Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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been widely published. The ad hoc Expert Group pro-

posed that infant feeds should contain around 0.35%

of thefat in the form of the long-chain o-3 polyunsatur-

ate DHA, together with 0.5% in the form of the long-

chain o-6 polyunsaturate arachidonic acid.

Conclusion

0038 At first sight, the idea that a simple dietary alteration

can bring about such significant changes in so many

areas of the body is difficult to accept. The key to

understanding this is the cell membrane, and the role

of polyunsaturated fatty acids in the health and well-

being of that membrane. Over the past 50–100 years,

the level and amount of the two families of poly-

unsaturates, the o-6 family and the o-3 family, have

changed. o-6 intake has doubled, whereas o-3 intake

has halved. The impact of this change is not immedi-

ately obvious; the effects are subtle and take a long

time to manifest themselves. During that time-scale,

other things have changed also, so that pinpointing

the factors responsible for certain effects is difficult.

What cannot be denied is that during the past 50–100

years, the West has seen more heart disease, more

depression, more aggression, more antisocial behav-

ior, more lung disease, more skin problems, and more

kidney ailments. Altering population intakes of

dietary polyunsaturates so as to consume more long-

chain o-3 polyunsaturates, and perhaps less of the

o-6s would help to bring about a reversal of these

trends.

See also: Cholesterol: Role of Cholesterol in Heart

Disease; Coronary Heart Disease: Etiology and Risk

Factor; Fatty Acids: Properties; Metabolism; Gamma-

linolenic Acid; Analysis; Dietary Importance

Further Reading

Boelsma E, Hendriks HFJ and Roza L (2001) Nutritional

skin care: health effects of micronutrients and fatty

acids. American Journal of Clinical Nutrition 73(5):

853–864.

Das UN (2000) Beneficial effect(s) of n-3 fatty acids in

cardiovascular diseases: but, why and how? Prosta-

glandins Leukotrienes and Essential Fatty Acids 63(6):

351–362.

Donadio JV, Larson TS, Bergstralh EJ and Grande JP (2001)

A randomized trial of high-dose compared with low-

dose Omega-3 fatty acids in severe Iga nephropathy.

Journal of the American Society of Nephrology 12(4):

791–799.

Hamazaki T and Okuyama H (eds) (2001) Fatty Acids and

Lipids – New Findings. Proceedings of the 4th Congress

of the International Society for the Study of Fatty Acids

and Lipids. Basel: Karger.

Holm T, Andreassen AK and Aukrust P (2001) Omega-3

fatty acids improve blood pressure control and preserve

renal function in hypertensive heart transplant recipi-

ents. European Heart Journal 22(5): 428–436.

Huang Y-S and Sinclair AJ (eds) (1998) Lipids in Infant

Nutrition. Champaign, IL: AOCS Press.

Jumpsen J and Clandinin MT (1995) Brain Development:

Relationship to Dietary Lipid and Lipid Metabolism.

Champaign, IL: AOCS Press.

Nettleton JA (1994) Omega-3 Fatty Acids and Health. New

York: Chapman & Hall.

tbl0003 Table 3 Adequate intake (AI)

for infant formula/diet (by an

ad-hoc Expert Workshop held in USA, April 2000)

Fattyacid Percentage of fattyacids

LA, 18:2; o-6.

10.00

ALA 18:3; o-3. 1.50

AA, 20:4; o-6.

0.50

DHA, 22:6; o-3.

0.35

EPA, 20:5; o-3.

<0.10

If sufficient scientific evidence is not available to calculate an estimated

average requirement, a reference intake called an Adequate Intake is

used instead of an RDA. The AI is a value based on experimentally derived

intake levels or approximations of observed mean nutrient intakes by a

group (or groups) of healthy people. The AI for children and adults is

expected to meet or exceed the amount needed to maintain a defined

nutritional state or criterion of adequacy in essentially all members of a

specific healthy population.

The Working Group recognized that in countries like Japan, the breast

milk content of LA is 6–10% of fatty acids, and the DHA is higher, about

0.6%. The formula/diet composition described here is patterned on infant

formula studies in Western countries.

The Working Group endorsed the addition of the principal long-chain

polyunsaturates, AA and DHA, to all infant formulas.

EPA is a natural constituent of breast milk but, in amounts more than

0.1% in infant formula, may antagonize AA and interfere with infant

growth.

tbl0002 Table 2 Recommended AI

for adults (by an ad-hoc Expert

Workshop held in USA, April 2000)

Fattyacid g per day (2000 kcal) Percentage

LA, 18:2, o-6 4.44 2.0

(upper limit)

6.67 3.0

ALA 2.22 1.0

EPA

þ DHA

0.65 0.3

DHA

minimum 0.22 0.1

EPA minimum 0.22 0.1

If sufficient scientific evidence is not available to calculate an estimated

average requirement, a reference intake called an Adequate Intake is

used instead of an RDA. The AI is a value based on experimentally derived

intake levels or approximations of observed mean nutrient intakes by a

group (or groups) of healthy people. The AI for children and adults is

expected to meet or exceed the amount needed to maintain a defined

nutritional state or criterion of adequacy in essentially all members of a

specific healthy population.

Although the recommendation is for AI, the Working Group felt that there

is enough scientific evidence to also state an upper limit for LA of 6.67 g

per day based on a 2000-kcal diet or of 3.0% of energy.

Elcosapentaenoic acid, C20:5; o-3.

