Character-impact components

Aroma and flavor components of roasted coffee were investigated by numerous authors. In 1926 Reichstein and Staudinger (J 8) characterized furfurylmercaptan (2-furyl-methanthiol) as an important aroma constituent of roasted coffee which is a character impact component. 

Table VIII shows the dramatic differences between fresh and dried leaves. In this case, as oj sed to peppermint, rosemary and thyme, trans-2-hexenal is more in the fresh than in the dried and aged. The same is true for phenyl ethyl alcohol. Interestingly, trans-cinnamic aldehyde constitutes 50% of the total living headspace volatiles, but it is still less than in the aged leaf and commercial oil. However, cinnaniyl alcohol represents 20% of the fresh volatiles but is only a trace conpcanent of the aged leaf and oil. 4-Methoxy cinnamic aldehyde, identified as a cassia constituent for the first time, also increases 3-fold on drying but has disappeared completely in the comtnercial oil. 2-Methoxy cinnamic aldehyde, sometimes called the character impact component of cassia oil, is present in the headspace of the leaves to only a minor extent but it is the second most abundant component of the oil.

The agricultural production of flavor and fragrance materials has several disadvantages, including variation in consistency and quality, and dependency on climatic, seasonal, geographic, and even political factors. The microbial production of flavor and fragrance materials may compliment or offer an alternative to traditional sources of these materials. Fermentation may be particularly suited to the production of unique, highly intense character impact components, i.e., substances that can potentiate the aroma and flavor of fruits, dairy and other flavors at low levels ( 100 ppm in the finished flavor). 

Figure 10.8 shows three monoterpenoid alcohols geraniol (10.16), citronellol (10.21) and linalool (10.22) all of which have been mentioned earlier as being key fragrance ingredients which can be obtained from natural sources. Geraniol is one of the character impact components of rose but it is only present in rose oils to the extent of about 30%. Much... 

A key component in both chili powder and curry powder, cumin is the dried seed of the herb Cuminum cyminum, a member of the parsley family. Cuminaldehyde is the principal contributor to the spice s aroma and flavor, which imparts a strong musty/earthy character, with green grassy notes contributed by p-1,3- and 1,4-men-thadienals. frfl 5-2-Dodecenal, possessing a persistent fatty-cifrus-herbaceous odor, is a character impact component of coriander, along with uf-linalool (15). 

The character impact component for Concord (Labruska) grape has been long known as methyl anthranilate. More recently, ethyl 3-mercaptopropionate was identified in Concord grape, and in the low-ppm range it possesses a pleasant fruity fresh Concord grape aroma (27). 2-Aminoacetophenone and mesifuran are... 

As these examples indicate, the characteristic flavor of a food, fruit, etc., usually derives from a complex mixture of components. In a few cases, one unique sulfur compound is a character-impact compound, a material recognized as having the same organoleptic character as the material itself. Although some 670 compounds, of which more than 100 are sulfur-containing, have been identified in roast coffee, one material, furfurylmercaptan (2-furylmethanethiol) is considered to be a character-impact compound.43,44 The threshold level for detection of 2-furylmethanethiol in water is 0.005 ppb, and at levels of 0.01-0.5 ppb, it has the very characteristic aroma of freshly roasted coffee. However, as in many other cases, there is a concentration effect. At levels from 1-10 ppb the aroma is that of staled coffee with a sulfury note .43 Hence, 2-furylmethanethiol has a two headed property - at low concentrations it is a character impact compound and at higher levels it is an off-flavor component. 

Esters also constitute a group of important flavour compounds. They are the main aroma components found in fruits (apples, pears,. ..). For example, bananas contain 12-18 ppm acetates. The price of the pure flavour compounds, when isolated from fruit, can range between 10,000 and 100,000 US /kg In the past, research has been carried out by our group about the microbial production of fruity esters by the yeast Hansenula mrakii and the fungus Geotrichum penicillatum [10]. A fermentation was developed whereby fusel oil was continuously converted into a mixture of 3-methylbutyl acetate (isoamyl acetate) and 2-methylbutyl acetate, the character impact compounds of banana flavour. 

The investigation of a series of model meat systems has demonstrated the important role of volatile sulfur-containing heterocyclic components substituted with sulfur in the 3-position. One of these 3-substituted sulfur compounds, 2-methy1-3-methy1thio-furan was identified recently in the volatiles from cooked beef aroma (5J and from a heated yeast extract composition (6J and is considered a meaty character impact compound. 

The tastes of all natural foods are imparted by complex flavour mixtures consisting of a multitude of different single substances. The total sensoric impression is, however, imparted already by a few significant components, so-called character impact compounds. The biotechnical reaction therefore only has to yield sufficient amounts of these compounds in the correct proportion. 

