Flavour-Impact Compounds

tallowy, green [57, 58, 65, 69] Green, metallic, fatty [57, 58, 65] Soapy, fatty, green [57] 

Compound Odour descriptor Retronasal threshold (pg/L) Orthonasal threshold (pg/L) Amount in fresh orange juice (pg/L) Amount in processed orange juice (pg/L) 

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Table 10.2 presents a summary of odour qualities, odour thresholds in water, and concentrations of some selected volatile compounds, which are characteristic flavour impact compounds, owing to their typical flavour quality and their rather low odour thresholds. These compounds are not formed during fermentation but originate from the raw material and contribute significantly to the typical flavour of a fruit. The components summarised in Table 10.2 are important compounds in wine and different fruits and are discussed later. 

The "impact compound that provides the primary stimulus for fruit character in the raspberry is the ketone, l-(p-hydroxphenyl)-3-butanone 11). Other important flavour contributors are cw-3-hexen-l-ol, a - and p - ionones, and a - irone (72, 13). In R. arcticus the characteristic aroma is considered to be from mesifiirane (70). It has, however, been reported that steam distillates of raspberries can be assessed for aroma content using a colorimetric procedure and 80% of aroma is accounted for by geraniol, nerol, linalool, a - terpineol and die ionones (13). 

The kiwi fruit is a cultivar group of the species Actinidia deliciosa. More than 80 compounds have been identified in fresh and processed kiwi [137]. Methyl acetate, methyl butanoate, ethyl butanoate, methyl hexanoate and ( )-2-hexenal have the most prominent effect on consumer acceptability of kiwi fruit flavour [137-140]. The volatile composition of kiwi fruit is very sensitive to ripeness, maturity and storage period [138, 139]. Bartley and Schwede [140] found that ( )-2-hexenal was the major aroma compound in mature kiwi fruits, but on further ripening ethyl butanoate began to dominate. Ripe fruits had sweet and fruity flavours, which were attributed to butanoate esters, while unripe fruits had a green grassy note due to ( )-2-hexenal [140]. The most important character-impact compounds of kiwi fruits are summarised in Table 7.4. 

The fruit of pumpkin (Cucurbita pepo) is eaten boiled or baked. About 30 compounds have been identified in the volatile extracts of raw pumpkin, with the major classes of compounds being aliphatic alcohols and carbonyl compounds, furan derivatives and sulfur-containing compounds. Hexanal, ( )-2-hexenal, (Z)-3-hexen-l-ol and 2,3-butanedione have been identified as important for the flavour of freshly cooked pumpkins (Table 7.7) [35] however, studies using GC-O techniques are needed to get a better understanding of the character-impact compounds of pumpkins. 

The root of parsnip Pastinaca sativa) is eaten boiled or baked. The major classes of compounds identified in raw and cooked parsnip are monoterpenoids, aliphatic sulfur compounds, and 3-alkyl-2-methoxypyrazines [35]. To the best of our knowledge, no investigations have been performed to elucidate the character-impact compounds in parsnip by modern GC-O techniques however, it has been suggested that volatile compounds such as terpinolene, myristicin and 3-sec-butyl-2-methoxypyrazine maybe important contributors to the flavour of parsnip owing to either their high concentrations or their low threshold values, or both [35]. 

Banana (Musa sapientum L.) is one of the most common tropical fruits, and one of Central America s most important crops. It is grown in all tropical regions and is one of the oldest known fruits [45]. From a consumer perspective, bananas are nutritious with a pleasant flavour and are widely consumed throughout the world [57]. Esters predominate in the volatile fraction of banana (Fig. 8.2). Acetates are present in high concentrations in the fruit and generally possess a low threshold. Isopentyl acetate and isobutyl acetate are known as the two most important impact compounds of banana aroma. Alcohols are the second most important group of volatiles in banana extracts. 3-Methyl-1-butanol, 2-pentanol, 2-methyl-1-propanol, hexanol, and linalool are the alcohols present in higher concentrations in the fresh fruit [45]. 

Spirit drinks which are produced by flavouring ethyl alcohol of agricultural origin with distillates of caraway or dill are called akvavit or aquavit and mainly come from Denmark and Scandinavia these spirits are flavoured using neutral alcohol distillates of caraway (Carvum carvi) and/or dill Anethum graveolens) the use of essential oils is prohibited. The impact compounds of these spirits are f+j-carvone and anethol. 

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 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. 

Glintert, M., Emberger, R., Hopp, R., Kopsel, M., Silberzahn, W., Werkhoff, R. (1991) Chirospe-cific analysis in flavour and essential oil chemistry. Rart A. EUbertone the character impact compound of hazelnuts. Z. Lebensm. Unters. Eorsch. 192. 108-110... 

A variety of different volatile compounds such as the terpenoids thymol, carvacrol. eugenol, carvone and thujone, which are character-impact compounds for important spices (23,24), have antioxidative activity but the use of these compounds as aiilioxi dants for different foods are limited by the characteristic flavour of the particular compound. 

In the food industry, the determination of key odorants in highly complex extracts is a common analytical challenge. Both the suitability of GCxGC-ToF MS and the inadequacy of GC-ToF MS in target flavour analysis were shown by Adahchour et al. [24]. Two odour-impact compounds, methional and sotolon, were identified and quantified in a very complex dairy spread extract by using the three-dimensional approach. In contrast, GC-ToF MS failed in the isolation of these two minor compounds from high-concentration interferences. 

Lin, J. and R.L. Rouseff, 2001. Characterization of aroma-impact compounds in cold-pressed grapefruit oil using time-intensity GC-olfactometry and GC—MS. Flavour Fragr. J., 16 457—463. 

Peterson, D.G., G.A.Reineccius, Determination of the aroma impact compounds in heated sweet cream butter. Flavour Fragrance /., 18(4), p. 320, 2003. 

Olivecrona, T, Bengtsson, G. Lipase in milk. In Lipases (Eds. Borgstrijm, B., Brockman, H.L.), p. 205, Elsevier Science Publ., Amsterdam. 1984 Ott, A. Fay, L.B., Chtiintreau, A. Determination and origin of the aroma impact compounds of yoghurt flavor. In Flavour perception. Aroma evaluation (Eds. H.P. Kruse, M. Rothe) Universitat Potsdam, 1997, p. 203... 

Sugars, acids and aroma compounds contribute to the characteristic strawberry flavour [85]. Over 360 different volatile compounds have been identified in strawberry fruit [35]. Strawberry aroma is composed predominately of esters (25-90% of the total volatile mass in ripe strawberry fruit) with alcohols, ketones, lactones and aldehydes being present in smaller quantities [85]. Esters provide a fruity and floral characteristic to the aroma [35,86], but aldehydes and furanones also contribute to the strawberry aroma [85, 87]. Terpenoids and sulfur compounds may also have a significant impact on the characteristic strawberry fruit aroma although they normally only make up a small portion of the strawberry volatile compounds [88, 89]. Sulfur compounds, e.g. methanethiol. 

Guava is native to Central America. It was distributed into other parts of tropical and subtropical areas such as Asia, South Africa, Egypt, and Brazil by the early seventeenth century [49]. Some examples of impact-flavour compounds have already been identified in guava -ionone [58], terpene hydrocarbons [63], and esters [43] could be mentioned. 

The sulfur components ethyl S-(+)-2-methylbutanoate and dimethyl trisulfide (with 0.006 and 0.01 pg/L odour thresholds in water, respectively) were reported as impact-flavour compounds in fresh Hawaiian pineapple essence prepared by solvent extraction. The major volatile components were methyl and ethyl esters [59]. 

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