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Understanding food flavour: the interaction of flavour chemistry and sensory science
D. Zabaras, D.C. Frank, P. O’Riordan
and P. Varelis
Centre for Food Quality and Stability
O
SH
2-methyl-3-furanthiol
SCHO
methional
Food Flavour: Definition
• Food flavour consists of three sensations:
• Odour (orthonasal perception)• Aroma (retronasal perception)• Taste
• Volatile compounds are responsible for the odour and aroma of a food
Precursors of Volatile Compounds
• Foods contain amino acids, carbohydrates and lipids, carotenoids
• Reactions involving amino acids, sugars and lipids are responsible for the formation of volatile compounds:
• Maillard reaction• Lipid decomposition
Maillard Reaction
− H2Orearrangement
NHROH
OOHH
OH
OH
Amadori intermediate
carbonyl compounds
− H2O− RNH2
O
OH
O
O
O CHOHO
O
OOH
O OH
OO CHO
O OH
O
ASPARAGINE
H2Saldehydes
H
O
OH OH
OHOH
OH
R NH2+
reducing sugar aminocompound
Amino acids
Lipid oxidation
(e.g PUFA) aldehydes
Acrylamide
Strecker reaction
Melanoidins
Flavour compounds
+ Lipid oxidation
Maillard reaction: Aromas generated from various sugars / amino acids
ChocolateOvercooked cabbage
Boiled meatCharred meatBeef broth
Sucrose
SweetHarsh horseradish
Stale potatoBaked hamBeef broth
Maltose
Dirty dog Bean soupFried potatoes
ChickenBeef broth
Fructose
CaramelCabbageBurnt fried potatoes
Chicken trayBurnt candy
Glucose
PhenylalanineMethionineLysineGlutamic AcidGlycine
(obtained from various literature sources)
Food volatiles
• Analytical investigations employed mostly GC and GC/MS.
• An estimated 8000 food volatiles had been reported until 1997.
• Initially it was assumed that all volatiles contribute to food aroma.
• The determination of odour activity values (OAV) showed that not all volatiles were important as flavour compounds
OAV = Odorant concentration/Odour threshold value
Odour analysis
• Results in the qualitative and quantitative determination of the important odorants in a food product:
• identity of important odorants• relative concentration in food of interest
• This information is useful for the prediction, control and re-creation of the flavour of a food product.
Odour analysis: Steps
1. Extraction of the volatiles from the food matrix
• dynamic headspace or purge-and-trap (DHS)• static headspace (SHS)• liquid or solvent extraction • solvent-assisted flavour evaporation (SAFE)• simultaneous distillation-extraction (SDE)
high purity N2
Sample
Tenax-TA® trap
Rapid sampling: 30 minutes
Up to six samples simultaneously
Extraction of highly volatile components
No heat-related artefacts
Odour analysis: purge-and-trap
Odour analysis: Steps
2. Separation and tentative identification of the volatiles in theextract by GC/MS and localisation of the odorants by olfactometry (GC/MS-O)
• Commonly employed GC/MS-O approaches:
• OSME (perception measurements of a non-diluted extract by trained panelists averaged)
• AEDA (extract serially diluted and measured until no perception)
Real time GC/MS trace
voice recorder
sample introduction
GC/MS
perceptualtrace
time intensityrecorder
GC-MS-olfactometer and time intensity recorder
instrumental trace
Time-intensity recorder interface
mouse-controlled sliding intensity scale
0 100
Information obtained from GC/MS-O
Damian Lindt
0
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1 205 409 613 817 1021 1225 1429 1633 1837 2041 2245 2449 2653
5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00
100000
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1000000
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Time-->
Abundance
TIC: LINXC.DGC/MS trace (from detector)
Aromagram (from human nose)
The human nose still remains the most sensitive detector of odour-active volatiles!!
