1. No category

Not all in the mind – the
chemistry of flavour
John R. Piggott
Faculdade de Ciências Farmacêuticas
Universidade Estadual Paulista
Araraquara
Brasil
j.r.piggott@fcfar.unesp.br
What is flavour?
• “The sensation arising from the integration or
interplay of signals produced as a
consequence of sensing smell, taste and
irritating stimuli from a food or beverage”
• The “psychological interpretation of a
physiological response to a physical stimulus”
Laing & Jinks, Trends in Food Science & Technol. 7, 387, 1996; Noble, Trends in Food
Science & Technol. 7, 439, 1996
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Flavour is
• “Flavour … is an interaction of food and
consumer”
• Therefore sensory methods must be used to
measure flavour (and all other sensory
characteristics)
• However, physical/chemical methods, if
properly validated by sensory tests, are
often cheaper and more efficient
von Sydow, Food Technol. 25(1), 40, 1971; Piggott, Food Qual. Pref. 6, 217, 1995
The stimulus
• Flavour cannot exist without a physical
stimulus
• Compounds must be released from food to
interact with the receptors
– Volatile compounds provide smell
– Non-volatile compounds provide taste
– Spiciness, pungency, etc.
2
Key questions
•
•
•
•
What is in there?
Does it matter?
Where did it come from?
How can it be changed or controlled?
Contents
• This is not a complete review
– 4,500 items in Web of Science in 5 years
• Some topics which I think are interesting
• Examples
• Cachaça
3
Cachaça, sugar-cane spirit
• Brazilian “national drink”
• Process overlaps with some definitions of
rum
• Accepted as being a uniquely Brazilian
product
• Often drunk as a caipirinha, with sugar,
lime, and ice
Photo: Christian "VisualBeo" Horvat
http://commons.wikimedia.org/wiki/File%3AZutaten_caipirinha.jpg
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Photo: Christian
http://commons.wikimedia.org/wiki/File%3ACocktail_Caipirinha_raw.jpg
Process
•
•
•
•
•
Cane harvested
Milled to produce juice
Clarified
Spontaneous or pitched fermentation
Distillation
– Single distillation in small pot still
– Some double distillation
– Some column distillation
• Maturation in casks (optional)
Faria, in Distilled Spirits Production, Technology and Innovation, Bryce et al. (eds), Nottingham
Univ Press, 2008, p 327
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Photo: J.R. Piggott
Photo: J.R. Piggott
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Photo: J.R. Piggott
Photo: J.R. Piggott
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Photo: J.R. Piggott
Photo: J.R. Piggott
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Photo: J.R. Piggott
Photo: J.R. Piggott
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Photo: J.R. Piggott
What is in there (and how much)?
• Representative extract for analysis
– Odour-active volatiles
– Taste-active non-volatiles
– Avoid changing the compounds present in the
food
– Sufficient extract to identify compounds at very
low levels
– Methods select for certain compound classes
– Combine techniques for analysis
Croissant et al., Annu. Rev. Food Sci. Technol. 2, 395, 2011
10
Common methods
• Simultaneous distillation extraction
– Cooked foods
• Liquid extraction
• Direct injection
– Distillates
• Headspace sampling
– Static or dynamic, SPME, full evaporation
• In-mouth analysis
Analysis
• Gas chromatography
• Modern analytical instruments can often
identify dozens or hundreds of volatile
compounds in an extract
11
Common GC detectors
• Flame Ionisation Detector (FID) – good for
quantitation
• Mass spectrometer (MS) – very sensitive
• Various specialised detectors e.g. for
sulphur or nitrogen – can be very sensitive
• Disadvantage: they do not tell you what is
important
http://www.chromatography-online.org/2/contents.html
Dimethyl sulphide (DMS) in cachaça
• Off-flavour at > 8 x 10-7 mol L-1 (50 µg L-1)
• Threshold (in wine) 10 – 160 µg L-1
• Use of copper in stills has been shown to
reduce DMS concentration in distillates
• Purge-and-trap concentrator
• Quantitation by GC with mass selective
detector
Cardoso et al., J. Braz. Chem. Soc. 15, 277, 2004; Ledauphin et al., J. Food Comp. Anal. 19,
28, 2006
12
DMS in spirit samples
• Averages of non-zero samples (mol L-1)
–
–
–
–
–
–
Cachaça 1.6 x 10-5
Grappa 1 x 10-7
Whisky 4 x 10-7
Brandy 1 x 10-7
Tiquira 1 x 10-7
Vodka and Rum: < detection limit
Cardoso et al., J. Braz. Chem. Soc. 15, 277, 2004
Does it matter?