A professional description of flavours uses as precise descriptors as possible. Chemical analytical results are combined with sensory analysis of the identified components to assess the relative importance and contribution to the flavour profile. Key ingredients or character impact compounds (CIC) are important components sine qua non to impart the typical, product characteristic, flavour, e.g. anethol for anise, eugenol for clove, 3-methyl butyl acetate for banana or ethyl butyrate to improve the juiciness of orange juice. 

Characteristic aroma components in foods and off-flavor substances in processed foods are called character impact compounds. It would be desirable to develop methods for finding such compounds with sensory methods because such information is useful in the food industry. A compilation of odor and taste threshold values was edited by Fazzalari (7). Olfactory-trigeminal response to odorants was measured using rabbits (2). However, aroma quality can be evaluated only by human sense. In spite of this fact, olfactory judgment by humans can not give constant data like... 

Figure 7 shows the El-mass spectra for wr-turmerone, the character impact compound for turmeric, fhe identification of this component was based on uitei prctalioii of the mass spectrum and correlation with previously reported data (9,10). Figure 8 shows the mass. spectrum of turmerone. Mass spectral data for this component was also reported by Su, et (tl (9). I hey reported a base peak at m/z =121 with a probe temp equal to 70 C. llicy also reported the appearance of an ion at ro/z = 119 when the probe temperature was increased 150 C which they attributed to the aromatization of the cyclohexadicny) moiety at the high temperatures of the GC-MS interface line. Figure 9 shows the mass spectrum of curlone. This agrees with the data reported by Kisco, et al [12). 

Pear flavor Ethyl and methyl (2 ,4Z)-2,4-deca-dienoates (see fruit esters) are the characteristic impact compound of Williams Christ pears. Other fruit esters in B. ate butyl and hexyl acetate, ethyl butanoate and ethyl (-r)-2-methylbutanoate Pineapple flavor Numerous fniit esters, including ethyl 2-methylbutanoate and hexanoate, as well as some 4- and 5- alkanolides are responsible for the general fruity character. Key components include Fura-neol , mesifuran (see Furaneol ) and some sulfur-substituted esters, especially methyl 3-(methylthio)propa-noate (CjH.oOzS, Mr 134.19, CAS [13532-18-8]) and ethyl 3-(methylthio)pmpanoate (C6H12O2S, Mr 148.22, CAS [13327-56-5]). Both substances resemble pineapple at very high dilutions. Remarkable is the occurrence of 1,3,5-undecatriene (see galbanum oil) in fresh pineapple. 

The table 5 shows the odour descriptors and odour threshold of the aroma compounds in La Mancha Rojal wines obtained by the bibliographic references (Kotseridis Baumes, 2000 Lopez et al., 2003). With over 50 aroma components of wide-ranging intensities and no single character impact compounds, it is difficult to predict the overall aroma impact of these wines from the sheer size of the data. To estimate overall wine aroma, the odour descriptors were grouped in different aromatic series and every compound is assigned to one or several aromatic series based on similar odour descriptor used. 

The combination of GC with olfactometry is another possibility for detection that has been used in essential oils analysis. " " " Olfactometry adapters are commercially available and should include humidity of the GC effluent at the nose adapter and provide auxiliary gas flow. The correlation among eluted peaks with specific odors allows accurate retention indices or retention times to be estabhshed for the essential oil components. Some of them can be detected in this way after applying chemometric techniques, such as cluster analysis and principal component analysis, to the data from the sensors. A limitation of GC with olfactometry is that peak coelution in complex samples makes identification of the compound(s) responsible for an odor difficult, particularly where trace odorants coelute with larger odor-inactive peaks. One possible solution for identifying character-impact odorants where coelution occurs is to use comprehensive two-dimensional GC (GC X GC). " ... 

Flavors are never attributed to a single aroma compound rather, foods are flavored by multitudes of odoriferous components frequently present in trace concentrations. Thus, for instance, the volatile components of fruits only rarely exceed a quantity of 10 ppm (441) (Table 1). The isolation of the original aroma without any substantial modification requires special methods which have to be adapted with great care to the specific food 472). Some cases are known where a natural flavor impression is dominated by one single substance (character impact compound) (270) (Table 2) or a small number of compounds mostly of... 

