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

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and of the limitations on the quantity of taint that can

be isolated for identification, the analytical technique

best suited for detection and identification of taints is

high-resolution GC-MS. Detection and identification

of tainting compounds can usually be achieved using

GC-MS operated in full scan mode. However, GC-

MS operated in either the mass chromatography

mode or selected ion monitoring mode is unparalleled

in its ability to deliver both sensitivity and selectivity

of detection.

0032 Mass chromatography (MC) allows reconstruction

of the ion current profiles of selected ions as a func-

tion of time from continuously collected data. One of

the simplest uses of MC in taint studies is the location

of certain classes of compounds in complex mixtures

by looking for the presence of characteristic ions from

the total ion current trace. For example, by examining

at a resolution of 5000 the fragment ion m/z 45

(CHS

) that occurs widely in both aliphatic and

aromatic sulfur compounds, it is possible to separate

this species from others of the same nominal mass

(e.g., C

) and, moreover, to detect those regions

in the chromatogram where the sulfur-containing

species occur.

0033 With selected ion-monitoring (SIM), the peak

selector of the mass spectrometer can record either

single or multiple ion characteristics of any specific

compound being searched for to provide a series of

’fragmentograms’ from separated peaks during a GC

run. By monitoring ions of one or just a few specific

masses instead of the whole spectrum, a thousand-

fold increase in sensitivity (picogram quantities) can

be attained.

0034 The successful application of GC-MS operated

in the SIM mode to the identification of taints has

been readily demonstrated by several groups of

workers, and many case histories utilizing this tech-

nique have been extensively documented in the scien-

tific literature. (See Chromatography: Combined

Chromatography and Mass Spectrometry.)

Quantification of Taints

0035 In many taint studies where only a limited quantity of

tainted food is available for analysis, quantification

of the taints by GC-MS is achieved by comparing the

SIM responses for each ion monitored with those

obtained with standard solutions of the tainting

chemical. In these cases, it is usually assumed that

complete extraction of the taint from the foodstuff

has been achieved. This highlights the major difficulty

in obtaining accurate quantification of odorants in

general and taints in particular, namely the need to

extract, enrich, and separate the taint without losses.

0036The isotope dilution assay is probably the most

precise method for quantifying minor constituents of

food such as taints. In this technique, the tainting

chemical now labeled with deuterium or carbon-13

is used as an internal standard. Since the labeled

standards have virtually the same chemical and phys-

ical properties as the taint, the overall efficiency of the

extraction and enrichment stages does not influence

the result. However, for a solid food, usually only the

extract containing the volatile fraction, and not the

food itself, is spiked with the labeled internal stand-

ard, and 100% efficiency of extraction is again

assumed.

0037Despite the difficulties inherent in these method-

ologies, quantitative measurements are an essential

part of taint studies. In tandem with sensory evalu-

ation, they provide complementary data proving that

the compound identified is responsible for the taint.

0038It is important to remember that taint in foods is a

matter of perception: it is the taste/odor threshold

level of an odorant, not its presence per se, that deter-

mines if it will cause taint.

See also: Chromatography: Combined Chromatography

and Mass Spectrometry; Gas Chromatography; Quality

Assurance and Quality Control; Sensory Evaluation:

Food Acceptability and Sensory Evaluation; Aroma;

Taste; Taints: Types and Causes

Further Reading

Grosch W and Schieberle P (1991) Bread. In: Maarse H

(ed.) Volatile Compounds in Foods and Beverages, pp.

41–77. New York: Marcel Dekker.

Hirvi T and Honkanen E (1984) Selected ion monitoring

technique and sensory analysis in the evaluation of the

aroma of berries. In: Nykanen L and Lehtonen P (eds)

Flavor Research of Alcoholic Beverages, pp. 275–278.

Helsinki: Foundation for Biotechnical and Industrial

Fermentation Research.

Kilcast D (1996) Sensory evaluation of taints and

off-flavours. In: Saxby MJ (ed.) Food Taints and Off-

flavours, pp. 1–40. Glasgow: Blackie Academic &

Professional.

Leland JV, Schieberle P, Buettner A and Acree TE (2001)

Gas Chromatography–Olfactometry. The State of the

Art. ACS Symposium Series 782. Washington, DC:

American Chemical Society.

Maarse H and Belz R (eds) (1981) Isolation, Separation and

Identification of Volatile Compounds in Aroma Re-

search. Berlin: Akademie-Verlag.

