $8\%$ of the total protein in the kernel.     * Vitamins: Contains most of the thiamin ($B_1$).     * Mass: Composes approximately $2.5\%$ of the seed.     * Biological Function: It is the site where sprouting begins as a new plant grows.     * Lipid Content: It is the component with the highest percentage of lipids, containing between $6\%$ and $10\%$ lipid.     * Rancidity: The germ is susceptible to rancidity, which may result from the lipoxidase enzyme or nonenzymatic oxidative rancidity.

• The Endosperm:     * Mass: Represents the greatest percentage of the kernel, making up approximately $83\%$ of the seed.     * Composition: Primarily consists of starch held within a protein matrix. The exact composition differs among grain types and varieties.     * Protein Content: Contains approximately $70\%$ to $75\%$ of the kernel's protein.     * Lipid Content: The lowest in fat among seed components, containing up to only $1.5\%$ of the seed's lipid.     * Fiber Content: Contains less fiber than the bran.     * Primary Use: in wheat, the endosperm is the component used for making white bread.

• The Bran:     * Structure: The layered outer coat consisting of an outside pericarp layer (protection) and an inside seed coat.     * Processing: Often removed via abrasion or polishing during the milling process.     * Mass: Accounts for approximately $14.5\%$ of the seed.     * Nutrient Profile: Contains $19\%$ of the kernel's protein, $3\%$ to $5\%$ lipid, and various minerals like iron.     * Dietary Fiber: Provides cellulose and hemicellulose, serving as "roughage" in the diet.

Nutritional Composition of Cereal Grains

• Carbohydrates:     * Dominant Component: The main nutrient in cereal grains, making up $79\%$ to $83\%$ of the dry matter.     * Form: Predominantly exists as starch.     * Fiber: Composes approximately $6\%$ of the grain, specifically as cellulose and hemicellulose.

• Lipids:     * Variation: Makes up approximately $1\%$ to $7\%$ of a kernel depending on the grain type.     * Grain Specifics: Wheat, rice, corn, rye, and barley contain $1\%$ to $2\%$ lipid; oats contain $4\%$ to $7\%$.     * Fatty Acids: The lipid content is $72\%$ to $85\%$ unsaturated fatty acids, primarily oleic acid and linoleic acid.

• Proteins:     * Total Content: Composes $7\%$ to $14\%$ of the grain.     * Amino Acid Limitations: Cereals are generally low in tryptophan and methionine. Potential breeding may produce cereals higher in lysine.     * Gluten-Forming Proteins: Gliadin and glutenin are found in wheat, oat, rye, barley, and triticale. These determine the gluten-forming potential of flour.     * Gluten Structure: With sufficient hydration and manipulation, these proteins create a gummy, elastic structure.     * Enzymatic Proteins: Alpha-amylase is naturally present. It promotes the dextrinization of starch into shorter-chain polymers, maltose, and glucose. It can thin starch mixtures, which may be detrimental to bread-making.

• Vitamins:     * B-Vitamins: Predominantly Thiamin ($B_1$), Riboflavin ($B_2$), and Niacin ($B_3$).     * Loss and Enrichment: These are often lost during milling and added back through enrichment.     * Fat-Soluble Vitamins: Whole grain products contain some fat-soluble vitamins located in the germ.

• Water Content:     * Natural Levels: Present at $10\%$ to $14\%$ of the grain.     * Cooking Effect: Soaking and cooking add water, causing the grain to expand.     * Absorption: Flours high in protein absorb significantly more water.

• Minerals:     * Presence: Naturally higher in whole grains than refined grains.     * Fortification: Refined flour is commonly fortified with iron. Zinc, calcium, and vitamins may be added beyond original levels.

• Fiber Classification:     * Crude Fiber (CF): Composed of cellulose and the non-carbohydrate lignin.     * Total Dietary Fiber (TDF): Includes cellulose, lignin, hemicellulose, pectic substances, gums, and mucilages.

Analytical Data of Common Cereal Grains (Table 6.1)

Values are per $100\,g$.

• Wheat Flour: $71.0\,g$ Carbohydrate, $2.0\,g$ Fat, $13.3\,g$ Protein, $2.3\,g$ Fiber, $12.0\,g$ Water.

• Rice: $80.4\,g$ Carbohydrate, $0.4\,g$ Fat, $6.7\,g$ Protein, $0.3\,g$ Fiber, $12.0\,g$ Water.

• Corn Meal: $78.4\,g$ Carbohydrate, $1.2\,g$ Fat, $7.9\,g$ Protein, $0.6\,g$ Fiber, $12.0\,g$ Water.

• Oats, Rolled: $68.2\,g$ Carbohydrate, $7.4\,g$ Fat, $14.2\,g$ Protein, $1.2\,g$ Fiber, $8.3\,g$ Water.

• Rye Flour: $74.8\,g$ Carbohydrate, $1.7\,g$ Fat, $11.4\,g$ Protein, $1.0\,g$ Fiber, $11.1\,g$ Water.

