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

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method must be based on the types present. The

malto series will usually be hydrolyzed by the

combination of amylase enzymes used to hydrolyze

starch and, if no other oligosaccharides are present,

may be hydrolyzed with dilute acid and the free

sugars measured. Acid hydrolysis cannot be used if

fructose-containing polymers are present because

fructose is destroyed by acid; fructanase enzymes are

available for selective hydrolysis. HPLC is the pre-

ferred method for the separation and analysis of

oligosaccharides.

0036 Treatment of the Residue: Hydrolysis of Starch The

residue in most foods is a mixture of starch, NSP,

proteins, the noncarbohydrate lignin, heat artifacts

formed during the heat processing of foods and

some inorganic matter.

0037 Treatment with dimethyl sulfoxide (DMSO)

renders any retrograded amylose soluble, and the

starch can be completely hydrolyzed using a mixture

of amylases. A heat-labile amylase is frequently used

to give rapid solubilization of the starch followed by a

mixture of pullulanase and amyloglucosidase or a-

amylase to hydrolyze starch to glucose which can

then be measured after precipitating the unchanged

NSP with 80% v/v ethanol. The use of a glucose-

specific method such as the colorimetric glucose oxi-

dase method is preferred for analysis of glucose

released by starch hydrolysis, but in practice any

approach can be adopted.

0038Analysis of Nonstarch Polysaccharides NSPs form a

complex mixture (Tables 4 and 5) and separation

of the various types of polysaccharide is usually

only carried out by those concerned with the study

of the structure of the plant cell wall. A typical frac-

tionation and analysis scheme is illustrated in outline

in Figure 2.

tbl0003 Table 3 Enzymes used in carbohydrate analyses

Enzyme class Substrate EC number Source

Oxidoreductases

Lactate dehydrogenase Lactic acid 1.1.1.27 Pig muscle

6-Phosphogluconate dehydrogenase 6-Phosphogluconate 1.1.1.44 Saccharomyces cerevisiae

b-galactose dehydrogenase

D-galactose, L-arabinose 1.1.1.48 Pseudomonas fluorescens

Glucose-6-phosphate dehydrogenase

D-glucose 6-phosphate 1.1.1.49 S. cerevisiae

Glucose oxidase

D-glucose 1.1.34 Aspergillus niger

Diaphorase NADH 1.6.4.3 Pig heart

Catalase Hydrogen peroxide 1.11.1.6 Beef liver

Kinases

Hexokinase

D-hexoses 2.7.1.1 S. cerevisiae

Gluconate kinase

D-gluconic acid 2.7.1.12 Escherichia coli

Hydrolases

Amyloglucosidase a-Glucans 3.2.1.3 A. niger

a-Amylase a-Glucans 3.2.1.1 Pig pancreas

Pullulanase 1–6 a-Glucoside links 3.2.1.41 Bacillus acidopullulyticus

Thermamyl a-Glucans (heat-labile) 3.2.1.1 B. licheniformis

Invertase Terminal b-fructoside links 3.2.1.26 S. cerevisiae

Isomerases

Phosphoglucose isomerase

D-glucose 6-phosphate 5.3.1.9 S. cerevisiae

Modified from Determination. In: Chaplin MF (1998) Encyclopedia of Food Science and Nutrition. 1st edition, pp. 684–691.

tbl0004 Table 4 Major carbohydrates in the nonstarch polysaccharides

Major group Components Structural features Distributionin foods

Plant cell wall

Cellulosic Cellulose Linear b-glucans All cell walls

Noncellulosic

Pectic substances Rhamnogalacturonans Mainly in fruits and vegetables

Arabinogalactans Fruits and vegetables

Hemicelluloses Arabinoxylans Cereals

Glucuronoarabinoxylans Cereals

Glucuronoxylans Fruits and vegetables

Xyloglucans Fruits and vegetables

b-Glucans Cereals

896 CARBOHYDRATES/Determination

0039 The polysaccharides in the extracts are concen-

trated and cleaned up by extensive dialysis and may

occasionally be measured after freeze-drying the

extract. More commonly, the extracts are further

fractionated by size exclusion chromatography to

separate the noncellulosic polysaccharides (pectins

and hemicelluloses) into fractions based on molecular

size. They may then be further characterized by

methylation and hydrolysis for structural studies

using chromatographic systems linked to mass spec-

trography. Monosaccharide composition is measured

as described for the less detailed NSP analyses

described below.