Pawliszyn J (1997) Solid Phase Microextraction. Theory

and Practice. New York: Wiley-VCH.

Pawliszyn J (ed.) (1999) Applications of Solid Phase Micro-

extraction. Cambridge: Royal Society of Chemistry.

Schreier P (ed.) (1984) Analysis of Volatiles – Methods.

Applications. Amsterdam: de Gruyter.

5728 TAINTS/Analysis and Identification

TANNINS AND POLYPHENOLS

B G Swanson, Washington State University, Pullman,

WA, USA

Background

0001 Tannins are generally defined as soluble, astringent

complex phenolic substances of plant origin used

in tanning of animal skins or precipitation of pro-

teins. Tannins are chemically defined as phenylpropa-

noid compounds often condensed to polymers of

variable length. Phenolic compounds are chemically

defined as compounds containing hydroxylated

aromatic rings, the hydroxy group being attached

directly to the phenyl, substituted phenyl, or other

aryl group. Tannins and phenolic compounds are

widely distributed secondary metabolites in plants,

and play a prominent role in general defense

strategies of plants, as well as contributing to food

quality. The terms ’hydrolyzable’ and ’condensed’

tannins are used to distinguish between the two im-

portant classes of vegetable tannins, namely gallic

acid-derived and flavan-3,4-diol-derived tannins, re-

spectively. (See Phenolic Compounds; Vegetables

of Temperate Climates: Commercial and Dietary

Importance.)

Phenolic Compounds

0002 Phenolic compounds are widely distributed in plant

tissues, particularly contributing color, flavor, and

astringency to fruits. The concentration of phenolic

compounds may vary from 0.5 to 5.0 g per 100 g dry

weight of plant tissues. Phenolic compounds are often

considered secondary metabolites of plant metabol-

ism that contribute little to the physiological or

ecological functions of the plant. (See Colorants (Col-

ourants): Properties and Determination of Natural

Pigments; Flavor (Flavour) Compounds: Structures

and Characteristics.)

0003 Most phenolic compounds are believed to be

byproducts of the metabolism of the aromatic

amino acid phenylalanine. A major group of water-

soluble phenolic compounds, the anthocyanins, con-

tribute colors to fruits. Two identified anthocyanins,

phloridzin in apples and arbutin in pears, occur only

in plant tissues and are absent in associated fruits.

0004 The greatest concentrations of phenolic com-

pounds in plants are normally present as cinnamic

acid derivatives and flavan monomers, dimers, and

polymers.

Cinnamic Acid Derivatives

0005Cinnamic acids play key roles in the formation of

other more complex phenolic compounds. The

cinnamic acids (Figure 1) are rarely present in

uncombined forms, occurring primarily as esters of

quinic acid, but may also be esterified to malic or

tartaric acids, or sugars. Chlorogenic acid (5-

caffeoylquinicacid) (Figure 2) is perhaps the most

important cinnamic acid observed in fruits, contrib-

uting 25% of the dry weight of the bilberry (Vacci-

nium) fruit. Chlorogenic acid can be isolated from

green coffee beans, and forms a black compound

with iron, believed to be responsible for the

blackening of cut or cooked potatoes. Anthocyanin

and flavonoid glycosides are also acylated by cin-

namic acids through sugar hydroxyl groups, with

p-coumaric acid the most common acylating agent.

In addition to forming esters, hydroxylated cinnamic

acids also form glycosides with sugars. (See Coffee:

Green Coffee; Fruits of Temperate Climates: Fruits

of the Ericacae.)

Cinnamic Acids in Fruits

0006The concentration of cinnamic acid derivatives de-

clines as fruits mature. However, the total quantity

CH CHCOOH

COOH

...φ

fig0001Figure 1 Tr a n s -cinnamic acids: p-coumaric, R¼R

¼H; caffeic,

R¼OH, R

¼H; ferulic, R¼OCH

¼H; sinapic R¼R

¼OCH

HOOC

OOCCH CH

fig0002Figure 2 Chlorogenic acid.

TANNINS AND POLYPHENOLS 5729

of cinnamic acids increases as the fruits enlarge

during the growing season. Cinnamic acids accumu-

late in the skin or peel of fruits. Cinnamic acids,

especially chlorogenic acid, which is extensively des-

troyed during roasting, are important to the accept-

ability of coffee. (See Ripening of Fruit.)

