Food chemistry

The molecular structure of sucrose, or ordinary table sugar. This sugar is probably the most familiar carbohydrate.

Food chemistry is the study of chemical processes and interactions of the biological and nonbiological components of foods. It overlaps with biochemistry in that it deals with the components of food such as carbohydrates, lipids, proteins, water, vitamins, and dietary minerals. In addition, it involves the study and development of food additives that can be used to preserve the quality of food or to modify its color, flavor, and taste. It is, thus, closely linked to food processing and preparation techniques. There is, however, an ongoing debate about the health effects of a number of food additives.

Brief history of food chemistry

The history of food chemistry dates back to the late 1700s, when many famous chemists were involved in discovering chemicals important in foods. In 1785, for example, Carl Wilhelm Scheele isolated malic acid from apples. In 1813, Sir Humphry Davy published the first book on agricultural and food chemistry, titled Elements of Agricultural Chemistry, in a Course of Lectures for the Board of Agriculture, in the United Kingdom. This book served as a foundation for the profession worldwide and went into a fifth edition.

In 1874, the Society of Public Analysts was formed, with the aim of applying analytical methods to benefit the public. Its early experiments were based on bread, milk, and wine.

It was also out of concern for the quality of the food supply, mainly food adulteration and contamination issues stemming first from intentional contamination and proceeding later to chemical food additives by the 1950s. The development of colleges and universities worldwide, most notably in the United States, expanded food chemistry through research of dietary substances, most notably the single-grain experiment during 1907-11. Additional research by Harvey W. Wiley at the United States Department of Agriculture during the late nineteenth century played a key role in creation of the United States Food and Drug Administration in 1906. The American Chemical Society established their Agricultural and Food Chemistry Division in 1908, and the Institute of Food Technologists established their Food Chemistry Division in 1995.

Water

A major component of food is water, which can range in content from 50 percent in meat products to 95 percent in lettuce, cabbage, and tomato products. It also provides a place for bacterial growth and food spoilage if it is not properly processed. One way of measuring this in food is by water activity, which is very important in the shelf life of many foods during processing. One of the keys to food preservation is to reduce the amount of water or alter the water's characteristics to enhance shelf-life. Such methods include dehydration, freezing, and refrigeration.

Carbohydrates

Carbohydrates form the largest group of substances in food consumed by humans. A common carbohydrate is starch.

The simplest version of a carbohydrate is a monosaccharide, made up of molecules in which carbon, hydrogen, and oxygen atoms are in the ratio 1:2:1. Thus, the general formula of a monosaccharide is C_nH_2nO_n, where n is a minimum of 3. Glucose and fructose are examples of monosaccharides. The familiar table sugar is sucrose, a disaccharide. Each molecule of sucrose is made up of a combination of one glucose and one fructose molecule.

A chain of monosaccharides forms a polysaccharide. Such polysaccharides include pectin, dextran, agar, and xanthan.

Sugar content is commonly measured in degrees brix.

Lipids

The term lipid encompasses a diverse range of molecules and to some extent is a catchall for relatively water-insoluble (nonpolar) compounds of biological origin. Examples of lipids are waxes, fatty acids, fatty-acid derived phospholipids, sphingolipids, glycolipids, and terpenoids, such as retinoids and steroids. Some lipids are linear aliphatic molecules, while others have ring structures. Some are aromatic. Some are flexible, and others are rigid.

Most lipids have some polar character, in addition to being largely nonpolar. In other words, the bulk of the structure of a lipid molecule is nonpolar or hydrophobic, meaning that it does not interact well with polar solvents like water. Another part of the molecular structure is polar or hydrophilic and will tend to associate with polar solvents like water. Thus lipid molecules are amphiphilic, having both hydrophobic and hydrophilic portions. In the case of cholesterol, the polar group is a mere -OH (hydroxyl or alcohol).

In food, lipids are present in the oils of grains such as corn and soybean, and they are also found in meat, milk, and dairy products. They act as vitamin carriers as well.

Proteins

Proteins make up over 50 percent of the dry weight of an average living cell and are very complex macromolecules. They play a fundamental role in the structure and function of cells. Protein molecules are constructed mainly of carbon, hydrogen, oxygen, and some sulfur, they may also contain iron, copper, phosphorus, or zinc.

In food, proteins are essential for growth and survival, but the amount of protein needed by an individual varies, based on the person's age and physiology (such as during pregnancy). Proteins in food are commonly found in peanuts, meat, poultry, and seafood.

Enzymes

Many proteins are enzymes that catalyze biochemical reactions. They reduce the amount of time and energy required to complete the reactions. Many areas of the food industry use enzyme catalysts, including baking, brewing, and dairy, to make bread, beer, and cheese.

Vitamins

Riboflavin (Vitamin B₂) is a water-soluble vitamin.

Vitamins are nutrients required in small amounts for essential metabolic reactions in the body. They are subdivided as either water-soluble (such as Vitamin C) or fat-soluble (such as Vitamin E). An adequate supply of vitamins can prevent such diseases as beriberi, anemia, and scurvy, but an overdose of vitamins can produce nausea and vomiting or even death.

Minerals

Dietary minerals in foods are large and diverse, with many required for health and survival. Some minerals, however, can be hazardous if consumed in excessive amounts. Bulk minerals with a Reference Daily Intake (RDI; formerly, Recommended Daily Allowance (RDA)) of more than 200 mg/day include calcium, magnesium, and potassium. Important trace minerals, with RDI less than 200 mg/day, include copper, iron, and zinc. They are found in many foods but can also be taken in dietary supplements.

Food additives

Food additives are substances added to food for such purposes as preserving its quality, adding to or enhancing its flavors, improving its taste, or modifying its appearance. Additives used today can be placed in a wide range of groups, such as food acids, anticaking agents, antioxidants, bulking agents, food coloring, flavoring agents, humectants, preservatives, stabilizers, and thickeners. They are generally listed by "E number" in the European Union or GRAS ("Generally recognized as safe") by the United States Food and Drug Administration.

Coloring

Food coloring is added to change or enhance the color of any food, mainly to make it look more appealing. It can be used to simulate the natural color of a product as perceived by the customer, such as adding the red dye FD&C Red No.40 (Allura Red AC) to ketchup. Alternatively, unnatural colors may be added to a product like Kellogg's Fruit Loops. Caramel is a natural food dye; the industrial form, caramel coloring, is the most widely used food coloring and is found in foods ranging from soft drinks to soy sauce, bread, and pickles.

Flavors

Flavor in food is important in determining how food smells and tastes to the consumer, especially in sensory analysis. Some of these products occur naturally, such as salt and sugar, but flavor chemists (called "flavorists") develop many flavors for food products. Such artificial flavors include methyl salicylate, which produces the wintergreen odor, and lactic acid, which gives milk a tart taste.

References

ISBN links support NWE through referral fees

• Belitz, H.-D., W. Grosch, and Peter Schieberle. Food Chemistry, 3rd edition. Berlin: Springer, 2004. ISBN 978-3540408185.
• Damodaran, Srinivasan, Kirk Parkin, and Owen R. Fennema (eds.). Fennema's Food Chemistry, 4th ed. Boca Raton: CRC Press/Taylor & Francis, 2008. ISBN 978-0824723453.
• Newton, David E. Food Chemistry. New York: Facts On File, 2007. ISBN 978-0816052776.
• Potter, Norman N., and Joseph H. Hotchkiss. Food Science, 5th ed. Springer, 1999. ISBN 083421265X.
• U.S. Food and Drug Administration. Everything Added to Food in the United States. Boca Raton, FL: C.K. Smoley, 1993. ISBN 084938723X.

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