Table Of ContentHandbook of Aroma Research
MANFRED ROTHE
Introduction to Aroma Research
Handbook of Aroma Research
Collection of monographs written by international flavour specialists
Edited by
MANFRED ROTHE
Potsdam-Rehbriicke
Introduction to
Aroma Research
By
MANFRED ROTHE
Department of Aroma Research, Central Institute of Nutrition, Academy of Sciences, GDR,
Potsdam-Rehbriicke
First English Edition
With 71 Figures and 35 Tables
Kluwer Academic Publishers
Dordrecht / Boston / London
Library of Congress Cataloging-in-Publication Data
Rothe, Manfred.
Introduction to aroma research.
(Handbook of Aroma Research)
Translation of: Einfiihrung in die Aromaforschung.
Bibliography: p.
Includes indexes.
1. Food-Analysis. 2. Food-Odor. I. Title.
II. Series
TX535.R6713 1986 664'.07 86-178l9
ISBN-\3:978-94-010-7\35-2 e-ISBN-\3: 978-94-009-1419-3
DOl: 10.1007/978-94-009-1419-3
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Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff,
Dr. W. Junk and MTP Press.
Original title: Einftihrung in die Aromaforschung
All rights reserved.
((:i 1988 by Akademie-Verlag Berlin.
Softcover reprint of the hardcover 1st edition 1988
No part of the material protected by this copyright notice may bereproduced or utilized in any form or by any
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Preface to the first English edition
In 1976 when the first German manuscript non-specialist who may be entering the field
of this "Introduction" was completed aroma for the first time. Furthermore there was a
research was described as being in a phase demand for a translation into the English
of rapid development. This new scientific language. In spite of a concept that the indi
discipline had spread, from its origin as a vidual monographs of this series were to be
specialized part of food chemistry, over a written either in English or in German lan
broad and differentiated area between physio guage we feel that some volumes should be
logy of flavour sensation, aroma analysis available in both languages. Moreover, we
- with a fascinating spectrum of instrumental had to consider that, in the main, activities
and sensory techniques - to such practical in the flavour field have developed within
fields as food technology and flavouring pro English speaking countries. Consequently,
duction. In the meantime this tendency has most authors and experts have published
continued. In many aspects our knowledge their results in English.
has now reached a higher level, and we can I want to thank the Akademie-Verlag Berlin
recognize many more connections between and especially lector Karl ABEL for an always
different aroma problems. It has therefore good and effective collaboration. All our
been necessary to complement the original problems were discussed and solved in a fruit
material by new results, and to summarize ful and cooperative way stimulated by an
some aspects in order to give the most up-to open and friendly atmosphere. Within the
date picture possible of our discipline. Central Institute for Nutrition Potsdam
One problem, however, remained unchanged: Rehbriicke I am indebted to our director,
An introduction has to present a review of the Prof. H. SCHMANDKE, as well as to Prof.
field under discussion without going into too H. RUTTLOFF for their understanding and
much detail. A detailed discussion should help. Finally I should like to thank Mrs.
principally be confined to the special mono Edith WEISE for typing the manuscript and
graphs of this series. The author had to select for assistance in the English translation.