Flavans

0007 Flavans are widely distributed in nature and result

from a double reduction of a flavanone. The general

biochemical derivations of flavonoids are presented

in Figure 3. Many natural flavans are lipid-soluble

and are prominent in the skin or peel of fruits and in

the cutin of leaf surfaces. A number of flavans are

phytoalexins, which impart fungi or insect resistance

to the plant tissues. Flavans are generally found in

greater concentrations in immature fruits compared

with mature fruits.

0008 Flavans are not generally observed in plant tissues

as monomers, glycosides, esterified, methylated, or in

any heterogenous combination, except for galloyl

esters in grapes and tea. Flavans generally are con-

densed to form ’condensed tannins,’ more correctly

referred to as ’proanthocyanidins.’ Flavan-3-ols, cate-

chin and epicatechin, are the largest class of mono-

meric flavans. A considerable number of flavan-3-ol

glycosides can be isolated from plant tissues. (See Tea:

Chemistry.)

0009 The nomenclature of flavonoid and proanthocya-

nidin structures changes as the number and com-

plexity of this group of plant metabolites expand.

Leucoanthocyanidins are defined as monomeric fla-

vonoids that produce anthocyanidins by cleavage of a

carbon–oxygen bond on heating with mineral acid.

Condensed proanthocyanidins are defined as flavan-

3-oligomers, or more generally as proanthocyanidins

that produce anthocyanidins by cleavage of a carbon–

carbon bond. The isolation, structure, and properties

of ’insoluble’ proanthocyanins constitute a major un-

resolved problem for phytochemists, and enologists

in particular.

Anthocyanidins and Anthocyanins

0010 Anthocyanins are glycosides composed of the antho-

cyanidin aglycone plus one or more glycosidically

bonded mono- or oligosaccharidic units. Anthocya-

nins are identified structurally by name (Figure 4). Six

anthocyanins are water-soluble pigments common in

flowers and plant tissues; although many other antho-

cyanins exist, they are rather limited among common

food plants.

0011Color variations among the anthocyanins reflect

structural differences in the number of hydroxyl

groups, the presence or absence of methylation and

glycosylation, as well as the distribution of positive

charge about the aryl-substituted chroman ring

system. Anthocyanins undergo structural alterations,

depending upon the pH and ionic strength of the

aqueous environment.

Tannins

0012Tannins are generally defined as polyphenolic com-

pounds, with a molecular weight greater than 500,

that precipitate proteins from an aqueous solution.

Tannins precipitate proteins owing to functional

groups that interact with two or more protein

molecules, to form hydrophilic or hydrophobic

complexes, building large cross-linked insoluble pro-

tein-tannin complexes. Hydrolyzable tannins are

classified as gallotannins or ellagitannins on the

basis of tannic acid structure relative to gallic or

ellagic acids. Hydrolyzable tannins, including tannic

acid, can be acid- or enzymatically hydrolyzed to

yield glucose and gallic acid.

0013A second category of polymeric flavonoids, the

condensed tannins are not hydrolyzed under physio-

logical digestive conditions, but upon severe acid or

alkaline treatment, yield less-soluble polymeric phlo-

baphanes or monomeric flavonoids such as catechin

or epicatechin. Condensed tannins notably contain

linkages between the 4-position of one catechin resi-

due and the 6- or 8-position of another flavonoid. The

condensed tannin structures are not to be confused

with tannic acid, the representative structure of the

hydrolyzable tannins.

Analysis of Polyphenolic Compounds

0014Extraction and separation of anthocyanin com-

pounds generally involve maceration of plant tissue

in methanol containing 1% HCl. Qualitative assays

with thin-layer chromatography (TLC) have evolved

to quantitative assays with high-performance liquid

chromatography (HPLC), often utilizing selective

absorption wavelengths to determine the identity

and concentration. (See Chromatography: Thin-

layer Chromatography; High-performance Liquid

Chromatography.)