Docosahexaenoic acid, C22:6; o-3.

For pregnant and lactating women, ensure 300 mg per day of DHA.

2508 FISH OILS/Dietary Importance

O’Keefe JH (2000) From Inuit to implementation: Omega-3

fatty acids come of age. Mayo Clinic Proceedings 75(6):

607–614.

Price PT (2000) Omega-3 polyunsaturated fatty acid regu-

lation of gene expression. Current Opinion in Lipidol-

ogy 11(1): 3–7.

Rogers PJ (2001) A healthy body, a healthy mind:

Long-term impact of diet on mood and cognitive

function. Proceedings of the Nutrition Society 60(1):

135–143.

SanGiovanni JP (2000) Meta-analysis of dietary essential

fatty acids and long-chain polyunsaturated fatty acids as

they relate to visual resolution acuity in healthy preterm

infants. Pediatrics 105(6): 1292–1298.

Simopoulos AP (ed.) (1998) The Return of o-3 Fatty Acids

to the Food Supply. 1. Land-based Animal Food Prod-

ucts and their Health Effects. Basel: Karger.

Teitelbaum JE and Walker WA (2001) Review: the role of

omega 3 fatty acids in intestinal inflammation. Journal

of Nutritional Biochemistry 12(1): 21–32.

FLAVOR (FLAVOUR) COMPOUNDS

Contents

Structures and Characteristics

Production Methods

Structures and Characteristics

T Cserha

ti and E Forga

cs, Chemical Research

Center, Budapest, Hungary

Introduction

0001 The quantity and composition of flavor compounds

in foods and food products exert a marked influence

on consumer acceptance and, consequently, on the

commercial value of the products. It has been estab-

lished many times that one of the main properties

employed for the evaluation of product quality is

flavor, that is, an adequate flavor composition con-

siderably enhances the marketability of products. A

desirable flavor is due to the complex mixture of

various volatile and nonvolatile constituents mixed

in proper proportions. However, flavor is not only a

physical and/or chemical term; it includes the inter-

action of food and consumer. Flavor sensation is a

dynamic process: the volatile or nonvolatile flavor

compounds first have to be released from the food-

stuff and then transferred to the adequate receptor

organs. An exact knowledge of the stability of the

flavor compounds in the face of hydrolysis, oxida-

tion, and other environmental and technological con-

ditions is also of paramount importance, because it

may help to predict the shelf-life of products and to

assess the influence of technological steps on flavor

compounds, resulting in more consumer-friendly

processing methods. Furthermore, the qualitative de-

termination and identification of flavor compounds

may contribute to the establishment of the proven-

ance of the product and to its exact qualification.

Unfortunately, traditional analytical methods are

generally unsuitable for the separation and accurate

determination of particular fractions of flavor com-

pounds. Moreover, they do not contain any useful

information on the concentration of the individual

flavor compounds and are not suitable for their iden-

tification. The high separation capacity of various

chromatographic techniques makes them a preferred

method for the analysis of flavor compounds in

foods. In addition to influencing commercial value,

some flavor compounds are believed to have advan-

tageous effect on human well-being as enhancers of

appetite and promoters of digestion.

0002This article overviews the flavor compounds found

in various foods and food products, their chemical

composition, physicochemical parameters, sensorial

characteristics and their separation, quantitation,

and identification by various chromatographic tech-

niques.

Chemical and Physical Characteristics of

Flavor Compounds

0003A considerable amount of compounds have been

identified in a wide variety of foods producing flavor

sensation. The chemical structures of these molecules

show high diversity and even flavor compounds with

FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics 2509

highly similar chemical structures may have an

entirely different sensorial effect. Therefore, the clas-

sification of flavor compounds according to their

chemical structure (i.e., linear aldehydes, alcohols) is

possible but from a practical point of view is irrele-

vant. Most flavor molecules are hydrocarbons, alco-

hols, aldehydes, ketones, or esters. The backbone of

these compounds generally consists of a linear or

branched alkane or alkene chain. Saturated and un-

saturated ring structures and terpenoids also occur

among the basic structures of flavor compounds.

Much effort has been devoted to elucidating the

quantitative relationship between organoleptic char-

acteristics and molecular structure or physicochem-

ical parameters of flavor compounds. Because of the

complexity of molecular structures and organoleptic

properties, these calculations have been of moderate

success. Correlations can be observed for only a def-

inite set of structurally similar compounds that have a

very low predictive value for flavor compounds with

different molecular characteristics. Most of these

molecules are relatively small; they are volatile or

semivolatile and especially suitable for gas chromato-

graphic (GC) analysis. As flavor compounds gener-

ally occur in foods in very low concentrations, their

enrichment before the chromatographic separation

process is a prerequisite of any successful analysis.

However, it has to be borne in mind that the efficacy

of various preconcentration methods such as steam

distillation, solvent extraction, Soxhlet method and

supercritical fluid extraction (SFE) considerably

depend on the flavor compound to be extracted and

on the conditions of extraction. Organic solvent par-

tition and solid-phase microextraction (SPME) can

also be employed for the enrichment of flavor com-

pounds. Furthermore, volatile flavor compounds can

be purged from the accompanying matrices carried to

a cold trap and then can be cryofocused.