• Barley: $78.9\,g$ Carbohydrate, Trace Fat, $10.4\,g$ Protein, $0.4\,g$ Fiber, $10.0\,g$ Water.

• Buckwheat Flour (Non-Cereal): $72.1\,g$ Carbohydrate, $2.5\,g$ Fat, $11.8\,g$ Protein, $1.4\,g$ Fiber, $12.1\,g$ Water.

• Soybean Flour (Defatted): $38.1\,g$ Carbohydrate, $0.9\,g$ Fat, $47.0\,g$ Protein, $2.3\,g$ Fiber, $8.0\,g$ Water.

Vitamin and Mineral Content of Wheat Flours (Table 6.2)

Values are per $100\,g$.

• Whole Wheat Flour: $0.66\,mg$ Thiamin, $0.14\,mg$ Riboflavin, $5.2\,mg$ Niacin, $4.3\,mg$ Iron, $2.8\,g$ Fiber.

• Enriched Flour: $0.67\,mg$ Thiamin, $0.43\,mg$ Riboflavin, $5.9\,mg$ Niacin, $3.6\,mg$ Iron, $0.3\,g$ Fiber.

• White Flour (Refined): $0.07\,mg$ Thiamin, $0.06\,mg$ Riboflavin, $1.0\,mg$ Niacin, $0.9\,mg$ Iron, $0.3\,g$ Fiber.

Specific Grain Varieties and Uses

Wheat

• Classifications: Hard red winter, winter red spring, soft red winter, hard white wheat, soft white wheat, and durum wheat. These are named by season, texture, and color.

• Seasonality:     * Winter Wheat: Planted in fall/winter, harvested in June or July.     * Spring Wheat: Planted in spring, harvested in late summer or fall.

• Texture and Protein Content:     * Hard Wheat: Contains strong protein-starch bonds, tightly packed kernels with minimal air space. Examples include hard spring wheat ($12-18\%$ protein) and hard winter wheat ($10-15\%$ protein).     * Hard Wheat Flour Characteristics: Produces elastic dough high in gluten-forming protein. Best for bread making. Typically holds high water capacity (2 cups flour to 1 cup water).     * Soft Wheat: Lower protein content ($8-11\%$ or $7-9\%$ depending on type). Used for cakes and pastries. Holds less water (2-3/4 cups cake flour to 1 cup water).

• Specific Flour Types:     * Bread Flour: Made from hard red spring wheat; high protein-to-starch ratio; not finely milled.     * All-Purpose Flour (APF): A blend of hard and soft wheat; approximately $10.5\%$ protein. Does not contain bran or germ (white flour).     * Cake Flour: High starch, low protein ($7-9\%$), highly bleached, and finely milled.     * Pastry Flour: Intermediate between APF and cake flour; less starch than cake flour and less protein than APF.

• Color: Depends on pigments like carotenoids. Durum wheat is highly pigmented and its endosperm is used for semolina pasta and couscous.

Rice

• Form: Eaten as whole grain or polished (removing the bran).

• Enrichment Methods:     1. Coating the grain with a powder of thiamin and niacin (waterproof), drying, then coating with iron and drying again.     2. Parboiling (converting): Pressure steam treatment allows water-soluble nutrients from the bran and germ to travel into the endosperm.

• Grain Length:     * Long Grain: 3x length relative to width; high in amylose.     * Medium/Short Grain: Contains less amylose.

Corn

• Usage: Majority is used for animal feed. Lacks tryptophan and lysine.

• Sweet Corn: Eaten as a vegetable.

• Popcorn: Specific breeds with $11-16\%$ moisture; water escapes as steam, increasing volume.

• Processing:     * Cornmeal: Coarsely ground kernels.     * Hominy and Grits: Produced from the endosperm.     * Starch and Syrup: Endosperm is used for cornstarch or hydrolyzed into corn syrup/high fructose corn syrup.     * Corn Oil: Derived from the germ.

Other Grains

• Barley: "Winter-hardy"; served as cooked cereal or pearled (hull removed). Malt is barley with high enzyme content used to hydrolyze starch into sugar.

• Millet: Small seed grass crops related to sorghum. Teff is a tiny variety (approx. $1/32\,inch$ diameter).

• Oats: Valued for high protein. Processed into "rolled" or flattened oats. Oat bran contains soluble fiber effective in reducing serum cholesterol. High fat content makes it prone to rapid rancidity.

• Quinoa: The grain highest in protein; small round light brown kernels used as cooked cereal.

Pasta

• Extrusion: A paste of milled grains extruded through a die or put through a roller.

• Semolina: Used for high-quality pasta products.

• Varieties: Can be cholesterol-free or made from non-wheat flours. Examples of shapes include Penne, Fusilli, Tortiglioni, Farfalle, Rigatoni, and Maccheroni.

Flour Milling Process (Simplified)

1. Receipt and Storage: Grain is received and stored.

2. Cleaning: Removal of impurities.

3. Conditioning: Preparing the grain for milling.

4. Milling: The actual grinding and separation process.

5. Storage and Dispatch: Final products (flour) and by-products are stored and shipped.