0015Much of the emphasis in contemporary natural

products chemistry lies in the elucidation of the bio-

logical activity of plant metabolites, rather than in the

intrinsic interest of the structures themselves. The

rationale for the study of proanthocyanidins is to

develop a knowledge of proanthocyanidins in plant

5730 TANNINS AND POLYPHENOLS

Malonyl CoA

3 CH

SCoA

Acetyl CoA

ATP + HCO

(a)

ADP + P

+ H

−

OOC CH

SCoA

COO

−

Phenylalanine

Several

steps

SCoA

4-Coumaroyl CoA

(2)

(b)

(1)

(c)

OH OH

(3)

(5)

(8)

(6)

O-Sugar

(4)

Glycosylation

(9)

(7)

(d)

Flavones Flavonols Flavanones Flavanonols Isoflavones

−

fig0003 Figure 3 General biochemical derivations of flavonoids. A structural key for the group of compounds is indicated at the bottom of the

figure: flavones, position 2,3 is unsaturated; flavonols, C-3 hydroxyl is present; flavanones, 2,3-site is saturated; flavanols, C-3 hydroxyl

is present and site 2,3 is saturated; and isoflavones, C-3 phenyl ring substituent is displayed. Pathway key: (a) acetyl-CoA carboxylase;

(b) chalcone synthase; (c) chalcone isomerase; (d) flavanone 3-hydroxylase; (1) chalcone; (2) aurone; (3) flavanone; (4) dihydroflavo-

nol; (5) flavone; (6) catechin; (7) flavonol; (8) anthocyanidin; (9) anthocyanin. Isoflavone in the interim formation of chalcones (1) to

flavanones (2).

TANNINS AND POLYPHENOLS 5731

biochemistry relative to structure and chemistry. To

understand the biochemistry of physiologically active

proanthocyanidins, the development of strategies to

separate and purify proanthocyanidins in an unmodi-

fied state is necessary. Using alcoholic solvents, aque-

ous methanol or ethanol, mono-, di- and trimeric

flavon-3-ols are separated from plant tissue with

Sephadex LH-20 or a high-porosity polystyrene gel

(CHP 20P). More recently, column chromatography

on reversed-phase C8, C18 or CN supports has pro-

vided alternative separation techniques. HPLC on

reversed-phase columns is used extensively for ana-

lytical and preparative separation of proanthocyani-

dins. High-resolution separation is achieved with

solvent programming and dilute acid suppression of

hydroxyl group ionization. Structural elucidation of

proanthocyanidins may be readily determined with

nuclear magnetic resonance and circular dichroism

spectroscopy. (See Spectroscopy: Nuclear Magnetic

Resonance.)

0016 The condensed tannin content of plant tissues is

generally determined by the traditional vanillin-HCl

method or protein precipitation.

Physiological and Health Effects

0017Tannins are generally considered nutritionally un-

desirable, because they precipitate proteins, inhibit

digestive enzymes, and have a detrimental effect on

the absorption and utilization of vitamins and min-

erals. Tannin components have been implicated in

incidences of cheek and esophageal cancers in specific

regions of the world, and cited as antimutagenic and

anticarcinogenic in other studies. Tannins are antimi-

crobial, inhibiting the invasion and growth of fungi,

bacteria, and viruses in food plants. Tannins can

theoretically serve as natural regulators of the micro-

bial population in many habitats including the gastro-

intestinal tract. Tannins are also reported to produce

other physiological effects such as immune response,

hepatotoxicity, and lipid metabolism. Ingestion of

large quantities of tannins may result in adverse

health effects. However, the ingestion of small quan-

tities of selected tannins may be beneficial to human

health.

0018Polyphenols in herbal medicines, fruits, and vege-

tables are often presumed to play an important

(I)

(IV)

(II)

OCH

(III)

(a)

(V)

(VI)

(b)

fig0004 Figure 4 (a) Selected structures for six of the most common anthocyanidins. All anthocyanidins have hydroxyl groups in the 3-, 5-

and 7-positions, although each structure may have its own characteristic hydroxyl or methoxyl groups on the so-called B ring: (I)

cyanidin, (II) delphinidin, (III) malvidin, (IV) peonidin, (V) pelargonidin, and (VI) petunidin. These compounds occur in many species of

fruits and vegetables: apple (I); blackcurrant (I, II); blueberry (I, II, III, IV, VI); cherry (I, IV); grape (I–VI); orange (I, II); peach (I); plum (I,

IV); radish (V); raspberry (I); red cabbage (I); strawberry (V-major,I). (b) Possible positive charge distribution over a chroman ring

system found in the structure of anthocyanidins.

5732 TANNINS AND POLYPHENOLS

physiological role in the maintenance of good

health. Polyphenols generally exert their effects by

associating with metals, their antioxidant and rad-

ical-scavenging activities, and interaction with other

molecules, including proteins and polysaccharides.

The antioxidant capacity of flavanoids is deter-

mined by a combination of the O-dihydroxy struc-

ture in the B-ring, the 2,3-double bond in

conjugation with a 4-oxo function, and the presence

of both hydroxyl groups in positions 3 and 5.