Flavor Compounds in Foods and Food

Products

Spices

0004 Spices are important commercial commodities with

diverse applications in foods and food products. The

accurate measurement of the composition of flavor

reveals not only the sensory value of the spice but can

also be used as a marker of authenticity. Because of

the marked structural diversity of flavor compounds

in different spices, a large number of chromato-

graphic methods have been developed and applied

for the separation, quantitation, and/or identitifica-

tion of individual components of flavor in spices.

Thus, flavor compounds extracted from cinnamon

(inner bark of Cinnamon zeylanicum Nees) by solv-

ent-assisted SFE have been analyzed by series coupled

capillary GC (cGC). The presence of the structurally

similar aldehydes and alcohols as the main flavor

components has been verified (Table 1). SPME, SFE

followed by cGC, and mass spectrometric (MS) de-

tection have been employed for the analysis of flavor

compounds of commercial cassia. The results proved

that cassia contains not only linear but also benzene-

based flavor components (Table 1). A simple and

easy-to-carry-out thin-layer chromatographic (TLC)

method has been employed for the separation of

vanilla bean extracts using automated multiple

development. The occurrence of 5-(hydroxymethyl)-

2-furfural, 4-hydroxybenzoic acid, 4-hydroxybenzal-

dehyde, vanillic acid, and vanillin has been identified.

It was stated that the method is suitable for a botan-

ical identification and authenticity test of mercantile

vanilla products. High-performance liquid chroma-

tography (HPLC) has also found application in the

analysis of flavor compounds extracted from cured

vanilla beans (Vanilla fragrans). The measurements

indicated that the extract contained glucovanillin, p-

hydroxybenzoic acid, p-hydroxybenzaldehyde, vanil-

lic acid, vanillin, and ethyl vanillin. The characteristic

tbl0001Table 1 Alphabetic list of chemical names of flavor compounds

found in cinnamon and commercial cassia

No. of flavor compound Chemical name

Cinnamon (inner bark of Cinnamon zeylanicum Nees)

1 trans-Cinnamaldehyde

2 Cinnamyl acetate

3 Cinnamyl alcohol

4 Eugenol

5 2-Hydroxycinnamaldehyde

6 2-Methoxycinnamaldehyde

Commercial cassia

1 Benzaldehyde

2 d-Cadinene

3 b-Caryophyllene

4 Cinnamaldehyde

5 Cinnamyl acetate

6 Cinnamic acid

7 Cinnamyl acetate

8 Cinnamyl alcohol

9 p-Cymene

10 Coumarin

11 Ethyl cynnamate

12 a-Humulene

13 Linalool

14 Methyl cinnamate

15 a-Phellandrene

16 b-Pinene

17 Safrole

18 Terpinene-4-ol

19 a-Terpineol

2510 FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics

odorants of fresh rhizomes of ginger (Zingiber offici-

nale Roscoe) have also been studied by aroma extract

dilution analysis and multidimensional cGC-MS. The

chemical name and odor descriptors of flavor

compounds identified in the fresh rhizomes of ginger

are listed in Table 2.

0005 The data prove again that compounds with similar

molecular structure may have highly different or-

ganoleptic properties and the sensory effect of flavor

compounds with different structures may be similar.

Another study established that the pungent flavor

compounds in the extract of ginger consist of 3-, 4-,

5-, 6-, 8-, 10-, 12-, and 14-gingerol, 6-, 8-, and 10-

shogaol and zingerone. An online SFE-cGC-MS

method was developed and employed for the separ-

ation and identification of flavor compounds in the

extract of caraway fruits (Carum carvi L.). The pres-

ence of 23 flavor compounds has been verified, indi-

cating the contribution of a considerable number of

different molecules to the organoleptic characteristics

(Table 3).

0006The flavor compounds in turmeric powders have

been separated by both HPLC and cGC. The HPLC

method quantitated bisdemethoxycurcumin (0.49–

0.90 wt%), demethoxycurcumin (0.58–1.10 wt%),

and curcumin 0.94–3.18 wt%). The cGC method

identified 10 structurally different compounds, sug-

gesting that the analytical method applied exerts a

marked influence on the results (Table 3). A com-

bined method (cGC-MS/sniffing port analysis) has

been used for the evaluation of commercially dried

tbl0002 Table 2 Alphabetic list of chemical names and odor

descriptors of flavor compounds found in the fresh rhizomes of

ginger (Zingiber officinale Roscoe)

