Non-Nutritive Food Components
Foods contain some compounds that are not classified within the six basic nutrient groups. All sorts of substances can be found in food—natural, intentional, and unintentional. Among the beneficial compounds naturally found in foods are those that provide color and flavor, along with certain plant compounds.
Food is made more appetizing and interesting to behold by the wide spectrum of colors made possible through pigments. Most natural pigments are found in fruits and vegetables; the colors of foods from animal products and grains are less varied and bright. The dominant pigments found in plants are carotenoids (orange-yellow), chlorophyll (green), and flavonoids (blue, cream, red).
Although foods of animal origin are less colorful, even meat varies in color depending on its stage of maturity. When first sliced with a knife, a cut of beef is purplish red from the presence of a pigment called myoglobin. As it is exposed to air, the myoglobin combines with oxygen to turn the meat a bright red color. The meat then turns grayish brown during cooking when the protein holding the pigment becomes denatured. Cured meats present an altogether different scenario as added nitrites, compounds which are used as a preservative, react with the myoglobin to cause the meat to be a red color, which converts to pink (denatured protein) when cooked. Milk appears white as light reflects off the colloidal dispersion of milk protein. The yellowish hue of cream comes from carotene and riboflavin (vitamin B2). Carotene, a fat-soluble pigment, is also the substance that gives butter its yellow color.
The flavors in foods are derived from both nutrient and non-nutrient compounds. These are sometimes too numerous to track as the source of a specific flavor. Among the non-nutrient compounds in foods are the organic acids that determine whether foods are acidic or basic. An acidic pH in foods not only contributes to a sour taste, but the color of fruit juices, the hue of chocolate in baked products, and the release of carbon dioxide in a flour mixture. An alkaline pH contributes a bitter taste and soapy mouth feel to foods.
In addition to color and flavor compounds, some plants contain other nonnutritive substances that, when ingested. may have either beneficial or harmful effects.
Many of the possible anti-carcinogens, or compounds that inhibit cancer, come from plants. In particular, phytochemicals, a special group of substances found in plants, appear to have a protective effect against cancer. One class of these phytochemicals, called indoles, is found in vegetables such as cabbage, cauliflower, kale, kohlrabi, mustard greens, swiss chard, and collards. Laboratory animals given indoles and then exposed to carcinogens developed fewer tumors than animals exposed to the same carcinogens, but not given indoles.
There are several potentially harmful substances in plants. The U.S. Department of Health and Human Services has gone so far as to say that natural toxins are so widespread that the only way to avoid them completely is to stop eating. Chapter 6 covers these compounds under “Natural Toxicants.” Other substances, although not strictly toxins, can cause problems for certain people if ingested in excess. One such substance is caffeine.
Caffeine is a natural stimulant that belongs to a group of compounds called methylxanthines. The most widely used sources of caffeine include coffee beans, tea leaves, cocoa beans, and cola nuts. Caffeine is also found in the leaves of some plants, where it acts as a protection against insects.
Caffeine ingested at high concentrations may temporarily increase heart rate, basal metabolic rate, secretion of stomach acid, and urination. The increased secretion of stomach acids may cause problems for people with ulcers. In healthy adults, however, a moderate intake of caffeine does not appear to cause health problems. Individuals who habitually drink a lot of caffeine-containing beverages may. however, experience withdrawal headaches and irritability if they stop drinking the beverage. Another possible side effect in sensitive individuals is fibrocystic conditions in the breast, which is the painful but usually harmless occurrence of lumpiness in the breasts and under the arms. Excessive caffeine intake, defined as more than five 5-ounce cups of strong, brewed coffee, can also cause “coffee nerves.”
The Diagnostic and Statistical Manual of Mental Disorders published by the American Psychiatric Association defines caffeine intoxication as exhibiting at least five of the following symptoms: nervousness, agitation, restlessness, insomnia, frequent urination, gastrointestinal disturbance, muscle twitching, rambling thought and speech, periods of exhaustion, irregular or rapid heartbeat, and psychomotor agitation. Infants who ingest caffeine through their mother’s milk may also get the “jitters.” Because infants are unable to metabolize caffeine efficiently, the compound may stay in their system up to a week, compared to about twelve hours in a healthy adult.