a few appropriate examples out of a large
number of possibilities, which is really a rather
difficult task. Another aspect to be considered
is the necessity of demonstrating the actual Potsdam-Rehbriicke
facts in a readily understandable way for the Manfred ROTHE
V
Contents
1. Research in the flavour field - present situation and trends I
1.1. Human perception of odour and taste. . . I
1.2. Attributes contributing to flavour sensation 4
1.3. Terminology . 7
1.3.1. Main terms . . . . . . . . . . . . 7
1.3.2; Off-flavour............ 8
1.3.3. Flavour potentiation and modification. 12
1.4. Aroma and flavour: the consumer's point of view. 14
1.5. Development of aroma research . . . . . . 16
1.5.1. Historical and modem aspects . . . . . . . 16
1.5.2. Problems and perspectives in food flavouring. 22
2. Aroma analysis. . . . . . . . . . . 30
2.1. Sensory analysis . . . . . . . . . . 30
2.1.1. Sensory testing and evaluation methods 30
2.1.2. Sensory versus instrumental analysis . 38
2.2. Chromatographic analysis . . . . . . 40
2.2.1. Development of chromatographic techniques . 40
2.2.2. Isolation and concentration procedures 41
2.2.3. Thin layer chromatography 44
2.2.4. Gas chromatography . . . 45
2.3. Spectrometric identification 54
2.4.' Food aroma components . 58
2.4.1. Occurrence in food and beverages 58
2.4.2. Aroma efficacy and threshold value . 62
2.4.3. Weighting problems. . . . . . . . 65
2.5. Relationship between sensory and instrumental data. 70
3. General problems in aroma research . . . . . 79
3.1. Chemistry and biochemistry of aroma formation 79
3.2. Interrelation between practical aroma problems. 87
3.3. Nutritional aspects of food flavour . . . . . '. 90
4. Future aspects . . . . . . . . . . . . . . . 98
5. Time table about the history of production, processing and consumption of aroma-rich foods
and flavourings. 101
Literature . . . . . . . . . . . . . . . . III
Appendix . . . . . . . . . . . . . . . . 125
Bibliography of actual literature to the topic. 125
Author index. 126
Subject index. . . . . . . . . . . . . . . 132
VII
1. Research in the flavour field - present situation and trends
1.1. Human perception of odour and taste
All living beings perceive their environment riodically at special times fixed, for example,
by sensory contacts registered from the sur at meal times.
roundings, and by comparison of these im Comparing the human senses of smell and
pressions with similar ones kept and stored in taste with those of other higher organisms,
memory. The sum of such effects provides a we find -many examples of higher sensitivity
concept of the environment. A continuous (dog, fish, butterfly and other insects), but few
increase in such experiences results in an ever with more effectiveness. In the case of the silk
improved adaptation to living conditions, and worm moth Bombyx mori, a few molecules
to an optimized pattern of life behaviour of the sex attractant llexadeca -1 Otrans-12cis
and life circumstances. dienol (bombycol) are sufficient to produce
The contribution of the individual sense organs an irritation signal. Only this one special
to our world picture depends on the number chemical, however, can produce an effect
of stimuli as well as on their quality. Sensiti with such a high sensitivity. Very small chan
vity and effectiveness of the various sense ges in the structure decrease the odour effect
organs are increased in the course of genera by orders of magnitude (D. SCHNEIDER 1971,
tions, the more they are used and stressed. see also table 20).
The stage of development of living beings The efficacy of the human senses of smell and
indirectly characterizes their ability to register taste is characterized not only by high sensiti
and to integrate stimuli of various types and vity but also by a very good ability to
intensities and to compare the result with discriminate between the various nuances of
earlier information stored. It is this type of flavour qualities. Normal adults can disting
comparison which causes conclusion and ex uish between nearly 2000 odour impressions.
perience and is finally reflected by behavi There is, however, a certain indolence in our
our. chemical senses, because of their normally
If we compare human senses of odour and low claim to recognition and definition of
taste perception with the other sense organs, known odour effects. Thus the qualification
we cannot overlook the fact that they are less for participating in a sensory test panel can be
well adapted than our senses of sight and achieved or improved by training. A trained
hearing. In modern industrial society, we are panelist in the flavour industry discriminates
continuously exposed to optical and acousti between up to 10000 odour impressions
cal stimuli. Speech, traffic, industrial noise, (K. B. DOVING 1963). Flavour perception is
displays from technical equipment, music, influenced by interactions between our differ
theatre, radio or television, they can all be ent sense organs. Frequently there is some
considered as examples. In contrast to this difficulty in differentiating between odour and
frequent use of our physical senses the 'che taste as two separate physiological senses.
mical senses'!) are called into use only pe- Of these two senses, odour perception is much
more complicated. In contrast to the ability
of adults to discriminate between much more
1) Odour and taste are stimulated by chemical stimuli, than 1000 single aroma impressions, there are
the other senses by physical stimuli only four basic taste qualities.
partially volatilized after coming into contact
wjth saliva and slightly increased temperature.
In both cases volatilized molecules of aroma
components pass the regio olfactoria.
After sorption in the mucus layer over the
active surface the stimulus sets off an elec
trical signal within the smelling cells which
are fitted with six to eight micro hairs per cell.
This signal is conducted via the cribriform
plate to the so-called bulbus olfactorius (ol
factory bulb) in the front brain. The further
way of the information to the odour field of
the brain is unknown neither its registration
nor the method of ~torage, or the comparison
with impressions received and stored earlier
is understood: in fact we do not completely
understand even the most elementary aspects
of receptor function (D. G. MOULTON 1971).