• The closer the relationship between the
instrumental method and the actual
perception of the food properties, the more
relevant and valid the instrumental method
• Sensory impact may be related to rate of
release of a volatile, not its concentration
Dijksterhuis & Piggott, Trends in Food Science & Technol. 11, 284, 2001; Baek et al.,
Chemical Senses 24, 155, 1999
13
Resolution and relevance
• Table showing methods providing differing
temporal resolution and differing relevance
and validity
Dijksterhuis & Piggott, Trends in Food Science & Technol. 11, 284, 2001
Sensory-instrumental relations
• Attempts to model flavour in chemical
terms are not always successful
• Sensory analysis
• Instrumental analysis
• Complexity of flavour
Chambers & Koppel, Molecules 18, 4887, 2013
14
Finding the important compounds
• A few “flavour impact compounds” might
represent a flavour
• Even in simple cases they are unlikely to
convey the complete sensation
• Most convincing demonstration of success
is a reconstructed flavour which is
indistinguishable from the original
Grosch, Chemical Senses 26, 533, 2001
How to use a sensory method?
• Use a human nose as the detector – GCOlfactometry
• Advantages:
– Validity and relevance
• Disadvantages:
– Individual variations
– Variable sensitivity
– Unreliable computer (the brain)
15
Developments of early GC-O
• Dilution methods
– CHARM (Combined Hedonic Aroma Response
Measurement)
– AEDA (Aroma Extract Dilution Analysis)
• Intensity methods
– OSME (Odour Specific Magnitude Estimation)
• Detection frequency
Van Ruth, Biomol. Eng. 17, 121, 2001
Cachaça and rum aroma:
descriptive sensory analysis
• “Spider’s web” plot showing sensory
profiles of cachaça and rum
De Souza et al., J. Agric. Food Chem. 54, 485, 2006
16
Most potent odorants (CHARM
values)
• “Spider’s web” plot showing most potent
odorants in cachaça and rum
• Eugenol particularly strong in cachaça
De Souza et al., J. Agric. Food Chem. 54, 485, 2006
Gas Chromatography Recomposition
• Extract (SPME) is separated by GC
• Sections of the chromatogram are
recombined for sensory analysis and
comparison with the original
Johnson et al., PLOS One. 7, e42693, 2012
17
Changes the questions
Not
• What is it, and does it matter?
But
• What is important, and what is it?
GC-R instrumentation
• Flow diagram showing GC fitted with a
switch to pass part of the column effluent to
waste, and a cryo trap before the sniff-port
Johnson et al., PLOS One. 7, e42693, 2012
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Application to lavander aroma
• Chromatogram showing sensory
descriptions applied to various cuts from
chromatogram of lavender
Johnson et al., PLOS One. 7, e42693, 2012
Flavour release
The process of flavor release and perception is
controlled
• by the properties of the flavor compounds
• by the nature of the food matrix
• by the physiological conditions of the
mouth, nose and throat during consumption
Ross, Trends in Food Science & Technol. 20, 63, 2009
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Individual differences
• Biting force
• Incisors – 110 – 370 N (n = 18)
• Mean force (N)
– American males 534, females 378
– Eskimo males 1202, females 890
Chen, Food Hydrocolloids 23, 1, 2009
Saliva flow
•
•
•
•
•
Unstimulated, range 0.04 – 1.83 ml/min
Stimulated, range 0.77 – 4.15 ml/min
Variation during the day
Reduction with age (> 70 years)
Variation with health status and drugs
Chen, Food Hydrocolloids 23, 1, 2009
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Effect of the matrix
• Reconstitution of Dornfelder red wine
• Aroma profiles of
– Wine
– Recombinates in aqueous ethanol
• A: 28 aroma compounds
• B: Aroma and 35 LMW taste compounds
• C: Aroma and all taste compounds
Frank et al., J. Agric. Food Chem. 59, 8866, 2011
Aroma profiles
3
Intensity
2.5
wine
C
B
A
2
1.5
1
0.5
flo
w
er
y
m
al
ty
co
ok
fr
ed
ui
-a
ty
pp
le
-li
ke
cl
ov
elik
e
sw
ea
ty
sm
ok
va
y
ni
lla
lik
co
co
e
nu
t- l
ik
vi
e
ne
ga
rlik
bu
co
e
tte
ok
ed
rlik
-p
e
ot
at
olik
e
0
Frank et al., J. Agric. Food Chem. 59, 8866, 2011
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Where did it come from?
• Materials
– May be simple – fresh fruit
• Process
– Main compounds produced in alcoholic
fermentation by yeast are well known
– There may be many steps in a manufacturing
process
– They can all add, subtract, or change flavour
compounds
Post-fermentation processing
of Pisco
• Analysis of distillate fractions to identify
chemical markers for each stage
Peña y Lillo et al., J. Food Science 70, S432, 2005
22
Correlations of markers with
sensory notes
• Table showing correlations between sensory
notes and chemical components,
characteristic of stage fractions taken from
Pisco production process
Peña y Lillo et al., J. Food Science 70, S432, 2005
How can it be controlled or changed?