Recent research efforts are highlighting the exciting

and exceptionally dynamic role of polyphenolic

components actions as antioxidants or agents of

other mechanisms that contribute to their anticarci-

nogenic, antiviral, antiinflammatory, and cardiopro-

tective effects derived from consumption of plant

foods.

Sensory Properties

0019 Flavonoids and anthocyanins contribute yellow, red,

and blue colors to flowers, leaves, and fruits. Poly-

phenolic compounds also contribute sweet, bitter,

or astringent flavors, depending on solubility and

structure. Flavonoids such as rutin, a 3-rhamnosyl-

d-glycosyl derivative of quercetin, contribute undesir-

able precipitates to processed foods. Tannins and

tannin–protein complexes may give fruit juices a

desirable body or consistency, or may contribute to

undesirable hazing or loss of clarity or sparkle. (See

Sensory Evaluation: Appearance; Taste.)

0020 Pharmacological effects related to estrogen pro-

duction and induction of infertility, enzyme cofac-

tors beneficial to health, and counteracting of

glucose resorption are attributed to consumption

of specific polyphenolic compounds. Tannins are

often related to astringency and bitterness in wines

or foods, and are thought to play a significant role

in the reduction of dietary protein digestibility by

complexing with either dietary protein or digestive

enzymes. (See Coenzymes; Glucose: Function and

Metabolism.)

See also: Chromatography: Thin-layer Chromatography;

High-performance Liquid Chromatography; Coenzymes;

Coffee: Green Coffee; Colorants (Colourants):

Properties and Determination of Natural Pigments; Flavor

(Flavour) Compounds: Structures and Characteristics;

Fruits of Temperate Climates: Fruits of the Ericacae;

Glucose: Function and Metabolism; Phenolic

Compounds; Ripening of Fruit; Sensory Evaluation:

Appearance; Taste; Spectroscopy: Nuclear Magnetic

Resonance; Tea: Chemistry; Vegetables of Temperate

Climates: Commercial and Dietary Importance

Further Reading

Benavente-Garcia O, Castillo J, Marin FR, Ortuno A, and

Del Rio JA (1997) Uses and properties of Citrus flavo-

noids. Journal of Agricultural and Food Chemistry 45:

4505–4515.

Chung K-T, Wei C-I, and Johnson MG (1998) Are tannins a

double-edged sword in biology and health? Trends in

Food Science and Technology 9: 168–175.

Earp CF, Akingbala JO, Ring SH, and Rooney LW (1981)

Evaluation of several methods to determine tannins in

sorghums with varying kernel characteristics. Cereal

Chemistry 58: 234.

Hagerman AE and Butler LG (1978) Protein precipitation

method for the quantitative determination of tannins.

Journal of Agricultural and Food Chemistry 26: 809.

Harbourne JB and Mabry TJ (eds) (1988) The Flavonoids –

Advances in Research, 621pp. London: Chapman &

Hall.

Haslam E (1982) Proanthocyanidins. In: Harborne JB and

Mabry TJ (eds) The Flavonoids – Advances in Research,

pp. 417–447. London: Chapman & Hall.

Haslam E (1989) Plant Polyphenols, 230pp. Cambridge:

Cambridge University Press.

Haslam E (1998) Practical Polyphenolics: From Structure

to Molecular Recognition and Physiological Action,

422 pp. Cambridge: Cambridge University Press.

Kapsalis C and Beck RA (1985) Phenolic Plant Pigments. In:

Kapsalis C and Beak RA (eds) Food Chemistry and

Nutritional Biochemistry, pp. 554–563. New York:

Wiley.

Lewis NG and Yamamoto E (1989) Tannins – their place in

plant metabolism. In: Hemingway RW and Karchesy JJ

(eds) Chemistry and Significance of Condensed Tannins,

pp. 23–46. New York: Plenum.

Taste See Sensory Evaluation: Sensory Characteristics of Human Foods; Food Acceptability and Sensory

Evaluation; Practical Considerations; Sensory Difference Testing; Sensory Rating and Scoring Methods;

Descriptive Analysis; Appearance; Texture; Aroma; Taste

TANNINS AND POLYPHENOLS 5733

TASTE ENHANCERS

S S Schiffman, Duke University Medical School,

Durham, NC, USA

Introduction

0001 The term ’taste enhancer’ is used in the food industry

to describe a substance that enhances the sensations

of food (or food ingredients) when introduced into

the mouth. The use of the term ’taste’ is colloquial

and actually refers to flavor (both taste and smell)

because chemicals from food activate receptors in

the nose as well as the mouth. Enhancement of the

taste and smell of food is desirable to improve palat-

ability, increase total intensity, potentially reduce the

cost of ingredients, and compensate for chemosen-

sory (taste and smell) losses in vulnerable populations

such as the elderly. Enhancement can be achieved in

two ways: (1) by simply adding more molecules to the

food or (2) by potentiating the intensity through

synergism and/or alteration of receptor mechanisms

without altering the total number of molecules.