The receptors for taste on the tongue sur-
face register the four basic qualities sweet,
Fig. I sour, salty and bitter. The perception is lo
Olfactory prgans of man cated in special areas of this sense organ
I = regio olfactoria (see figure 2). Anyone can confirm this pheno
2 = cribriform plate
menon by careful observation.
3 = olfactory bulb
Odour perception takes place in the upper part
of the nasal cavity only, the so-called regio
olfactoria (olfactory sensory epithelium). This
part of the nasal mucosal is only 10 cmz
in area, but it contains some 10 million re
ceptors. There are three principle cell types:
I. Olfactory receptors which detect, decode
and transmit the sensory information about
Fig. 2
quality and intensity of odour
Sensitivity of tongue areas for the basic tastes
2. Sustentacular cells which add gland-pro (R. W. MONCRIEFF 1967)
duced mucopolysaccharides to the mucus
layer on the epithelial surface Each of the mushroom-shaped papillae on the
3. Basal cells which seem to be stem cells be tips and edges of the tongue bears 8 to 10
coming active in the course of normal taste buds; each of the circumvallate papillae
cell turn-over (T. V. GETCHELL and M. L. at the base of the tongue has 100 to 300. Each
GETCHELL 1977). bud lies beneath a pore, and is composed of
There are two possible ways for odorous 40 to 60 spindle-shaped taste cells packed
substances to reach the regio olfactoria. One together like segments of an orange. So-called
way is the transport of volatiles together with microvilli are extendend into the pit of the
the breath air stream, via the nasal cavity to pore. Here the interaction between stimulus
the loungs and vice versa. Another way is via and receptor is assumed to occur (D. G.
the nasopharynx connecting the mouth with MOULTON 1982).
the nasal cavity. This is what happens during Besides the four main principles mentioned,
the chewing and swallowing process in the a few more effects are discussed as taste sen
mouth, when food aroma compounds are sations. G. LILJESTRAND and Y. ZOTTERMAN
2
(1956) added the perception of alkaline taste, Another current research area uses the deter
R. W. MONCRIEFF (1967) the metallic taste mination of electrophysiological signals in
to the four main principles. Another typical connection with similarity studies of odour
taste effect is the so-called Umami (Y. KAWA qualities. Electro olfactograms from frogs and
MURA 1987) observed in connection with the rabbits as test animals indicate a number of
consumption of meat. It is discussed as an ef high correlation effects between homologues
fect of substances called flavour potentiators. of odorous substances or between pairs of
Monosodium glutamate and 5'-ribonucleotid odour stimuli (K. B. DOVING 1966; P. MAC
es belong to this group (see chapter 1.3.3.). LEOD 1971).
Apart from the histological structure of its Starting-points for future activities in the com
elements the physiology of odour and taste plicated field of reception mechanism can
reception has not yet been elucidated never also be found in publications about sweet
theless several odour and taste theories have and bitter sensations. S. SHALLENBERGER and
been published. They are all based on presu T. E. ACREE (1967) claim the presence of
med connections between the molecular struc two functional groups within tht: molecule
ture and the shape of special odour or taste of a sweet substance which can form hydro
molecules and their aroma and/or flavour gen bonds. They must be separated from one
impression. The principle was discussed first another by a particular distance. These attri
ly by L. PAULING (1946). Examples are the butes are claimed to be a common characte
Stereochemical Theory (J. E. AMooRE 1952, ristic of many sweetening agents. Thiocar
1971, 1982; J. E. AMooRE and D. VENSTROM bonyl compounds equipped with neighbou
i 966), the Vibrational Theory (R. H. WRIGHT ring n-systems represent one example of simi
1954, 1969) and die Adsorption Theory (M .. lar relationships for the bitter taste (R. MAYER
G. J. BEETS 1957, 1982; E. T. THEIMER and and F. WITTIG 1972). For bitter peptides,
J. T. DAVIES 1967; P. LAFFORT 1969). So far, interactions between hydrophobic side chains
however, the application and validity of all in the molecule and the receptor protein are
these theories is limited to a relative small discussed (A. PETRITSCHEK et al. 1972). The
number of flavour substances only. Moreover, intensity of the bitter taste after hydrolysis
none of these theories can give a clear answer can be calculated if the amino acid composi
to the question of what molecular or functional tion of the protein is known (K. H. NEY 1972).
properties are responsible for the inclusion A recent review of H.-D. BELITZ and H.
of a substance among the aroma of taste WIESER (1985) summarizes our knowledge
compounds (W. STEINER 1973). on structure - activity relationship in the
There have, however, been various attempts field of bitter compounds. From the tongue of
to elucidate the complex field of odour and beef and pork proteins have been isolated
taste perception. Only a little of this very which possess binding capacity for sweet or
interesting research can be mentioned here. bitter substances (F. R. DASTOLI et al. 1968).