Det
ecto
r res
pons
eP
anel
ist r
espo
nse
Time (sec)
Odour analysis: Steps
3. Quantification of important odourants using GC/MS
• Potentially most reliable quantification approach:
• SIDA (stable isotope dilution analysis)
30 40 50 60 70 80 90 100 110 120 130 1400
2000
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m/z-->
Abundance
Scan 4498 (25.391 min): SL_100.D (-4484) (-4517) (-)126
7945
64
111
9633 54 13338
30 40 50 60 70 80 90 100 110 120 1300
5000
10000
15000
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25000
30000
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m/z-->
Abundance
Scan 4496 (25.376 min): SL_101.D (-4480) (-4511) (-)128
8046
64
112
9633 54 5938
00 20.00 25.00 30.00
on 126.00 (125.70 to 126.70): SL
00 20.00 25.00 30.00
on 128.00 (127.70 to 128.70): SL
Example: 13C2-dimethyl trisulfide
H313C
SS
S13CH3
H3CS
SS
CH3
Odour analysis: Steps
4. Preparation of ‘synthetic’ blends of odourants in ‘blank’ matrices using the quantitative data (including omission experiments)
5. Sensory evaluation of the prepared blends by trained panels
Whole process successful when:
Aroma of synthetic blend (usually containing 3-4 odourants) = aroma of original food
Example: Chocolate aroma
• Chocolate: a matrix of solid particles (cocoa, sugar, milk) set in a continuous fat medium
• Characteristic flavour is a result of several manufacturing steps
• Flavour depends on many parameters including cocoa variety used, bean fermentation, conching process, added ingredients (e.g. vanillin)
Example: Chocolate aroma
• Total volatile and aroma profiles of two milk chocolates compared
• Both chocolates contained a similar amount of cocoa and milk solids (approx. Cocoa Solids 26%, Milk Solids 27%, Fat 30%)
GC/MS profiles
5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00
-600000
-400000
-200000
0
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1000000
Time-->
Abundance
TIC: LINCH.D (*)TIC: CADMILK.D (*)
acetic acid
3-methylbutanal
vanillin
• Traces very similar (> than 90 volatiles detected)
Chocolate 1
Chocolate 2
Aromagrams
• Traces different (> than 70 odour-active volatiles detected)
0102030405060708090
100
1 205 409 613 817 1021 1225 1429 1633 1837 2041 2245 2449 2653
Chocolate 1
0102030405060708090
100
1 205 409 613 817 1021 1225 1429 1633 1837 2041 2245 2449 2653
Chocolate 2
Odo
ur in
tens
ity (0
-100
)
Time (sec)
Instrumental and perceptual data combined Chocolate 1
0102030405060708090
100floral,mandarin (linalool)honey/rotten,cheesy (phenylacetaldehyde/butanoic
acid)green, floral (unknown)sweet, floral (unknown)honey, sweet (5-methyl-2-furanmethanol)fruity (ethyl-2-methylpropanoate)herbal,fresh (unknown)herbal,pine (a-pinene)
herbal (unknown)fruity, bubblegum (ethyl-2-methylbutanoate)
pineapple (unknown)crushed leaves (hexanal)
herbal (b-pinene)herbal,dirty (a pyrazine)fruity, sweet (unknown)sweet,fresh (2-heptanone/limonene)fruity (unknown)sweet (unknown)melon,green (octanal)sweet,peach (unknown)baked potato (methional)
mushroom (1-octen-3-one)mushroom, fungus (unknown)
garlicky (unknown)rotten egg (dimethytrisulfide)
curry, spicy (abhexon)bacon (unknown)
cooked spaghetti (unknown)bacon, smoked ham (unknown)
spicy, spaghetti (sotolon)fatty (1-hexanol)fatty, green (E-2-octenal)fatty,cheesy (unknown)fatty, oxidised (Z-2-nonenal)fatty, oxidised (E-2-nonenal)sweet, fatty (unknown)
cheese (unknown)cheesy, smelly socks (2-methylpropanoic acid)rotten, parmesan (2/3-methylbutanoic acid)popcorn,cheesy (butyrolactone)fatty, burnt (unknown)stewed apple (phenylethylacetate)wine, fermented (2-phenylethanol)
vinegar (acetic acid)vitamin B (2-furanmethanol)
medicinal (guaiacol)medicinal (unknown)
sweet, phenolic (unknown)metalic (unknown)
phenolic (unknown)sweet (2,3-pentanedione)
sweet,caramel (unknown)sweet,caramel (unknown)
chocolate, malty (3-methylbutanal)caramel (2,3-butanedione)
sweet (unknown)caramel (d-pentolactone)coconut (d-octenolactone)
sweet, vanilla (vanillin)sweet, vanilla (unknown)
sweet, vanilla (unknown)malty (unknown)
sweet (benzyl alcohol)sweet (unknown)
chocolate (unknown)coffee, chocolate (2-methyl-3-(methyldithio)furan)peanut, green (2-methoxy-3-isopropyl pyrazine)dirt (2-ethyl-3,5-dimethylpyrazine)nutty, herbal (trimethylpyrazine)roasted nut (tetramethyl pyrazine)
Aroma profile comparison
0
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0
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Vinegar/Wine
Chocolaty/Nutty
Sweet/Caramel
Mushroom/Spicy
Fatty/Cheesy
Floral/Herbal
Chocolate 1 Chocolate 2
Chocolaty/Nutty
Floral/Herbal
Mushroom
/Spicy
Fatty/Cheesy
Sweet/Caramel
Vinegar/Wine
Medicinal
Volatiles contributing most to milk chocolate aroma
• 3-methylbutanal (malty)• 2-ethyl-3,5-dimethylpyrazine (potato, green)• Z-2-nonenal (green, fatty)• acetic acid (vinegar)• methional (baked potato)• 2-methyl-3-(methyldithio)furan (coffee, chocolate)• hexanal (crushed leaves)• phenylacetaldehyde/butanoic acid (honey/cheesy, rotten)
• These volatiles could be now used (by going through the remaining steps of the process) to re-create chocolate aroma.
This has recently been achieved at FSA with kiwifruit flavour.
Bibliography
Belitz, H.D, Grosch, W. Food Chemistry, 2nd edition, Springer-Verlag, 1999.
Grosch, W. Evaluation of the key odorants of foods by dilution experiments, aroma models and omission. Chem. Senses 2001,26, 533-545.
Sides A, Robards K, Helliwell S. Developments in extraction techniques and their application to analysis of volatiles in foods. TiAC 2000,19, 322-329.
Pillonel L, Bosset J.O, Tabacchi R. Rapid pre-concentration and enrichment techniques for the analysis of food volatile: A review. Lebensm.-Wiss. u-Technol. 2002, 35, 1-14.
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