Vegetable aroma substance

Le Thanh, M., Pham Thi, S. T. and Voilley, A. (1992) Influence of the presence of vegetable oil in emulsion on the volatility of aroma substances during the course of the extraction. Sciences des Aliments, 12, 587-92. 

Fruits and vegetables (e. g., pineapple, apple, pear, peach, passion fruit, kiwi, celery, parsley) contain unsaturated Cn hydrocarbons which play a role as aroma substances. Of special interest are (E,Z)-l,3,5-undecatriene and (E,Z,Z)-1,3,5,8-undecatetraene, which with very low threshold concentrations have a balsamic, spicy, pinelike odor. It is assumed that the hydrocarbons are formed from unsaturated fatty acids by P-oxidation, lipoxygenase catalysis, oxidation of the radical to the carbonium ion and decarboxylation. The hypothetical reaction pathway from linoleic acid to (E,Z)-l,3,5-undecatrieneis shown in Formula 5.25. 

Z)-3-Hexenal (or m-3-hexenal) is the key aroma substance emitted when grass is cut and other types of vegetation are damaged. It has a very low odor threshold of 0.25 parts per billion. 

The aroma substances that comprise flavors are found in nature as complex mixtures of volatile compounds. A vast majority of volatile chemicals that have been isolated from natural flavor extracts do not provide aroma contributions that are reminiscent of the flavor substance. For instance, n-hexanal is a component of natural apple flavor (1) however, when smelled in isolation, its odor is reminiscent of green, painty, rancid oil. Similarly, ethyl butyrate has a nondescript fruity aroma although it is found in strawberries, raspberries, and pears, it does not uniquely describe the aroma quality of any of these individual fruits. It has long been the goal of flavor chemists to elucidate the identity of pure aroma chemicals that have the distinct character impact of the natural fruit, vegetable, meat, cheese, or spice that they were derived from. Often, these are referred to as character impact compounds (2). 

Historically, most studies on plant volatiles were undertaken with the aim of identifying the substances responsible for the characteristic aroma and flavor of plant materials. Since the 1970 s studies on the pathways and control mechanisms of flavor formation have been carried out ( 1), showing that fruits, vegetables and spices contain volatiles originating predominantly from secondary plant metabolism (2j. 

Spices are aromatic vegetable substances used to provide flavor and aroma. A convenient classification for spices might be the following (a) the tropical spices such as pepper and cinnamon, (b) herbs such as sage and rosemary, and (c) seed spices such as mustard and sesame [4]. 

While the preservation techniques outlined in earlier sections were aimed at retention of the original odor and flavoring substances of the raw material, including regeneration of lost aroma constituents, this is not important in pickled vegetables since a new typical aroma is developed. 

The biochemical processes of maturation have traditionally been summarized by the transformation of a hard, acidic green grape into a soft, colored fruit rich in sugar and aromas. As already indicated, these transformation can only occur when the grape is attached to the rest of the plant. In this case, the increase in the concentration of a substance in the berry can be due to importation of this substance, on-location synthesis or water loss in the vegetal tissue. Conversely, its diminution can result from exportation, degradation or water gain in the tissue. 

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