One of the new concepts, for example, is the So far, the activity of physiological research
electrophysiological study of odour percep has dealt only with the first step, the reception
tion by insects. These animals are equipped of chemically produced sensory impressions.
with reCeptors of an extremely high sensiti The subsequent processes may be still more
vity for some volatile compounds and thus complicated. Our ability to perceive and to
have been used successfully for test purposes. integrate a very complex mixture of flavour
Many interesting results have been published compounds in less than a second. and to com
in this field within the last three decades. pare this sensation with earlier s[orl'd impres
Of special interest is not only the high sensi sions, still remains 'a mystery' (A. A. AL
tivity of the antennae of male insects, which BRECHT and L. M. BIEDLER 1966). However, in
can register the female over distances of kilo recent years our knowledge in this field has
meter~, but also a very high selectivity and begun to increase. There are some preliminary
specificity (D. SCHNEIDER 1969, 1971; W. A. ideas about the sequence of molecular, mem
KAFKA 1971; see also table 19 and 20, p. 64). branous and neural events responsible for the
3
transmlsslOn of the reception signals to the The concerted action of these three groups of
brain (T. B. GETCHELL and M. L. GETCHELL sensations constitutes the flavour.
1977). As shown in figure 3 there are many cross
links. What we define as the typical flavour
of a food in most cases is mainly identical with
1.2. Attributes contributing to flavour pleasant odour (= aroma) perceptions. Thus
sensation aroma is central to total flavour perception.
Products absolutely lacking in aroma will
never be characterized as having 'good fla
As already mentioned flavour sensation re vour'. Aroma, however, is frequently plea
sults from a cooperative effect of odour sen sant only if we feel a simultaneous taste sen
sation and taste sensation. Whereas taste sation. A well-known example is the importan
substances like sugar, sodium chloride, acids ce of a special sugar/acid ratio for the flavour
or bitter compounds are registered during quality of fruits or of wines. Canned fruits
the mouth passage by the taste receptors, without added sugar seem to be low in flavour
volatile odorous components reach the sensory so do fully-ripe oranges, apples or pears which
olfactory region directly 'via the nose or indi may have sufficient aroma components and
rectly via the connection between mouth and a sweet taste, but no acid. Salt-reduced bread,
nose cavity. In the case of solid foods, the sausages produced without addition of so
chewing and grinding process, together with dium chloride or beerwi thout bitter substances
the influence of temperature and saliva, cau are further examples of tasteless and insipid
ses a partial volatilization which allows entry flavour. In all these cases the content of
through the pharynx cavity to the nasal volatile aroma components may be just as
area. high as normal.
In English as well as in German the combined Besides odour and taste, further sensations
odour/taste sensation is often described sim contribute to the overall flavour impression
ply as taste (Geschmack), although usually in most foods and dishes. Among these con
the total sensation is under discussion. This sistency effects are the most important. Many
was one of the reasons for introducing the examples indicate our ability to integrate
term flavour. Flavour describes lhe overall consistency impressions, such as hardness,
sensation and that means something more toughness, stickiness, elasticity, plasticity or
than odour and taste alone. In figure 3 which viscosity, into flavour.
demonstrates the relationship between these Texture and consistency of food and meals
terms haptic or tactile feelings are included produce physical impressions like touching,
additionally as a third group of sensations. pressing, resistance against grinding, or, in the
Flavour
,------0--1 (total sensory impression 1------,
during food consumption)
Aroma /
(pleasant odour /
impression during
food consumption)
Odour Fig. 3
(volatiles directly
via the nose) Relationship between diffe
rent senses in 'flavour' and
*) includinq chemical irritations within the mouth
H) including other physical irritations within the mouth 'aroma' perception
4
