Joseph H. Hotchkiss

Food Dehydration and Concentration

Water is removed from foods under natural field conditions, by a variety of controlled dehydration processes and during such common operations as cooking and baking. However, in modern food processing, the terms food dehydration and food concentration have acquired rather special meanings.

Fats, Oils, and Related Products

Fats and oils have been discussed in several previous chapters. The major portions of fats and oils are made up of fatty acid esters of glycerol. Edible fats and oils come from both plant and animal sources and have important functional and nutritional properties in foods. Certain components of fats are required nutrients as well as carriers of the fat-soluble vitamins. Fats and oils can deteriorate in foods and are susceptible to oxidation and rancidity. They also have shortening, lubricating, emulsifying, and whipping properties, and high caloric value. The terms fat and oil only indicate whether the material is liquid or solid: fats that are liquid at room temperature are called oils.

Irradiation, Microwave, and Ohmic Processing of Foods

Both irradiation and microwave heating employ radiant energies which affect foods when their energy is absorbed, whereas ohmic heating raises the temperature of foods by passing an electrical current through the food. Each requires special equipment to generate, control, and focus this energy. Each of these are relatively new technologies as applied to foods. Food irradiation is used primarily as a preservation method, but it also has potential as a more general unit operation to produce specific changes in food materials. Microwave energy, on the other hand, has been employed especially to produce rapid and unique heating effects, one application of which can be food preservation. Ohmic heating is the newest and least used of the three technologies. Like microwave heating, ohmic heating can preserve foods by the application of heat and has the ability to very rapidly heat foods with minimal destruction.

Heat Preservation and Processing

Of the various means of preserving foods, the use of heat finds very wide application. The simple acts of cooking, frying, broiling, or otherwise heating foods prior to consumption are forms of food preservation. In addition to making foods more tender and palatable, cooking destroys a large proportion of the microorganisms and natural enzymes in foods; thus, cooked foods generally can be held longer than uncooked foods. However, cooking generally does not sterilize a product, so even if it is protected from recontamination, food will spoil in a comparatively short period of time. This time is prolonged if the cooked foods are refrigerated. These are common household practices.

Milk and Milk Products

Milk and milk products cover a very wide range of raw materials and manufactured products. No attempt is made in this chapter to deal with all of them. Rather, the properties and processing of fluid milk and some of the more common products manufactured from it, such as specialty milks, ice cream, and cheese, are discussed. Butter and margarine are considered in Chapter 16 on fats and oils.

Meat, Poultry, and Eggs

Humans are omnivorous and have consumed both animals and plants as foods throughout recorded history. However, before animals, birds, and fish can provide meat, eggs, or milk, their own physiological requirements for energy and synthesis must be satisfied. These requirements are met largely through the consumption of plant materials, which, if consumed directly by humans, could support a greater population than can the animal products derived from them. This is true with respect to total available calories, protein, and other nutrients needed to sustain life. In most cases, the amount of animal products consumed by a society is positively correlated with the affluence of the society.

Nutritive Aspects of Food Constituents

Food supplies both the energy for all of the body’s functions and the building blocks for growth and maintenance. Even in fully grown adults there is a requirement for energy and to build and maintain body components that are being replaced. For example, the human stomach is constantly being lost and replaced. Also, there is increasing evidence that diet plays a major role in our defense against disease, including chronic diseases such as cancer and heart disease. Mental processes and behavioral attitudes appear to be influenced by nutritional status and specific nutrients.

Cold Preservation and Processing

Freezing and refrigeration (i.e., cold storage) are among the oldest methods of food preservation, but it was not until 1875 that a mechanical ammonia refrigeration system capable of supporting commercial refrigerated warehousing and freezing was invented. This major advance was hampered by the lack of proper facilities, a prime requirement for any refrigerated or frozen food industry. Thus, as late as the 1920s, food delivered to a market in a frozen state commonly thawed before it could be brought home or else thawed in household ice boxes and generally was of marginal to poor quality. Starting in the 1920s, Clarence Birdseye pioneered research on quick-freezing processes, equipment, frozen products, and frozen food packaging. As household refrigerators and freezers became more common, the modern frozen food industry grew rapidly.

Introduction: Food Science as a Discipline

Food Science can be denned as the application of the basic sciences and engineering to study the fundamental physical, chemical, and biochemical nature of foods and the principles of food processing. Food technology is the use of the information generated by food science in the selection, preservation, processing, packaging, and distribution, as it affects the consumption of safe, nutritious and wholesome food. As such, food science is a broad discipline which contains within it many specializations such as in food microbiology, food engineering, and food chemistry. Because food interacts directly with people, some food scientists are also interested in the psychology of food choice. These individuals work with the sensory properties of foods. Food engineers deal with the conversion of raw agricultural products such as wheat into more finished food products such as flour or baked goods. Food processing contains many of the same elements as chemical and mechanical engineering. Virtually all foods are derived from living cells. Thus, foods are for the most part composed of “edible biochemicals,” and so biochemists often work with foods to understand how processing or storage might chemically affect foods and their biochemistry. Likewise, nutritionists are involved in food manufacture to ensure that foods maintain their expected nutritional content. Other food scientists work for the government in order to ensure that the foods we buy are safe, wholesome, and honestly represented.

Confectionery and Chocolate Products

Confections (i.e., candy) can be divided into two broad categories: those in which sugar is the principal ingredient and those which are based on chocolate. Differences in sugar-based candies depend largely on manipulating the sugar to achieve special textural effects. This is accomplished primarily by controlling the state of crystallization of the sugar and the sugar-moisture ratio. Examples of sugar-type confections include nougats, fondants, caramels, taffees, and jellies. Examples of chocolate-based confections include chocolate-covered confections, chocolate-panned confections, chocolate bars, and chocolate-covered fruits, nuts, and cremes. Many ingredients, including milk products, egg white, food acids, gums, starches, fats, emulsifiers, flavors, nuts, fruits, and others are used in candy-making.