No. of

flavor

compound

Chemicalname Odor descriptor

1 Borneol Dry, camphoraceous

2 Bornyl methyl ester Earthy, musty

3 Camphene hydrate Camphoraceous

4 1, 8-Cineole Camphoraceous

5 Citronellal Japanese pepper tree-like

6 Citronellyl acetate Musty, dusty, rosy

7 Decanal Green, waxy

8(E)-2-Decenal Fatty, green

9 2, 6-Dimethyl-5-heptenal Green, fruity, melon-like

10 (Z)-3, 7-Dimethyl-3,

6-octadienal

Green

11 (E)-3, 7-Dimethyl-3,

6-octadienal

Green

12 (E)-2-Dodecenal Fatty, green

13 2-(2

-Epoxy-3

methyl-butyl)-

3-methylfuran

Green, earthy, citrus-like

14 Geranial Citrus-like

15 Geraniol Floral, rosy

16 Geranyl acetate Floral, rosy

17 2-Heptanol Mushroom-like,

herbaceous

18 Isoborneol Musty, dusty

19 Isoeugenol Spicy, floral

20 Linalool Floral

21 2-(3

-Methyl-2

-butenyl)-

3-methylfuran

Green, minty

22 Neral Citrus-like, peely

23 Nerol Floral

24 Nonanal Floral, waxy, green

25 2-Nonanone Fruity, fatty

26 (E)-2-Octenal Green, nutty, burdock-like,

fatty

27 Octanol Mushroom-like

28 2-Octyl acetate Fruity, floral

29 2-Pinen-5-ol Musty, dusty

30 cis-Rose oxide Floral

31 trans-Rose oxide Floral

32 4-Terpineol Camphoraceous

33 2-Undecanone Musty, dusty, green

34 Zingiberenol Metallic, lemony

tbl0003Table 3 Alphabetic list of chemical names of flavor compounds

found in the extract of caraway fruits and turmeric powder

No. offlavor compound Chemicalname

Extract of caraway fruits (Carum carvi L.)

1(E)-Carveol

2 Carvone

3 b-Caryophyllene

4 Decanal

5(E)-Dihydrocarvone

6(Z)-Dihydrocarvone

7 3, 7-Dimethyl-2, 6-octa-dienoate

8 t-Elemene

9 Geranial

10 2, 4-Hexadienal

11 Limonene

12 Linalool

13 (E)-p-mentha-2, 8-dien-1-ol

14 (Z)-p-mentha-2, 8-dien-1-ol

15 2-Methylbenzaldehyde

16 4-Methylbenzaldehyde

17 b-Myrcene

18 (E)-b-Ocimene

19 (Z)-b-Ocimene

20 Perillaldehyde

21 a-Pinene

22 Sabinene

23 a-Terpineol

Turmeric powder (capillary gas chromatography)

1 b-Bisabolene

2 Coumaran

3 Curcumene

4 Curlone

5 Dehydrozingerone

6 2-Hydroxy-5-methyl-aceto-phenone

7 3, 4, 5-Trimethyl-2-cyclo-pentene-1-one

8 ar-Tumerol

9 ar-Tumerone

10 Zingiberene

FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics 2511

bell peppers (Capsicum annum) after rehydration.

The chemical names of volatile components and

their odour descriptors in parenthesis are compiled

in Table 4.

0007 The data prove that flavor compounds with non-

typical odor may also contribute to the formation of

the sensorial properties of red pepper. The effect

of thermal decomposition of capsaicin on the

composition of flavor compounds in the absence

and in the presence of oleic acid has also been

assessed by cGC-MS. It was found that 9-octadece-

namide and N-vanillyl-9-octadecenamide are only

formed in the presence of oleic acid. Characteristic

flavor compounds of onion generally formed enzy-

matically from odorless precursors when it is cut or

crushed. Various cGC-MS methods have also been

applied for the identification of these onion volatiles,

and the occurrence of unstable thiosulfinates such as

(E)-ethylidene sulfoxide, (Z)-ethylidene sulfoxide,

methanesulfenic acid methylthio ester, methanesulfe-

nic acid n-proprylthio ester, methanesulfenic acid

n-propenylthio ester, propanesulfenic acid methylthio

ester, propenesulfenic acid methylthio ester, propane-

sulfenic acid n-propylthio ester, propenesulfenic acid

n-propyl-thio ester, and isomers of zwiebelane has

been demonstrated. Similar cGC-MS technique

has been used for the separation and quantitative

determination of volatile sulfur compounds in garlic.

The compounds and their concentration in mg

100 g

1

fresh tissue are as follows: allyl methyl sulfide

(0.167 + 0.015); dimethyldisulfide (0.204 + 0.026);

diallyl sulfide (0.122 + 0.014); allyl methyl disulfide

(1.193 + 0.068); dimethyl trisulfide (0.075 + 0.011);

diallyl disulfide (5.297 + 0.846); allyl methyl

trisulfide (0.562 + 0.078); 3-inyl-4(H)-1,2-dithiin

(4.088 + 2.266); diallyl trisulfide (1.288 + 0.183),

and 2-vinyl-4(H)-1, 3-dithiin (830.069 + 1.757).

(See Herbs: Herbs of the Compositae.)

Wine and Cider

0008Besides the characteristic and attractive color, the

qualification of wine and cider markedly depends on

the quantity and composition of flavor compounds.

Because of their impact on the commercial values of

these products, flavor compounds in wine and cider

have been intensively investigated. Volatile molecules

in wines have generally been analyzed by cGC-MS

too. The flavor compounds found by this method in

Galician (Spain) white wine are compiled in Table 5

illustrating again the complexity of the composition

of flavor compounds. A similar cGC method found a

fairly different profile of flavor compounds in the

wine of Verdejo (Spain): ethyl lactate þ cis-hexen-1-

ol; acetic acid; propanoic acid; linalool; t-butyrolac-

tone; butanoic acid; a-terpineol; hexanoic acid;

benzyl alcohol; 2-phenylethanol; octanoic acid;

ethyl hexadecanoate, and decanoic acid. As volatile

components also play an important role in the

quality of cider they have been separated and identi-

fied by cGC-MS. The flavor compounds and their

concentrations in fruity and sharp ciders in mg l

1

are compiled as follows: 1-butanol (2.24;4.09), amyl

alcohols (134.29;170.85), isobutanol (7.73;21.92),

tbl0004 Table 4 Alphabetic list of chemical names and odor

descriptors (in parantheses) of volatile flavor compounds found

in the dried bell peppers (Capsicum annuum) after rehydration.

