Cereals and Their Composition

LEARNING OUTCOMES

  • Outline the chemical composition of cereals and their derived products.
  • Discuss the chemical, biochemical and physical changes occurring during cooking of cereals.
  • Describe technological aspects of handling, storage, and processing of cereals.

CEREALS

  • Definition: Edible seeds of grasses.
  • Common cereal types:
    • Wheat
    • Barley
    • Corn
    • Rye
    • Rice
    • Oats
    • Millet

STRUCTURE OF CEREALS

  • Bran:

    • Layered outer coat of the grain.
    • Removed during the milling process.
    • Contains proteins, trace minerals, dietary fiber, and lipids.
    • Breakdown:
    • Wheat bran: insoluble fiber
    • Oat bran: soluble fiber
    • Composition:
    • 12% WATER
    • 13–18% PROTEIN
    • 3.5% FAT
    • 56% CARBOHYDRATES

  • Endosperm:

    • Makes up 83% of the kernel.
    • Primarily starch (most of the grain's protein).
    • Lowest in fiber and fat.
    • Source of white flour.
    • Starch to protein ratio varies by grain.

  • Germ:

    • Inner portion of the kernel.
    • Highest in lipids (prone to rancidity).
    • Rich in B vitamins and trace minerals.
    • Often removed during milling.

CHEMICAL COMPOSITION

  • Typical compositions of various grains:
    • Wheat:
    • Protein: 15.3%, Fat: 1.9%, Carbohydrates: 72.0%
    • Barley:
    • Protein: 8-13%, Fat: 2-3%, Carbohydrates: 77.0%
    • Corn:
    • Protein: 10.0%, Fat: 4.3%, Carbohydrates: 71.0%
    • Oats:
    • Protein: 17.3%, Fat: 5.1%, Carbohydrates: 66.0%
    • Brown Rice:
    • Protein: 7.3%, Fat: 2.2%, Carbohydrates: 64.3%
    • Rye:
    • Protein: 8.7%, Fat: 1.5%, Carbohydrates: 72.3%
    • Soybean:
    • Protein: 40%, Fat: 21%, Carbohydrates: 34%

NUTRIENT COMPOSITION

  • Endosperm (80-85%):

    • Primary source of protein, starch, & lipids.
    • Contains vitamins (E, B) and enzymes.
    • Low in dietary fiber.

  • Aleurone Layer (6-9%):

    • Contains proteins, enzymes, and phenolic compounds.

  • Germ (3%):

    • Source of antioxidants and some dietary fiber.

FOOD FORTIFICATION

  • Process of adding micronutrients to food to enhance nutrient value.
  • Strategy recommended by WHO and FAO to combat global nutrient deficiencies.
  • Commonly fortified foods:
    • Cereals and cereal products
    • Milk and dairy products
    • Oils and fats
    • Infant formulas

WHOLE GRAIN FOODS

  • Retain the fibrous bran, unlike refined products.
  • Benefits include:
    • Maintain digestive health (prevention of constipation).
    • Lower levels of bad cholesterol.
    • Reduced risk of cardiovascular disease and type 2 diabetes.
  • Examples include whole-wheat bread and brown rice.

STORAGE AND SAFETY

  • Cereals resistant to deterioration if stored correctly:
    • Store in airtight containers in a cool, dry place.

COMMON CEREALS

  • Wheat:

    • Most consumed cereal grain, primarily used in baked goods.
    • Contains gluten-forming proteins: gliadin and glutenin.

  • Corn (Maize):

    • Contains high starch content and provides dietary fiber.

  • Rice:

    • Major global grain, available in various forms (white, brown).
    • Differences include amylose content and cooking characteristics.

COELIAC DISEASE

  • Autoimmune disorder triggered by gluten, leading to nutrient malabsorption.
  • Symptoms: bloating, diarrhea, anemia, fatigue.

COOKING PROCESSES

  • Effects of Heat on Cereal Cooking:
    • Starch absorbs liquid and swells.
    • Cellulose softens, and some vitamins may be lost.

GELATINIZATION AND STARCH

  • The heating of starch in the presence of water causes granules to swell as hydrogen bonds are broken.
  • Optimal temperature for gelatinization ranges between 75°C and 87°C.

FACTORS AFFECTING GELATINIZATION

  • Liquid Amount:
    • Affects thickness; too little liquid results in thick sauce.
  • Starch Type:
    • Different starches (corn vs wheat) vary in their thickening abilities.
  • Agitation:
    • Essential for creating a smooth sauce; prevents granule settling.
  • Additives (Sugar, Acid):
    • Should be added at proper stages to avoid affecting thickness.

GELATION

  • As cooled starch paste forms a gel, a network from amylose is created, holding granules in place.

AGING GELS AND SYNERESIS

  • Water loss can occur from gels as amylose molecules align more closely, affecting texture.

DEXTRINIZATION

  • Dry heat treatment on starch; bonds break creating dextrins and changing the thickening properties.

TUTORIAL QUESTIONS

  1. Identify parts of cereal grains and their nutritive values.
  2. Discuss advantages of whole grains vs refined grains.
  3. Examples of cereals used for breakfast foods.
  4. Differentiate between fortification and enrichment.
  5. Differences between amylose & amylopectin and gelatinization & gelation.
  6. Explore factors affecting gelatinization turning points.
  7. Discuss fermentation improvement in protein quality.
  8. Assess how phytates impact nutritional values.