Enhancement by Addition of Molecules

0002 Many food ingredients, including monosodium glu-

tamate (MSG), NaCl, and sweeteners have been

termed ’taste enhancers’ but their main effect is

simply to add more molecules that generate add-

itional taste or smell sensations. Tastants such as

MSG, salt, and sweeteners don’t actually boost

other chemosensory properties but rather contribute

additional meaty/savory, salty, or sweet properties

respectively.

0003 Experimental studies have shown that MSG at

concentrations up to 0.005 mol l

1

does not alter the

intensities of other food ingredients including salts,

sweeteners, amino acids, acids, or bitter compounds.

MSG is a taste enhancer strictly from the standpoint

that it adds another taste quality to the food (called

umami in Japanese) which improves palatability

rather than altering the intensity of other ingredients.

Similar conclusions pertain to the ’enhancing’ effects

of NaCl and sweeteners that add saltiness or sweet-

ness to food, respectively; they also improve palat-

ability by reducing bitter components of some food

substances. Thus MSG, salt, and sweeteners are taste

enhancers from the standpoint that they add add-

itional tastes to the food and improve palatability

rather than potentiate the taste intensity of other

ingredients.

0004Analogous reasoning can be applied to flavors.

Commercial flavors are often added to food for the

elderly (called ’flavor enhancement’) to compensate

for losses in smell perception that occur in elderly

individuals. Flavors consist predominantly of mix-

tures of odorous molecules that can be extracted

directly from natural foods or can be synthesized

after chromatographic and mass spectrographic an-

alysis of natural products. Simulated flavors are

flavor enhancers only from the standpoint that they

increase the total number of molecules that interact

with receptors on chemosensory membranes in the

nose and mouth. Intensification of odor can improve

palatability, induce more salivation, produce greater

stimulation of the olfactory and limbic system of the

brain, and promote immune function via mechanisms

described below under positive health benefits of

chemosensory enhancement.

0005Although odorants and tastants are perceived by

two different senses, the perceived intensity of a

tastant may also increase with the addition of odorant

molecules. For example, perceived sweetness intensity

is enhanced by the addition of odorants, especially

for congruent taste/odor mixtures such as sucrose/

strawberry and sucrose/lemon. (See Flavor (Flavour)

Compounds: Structures and Characteristics.)

Enhancement by Synergism

0006Taste enhancement also occurs via synergism in

which the total intensity of a mixture is greater than

the expected intensity based on the concentration of

the individual components. Two methods of calculat-

ing the degree of synergy have been used: one which

simply compares the perceived intensity of a binary

mixture (for example) with the sum of the intensities

of the unmixed components, and a second which

compares the intensity of binary blends to the average

of the two pure components of the blends. The most

common practical application of synergism occurs

with the use of certain binary or ternary sweetener

combinations in beverages. That is, when one sweet-

ener is combined with certain other sweetener(s), it

produces a synergistic sweetening effect. Synergism

permits the blending of low concentrations of sweet-

eners such as saccharin or acesulfame-K, that are

bitter at higher concentrations, with sweeteners with-

out salient bitter components such as aspartame and

fructose to achieve a desired level of sweetness.

Synergistic effects are idiosyncratic and vary with

the chemical structure of the individual ingredients.

Synergistic effects can occur between two or more

5734 TASTE ENHANCERS

high-potency sweeteners (such as aspartame and ace-

sulfame-K), between a high-potency sweetener and

sugars (such as acesulfame-K and fructose), and be-

tween combinations of sugars such as fructose and

sucrose. The maximum synergy found for binary

mixtures of sweeteners is about 74%; the maximum

synergy found for ternary mixtures of sweeteners is as

much as 99%. The precise mechanisms that produce

synergism among sweeteners are not known at the

present time. However, it is probable that multiple

receptors as well as biochemical transduction

mechanisms in taste cells play a role.