(Odor descriptors have not been determined for each

component)

No. of flavor compound Chemicalname

1 Acetic acid

2 Benzaldehyde

3 2, 3-Butadione (caramel, butter)

4 Butanal

5 1-Butanol

6 2-Butanone

7 2-Buten-2-one

8 b-Cyclocitral

9 Diethoxyethane

10 Dimethyldisulfide

11 Dimethylsulfide

12 Dimethyltrisulfide (rotten, onion, leek)

13 tert-Dodecanethiol

14 Heptanal(lemon, orange)

15 cis-2-Heptenal

16 2-Heptanone

17 trans-3-Heptene-2 -one (mushrooms)

18 2, 3-Hexadione

19 Hexanal (grassy, green)

20 trans-2-Hexenal

21 1-Hexanol

22 Limonene

23 2-Methoxy-3-isobutyl-pyrazine (bell

pepper)

24 Methyl acetate

25 2-Methylbutanal (chocolate)

26 3-Methylbutanal (chocolate)

27 3-Methyl-1-butanal

28 2-Methylfurane

29 6-Methyl-5-hepten-2-one

30 4-Methyl-2-hexanone

31 5-Methyl-2-hexanone

32 2-Methylpropanal (chocolate)

33 1-Methyl-1H-pyrrole

34 Nonanal

35 b-Ocimene (fish, rotten, sickly)

36 Octanal

37 1-Octane-3-ol

38 2, 3-Pentadione

39 Pentanal

40 1-Pentanol

41 2-Pentanone

42 1-Pentene-3-ol

43 1-Pentene-3-one (plastic/chemical)

44 3-Pentene-2-one

45 Propanal

2512 FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics

2-phenylethanol (185.24;57.30), benzyl alcohol

(0.53;1.54), ethyl lactate (11.86;100.27); diethyl suc-

cinate (2.27;2.32), ethyl caprylate (2.22;1.92), ethyl

caprate (3.39;2.15), ethyl laurate (0.68;0), ethyl

palmitate (0.38;0.66), i-amyl acetate (0.28;0.58),

2-phenylethyl acetate (1.21;0), dihydro-2(3H)-

furanone (3.50;7.90), acetoin (0;1.92), 2,3(R,R,S,S)-

butenediol (37.63;90.89), 2,3-butenediol (meso

form) (22.10;75.34), 3-(methylthio)-1-propanol

(1.41;1.80), 4-ethylphenol (1.37;3.33), caprylic acid

(1.22;3.51), capric acid (1.25;2.20), lauric acid

(4.88;0.77), and myristic acid (1.91;0). The data in-

dicate that the marked variation in the concentration

of flavor compounds really reflects the difference be-

tween the two cider varieties. (See Wines: Wine

Tasting.)

Beer and Hop

0009Similarly to wine and cider, and for the same reasons,

flavor compounds in beer have also been vigorously

investigated. It has been emphasized many times

and empirically proved that the yeast used for ferm-

entation and the conditions of fermentation play a

decisive role in the development of flavor compounds

and a considerable number of compounds contribute

to the organoleptic aspects of beer quality. The

presence of anethole, apiole, asaron, camphor, caryo-

phyllene, carvone cedrol, cineol (eucaliptol), cinnam-

ladehyde, citronellal, cuminaldehyde, cymole,

eugenol, farnesol, geraniol, limonene, linalool,

menthol, 2-methylbutanal, 3-methylbutanal, methyl

ketone, methyl slicylate, myrcene, paradol, a-pinene,

thujone, and thymol in beers has been demonstrated. It

was further found that the oxidation products of

humulene present in hop (five isomers of humulene

diepoxy) have a typical herbal/spicy flavor and influ-

ence advantageously the organoleptic properties of

beer. It has been further verified that nonvolatile com-

pounds such as purine nucleosides and free bases may

also contribute to the sensory characteristics of beer.

(See Beers: Chemistry of Brewing.)

0010Size exclusion chromatography has been employed

for the separation and quantitative determination of

this class of aroma compounds and the concentration

ranges (mg l

1

) found in 18 commercial beers were as

follows: guanosine and deoxyguanosine (19–110);

adenosine and deoxyadenosine (3–43); xanthin

(1–41); guanine (1–11), and adenine (1–17). As the

occurrence of 2-furalaldehyde (FA) and 5-hydroxy-

methyl-2-furaldehyde (HMFA) is considered as an

indicator of the deterioration of quality, an HPLC

method has been developed and employed for their

determination in commercial beers. Concentrations of

FA and HMFA (mol l

1

) varied between 1.01–8.41

and 2.62–6.80, respectively. Because of their consid-

erable contribution to the bitter taste and typical taste

of beer, the composition and amount of so-called hop

bitter acids have been extensively studied. The suc-

cessful HPLC separation of cohumulone, humulone,

adhumulone, colupulone, lupulone, and adlupulone

from the SFE extract of hop has been reported. The

same aroma compounds has also been separated by

microemulsion electrokinetic chromatography in

10 min analysis time.

Coffee and Tea

0011Flavor characteristics play a decisive role in the evalu-

ation and commercial acceptance of coffee and tea.