0040Most food analyses are restricted to the analysis

of total NSP, although measurement of the cellu-

losic and noncellulosic fraction is often of value

tbl0005 Table 5 Polysaccharide food ingredients in nonstarch polysaccharides

Major group Components Structural features Use in foods

Gums Gum arabic Arabinogalactans Confectionery

Guar, locust bean Galactomannans Soups as thickeners

Algal polysaccharides

Agar Galactoanhydrogalactans Powerful gelling agent

Alginates Guluronomannuronans Powerful gelling agents

Carageenans Several different sulfated

galactoanhydrogalactans

Interact with proteins to

control physical properties

Modified starches Phosphated and cross-linked, esters

and ethers

Used to control starch retrogradation

and as gelling agents

Cell wall extracts Pectins Gelling agent in jams

Modified pectins (amidated) Gelling agent

Cellulose, esters, and ethers

Example of fractionation and analytical scheme

for the carbohydrates in the plant cell wall

Plant tissue

Freeze-dried and finely ground

Extract with CDTA at room temperature

Pectins from middle lamella

Pectins from primary wall

Extract with 0.05 mol l

−1

sodium carbonate

Extract with 1mol l

−1

KOH

Extract with 4 mol l

−1

KOH

Reextract with 1mol l

−1

KOH

Residue

Acidify extract

p.p.t. Hemicellulose A

Hemicellulose B

Supernatants

Dialyze and concentrate

Residue = a-cellulose

fig0002 Figure 2 Typical scheme for fractionating and analyzing the carbohydrates in the plant cell wall. CDTA, cyclohexane diamine

tetraacetate.

CARBOHYDRATES/Determination 897

nutritionally. Some procedures include treatment

with a protease alongside the removal of starch, to

reduce protein contamination before precipitating

the NSP. This provides a procedure for measuring

nonstarch components gravimetrically, and forms

the basis of the official method of the Association

of Official Analytical Chemists (AOAC) for measur-

ing total dietary fiber. The residue contains the non-

carbohydrate lignin and any heat-induced artifacts

in processed foods. There is also some residual

protein and inorganic matter and in the official

method these are measured and deducted from the

residue weight.

0041 Measurement of the insoluble and soluble NSP

fractions was until recently seen to be of nutritional

value but this division is not now considered useful.

This is because solubility is highly method-dependent

in the choice of aqueous buffer used and the condi-

tions under which it is measured and these have

yet to be related to solubility under physiological

conditions.

0042 Hydrolysis of NSP Complete hydrolysis to the com-

ponent monosaccharides is achieved using initially

solubilization in 12 mol l

1

followed by dilu-

tion to 2 mol l

1

and heating to 100



C for 1 h. The

conditions do not release uronic acids which require

enzymatic hydrolysis of the polysaccharides. In the

Englyst method the uronic acids were measured

colorimetrically and the monosaccharides by gas

liquid chromatography (or HPLC). The noncellulosic

polysaccharides are hydrolyzed in 2 mol l

1

by heating at 100



C for 1 h.

0043 The monosaccharide constituents in both types of

hydrolysates are measured after neutralization. For

gas liquid chromatography the monosaccharides are

reduced with sodium borohydride and then acety-

lated. It is necessary to use an internal standard such

as allose to control these stages. Gas liquid chroma-

tography is performed on a wide-bore capillary

column with a flame ionization detector.

0044 HPLC is controlled with an internal standard using

a pulsed amperometric detector. Standard mixtures of

the monosaccharides are analyzed in the same way

and used to derive correction factors. Colorimetric

procedures using the ferricyanide reaction may also

be used to measure the total monosaccharides

released by the 12 mol l

1

hydrolysis. The

standard mixture should reflect the ratios of the com-

ponents in the samples under analysis to allow for

differences in reduction equivalents.

0045 Polyuronans which form part of the NSP are not

completely hydrolyzed under these conditions and for

this reason the uronic acids are measured separately

colorimetrically in the 12 mol l

1

hydrolysates using

dimethyl phenol in 2 mol l

1

Modes of Expression

0046The carbohydrates in foods may be expressed in a

number of ways. Total carbohydrate is often ex-

pressed as the value obtained by difference. This

mode of expression is still widely used in food label-

ing. In the USA and the European Union (EU) this

excludes dietary fiber. In the USA this implies total

dietary fiber, as measured by the official AOAC

method. In the EU, agreement on the procedure for

dietary fiber has been slow to be reached and may be

the AOAC value or a NSP value.

0047Total carbohydrate may also be expressed as the

sum of the directly measured carbohydrates as they

are present in the food, i.e., starch as starch or sucrose

as sucrose. Once again, dietary fiber values are ex-

cluded. In the UK and some other nutritional data-

bases, the carbohydrates are expressed as the

monosaccharides. This can cause confusion if the

mode of expression is not recognized because 100 g

starch gives 110 g glucose and 100 g of disaccharide

give 105 g monosaccharides.

0048Current international opinion on the measurement

of carbohydrates in foods is that, wherever possible,

direct and specific analytical methods should be

preferred.

See also: Dietary Fiber: Properties and Sources;

Determination; Physiological Effects; Effects of Fiber on

Absorption; Bran; Starch: Structure, Properties, and

Determination; Sources and Processing; Functional

Properties; Modified Starches; Resistant Starch; Sugar:

Sugarcane; Sugarbeet; Palms and Maples; Refining of

Sugarbeet and Sugarcane

Further Reading

Anonymous (1989) Methods of Biochemical Analysis.