Aliphatic esters in various combinations play a major part in many flavors, particularly fruit flavors 441), Hexyl acetate develops the strongest and most typical odor in Cox s Orange Pippin apples (279). Hexyl 2-methylbutyrate contributes highly to the flavor of Golden Delicious apples (265). Methyl and ethyl esters of ( )-3-hexenoic, (Z)-4-decenoic (32) and )- and (Z)-4-octenoic acids have some importance in the flavor of pineapple 408). Methyl (Z)-4-decenoate (32) and methyl thiohexanoate account for about 56% of the odor provided by the components of the oxygenated fraction of hop oil 202). Ethyl (jE, Z)-2,4-decadienoate (35) is considered as the character impact compound in the aroma of Bartlett pears (227) (Table 2). The application of this pear ester in reconstitution work has been facilitated by the development of highly stereospecific syntheses 405, 407, 457). Isobutyl an-gelate is considered as an essential constituent of Roman camomile oil 85). 

Preparation of a trial blend. The flavorist prepares a first blend of ingredients. Fischetti [3,5] does this by breaking the flavor down into parts The first being the character impact portion, the second being contributory compounds and the final being differential components. These parts may be further described as ... 

Diallylthiosulfinate (allicin) and diallyldisulfide are formed from the main component by means of the enzyme alliinase. Both are character impact compounds of garlic. 

Benzaldehyde is considered to be the character-impact compoimd for cherry aroma (77), and is the key component in imitation cherry flavor compositions (18), The biosynthesis of this character-impact compound has been attributed to the acid or enzymic hydrolysis of the glucoside amygdalin in cherry pips. The importance of benzaldehyde in the aroma of cherry is emphasised by Schmid and Grosch (19), On sniffing stepwise diluted flavor extracts from cherries, seven compounds were revealed to have the highest aroma values - these compounds were benzaldehyde, linalool, hexanal, /ran5-2-hexenal, phenylacetaldehyde, (Z, )-2,6-nonadienal and eugenol. 

KR Cadwallader, R Surakamkul, SP Yang, TE Webb. Character-impact aroma components of coriander (Coriandrum sativum L.) herb. In F. Shahidi, C.-T. Ho, ed. Flavor Chemistry of Ethnic Foods. New York Kluwer Academic/Plenum Publishers, 1999, pp. 77-84. 

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). 

Turmeric is also primarily used as a spice component in curry dishes and as a coloring agent in dried and frozen foods. The character impact compound for turmeric is reported as ar-turmerone (13). Saffron, the dried red stigmas of Crocus sativus L. flowers, is utilized to impart both color and flavor, which is described as sweet, spicy, floral, with a fatty herbaceous undertone. Safranal (2,6,6-trimethyl-l,3-cyclohexadiene-l-carboxaldehyde) has been generally considered to be the character impact compound of saffron however, a recent investigation has also identified two other potent compounds, 4,4,6-frimethyl-2,5-cyclohexadien-l-one and an unknown, possessing saffron, stale, dried-hay aroma attributes (14). Representative structures for spice impact compounds are shown in Fig. 1. 

Potato flavor is greatly influenced by methods of cooking or preparation. Raw potato contains the characteristic earthy aroma component, 2-ixo-propyl-3-methoxypyrazine. A character impact compound common to boiled and baked potatoes is methional (3-[methylthio]propanal). Baked potatoes contain Maillard products such as 2-ethyl-3-methylpyrazine (earthy, nutty) and 2-ethyl-6-vinylpyr-azine (buttery, baked potato) (34). In potato chips and French-fried potatoes, the potato flavor character of methional is modified by volatile aromatics from frying oils, such as ( , )-2,4-decadienal, and thermally generated alkyl oxazoles possessing lactone-like flavors (34,39). The pyrazines 2-ethyl-3,5-dimethyl and 2,3-diethyl-5-methylpyrazine are described as potato chip like (40). 

Lipid components associated with meat fat, especially unsaturated aldehydes, play a significant role in species-characterization flavors. For example, ( ,Z)-2,4-decadienal exhibits the character impact of chicken fat and freshly boiled chicken (66). ( , )-2,6-Nonadienal has been suggested as the component responsible for the tallowy flavor in beef and mutton fat (63). 12-Methyltridecanal was identified as a species-specific odorant of stewed beef and provides a tallowy, beeflike flavor character (67). Aldehydes provide desirable flavor character to cooked meat, but they can contribute rancid and warmed-over flavors at high concentrations, resulting from autoxidation of lipids (68). 

The formulated principals correlating crystal structure features with the X Nb(Ta) ratio do not take into account the impact of the second cation. Nevertheless, substitution of a second cation in compounds of similar types can change the character of the bonds within complex ions. Specifically, the decrease in the ionic radius of the second (outer-sphere) cation leads not only to a decrease in its coordination number but also to a decrease in the ionic bond component of the complex [277]. 

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