Because of their outstanding importance many

methods have been developed and successfully

applied for the separation, identification, and

tbl0005 Table 5 Alphabetic list of chemical names of flavor compounds

found in Galician wine (Spain)

No. of flavor compound Chemicalname

1 Benzyl alcohol

2 Butiric acid þhotrienol

3 2-Butoxyethanol

4 Citronellol

5 Decanoic acid

6 Diendiol

7 Diethyl malate

8 Diethyl succinate

9 3-Ethoxypropanol

10 Ethyl-2-butanoate

11 Ethyl-2-butyrate

12 Ethyl decanoate

13 Ethyl hexanoate

14 Ethyl-3-hydroxybutirate

15 Ethyl lactate

16 Ethyl-octanoate

17 Furfural

18 Geraniol

19 Hexanoic acid

20 cis-3-Hexen-1-ol

21 trans-3-Hexen-1-ol

22 Hexyl acetate

23 3-Hydroxybutiric acid

24 Isoamyl acetate

25 Isobutanol

26 Isobutyric acid

27 Isovaleric acid

28 Linalool

29 2-Methylbutanol

30 3-Methylbutanol

31 4-Methyl-1-pentanol

32 3-Methylthioethanol

34 Nerol

33 2-Methylthiopropanol

35 Octanoic acid

36 2-Phenylethanol

37 2-Phenylethyl acetate

38 Terpineol

FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics 2513

quantitative determination of flavor compounds in

coffee and tea. Thus, aroma components of two var-

ieties of roasted coffee (Coffea arabica, C. canephora

var. robusta) have been analyzed by cGC-olfactome-

try. The chemical names of flavor compounds and

their organoleptic evaluation are listed in Table 6.

The composition of the flavor constituents was differ-

ent in the coffee varieties, suggesting that similar data

sets can be employed for the identification of the

origin of the product. Nonvolatile aroma precursors

present in green coffee have also been separated by

high-performance gel filtration chromatography. The

data indicated that the concentration of total chloro-

genic acid, trigonelline, and caffeine show a marked

variation according to the green coffee samples. (See

Coffee: Analysis of Coffee Products; Tea: Chemistry.)

0012 The production of tea is a complicated biochemical

and biological process. The final quality depends on

the chemical composition of the original green leaves,

and on the enzymatic processes. A cGC method has

been used to study the effect of the concentration of

sodium chloride on the efficacy of head-space analy-

sis of volatiles present in heat-treated green tea leaves.

The results indicated that NaCl markedly increase the

recovery of furfural (from 7.94 to 11.59 mgml

1

)and

5-methylfurfural (1.65 to 2.95 mgml

1

) but did not

influence the recovery of benzaldehyde (0.30 mgml

1

)

and ethyldimethylpyrazine (0.69 mgml

1

). Another

study indicated that the decomposition rate of lipids

during tea processing results in the formation of the

flavor compounds n-hexanal and trans-hexanal.

Dairy Products

0013Sensorial properties also determine the type and

marketability of dairy products. Because of their

paramount importance, flavor compounds have

been extensively studied, mainly in cheeses. Cheese

flavor is influenced by the biodegradation of milk

protein, fat, lactose due to the enzyme systems of

milk, rennet, and microorganisms. The composition

of volatile flavor compounds in Roncal (Spain) cheese

has been investigated by preconcentrating the analytes

by the ‘purge-and-trap’ method and then separating

them by cGC-MS. The combined technique sussess-

fully separated hydrocarbons, alcohols, aldehydes,

ketones, acids, esters, and sulfur compounds. The

flavor compounds identified are shown in Table 7

and prove again the high complexity of aroma com-

position. (See Cheeses: Chemistry and Microbiology

of Maturation.)

0014The flavor compounds of Swiss cheese and Gor-

gonzola have also been analyzed by simultaneous

distillation-solvent extraction-cGC. In contrast to

Roncal cheese, the main aroma components of

Swiss cheese consisted of (in mgkg

1

) 2-heptanone

(3776), 2-nonanone (1992), 3-methylbutanal (1292),

2-octanone (1188), 2-undecanone (1178), 2-penta-

none (999), 2-tridecanone (873), dimethylsulfide

(619), phenyl acetaldehyde (500), and heptanal

(429). The aroma composition of Gorgonzola

cheese was markedly different, containing 2-nona-

none (3212), 2-heptanone (2916), 3-methyl-1-buta-

nol (2534), 2-undecanone (1884), 3-methylbutanal

(1120), 2-pentanone (955), 2-tridecanone (890),

phenyl acetaldehyde (643), 1-octen-3-ol (601), and

methyl propanoate (379).

0015It has been further demonstrated that the compos-

ition of flavor compounds depends not only on the

variety of cheese but also on the character of starter

culture. In the case of Hispa

nico cheese it has been

demonstrated that the concentration of some flavor

compounds considerably depended on the properties

of starter culture. The chemical names of flavor com-

pounds identified are listed in Table 8. The stereose-

lective separation of gamma and delta lactones has

been achieved by enantioselective multidimensional

cGC. It was found that butter, whipped cream, evap-

orated milk, full-cream milk, cheddar, parmesan,

limburger, emmental and blue cheese contain a con-

siderable amount of C

and C

lactones which

tbl0006 Table 6 Alphabetic list of chemical names and odor

descriptors of flavor compounds found in two varieties of

roasted coffee (Coffea arabica, C. canephora var. robusta)