Mannheim: Boehringer Mannheim.

Chaplin MF and Kennedy JF (eds) (1986) Carbohydrate

Analysis: A Practical Approach. Oxford: IRL Press.

FAO/WHO Joint Expert Committee (1998) Food and Nu-

trition Paper 66. Rome: Food and Agricultural Organ-

isation.

Nielson SS (ed.) (1998) Food Analysis, 2nd edn. Gaithers-

burg, MD: Aspen.

Southgate DAT (1991) Determination of Food Carbohy-

drates, 2nd edn. London: Elsevier Science.

Southgate DAT (1995) Dietary Fibre Analysis. Cambridge:

Royal Society of Chemistry.

Sullivan DM and Carpenter DE (eds) (1993) Methods of

Analysis for Nutritional Labeling. Arlington, VA: Asso-

ciation of Official Analytical Chemists International.

898 CARBOHYDRATES/Determination

Sensory Properties

C S Setser, Kansas State University, Manhattan, KS,

USA

G D Brannan, Customized Sensory Services,

Wyoming, OH, USA

Background

0001 The first sensory response expected of low-molecular-

weight carbohydrates is sweetness. More than 100

substances are sweet and chemically identified

as sugars, or nutritive carbohydrate sweeteners.

Many other unrelated substances of diverse mole-

cular geometry elicit the sweet taste, including

some aliphatic and aromatic organic compounds,

amino acids, and certain inorganic salts. However,

not all sugars are equally sweet, and, moreover,

the sensory properties of foods that are influenced

by carbohydrates extend beyond sweetness. Flavors,

in addition to the sweet taste, develop from browning

reaction products. Color is another sensory property

developed with browning reactions. Textural attri-

butes are influenced in numerous ways: the low-

molecular-weight carbohydrates contribute body

and viscosity or interact with other components,

including water and the high-molecular-weight

carbohydrates, to influence sensory properties of

food products; and the starches and gums contribute

thickening and gel structure alone and by interactions

with each other to alter other mechanical and geo-

metrical texture characteristics.

Sweetness of Sugars

Stereochemical Similarities of Sweet Compounds

0002 The common structural feature associated with all

compounds possessing the sweet taste is a glycophore

capable of concerted hydrogen bonding. A proton-

donating group, often called the AH group, and a B

group serve as a proton or hydrogen bond acceptor,

respectively. The primary AH,B system of the

common sugars is the a-glycol grouping, the portion

farthest from the reactive, anomeric center; for

example, the 3,4 a-glycol system of glucopyranose

structures is responsible for its sweet taste.

High-potency sweetness and bitterness can occur if a

third component (X, or g) functions as a ‘dispersion’

or hydrophobic site, and the electron-withdrawing

group enhances the activity of the AH,B dipole.

The sweet glycophores have AH–B distances of

approximately 2.6 angstroms (A

), AH–X distances

of 3.5 A

, and B–X distances of 5.5 A

0003A criticism of the AH,B system is that not all

compounds that possess the AH,B system taste

sweet, and some are actually bitter or tasteless. Sym-

metry principles help resolve this criticism. The

charge on the dipole of the sweet substance must be

bilaterally symmetrical, i.e., of opposite sign but

nearly equal, for sweetness to be perceived.

0004Another issue is related to the enantiomers. Ini-

tially, the belief was that the d-sugars (and amino

acids, for that matter) tasted sweet, but l-antipods

did not. If the AH,B system were correct, both d- and

l-sugars would be sweet. Later, it was learned that

some l-sugars do taste sweet. The AH,B system of a

stimulating compound would combine reversibly by

intermolecular, antiparallel hydrogen bonding with a

commensurate AH,B system on a proteinaceous re-

ceptor molecule of the tongue (Figure 1). The tripar-

tite two-dimensional attributes of the faces of tastants

determine the tastes of enantiomers. Such a fixed AH,

B system would approach the receptor from only one

direction, and l-forms of amino acids could be steri-

cally restricted by side-chains from interaction with

the receptor. This issue has not yet been resolved.

0005The AH,B model for the stimulus structure of

sweet compounds suggests that only one receptor

for sweetness is critical. However, current theories

of sweet taste perception make it unlikely that a single

receptor molecule can accommodate all sweet stim-

uli. Responses vary among species, individuals, and

cells. Receptor sites for sugars also are not identical

from one taste bud to the next.

H-A

~0.3 nm

~0.35 nm

~0.55 nm

Stimulant

Receptor

fig0001Figure 1 Representation of sweetness stimulant–receptor

interaction for the AH-B-X theory using

D-glucose as an example.

The location of the AH-B-X units on the

D-glucose template is

shown in relation to a corresponding receptor site. Reproduced

from Carbohydrates: Sensory Properties, Encyclopaedia of Food

Science, Food Technology and Nutrition, Macrae R, Robinson RK

and Sadler MJ (eds), 1993, Academic Press.

