Flavor trivia and tomato aroma: biochemistry and possible mechanisms for control of important aroma components.

Consumers are often dissatisfied with the flavor of fresh tomatoes (Lycopersicon esculentum Mill.) purchased in the supermarket. There are several reasons for this, ranging from poor genetic material to harvest and handling procedures. Research is ongoing to determine the important flavor components in tomato in order to give breeders and molecular biologists access to objective flavor criteria for use in selection of high-quality material. Furthermore, harvest and postharvest handling, and shipping and storage procedures can be analyzed for their effects on important flavor components. FLAVOR TRIVIA To successfully conduct this research, one must first understand what comprises flavor and how it is perceived. The nose has olfactory nerve endings at the back with receptors that bind volatiles emanating from food. These reactions are somewhat analogous to enzyme/ substrate stereochemical associations. Tastes such as sweet, sour, salty, or bitter are perceived because of reactions of sugars or polyalcohols, hydronium ions, sodium ions, glucosides , alkaloids, etc., with receptors located in certain regions of the tongue. The nerves in the tongue can also detect texture, temperature, metallic irritation, bite (carbonation), chemical heat [e.g., hot pepper ( Capsicum fruitescens L.)], etc., collectively known as trigeminal responses. The olfactory system is the more sensitive of the two organs, however, and the most sensitive of the five senses. It can detect odors in parts per trillion whereas receptors on the tongue can detect flavor compounds in parts per hundred. The adverse side of this extreme sensitivity is fatigue, which may be a protective mechanism against nerve damage (DeRovira, 1997). Nevertheless, the fatigue factor must be considered in sensory work with aroma compounds. The extreme sensitivity of the olfactory organ has played an important role in the evolutionary development of mammals, allowing for the odor imprinting involved in olfactory recognition. This has helped in developing behavioral relationships, such as mother-offspring, consort interactions, and general kin recognition, not to mention detection of predator and prey (Margot and Salvadori, 1995; Rouhi, 1996). Specific odors can evoke powerful thoughts and emotions in humans. The sense of smell, therefore, has played a key role in several areas important to species survival. In mammals at least 1000 receptor genes are devoted to encoding receptors that recognize odors; these comprise 1% to 2% of the mammalian genome (Rouhi, 1996). Many factors can affect our perception of flavor, especially the components of flavor made up of aroma compounds. Smelling an aromatic food through the front of the nose may produce a different