No. of

flavor

compound

Chemicalname Odor descriptor

1 Acetaldehyde Fruity, pungent

2 2, 3-Butanedione Buttery

3(E)-b-damascene Honey-like, fruity

4 2, 3-Diethyl-5-methylpyrazine Earthy

5 Dimethyl trisulphide Cabbage-like

6 2-Ethyl-3, 5-dimethylpyrazine Earthy, roasty

7 4-Ethylguaiacol Phenolic, spicy

8 2-Furfurylthiol Roasty

9 Guaiacol Phenolic, burnt

10 2-Isobutyl-3-methoxypyrazine Green, earthy

11 3-Mercapto-3-

methylbutylformiate

Catty, roasty

12 Methanethiol Putrid, cabbage-like,

sulfurous

13 Methional Boiled potato-like

14 2-Methylbutanal Malty

15 3-Methylbutanal Malty

16 2-Methyl-2-butenthiol Foxy, skunky

17 2-Methyl-3-furanthiol Boiled-meat-like

18 Methylpropanal Fruity, malty

19 1-Octen-3-one Mushroom-like

20 2, 3-Pentanedione Buttery

21 Propanal Fruity

22 4-Vinylguaiacol Phenolic, spicy

2514 FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics

markedly influence the sensorial properties of the

products.

0016 The compounds causing flavor defects in milk

powder and milk-based baby formula have been sep-

arated and identified by cGC and the involvement of

hexanal, heptanal, and nonanal in the development of

‘cardboard-like’ off-flavor has been established.

Meat, Fish, and Oils

0017A large amount of volatile and nonvolatile flavor

compounds has been found in foodstuffs containing

meat, fish, and oil as the main ingredient. The chem-

ical character and composition of flavor compounds

found in these classes of foodstuffs substantially devi-

ated from those determined in other food varieties. A

dynamic head space cGC method has been developed

and used for the analysis of flavor compounds in

chicken breast meat. The following compounds have

been found in chicken breast meat previously heated

to 70



C: H

S, CO

O, methanol, propanal, and

acetone, 2-propanol and thiobismethane, 2-methyl-

propanal, 1-propanol, 2,3-butanedione, hexane,

2-butanone, 3-methylbutanal, 2-methylbutanal,

tbl0007 Table 7 Alphabetic list of chemical names of flavor compounds

found in Roncal cheese (Spain)

No. of flavor compound Chemical name

1 Acetic acid

2 Acetic acid ethyl ester

3 Butan-2, 3-dione

4 Butanoic acid

5 Butanoic acid prop-2-enyl ester

6 Butan-1-ol

7 Butan-2-ol

8 Butan-2-one

9 Carbon disulfide

10 Decanoic acid ethyl ester

11 Decenal

12 Dimethyl disulfide

13 Dimethyl sulfide

14 Heptane

15 Heptanoic acid ethyl ester

16 Heptan-2-ol

17 Heptan-2-one

18 Hexane

19 Hexanoic acid

20 Hexanoic acid ethyl ester

21 Hexan-2-ol

22 Propan-2-en-1-ol

23 Hexan-2-one

24 Hexan-3-one

25 3-Hydroxybutan-2-one

26 Ethanol

27 Ethylbenzene

28 1-Methoxy-2-propanol

29 3-Methylbutanal

30 3-Methylbutane-1-ol

31 3-Methylbutanoic acid

32 3-Methylbut-3-en-1-ol

33 Methylcyclohexane

34 Methylcyclopentane

35 5-Methylhexan-2-one

36 2-Methylpropanoic acid

37 2-Methylpropan-1-ol

38 Nonanal

39 Nonan-2-one

40 Nonenal

41 Octanoic acid ethyl ester

42 Octen-2-ene

43 Pentane

44 Pentan-2-ol

45 Pentan-2-one

46 Propan-2-one

47 Propanoic acid

48 Propan-1-ol

49 Propan-2-en-1-ol

50 Styrene

51 Undecenal

tbl0008Table 8 Alphabetic list of chemical names of flavor compounds

found in Hispa

nico cheese

No. offlavor compound Chemicalname

Influenced by the starter culture

1 2-Butanol

2 2-Butanone

3 2, 3-Butenedion

4 Ethyl butyrate/1-propanol

5 Methyl acetate

6 2-Methyl-2-buten-1-ol

7 3-Methyl-2-pentanone

8 2-Methyl-1-propanol

9 2-Pentanone

10 2-Propanol

11 2-Propanone

12 Toluene

Not influenced by the starter culture

1 Acetaldehyde

2 Acetonitrile

3 Acetophenone

4 1-Butanol/m-xylene

5 Carbon disulfide

6 2, 3-Dimethyl benzofuran

7 Ethanol

8 Ethyl acetate

9 Ethyl benzene

10 Ethyl toluene

11 Heptane

12 1-Heptanol

13 2-Heptanone

14 Hexanal

15 1-Methoxy-3-propanol

16 3-Methyl-1-butanal

17 3-Methyl-1-butanol

18 3-Methyl-3-buten-1-ol

19 Naphtalene

20 2-Nonanone

21 Octane

22 2, 3-Pentanedione

23 1-Pentanol

24 2-Pentanol

25 o-xylene

26 p-xylene

FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics 2515

1-penten-3-ol, pentanal, dimethyl disulfide, hexanal,

1-hexanol, 2-heptanone, heptanal, 1-heptanol,

benzaldehyde, 7-octen-4-ol, octanal, d-limonene,

undecane, nonanal, and dodecane. Olfactometry

and cGC-MS have been employed for the identi-

fication of flavor compounds and their odor descrip-

tors in boiled cod and trout. It was found that

acetaldehyde (sweet), 2-methylpropanal (malty),

butane-2,3-dione (buttery-like), 3-methylbutanal

(malty), 1-octen-3-one (mushroom-like), and

(Z)-1,5-octadien-3-one (geranium-like) occurred in

both fishes. Moreover, boiled cod minces contained

methaneethiol (sulfurous), trimethylamine, dimethyl

sulfide (cabbage-like), 2-methylbutanal (malty),

methional (boiled potato-like), dimethyl trisulfide

(cabbage-like, putrid) and dimethyl tetrasulfide

(cabbage-like, putrid). (See Fish: Fish as Food; Meat:

Analysis.)