CARBOHYDRATES/Sensory Properties 899

Sweet Taste Transduction

0006 Perception begins with the contact of the sweet stimu-

lus and a surface receptor molecule on the taste cell

that leads to cellular changes via secondary messen-

gers, which are translated into ion-channel events.

Subsequently, the modified ion channels cause

changes in cell polarization, resulting in the release

of neurotransmitters to adjacent neurons and eventu-

ally an action potential. The theory of taste transduc-

tion, the process of translating sensory information

into a signal useful to the nervous system indicates

that high-intensity sweeteners, especially polyols,

react with a seven-transmembrane receptor protein

that is associated with a G-protein inside the cell.

Several mechanisms on multiple receptor sites are

possible; some, for example, use cyclic adenosine

monophosphate (cAMP) as a second messenger, and

others use inositol triphosphate (IP3). High-potency

compounds apparently disrupt the transduction pro-

cess at the G-protein. The number of sites involved

and the effectiveness of the interaction have been

related to the potency. Both sweet and bitter receptors

share some of the same transduction components,

such as IP3. These theories could help explain the

close association between sweet and bitter tastes of

some substances.

Sweeteners in Products

0007 Sweetener synergy is critically important to the

food processor. Synergistic effects are inferred if

the sweetness of the mixture is greater than the

sum of sweetness of the individual components.

Synergism might result from solute–solute, solute–

water, and solute–receptor interactions. The effects

with any given sugar are not universal. Fructose,

for example, shares a synergistic relationship

with glucose and with saccharin, but not with other

carbohydrate sweeteners. Recent evidence suggests

that synergy depends on the compatibility of com-

ponent hydration and the influence on water’s

structure. If components with identical types of

hydration are mixed, increased water mobility in

the proximity of the sweetener and a reduction

in volume of the hydrated solute molecule result in

synergy. Reduced water mobility in the medium

has been observed with sweetness suppression of

mixtures (sucrose–aspartame), and an increased

water mobility led to enhancement (synergism) of

sweet taste (sucrose–cyclamate and maltitol–

acesulfame K mixtures), but no effect on water mo-

bility and no appreciable synergy has been observed

with alitame plus either sucrose or maltitol or with

acesulfame K with sucrose.

Intensity of Sweetness

0008Sweetness generally decreases with the molecular

weight of the sugar, although the reason is unknown.

Perhaps, only one sugar residue in each oligosacchar-

ide binds to the taste cell receptors. Lack of sweetness

in some compounds is caused by steric interference

of one or both of the axial hydroxyl groups, thus

preventing binding to the taste cell receptor.

0009Food processors are interested in relative sweetness

scores. Such numerical values attempt to relate over-

all sweetness of one substance to that of another

substance. The value is defined as the ‘ratio of con-

centration of substances matching in sweetness,’ and

sucrose is used as the reference (Table 1). The relative

sweetness score has limited use, because it fails to

recognize different solution properties of dissimilar

substances and quality differences that occur because

of a sweetener’s multidimensional nature (onset,

duration, intensity) is integrated into a single value.

If the sweetener is in solution or in its crystalline

form, the age of the test medium and the degree to

which the sugar has mutarotated are further factors

influencing relative sweetness.

tbl0001Table 1 Relative sweetness of carbohydrate sweeteners

Sweetener Approximate

sweetness

Bulk solids

Fructose 1.2–1.7

Glucose 0.7–0.8

Invert sugar 1.0

Isomalt (Palatnit) 0.5–0.6

Lactitol 0.3

Lactose 0.2–0.4

Maltose 0.4–0.5

Mannitol 0.4–0.7

Mannose 0.6

Sorbitol 0.5–0.6

Xylitol 0.9–1.2

Xylose 0.7

Bulk syrups

Corn syrup, unmixed, acid-converted

30 DE

0.3–0.35

36 DE 0.35–0.4

42 DE 0.45–0.5

54 DE 0.5–0.55

62 DE 0.6–0.7

High-fructose corn syrup

42% 0.9–1.0

55% 1.0–1.1

90% 1.2–1.6

Hydrogenated glucose syrup (Lycasin) 0.4–0.75

Chloroderivatives of sucrose (Sucralose) 5–2000

Stevioside 300

Sucrose ¼1.0. Sweetness is a relative measurement dependent upon

many external factors including concentration, temperature, pH, structural

configuration, and degree of hydrolysis.

DE, dextrose equivalent.

900 CARBOHYDRATES/Sensory Properties

0010 Concentration effects between 2 and 16% are

approximately linear for sugars and sugar alcohols

relative to sucrose standards. However, the psychophys-

ical laws that govern responses indicate that increas-

ingly larger stimulus increments are required with

high concentrations to elicit measurable differences.

An additional factor operating with concentration in-

creases its adaptation. If a person is exposed repeatedly

to a stimulus, the perceived intensity is reduced.