Enhancement by Modifying Receptor

Mechanisms

0007 A variety of compounds have been shown in a labora-

tory setting to enhance taste perception including:

(1) caffeine (and other methyl xanthines); (2) 5

ribo-

nucleotides; (3) inosine; and (4) bretylium tosylate.

However, only 5’ ribonucleotides are commercially

practical enhancers because the other compounds

require pretreatment of the tongue to achieve

potentiation.

Methyl Xanthines

0008 Pretreatment (adaptation) of the tongue with methyl

xanthines has been shown to enhance other taste

stimuli. Methyl xanthines, including caffeine, theo-

phylline, and theobromine, are found in coffee, tea,

and chocolate, respectively. When the tongue was

adapted to caffeine, theophylline, or theobromine at

concentrations ranging from 10 mmol l

1

to 10 mmol

1

, the taste intensities of acesulfame-K (a sweet-

ener), sodium chloride, potassium chloride, and

quinine hydrochloride were enhanced. Furthermore,

10 mmol l

1

caffeine potentiated the taste of moderate

concentrations of other sweeteners, including neohe-

speridin dihydrochalcone, d-tryptophan, thaumatin,

stevioside, and sodium saccharin. Sweeteners potenti-

ated by caffeine had a bitter component; sweeteners

without prominent bitter components, including as-

partame, sucrose, fructose, and calcium cyclamate,

were not potentiated by caffeine. It has been hypothe-

sized that this enhancement by pretreatment with

methyl xanthines may be caused by the antagonistic

effect of methyl xanthines on adenosine receptors on

the tongue surface. (See Alkaloids: Properties and

Determination; Caffeine.)

Inosine-5

-Monophosphate (IMP)

0009 The 5

-ribonucleotides, inosine-5

-monophosphate

(IMP) and guanosine-5

-monophosphate (GMP),

have been shown to enhance certain tastes. A mixture

of 5

-ribonucleotides with MSG can potentiate the

taste of suprathreshold concentrations of MSG. The

nucleotides with the best enhancement capacity

appear to be those having a purine nucleus with a

hydroxy group in the 6-position and a ribose moiety

esterified in the 5

-position with phosphoric acid, e.g.,

IMP and GMP. Addition of 0.1 and 1 mmol l

1

IMP

to MSG also reduces the MSG taste threshold so that

it can be perceived at lower concentrations (fewer

molecules are needed for detection). Pretreatment of

the tongue with 1 mmol l

1

IMP enhanced the taste of

both sucrose and aspartame by approximately 60 and

40%, respectively. Biochemical studies indicate that

the synergism between MSG and certain 5

-ribonu-

cleotides is a peripheral event involving alterations in

glutamate receptors on the taste bud. Inosine, a

breakdown product of both IMP and of adenosine,

has also been found to enhance moderate tastes of

sucrose, aspartame, and sodium chloride when the

tongue is pretreated with inosine.

Bretylium Tosylate

0010Pretreatment of the tongue surface with bretylium

tosylate, a quaternary ammonium compound that is

used as an antifibrillary drug, enhanced the taste of

sodium chloride. Bretylium tosylate has been shown

to open amiloride-sensitive sodium channels in other

biological systems. Bretylium tosylate may act in a

similar fashion on the human tongue by increasing

sodium transport through the amiloride-sensitive

channels on the tongue that are known to be involved

with salty taste.

Positive Health Benefits of Chemosensory

Enhancement

0011Enhancement of the sensory properties of meats,

soups, vegetables, and other nutritious foods with

food flavors and MSG not only compensates for

taste and smell losses that occur in an elderly popula-

tion but can also improve health status. Four clinical

studies of frail elderly described here have shown that

amplification of the flavor levels of foods to preferred

levels is associated with increased total numbers of

lymphocytes (including T cells and B cells), increased

secretion rate of salivary immunoglobin A (IgA),

and improved functional status. Furthermore, flavor

enhancement resulted in improved immunity and

functional status even when macro- and micro-

nutrient intakes were uneffected.

Study 1: Flavor Enhancement Increases T- and

B-Cell Levels in the Elderly

0012Flavor enhancement of table food for independent

living residents at a retirement home has been

TASTE ENHANCERS 5735

shown to improve immune status as determined by

T- and B-cell levels as well asgrip strength. In onestudy,

39 elderly residents were divided into two groups.