0018 In contrast, boiled trout contained propionalde-

hyde (sweet), pentane-2,3-dione (buttery-like), hexa-

nal (green), (Z)-3-hexenal (green), (Z)-4-heptenal

(biscuit-like), (Z, Z)-3, 6-nonadienal (fatty, green),

and (E, Z)-2, 6-nonadienal (cucumber-like). A similar

method has been used for the study of the odor active

compounds in cooked mussel (Mytilus edulis) and the

following compounds have been identified: 2, 3-bute-

nedione (buttery, caramel), 1-propanol (fruity, plas-

tic), dimethyl disulfide (sulfury), hexanal (green),

m-xylene (plastic), heptanal (citrus fruit, green),

(Z)-4-heptenal (boiled potato), 1,2,4-trimethylben-

zene (plastic), octanal (citrus fruit, orange), (E)-2-

penten-1-ol (mushroom), (E)-2-heptenal (sulfury,

grassy), ethylpyrazine (nutty), dimethyl trisulfide

(sulfury, green, marine), methional (boiled potato),

2-nonanol (fruity, solvent), (E, E)-2,4-octadienal

(cucumber), 1-acetylpyrazine (nutty), 2-acetylthia-

zole (grilled hazelnut), 4-methylthiazol (roasted,

meaty), 4-ethylbenzaldehyde (fruity, anisic, minty),

2-acetyl-2-thiazoline (grilled hazelnut), and 2,6-

dimethylnaphtalene (grilled, grassy).

0019 Volatile aroma compounds have also been deter-

mined in oils using various cGC techniques. The

flavor compounds found in extra virgin, regular,

extra light and extra mild cooking oils are listed in

Table 9. The concentration of flavor constituents of

oils remarkably depended on the technological steps

applied for the production of oils. The amount of

aliphetic aldehydes indicating quality deterioration

has also been measured by a cGC method using deri-

vatization by thiazolidine. The presence of C

i-C

,andC

aldehydes in sesame, soybean, rape-

seed, cottonseed, corn, olive, and sardine oil, as well

as in beef fat, lard, butter, margarine, mayonnaise,

cheese, egg yolk, fresh milk, chocolate, and potato

chips has been demonstrated.

Miscellaneous Food Products

0020Because of the significant impact of flavor com-

pounds on the quality of foods and foodstuffs, they

have been analyzed in a considerable amount of other

food products using the well-established methods of

preconcentration followed by either cGC-MS or

HPLC. Thus, 46 volatile compounds have been sep-

arated and identified in fresh-squeezed unpasteurized

orange juice. Ionones, decalactone, and raspberry

ketone have been found in some raspberry cultivars

and 17 volatile compounds have been identified in

ready-made tomato sauces. The presence of 2-methyl-

propanal, 3-methylbutanal, and 2-methylbutanal has

been verified in chocolate flakes and the enzyme ac-

tivities involved in the flavor precursor formation

in unfermented cocoa beans have been elucidated.

tbl0009Table 9 Alphabetic list of chemical names of flavor compounds

found in extra virgin, regular, extra light, and extra mild cooking

oils

No. of flavor compound Chemical name

1 Acetic acid hexyl ester

2 Butanal

3 2-Cyclohexen-1-ol

4(Z)-2-Decanal

5 Ethyl acetate

6 Heptanal

7 Heptane

8 2-Heptanone

9(E)-2-Heptenal

10 (Z)-2-Heptenal

11 Hexanal

12 Hexane

13 (E)-2-Hexenal

14 (Z)-3-Hexenal

15 (E)-3-Hexen-1-ol

16 (Z)-3-Hexen-1-ol

17 4-Hexen-1-ol

18 (Z)-4-Hexen-1-ol

19 (Z)-3-Hexen-1-ol acetate

20 Limonene

21 2-Methylbutanal

22 3-Methylbutanal

23 Methylcycloheptane

24 Nonanal

25 Octanal

26 Octane

27 (E)-2-Octenal

28 1-Octene

29 2-Octene

30 (E)-2-Octene

31 (Z)-2-Octene

32 Pentanal

33 3-Pentanone

34 2-Pentylfuran

35 Styrene

36 Toluene

37 2-Undecenal

2516 FLAVOR (FLAVOUR) COMPOUNDS/Structures and Characteristics

The flavor profile of corn-based snacks and peanuts

has also been determined and the data have been used

for the better understanding of the sensory character-

istics of the products.

See also: Analysis of Food; Chromatography:

Principles; Thin-layer Chromatography; High-

performance Liquid Chromatography; Gas

Chromatography; Supercritical Fluid Chromatography;

Combined Chromatography and Mass Spectrometry;

Flavor (Flavour) Compounds: Production Methods