The relative sweetness of sucralose, a potent sweetener,

decreases with increases in the concentration at high

concentrations. For most high-potency, noncarbohy-

drate sweeteners, the concentration response plots

are hyperbolic. Concentration increases can negate or

alter intensity differences or induce unpleasantness.

The different behavior of polyols from high-potency

sweeteners supports the tentative conclusion that at

least two routes to receptor-cell activation exist.

0011 Temporal effects and the sweetness response Onset

time and duration of sweetness influence the accept-

ability of a sweetener. Consumers detect sucrose

sweetness within 1 s, and that sweetness lasts

about 30 s. Any sweetening agent that has a delayed

initial sweetness or a sharp or prolonged sweet-

ness sensation will taste unusual to many persons.

A localized concentration of stimulus molecules at

receptor sites is believed to govern the persistence

or duration of sweetness. The lipophilic site could

be responsible for directing potent sweeteners into

localized concentrations at a nonspecific area of

the cell membrane and account for persistence

of sweetness. Thus, the physical length of the

queue could determine the duration of sweetness

by the length of time the receptor is supplied with

stimuli.

0012 Temperature effects and the sweetness response

Temperature influences the sweet response, and

not all sweeteners respond to temperature similarly.

Heat can break intramolecular bonds of sweeteners,

which could free more hydroxyl groups to participate

in the AH,B system. Changes in structural form

with bond breaking can result in isomers that do not

have a sweetness equal to the original sweetener.

An increase in temperature results in increased

sucrose intensity, but decreased persistence. Tempera-

ture is believed by some to affect the approach of

the stimulus molecules to the receptor site prior to

the transduction process. However, others believe

that the optimum temperature for detection of sweet-

ness is near the temperature of the tongue, which is

explained by maximal electrophysical responses at

that point.

Synergism of Sugars with Other Food

Components

Interactions of Components and Effects on

Sweetness

0013The presence and concentration of other tastes,

sweeteners, and flavors; the structural matrix,

whether a solid, liquid, or gas; viscosity and solvent

polarity of the medium; extreme temperatures of pro-

cessing, storage, and preparation; and the microbes

and enzymes present all influence and modify percep-

tion of sweetness from the sugars. Typically, sweet

compounds are embedded in a complex matrix with

bitter, sweet, sour, and salty tastes, and the flavor

nuances of other ingredients. The ‘taste modifiers’

alter sweetness quality, increase or reduce intensity,

or mask aftertaste probably by exerting a physical or

chemical effect on the stimulus rather than the taste

receptor. Sensory acuity to carbohydrate sweetness

diminishes in the presence of other tastes, but the

degree of suppression depends on the nature of the

secondary agent, the concentration, and the intensity

of taste.

0014Sweetness seems to be enhanced at low (< 0.4%)

sodium chloride (NaCl) concentrations, but per-

ceived sweetness declines if the concentration of

NaCl is high. Sweetness of sucrose, fructose, and

glucose is affected differently by various acids and

the relative concentrations of each of the compon-

ents. Sweetener–acid interactions, as well as inter-

actions with fruit flavors, are important in the

formulation of several beverages. Fruit flavorings

alter the sweetness perception of aqueous systems,

generally enhancing the sweetness of the carbohy-

drate sweetener. The sugars decrease the perception

of bitterness in foods and beverages.

0015The relative initial and maximum sweetness of

sugars is different in food products than in model

systems. The texture and physical properties of a

food affect its taste, because texture partially controls

the amount and the rate which tastants reach the taste

buds. The thresholds for the four basic tastes are

higher in food products than in aqueous solutions.

Sweetness is maximal when little or no interference

from physical behavior of the taste medium exists.

Viscous and oil solvents exhibit an interfering behav-

ior that can raise the threshold and decrease the per-

ceived sweetness intensity.

Sugar–Protein Interactions

0016Flavors and colors of foods are altered by the non-

enzymatic browning of carbohydrates. Thermal de-

composition of simple and complex carbohydrates

usually occurs in combination with inorganic or

CARBOHYDRATES/Sensory Properties 901

organic catalysts and results in caramelization, the

key pathway for the formation of flavors associated

with molasses, maple syrup, and caramel flavorings

and colorings. The carbonyl-amine reaction involves

a thermally induced interaction between an amino

acid and a reducing sugar. Many pathways and reac-

tion schemes follow ring opening and enolization of

the sugars and their interactions with nitrogenous

amino groups. The unique color and flavor com-

pounds produced in roasted coffee, nuts, meats, choc-

olate, maple syrup, and bakery products result, in

large part, from the carbonyl-amine reaction. Prod-

ucts of the carbonyl-amine reaction and interactions

of the caramelization and carbonyl-amine reactions

include pyrroles, pyridines, imidazoles, pyrazines,

furfurals, furanones, oxazoles, and thiazoles, and

they can form numerous brown to black polymers.

