Chemistry in Food: Flavors - Scientific Article

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Chemistry in food: Flavours
ArticleinElectronic Journal of Environmental, Agricultural and Food Chemistry · February 2007
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Gonzalo Astray
University of Vigo
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Juan C. Mejuto
University of Vigo
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Lorenzo Pastrana
International Iberian Nanotechnology Laboratory
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ISSN: 1579-4377
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377
1742
CHEMISTRY IN FOOD: FLAVOURS
G. Astraya*, L. García-Ríob, J.C. Mejuto* a, L. Pastranac
a) Department of Physical Chemistry, Faculty of Sciences, University of Vigo, 32004, Ourense, Spain;
b) Department of Physical Chemistry, Faculty of Chemistry, University of Santiago de Compostela, 15706, Santiago de
Compostela (A Coruña), Spain;
c) Food and Analytic Chemistry Department, Faculty of. Sciences, University of Vigo, 32004, Ourense, Spain.
ABSTRACT
The British Standards Institution defines flavour as the combination of taste and odour
that may be influenced by painful, heat-cold and tactile sensations. The aroma and all the
sensory characteristics of food represent only a fraction of the phenomena recognised by the
individual when the food is consumed. The term aroma includes the global integral perception of
all the senses that are involved (smell, taste, sight, touch) in consuming food. The aromatic
substances present a wide range of chemical structures that stem from the main constituents of
food. In the present review some of the compounds responsible for the aroma present in the
food will be commented.
KEYWORDS: Flavours, savory substances, aroma enhancers, astringency, Vanillin
* Corresponding author. Tel.: [phone]; Email: [e-mail] Present address:
Department of Physical Chemistry, Faculty of Science of Ourense, University of Vigo at
Ourense, 32004-Ourense Spain

Astray et al. EJEAFChe, 6 (2), 2007. [1742-1763]
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377
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1. THE MEANING OF FLAVOUR
According to the UNE 87-001-86, standard flavour designates all the organoleptic
properties that are indirectly perceptible by the olfactory organ when tasting [1]. The
term flavour denotes a complex set of olfactory and gustatory properties that are
perceived when tasting and that can be influenced by tactile, thermal, painful, and even
kinaesthetic effects.
The British Standards Institution defines flavour as the combination of taste and
odour that may be influenced by painful, heat-cold and tactile sensations [2]. The aroma
and all the sensory characteristics of food represent only a fraction of the phenomena
recognised by the individual when the food is consumed.
It is not clear why food sensory characteristics coexist with aroma, texture and
appearance. Intuitively, it is suggested that the aroma may be perceived as an integrated
phenomenon (sensory complex) [3], while the sensory phenomena involved in texture
and appearance are perceived independently [4].
On the basis of these evidences, the exact psychological interpretation of aroma
is impossible. It is necessary to bear in mind that (i) the aroma exists only in
psychological terms, (ii) psychological phenomena like aroma cannot be observed in
the physical world, (iii) the aroma arises when a stimulus (food or beverage) interacts
with a vivid organism, and (iv) the aroma comprises a great number of sensory
characteristics that many times result from the stimulation of the senses of smell and
taste. [5].
A direct evaluation of aromas by physico-chemical methods is impossible. These
methods can only qualify and quantify certain physico-chemical properties of the
stimuli which will give rise to answers obtained by using sensory methods.
2. AROMA IN FOOD
The term aroma includes the global integral perception of all the senses that are
involved (smell, taste, sight, touch) in consuming food [6].
There are almost unlimited variations in the intensity and quality of odours that
can be perceived by the specialised cells of the olfactory epithelium from the nasal
cavity [7]. The gustatory papillae situated on the (top of the) tongue and on the posterior
part of the oral cavity facilitate the perception of sensations of sweetness, sharpness,

Astray et al. EJEAFChe, 6 (2), 2007. [1742-1763]
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377
1744
saltiness and bitterness [8-9]. The detection of sensations of spiciness, coldness and
umami [10-11] is realised by the cells from the trigeminus [12].
The aromatic substances present a wide range of chemical structures that stem
from the main constituents of food. They are characterised by the fact that they
stimulate the receptors of smell and/or taste in order to produce an integrated
psychological response.
In the present review some of the compounds responsible for the aroma present
in the food will be commented.
2.1 Savory substances: sweet, bitter, sharp and salty
There is a theory that relates the molecular structure to the sweet flavour [13-14] (fig. 1)
and satisfactorily explains the reason why certain compounds have a sweetening
capacity.
Cl Cl
Cl
H
AH
B
Cloroformo (I)
NH
S
O
O
OB
AH
Sacarina (II)
O
OH
OH
HOH2C
OH
OH
HA
B
D-Glucosa (III)
Fig. 1.- AH/B relations for structures of chloroform (I), saccharin (II), and D-glucose (III).
Bitterness is similar to sweetness since it depends on the stereochemistry of the
molecules that generate the stimulus. The quinine [15-19], an stereoisomer of quinidine
[20-24], is an alkaloid accepted as the standard substance that represents the bitter
gustatory sensation. (fig. 2). This natural alkaloid, of white and crystalline colour, is
extracted from the bark of the cinchona (fig. 3), an American tree belonging to the
family Rubiaceae that presents antipyretic, antimalarial and analgesic properties [25].
Due to the side effects of high doses of quinine, its concentration has been
limited by the legislations of each country.

Astray et al. EJEAFChe, 6 (2), 2007. [1742-1763]
Electron. J. Environ. Agric. Food Chem.
ISSN 1579-4377
1745
Quinine (I)
Quinolidine (II)
Fig. 2.- Quinine and quinolidine chemical structure.
Fig. 3.- Quinine tree.
The substance responsible for the bitter flavour of fruit, especially in the cases
of the grapefruit, navel orange, Valencia orange (fig. 4), is a triterpenoid dilactone
denominated limonin [26-30] (fig. 5). This is the substance which actually give citrus
fruits their characteristic sharpness. The limonin is a natural bactericide whose main
function is to prevent the plant from contracting diseases.