• Process development and control
– Controlling flavour to prevent or limit
deviations
– Understand how a food or beverage “works”
– Allow unimportant deviations in process or
composition
– Prevent important deviations
23
Cachaça fermentation (1)
• Typically, spontaneous fermentation
• Variable flavour
• Select yeast producing desirable chemical
profile
Congener production
by two isolated yeast
strains and a mutant
The strains show
different production
rates of isoamyl
alcohol and isoamyl
acetate, and different
final concentrations
Vicente et al., Int. J. Food Microbiol. 108, 51,
2006
24
Cachaça fermentation (2)
• Supplementation of sugar cane juice (SCJ)
with medium (MAS) and high (HAS) levels
of ammonium sulphate
Vidal et al., Food Chemistry 138, 701, 2013
Ester concentrations
Results show different
concentrations of the esters
depending on ammonium sulphate
addition
EO ethyl octanoate; EH ethyl hexanoate; 3-MBA 3-methylbutyl acetate;
EA ethyl acetate
Vidal et al., Food Chemistry 138, 701, 2013
25
Cachaça fermentation (3)
• Fermentation of cane juice with yeast (S.
cerevisiae), and with yeast plus
Lactobacillus fermentum (LAB)
Duarte et al., J. Food Science 76, C1307, 2011
Major volatiles
Yeast
Yeast + LAB
400
mg/L
300
200
100
M
3-
an
ol
he
ny
l
et
h
no
l
2P
et
h
yl
-1
yl
-1
-b
ut
a
-b
ut
a
no
l
an
ol
et
h
M
2-
l-1
-p
ro
p
an
ol
et
hy
12M
* Significantly
different at 0.05
Pr
op
te
ce
ta
Et
hy
la
*
*
Ac
e
ta
ld
eh
yd
e
0
Duarte et al., J. Food Science 76, C1307, 2011
26
Minor volatiles
• Some minor volatiles also showed
differences
• Gamma-lactones are formed by LAB, and
are thought to be important in malt whisky
• Not analysed in this case
Wanikawa et al., J. Inst. Brewing 106, 39, 2000
Whisky fermentation
• “Precondition” yeast cells with zinc
• Affects flavour congeners in the distillates
produced from fermented cultures
• Distillates had an altered flavour and aroma
profile
• Production of some higher alcohols
increased when yeast cells were
preconditioned with zinc
De Nicola et al., J. Institute Brewing 115, 265, 2009
27
Aldehydes and esters
800
600
mg/L
Control
Preconditioned
400
200
ta
te
ta
l
Is
oam
yl
-a
Fu
rf
ce
Ac
e
e
Et
hy
l
-a
ce
ta
t
ld
eh
yd
e
ta
Ac
e
ur
al
0
De Nicola et al., J. Institute Brewing 115, 265, 2009
Alcohols
600
400
Control
Preconditioned
mg/L
200
3M
et
hy
l-1
-b
ut
an
ol
ut
an
ol
l-1
-b
an
ol
2M
et
hy
nBu
t
ro
pa
no
l
nP
M
et
h
an
ol
0
De Nicola et al., J. Institute Brewing 115, 265, 2009
28
Cachaça distillation (1)
• Material of the still affects distillate
composition
• Comparison of still materials
Cardoso et al., Quim. Nova 26, 165, 2003
DMS in cane spirit distilled in
columns with different packing
700
600
DMS
500
400
300
200
100
0
Copper
Stainless
Aluminium
Ceramic
Cardoso et al., Quim. Nova 26, 165, 2003
29
Cachaça distillation (2)
• Double distillation:
– Increases ethanol content of distillate
– Reduces concentrations of congeners
• Comparison of single distillation with 3
procedures for double distillation
Alcarde et al., Ciência e Tecnologia de Alimentos 31, 355, 2011
Effects of distillation procedure
Single
Volatile acidity
Furfural
Aldehydes
Esters
Methanol
Higher alcohols
Congeners
Double
Cognac
Whisky
Varying concentrations of all
analytes according to the
distillation process used,
with generally lower
concentrations from the
whisky process
Alcarde et al., Ciência e Tecnologia de Alimentos 31, 355, 2011
30
Case study of a distilled spirit
• Grain spirits used as material for pure or
flavoured vodka in Poland
• To identify compounds responsible for offflavours
• 39 spirit samples
– 13 good, 13 doubtful, 13 poor
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
Experimental
• Assessor training for GC-O with model
mixtures of relevant compounds
• Sensory profiling
• HS-SPME
• GC-O-MS
– Fingerspan intensity scaling in GC-O
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
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Example olfactogram
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
Sensory profiling confirmed
original classification
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
32
Results
• About 40 odours in aroma profiles of spirits
• Some odour peaks not observed in
chromatograms
• Lag between chromatogram and
olfactogram
• Individual differences between asessors
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
Dimethyltrisulphide by GC-O and
GC-MS
• High levels of DMTS with corresponding
high GC-O scores in “poor” samples
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
33
Geosmin by GC-O and GC-MS
• High levels of geosmin with corresponding
high GC-O scores in “poor” samples
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009
Conclusion
• Dimethyltrisulphide (DMTS) and geosmin were
the two most useful indicators of poor sensory
quality
• Determination of these compounds could be used
for quality control of distillates in production
– DMTS (and DMDS) are associated with high
methional levels in grain fermentations
– Geosmin probably originates in contaminated
water
Plutowska & Wardencki, Flavour & Fragrance J. 24, 177, 2009; Prentice et al., J. Amer. Soc.
Brewing Chemists 56, 99, 1998
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