Maltol and isomaltol, with their fragrant, caramel-

like aromas, enhance both the flavor and sweetness of

many foods. In micowaved and extruded foods, the

time–temperature–moisture conditions result in a

lack of flavor and color, because only low levels of

the browning reaction products are formed. Strecker

degradation and the fragmentation of carbonyl–

amines are well-defined pathways that also can result

in many off-flavor compounds in foods. During the

final steps of the Strecker degradation reaction, for-

maldehydes and pyrazines evolve from amino ketone

fragments of the reducing sugar. Food processors

should optimize desirable caramel-type aromas but

must minimize the burnt, bitter, and acrid notes that

can be produced.

Sugar Interactions and Textural Changes in Foods

0017 Carbohydrate sweeteners’ colligative properties,

which depend on the concentration of the solute,

influence the body/viscosity of liquid and solid

foods, and alter the texture of other foods by the

effects on freezing point, boiling point, osmotic pres-

sure, and vapor pressure. Increasing the number of

sweetener molecules increases the boiling point and

osmotic pressure, and decreases the freezing point

and vapor pressure.

0018 In addition to solute concentration, the viscosity of

carbohydrate-sweetened solutions is governed by the

temperature. With an increased temperature, molecu-

lar motion is increased, reducing the friction among

the molecules and resulting in a decreased resistance

to flow. The viscosities of most carbohydrate-sweet-

eners in solution are similar with equivalent molar

weights except for glucose syrups. A large percentage

of high-molecular-weight polysaccharides increase

the relative viscosity of glucose syrups. Consequently,

these syrups impart more cohesiveness, body, and

adhesiveness to a food system than other types of

sweeteners. The viscosity of carbohydrate sweetened

solutions also is governed by solute concentration and

temperature. With an increased temperature, molecu-

lar motion is increased, reducing the friction among

the molecules and resulting in a decreased resistance

to flow.

0019Low-dextrose equivalent syrups are viscous and

increase the chewiness of products such as caramels

and cookies more than an equal concentration of a

higher-conversion, lower-viscosity syrup. The low-

viscosity syrups decrease the viscosity of a candy

mass of a given sucrose composition by decreasing

air retention. The candy is brittle, and good flavor

release in the mouth is promoted. The texture of

confections is dependent upon dissolution and re-

crystallization of the sugar. If a sugar solution cools

slowly and is not disturbed, large crystals are formed,

as in rock candy. Rapid cooling with agitation results

in fine crystals, as in creams.

0020The sharp, crystalline edges of sugars contribute to

the aerated nature of chemically leavened bakery

products by helping disperse the lipid portion of a

batter in the initial creaming stages of multistage

mixed batters and doughs. The creaming of the

shortening allows the formation of many air cells,

thus increasing the volume and tenderness. Sugars,

particularly glucose, are efficient fermentation

media, providing aeration in some bakery products.

Sugars further tenderize bakery products by control-

ling starch hydration and by dispersing protein and

starch molecules. Starch and protein molecules are

separated by the sugars, as well as by lipids, and are

prevented from forming a continuous mass. The

structure remains flexible and pliable enough to

allow for maximum expansion during leavening and

before thermal setting. Excessive sugar can increase

the fluidity of the batter, increase the coagulation

temperature of the egg proteins, and increase the

temperature at which starch gelatinization occurs to

the extent that the structure is too weak to support its

weight. The batter structure rises before it is thermal

set, but then it collapses.

0021Regulating the amount and type of sugar controls

cookie spread and surface cracking. Increasing the

amount of sugar with a given amount of water gener-

ates more solution than is available with water alone.

Small crystals increase cookie spread, because fine

crystals dissolve more readily, generating more

solution at a given time and temperature than do the

coarser particles. Consequently, gelatinization and

thermal set times are delayed, the dough is more

fluid, the cookie spreads farther before the structure

sets, and it is crisper. When cookies contain high

levels of sucrose, a hard, sweet cookie with ‘snap,’

or a crispness and crunchiness, and surface cracks

902 CARBOHYDRATES/Sensory Properties

results, because, after cooling, the sugar syrup recrys-

tallizes to form an amorphous glass. Molasses, honey,

glucose syrups, and high-fructose corn syrup inhibit

crystallization and result in softer cookies that are

chewy, rather than crisp.

Properties of Polysaccharides in Relation

to Food Product Structure

0022 Polysaccharides affect the sensory properties, particu-

larly the texture, of food products by retarding the

flow as well as by modifying the gelling characteris-

tics. Nonstructured, amorphous regions of polysac-

charides are highly hydratable and bind large

quantities of water. In contrast, areas that contain a

large portion of straight-chained, crystalline regions,

such as retrograded starch gels, exclude water. Most

natural and synthetic hydrocolloids, or gums, display

pseudoplastic flow properties, that is the viscosity of

the solution decreases as the shear rate increases.

