Vegetables, character impact flavor compounds

Figure 3 Representative vegetable character impact flavor compounds.

Table 3 Character Impact Flavor Compounds in Vegetables...

The mono- and sesquiterpenes in fruits (cf. 18.1.2.6) and vegetables (cf. 17.1.2.6), herbs and spices (cf. 22.1.1.1) and wine (cf. 20.2.6.9) are presented in Table 5.33. These compounds stimulate a wide spectrum of aromas, mostly perceived as very pleasant (examples in Table 5.34). The odor thresholds of terpenes vary greatly (Table 5.34). Certain terpenes occur in flavoring plants in such large amounts that in spite of relatively high odor thresholds, they can act as character impact compounds, e. g., S(+)-a-phellandrene in dill. 

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). 

Recent aroma research has been devoted to the identification of key flavor compounds in vegetables and is the subject of several contemporary reviews (31,34,35). Cucumbers, sweet com, and tomatoes are botanically classified as fmits however, for flavor considerations they are regarded as vegetables, because they are typically consumed with the savory portion of the meal. Overall, the knowledge base of character impact compounds for vegetables is much smaller than other flavor categories and warrants further investigation. 

A brothy compound associated with boiled beef, 4-methylthiazole-5-ethanol (sulfurol), is a reaction flavor product from hydrolysis of vegetable protein. It is suspected that a trace impurity (2-methyltefrahydrofuran-3-thiol) in sulfurol is the actual beef broth character impact compound (15). Another reaction product flavor chemical, mercaptopropanone dimer, has an intense chicken-broth odor. A synthetic pyrazine, 2-pyrazineethanethiol, provides excellent pork character (15). 

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