Cereals, Grains, and Tubers: Structure, Composition, and Cooking
Cereals
Grain crop farming is the oldest form of agriculture. The nutritional value and nature of cereal seeds were the primary reasons for their cultivation. Cereals have been known in Egypt since 4000 BC, but data suggests their existence as far back as 10,000 or 20,000 BC. Corn was a staple crop for the Aztecs and Incas. Nuts are part of the grass family, containing a single seed or grain. There are 8000 species of grains, the most important being: wheat, corn, rice, oats, barley, rye, triticale, and sorghum. They also include amaranth and quinoa. The main product derived from grains is bread. Bread is made from wheat and rye, grains that can be baked. Oats, rice, millet, and sorghum are cereal crops that can be ground into flour and used in various ways. All types of cereals are staple foods, high in carbohydrates and low in protein. Grain maturation cycles can be fast or slow, with faster cycles occurring in areas with high temperatures and little rain. Grains that mature quickly tend to have a higher protein content.
Wheat
Commercially, there are three types of wheat. They are distinguished by their hardness, which is determined by the content and arrangement of proteins in the grain. Hardness results from the higher density of the protein matrix encapsulating the starch granules. Higher protein content means lower starch granule content.
Corn
Types: yellow, white, cacahuazintle, popcorn, and blue. Nixtamalization: Corn is soaked in a 5% alkaline solution for 20-30 minutes. This solution can be calcium hydroxide (lime or tequesquite), sodium hydroxide (lye or soda), or potassium hydroxide (wood ashes).
Nixtamalization Benefits:
- Softens and loosens the hulls, releasing niacin bound to proteins.
- Promotes iron absorption.
- Increases calcium intake in consumers of nixtamalized maize.
After nixtamalization, the corn is strained, rinsed, shelled, dried, and ground into corn flour for making dough.
Rice
Major Producers: Morelos, Veracruz, and Sinaloa (Mexico). Parboiled or Precooked Rice: This type of rice is soaked, steamed, and then dried. Benefits: The grain becomes more resistant to breakage, retains most vitamins, and is less likely to stick together. Cons: It has a darker color and a slightly different flavor.
Oats
Oat flakes are made by slicing the de-husked grain, steaming it to soften it, passing it between rollers to crush it, and then drying it.
Barley
Pearl Barley: This highly refined type of barley cooks to four times its original volume. It is used in the production of malt (the base for beer and whiskey). The whole seed is soaked to facilitate germination. Germinated seeds exhibit high amylase enzyme activity (which converts starch to maltose). The sprouted seeds are then roasted to create malt.
Rye
Rye is prevalent in parts of Europe and Russia. It has a strong flavor. Rye breads are popular in Europe, Scandinavia, and Britain.
Structure and Composition
Basic composition of grains:
- Bran: 14%
- Endosperm: 83%
- Germ: 3%
Bran: The outer layer or husk of the grain, consisting of several layers. Its function is protection. It is high in cellulose, vitamins, and minerals. The aleurone layer separates the bran from the endosperm.
Endosperm: The part of the grain where starch granules and proteins are stored.
Germ: Contains the grain’s fat and some protein. It is a way for plants to store carbohydrates. Cereals have a high amount of starch in the endosperm. Starch is important in the preparation of foods like starch or flour. The size, shape, and composition of starch granules vary:
- Largest: Wheat
- Medium: Corn
- Smallest: Rice
Chemistry: Molecules
Starch molecules consist of thousands of glucose units linked together in long chains or polymers. Two types of starch molecules:
- Amylose: Linear chain (contributes to gelation)
- Amylopectin: Branched chain (contributes to viscosity and cohesiveness)
Starch granules are composed of approximately 25% amylose and 75% amylopectin, joined by hydrogen bonds. After grinding, the grain becomes flour. Proteins, particularly gluten, play an important role in cereals. All grains are rich in vitamin B but lack vitamin C. Some, like yellow corn, contain beta-carotene. They also contain vitamin E (tocopherol), an antioxidant that contributes to the cereal’s stability.
Changes Due to Dry Heat (Dextrinization)
Dextrinization refers to the change in color and size of starch molecules when exposed to dry heat. The starch molecules break down into smaller units. Longer and higher exposure to heat leads to greater dextrinization.
Changes Due to Moist Heat
Swelling: Starch granules are insoluble in cold water. When heated in water, they absorb water and swell. If left undisturbed, the starch will precipitate out.
Gelatinization: Heat causes the starch granules to swell, soften, and form a stable paste or emulsion.
Starch Changes During Cooking
Gelling: When a gelatinized mixture contains enough starch, it forms a solid or semi-solid gel. Gelation increases as the mixture cools or is refrigerated.
Retrogradation: When a starch gel cools, the starch molecules tend to reassociate and form a network. This can lead to a deterioration in product quality. The gel shrinks, and water is forced out.
Syneresis: When a cold starch gel is allowed to rest and is then cut, fluid drainage occurs.
Factors Affecting Viscosity
- Concentration of starch
- Type of starch
- Temperature and heating time
- Intensity of agitation
- pH of the mixture
- Addition of other ingredients
- Clumping
Tubers
Tubers are thickened underground stems or roots of certain plants, such as potatoes, yams, and sweet potatoes. They are rich in starch and contain a small amount of protein and fiber, and very few lipids (0.1%), except for groundnuts, which have 25% lipids. Potatoes are rich in potassium and vitamin C. This vitamin is preserved by cooking or roasting potatoes with their skins on and with minimal water. Sweet potatoes and yams have similar compositions.
Based on starch and sugar content, there are two main types of potatoes:
Yellow Potato:
- Brown or yellow skin
- Less sugar than starch
- Forms a paste when cooked
- Suitable for baked potatoes, mashed potatoes, fried potatoes, and soufflés
White Potato:
- Red or white skin and flesh
- More sugar, less starch
- Retains its shape when cooked
- Suitable for salads, scallops, and sliced potatoes
Cooking
When potatoes are boiled, they lose a significant amount of vitamin C, especially if peeled.
French fries and potato chips, fried in hot oil (140°C to 180°C), absorb a large amount of fat and experience a significant reduction in mineral and ascorbic acid content.
Baking potatoes in the oven results in slightly higher vitamin C losses than boiling because of the higher oven temperature. However, fewer vitamins and minerals are lost overall compared to frying.