With high shear rates, viscosity decreases because

the particles are oriented parallel to the shear field.

In general terms, viscosity also decreases as the tem-

perature increases.

Sensory Properties and Rheological Character

0023 The predominant sensory property of many gum

solutions is slimy characterized by a thick mouth

coating and by being difficult to swallow material.

Dispersions that approach Newtonian flow behavior

are associated with a high degree of sliminess, and

gums in solution that depart considerably from New-

tonian flow and have a high degree of shear-thinning

are less slimy in the mouth. Other sensory attributes

used to describe gum solutions are adhesive, starchy,

gummy, astringent, slippery, and oily. ‘Starchy’ is a

flavor related to an undercooked product, but the

other parameters are related to mouth feel and mech-

anical textural properties. Normally, blandness is the

desired flavor quality for carbohydrate thickeners in

food products.

0024 Pseudoplastic behavior is associated with a less

slimy mouth feel because the viscosity of the fluid

decreases at the shear rate encountered in the mouth

(approximately 50 s

1

). High-viscosity seed and ex-

udate gums – guar, tragacanth, and locust bean – are

more pseudoplastic than alginates and cellulose

ethers, whereas gum arabic has a low viscosity and

almost Newtonian flow properties up to a concen-

tration of at least 40%. Dispersions of microcrystal-

line cellulose, a synthetic gum, show both thixotropic

and plastic behavior. The behavior that dominates

depends upon the concentration and shear history.

Starches can be modified to alter the consistency;

cross-linking contributes short, stringless consistency

in waxy and tapioca starches. The unmodified starch

dispersions will have a stringy, cohesive consistency.

High levels of highly cross-linked waxy corn starch

will increase the chewiness in a product.

Gel Properties

0025Several polysaccharides provide partial gel structure

in some food products and total structure in others.

High-methoxyl pectins in fruit jams and jellies; low-

methoxyl pectins for dietetic gels; starches in pud-

dings, agar in meat products; carrageenan for kosher

fruit gels and milk puddings; and alginate in pie fill-

ings, reformed vegetables, fruits, and meat chunks are

all examples.

0026Gels can be brittle, rigid, springy, firm, soft, spread-

able, cutable, rubbery, smooth, or grainy, depending

upon the concentration and the degree of interactions

of the polymers. Gelation balances polymer–polymer

and polymer–solvent interactions to form a tertiary

network or matrix; a gel is an intermediate state

between a solution and a precipitate. Enhanced inter-

actions among polymer molecules result as their solu-

bility decreases and generally lead to firm, rubbery,

springy, rigid gels. Gels tend to become more brittle as

the concentration increases, but also faster rates of

setting and decreased uniformity of matrices result in

increased brittleness. A crisp or crunchy mouth feel

for snack foods is obtained with high levels of amy-

lose of slightly degraded waxy starch pregels that

expand to tender structures with heating and drying.

Rubbery structures are obtained with thin boiling

corn starch in the presence of high concentrations of

sugars. In other instances, substances influence the

rigidity or strength by (1) competing with water for

the binding loci, such as sugar-softening a starch gel,

(2) competing with the solid phase for the liquid, as

sugar does in high methoxyl pectin gels, (3) altering

the pH, as acids do in pectin systems, (4) interacting

chemically with either or both phases, as calcium ions

forming cross-bridges with alginates or low-methoxyl

pectins, and (5) altering the charge distribution on the

polymer molecules.

0027Relationships of gel strength to interactive forces

The type and strength of the crystalline junction zones

in polysaccharide gel networks govern the strength,

elasticity, and flow behavior of the gel. If the junction

zone is short, and chains are not held together

strongly, the polysaccharide molecules will separate

under physical pressure or with slight increases in

temperature. One or more polysaccharides can be

involved in the junction zone; the zones can involve

multiple helices or aggregates of ordered ribbons.

Agar forms one of the strongest gels known via

bundles of associated double helices, and the gels

CARBOHYDRATES/Sensory Properties 903

remain stable at temperatures from 30 to 85



C. Hel-

ical junction zones also are involved in carrageenan

and furcelleran gels. Low-methoxyl pectins, with less

than 50% esterification, can form stable gels using

divalent ions, such as calcium, to form cross-links.

Alginate gelation occurs at room temperature in the

presence of calcium or other di- or trivalent ions, or in

the absence of ions at pH 3 or less. Gellan, in the

presence of ions, gels similarly to alginate but it gives

a similar brittleness, elasticity, and cohesiveness to

agar gels, except that the gellan gels are more firm.

In the case of carrageenans, ions are immobilized at

the junction zones, although the primary gelation

mechanism is believed to be hydrogen bonding.

Kappa carrageenans form firm gels with potassium,

but not with sodium ions, and iota carrageenan is

calcium-sensitive. Kappa and iota carrageenan form

a gel; however, lambda fractions are strongly anionic,

do not complex readily with cations, and do not gel.