Group 1 received food that was unenhanced by flavor

for the first 3 weeks, and food that was enhanced by

flavor for the second 3-week period. For group 2, the

order was reversed; they received enhanced food for

the first 3-week period and unenhanced food for the

second 3-week period. The menu plan during the 3

weeks of flavor enhancement was identical to the

menu plan during the unenhanced 3-week period.

During the 3 weeks of flavor enhancement, six differ-

ent flavors were added to selected nutrient-dense

foods: roast beef, ham, natural bacon, prime beef,

maple, and cheese. Flavors were added to some, but

not all, foods at a meal in the flavor-enhanced condi-

tion. Analysis of the data indicated that the elderly

subjects consumed the same macro- and micronu-

trients on the two arms of the study. This occurred

because not all foods at a meal were enhanced

during the 3-week experimental period of flavor

enhancement; subjects simply ate less of foods

that were not enhanced. This study was repeated

with 4-week (rather than 3-week) food rotations

in which MSG as well as flavors were added on the

4-week enhancement arm of the study. In both studies

there was an increase in T- and B-cell levels and

improved grip strength after flavor enhancement,

even though macro- and micronutrient intakes were

not affected.

Study 2: Flavor Enhancement Improves Secretion

Rate of Salivary IgA

0013 Taste and odor stimuli have also been shown to in-

crease the secretion rate of IgA in the saliva of both

young and elderly individuals. IgA is an antibody that

protects mucosal surfaces. Flavors can either be

dropped on the tongue from an eye dropper or de-

livered in food. The main finding of such studies is

that chemosensory stimulation improves mucosal im-

munity in two ways: (1) by increasing saliva produc-

tion and (2) by increasing the absolute concentrations

of secretory IgA in the saliva. These results have

important implications for the elderly, who often

suffer from dry mouth and reduced salivary flow

(and hence reduced mucosal immunity) due to

normal aging, diseases, and medications they are

taking.

Study 3: Sensory Enhancement of Foods Increases

Intake in Sick Elderly

0014 Enhancement of hospital food with a combination of

flavors and MSG has been shown to improve intake

in over 90% of patients. In addition, when sensory

enhancement was performed for a week or more,

there was improvement in plasma protein levels (in-

cluding somatomedin-C/insulin-like growth factor I,

albumin, and transferrin) and T lymphocytes in some

patients.

Study 4: Flavor Enhancement of the Entre

eat

Dinner can Reduce Sodium Intake by 500 mg

0015Enhancement of an unsalted entre

e with salt-free

flavors can reduce the sodium levels in a meal without

compromising ratings of satisfaction. This finding

was obtained in a study at a retirement home per-

formed over an 8-week period during which salt

shakers were removed from the tables. During the

study, two entre

es (beef steak and chicken breast)

were each served once a week. For the first 2 weeks

(control period), the entre

es (beef or chicken) were

salted with 500 mg sodium (the minimum preferred

level of table salt for this population). For the subse-

quent 6 weeks (experimental period), the flavor of the

entre

es was enhanced by marination in sodium-free

beef or chicken flavor prior to cooking; no table salt

was added to the beef or chicken. Two vegetables

which were lightly salted in the kitchen accompanied

the entre

e. During the 6 weeks of flavor enhance-

ment, the sodium content of the meal was reduced

by 500 mg. Throughout the study, residents were

asked to rate their satisfaction with the sensory prop-

erties of each meal after eating. Analysis of the data

indicated no significant difference in the degree of

satisfaction between meals with the salted version of

the entre

e and the flavor-enhanced (sodium-free) ver-

sion. This suggests that enhancement of odor can

replace salt in an entre

e with no adverse affects on

acceptability when two lightly salted vegetables ac-

company the meal. Thus, providing more sensory

input in the form of odor can reduce the need for

taste stimulation by salt, and could make it easier to

comply with recommended daily intake of sodium

(3000 mg or less).

Conclusion

0016Enhancement of the taste and smell of food can be

achieved in two ways: (1) by adding more molecules

to the food or (2) by potentiating the intensity

through synergism and/or alteration of receptor

mechanisms without increasing the total number of

molecules. Taste (and smell) enhancement can im-

prove palatability, increase total intensity, potentially

reduce the cost of ingredients, compensate for

chemosensory (taste and smell) losses in vulnerable

populations such as the elderly, and improve a

number of nutritional and health parameters.

5736 TASTE ENHANCERS

See also: Acesulfame/Acesulphame; Aspartame;

Sensory Evaluation: Aroma; Taste; Sodium: Properties

and Determination; Physiology