Flavor of tomato and tomato products

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Abstract
The characteristic sweet‐sour taste of tomato and its overall flavor intensity are due to the following components: reducing sugars (fructose and glucose), free acids (mainly citric’ acid), their ratio, as well as some volatile substances, not identified so far, and the interplay between the above‐mentioned groups of compounds. Of the minerals, potassium (by influencing the free acid content) and phosphate (due to its buffering capacity) indirectly affect the taste. The effect of the free amino acids (glutamic acid, glutamine, gamma‐aminobutyric acid, and aspartic acid) is not unambiguously proven. The characteristic tomatolike flavor is predominantly determined by volatile substances. Volatile substances develop partly during ripening, partly during the comminution of the ripe fruit, as an effect of the enzymes activated. Volatile substances characterizing fresh tomato flavor are derived mainly from fatty acids and amino acids. Differences between the flavors of different varieties, the less characteristic, weaker flavor of hothouse‐grown tomatoes or artificially ripened ones, are explained by the different quantitative proportions of the volatile substances. So far no key substance playing a decisive role in the flavor of tomato has been detected. Of the approximately 400 volatile compounds so far identified, several were found, however, which have an important role in the flavor of fresh tomato (cis‐3‐hexenal, trans‐2‐hexenal, 2‐isobutylthiazole, hex‐anal, cis‐3‐hexen‐1‐ol, 2E,4E‐decadienal, 6‐methyl‐5‐hepten‐2‐one, etc.). In the course of tomato processing the flavor substances undergo substantial qualitative and quantitative change, which may or may not be favorable. Depending on the extent of heat treatment and its duration, the reducing sugar and amino acid content decreases while the acid content (by the formation of pyrrolidone carboxylic acid) increases. A part of the volatile substances (mainly those providing “green” smell) evaporates and at the same time—traceable back to the breakdown of sugars and carotenoids—new components, among them those which characterize the “cooked” smell of tomato products, are formed (e.g., dimethyl sulphide, acetaldehyde). Although our knowledge as to the qualitative and quantitative composition of tomato flavor, the factors affecting it, and the effect of certain compounds on it has substantially increased, we are still not in the position to consciously develop the flavor during cultivation and processing. To achieve this further systematic research work is necessary.