0028 Polysaccharides with carbonyl groups also do not

gel easily because of electrical repulsion between

approaching chain segments. High methoxyl pectin

(55–80% esterification) forms strong gels only if

(1) the pH is adjusted to 2.0–3.5 to prevent charge

repulsion and ionization of the carbohydrate groups

and (2) a dehydrating material is used to increase

the intermolecular interactions by hydrogen bonding

among the polymers. A synergism between alginates

and pectins for gel formation occurs if the system is

first acidified to reduce electrostatic repulsion and

permit molecular association.

0029 Molecular configuration and gel character Branched

molecules do not form strong junction zones, thus

they do not form strong, elastic gels. Studies on

cross-linking mechanisms of mixed gels suggest

an ordered binding between extended ribbon con-

formations of smooth, unbranched areas on galacto-

mannan chains and double helices of agarose or

carrageenan. The smooth, unstructured regions of

the mannan and xanthan gum are involved in

thermally reversible gels.

0030 Concentration effects Gel strength in simple algin-

ate and pectin gels and in the more complex starch gel

is strongly concentration-dependent. A critical con-

centration, specific for any given polymer–solvent

pair, is required. Firm gels can be prepared from a

few types of gums, such as pectins, at levels of 1% or

less. Other colloidal gelling agents require up to 10%.

The higher polymer concentrations necessary in some

systems likely allow aggregate formation at low tem-

peratures. The overall strength of starch gels depends

upon the residual swollen granules to reinforce the

strength of the amylose gel matrix. Soft gums can be

obtained with high-amylose starches. Retrogradation

of amylose is controlled to give textures ranging from

a short, clean bite to a long, somewhat chewy bite

in products such as gum drops, orange slices, and

gummy bears. Thin boiling starches obtained by

acid treatment to produce short chains in the amylo-

pectin portion are used with high concentrations of

starch and sugar for the manufacture of firm, rubbery

gum candies.

0031Crystalline junction zones can occur to such a

degree in polysaccharide gels that retrogradation

and syneresis occur. Increased polyguluronate junc-

tion zones in alginate gels result in rigid, brittle gels

with high syneresis, whereas few junction zones

produce an elastic gel with less tendency to synerese.

Generally, syneresis resulting from compression gives

a feeling of juiciness in the mouth.

Synergism of Polysaccharides with other Food

Components

0032Gel structures Mixed gels and filled or composite

gels are utilized to obtain specific textural properties

in food products. The texture is dependent upon

the relative proportions of each component and the

overall concentration. Locust bean gum with kappa-

carrageenan forms brittle, elastic gels, but xanthan

gum with kappa-carrageenan or low-methoxyl pectin

with iota carrageenan forms soft, cohesive gels. Low

levels of gellan gum can give similar gel characteris-

tics to high levels of k-carrageenan with locust bean

gum. Myoglobin and bovine serum albumin are pro-

teins that promote low-methoxyl pectin gelation,

but they inhibit the formation of gels using alginate.

Each gelling agent can contribute to the gel formation

in mixed gels, or one of the gelling agents can be

nonactive, modifying the characteristics but not inter-

acting to form the gel network. For example,

agar forms microgels in the gelatin matrix of an

agar–gelatin mixed gel.

0033Flavor carriers and encapsulation Carbohydrates

can enrobe, absorb, and retain flavor volatiles during

processing, which has important implications in food

systems. Gum arabic, guar gum, modified starches,

and maltodextrins as well as sucrose and lactose are

used for encapsulation by spray-drying or extrusion

processes. Inclusion complexing is used for encapsu-

lation by the b-cyclodextrins.

Glossary

0034Enantiomers – D and L forms of molecules;

0035Encapsulation – packaging of solids, liquids or gas-

eous materials in miniature, sealed capsules; that can

904 CARBOHYDRATES/Sensory Properties

release the contents at controlled rates under specific

conditions

0036 Newtonian – fluid with a rate of deformation directly

proportional to stress;

0037 Pseudoplastic – fluid that undergoes thinning with

increasing rates of shear;

0038 Pyschophysical – study of the relationship between

sensory stimuli and human responses;

0039 Stereochemical – referring to spatial arrangement of

atoms and groups in molecules;

0040 Synergism – action of two or more substances to

achieve effect of which each individually is incapable;

0041 Syneresis – leakage of liquid from a gel;

0042 Transduction – translating sensory stimuli informa-

tion into signals useful to the nervous system

See also: Biscuits, Cookies, and Crackers: Nature of the

Products; Chemistry of Biscuit Making; Browning:

Nonenzymatic; Cakes: Nature of Cakes; Chemistry of

Baking; Flavor (Flavour) Compounds: Production

Methods; Gums: Food Uses; Sensory Evaluation:

Appearance; Texture; Taste; Starch: Functional

Properties; Sucrose: Properties and Determination;

Sweeteners: Intensive; Sweets and Candies: Sugar

Confectionery; Syrups