pi is 0022030291783732

8/10/2019 Pi is 0022030291783732

1/15

8/10/2019 Pi is 0022030291783732

2/15

2028

KNEIFEL ET AL.

achieved by studying its physicochemical be-

havior as well as its micro)structure 52). As

can be derived from above, the total water held

or

trapped in the structure may

be

and often is

more

than the amount bo un d so tightly t hat it

is no longer available as a solvent. This excess

includes mechanically held water, i.e., capil

lary water, or water absorbed by the swelling

of the protein 36).

this paper, we present a review

of

the

different methods used for determining t he

water-holding capacity

of

proteins as well as

parameters influencing and contributing to this

property.

FUND MENT LS W TER HOLDING

C P CITY

spite

of

the difficulty to differentiate

exactly the different forms of water bound or

retained in a protein-rich food system, the fol

lowing definition will be made. Generally, the

water held in a protein structure can be divided

in to t wo ma in types: 1) that part b oun d

to

the

molecule and is no longer available as a sol

vent

and 2) the other part trapped i n the pro

tein matrix or a corresponding co-matrix poly

saccharide, fat). The first type can be regarded

as abs orbe d water an d the second as ret ained

water. most cases, the water-holding capac

ity of a protein matrix is determined by both

the amount

of

absorbed and retained water.

The absorbed water, which is more tightly

bound to the protein molecules, will be consid

ered first. This type

of

water is largely influ

enced by the physicochemical parameters that

directly affect the proteins 19, 51, 52, 53) and

the surface properties of the protein molecules

that interact with the dissolving solution 65,

89, 94, 97, 118). This means that the water

holding capacity depends not only on pore and

capillary size but also on the charges of the

protein molecules hydrophobic interactions,

hydrogen bonds, S-S bonds, acids, bases, and

zwitterions) as well as on Van der Waals

forces 14, 5 2, 66, 78, 96, 106).

addition to

these parameters, the surrounding medium may

also affect the protein due

to

ionic strength, ion

species, pH condition, temperature, and the

time

taken for equilibrating the protein with

the water 19, 32, 64, 81).

particular, low

molecular weight substances lactose and min

eral salts such as sodium chloride) are reported

Journal of

D ai ry Sc ie nc e Vol. 7 4,

No 7

1991

to have a significant effect on the water-hold

ing capacity of some proteins 1, 6, 5 3, 103).

Retained water, on the other hand, is influ

enced by different structures that establish net

works that immobilize water. This water

should not be considered as free water. Fr ee

wat er is more c omm on ly associat ed wit h t he

final product and means that it is retained by a

co-matrix that enables or contributes to gel

formation. Several subst ances mai nly pr o

teins, including milk proteins, and polysaccha

rides) are known to be capable of forming such

gels, which can absorb and retain a substantial

amount of water. This special feature may be

added to certain foods such as processed

cheese, cheese analogues, meat and fish prod

ucts, pastries, baked goods, and also to various

nonfood products e.g., pharmaceuticals,

paints, concrete, etc.)

by

incorporating the sub

stances into the matrices of varying degrees of

complexity.

W TER HOLDING C P CITY OF

D IRY PRODUCTS

dairy products, some types

of

caseins,

caseinates, coprecipitates, and whey proteins

can be incorporated into certain food products

and not only increase their water-holding ca

pacity but also improve other features such as

nutritional value, solubility, emulsification ca

pacity, viscosity, organoleptic properties, etc.

Results reported on the water-holding capaci

ties

of

dairy products are summarized in Table

De M oo r a nd Huyghebaert 17) reported

that the overall water-holding capacities of

whey powders and demineralized whey pow

ders are generally low but that the protein

component of these powders has a high water

holding capacity. The opposite effect was

noted for caseinates. Thus, the evaluation of

this parameter depends not only on the proper

ties of th e complete product but also on the

properties of the individual components of the

product. Preheating

of

the base milk prior to

the manufacture

of

sodium caseinate leads to a

concomitant adsorption

of

whey proteins onto

casein, increasing the water-holding capacity

of

the product 68, 131). This effect was

thought to

be

due to thermal denaturation of

the whey proteins creating a sponge-like sur

face on th e casei n, which retai ns more wat er

than a caseinate powder produced from un

heated milk. The water-holding capacity of

regul ar s od ium caseinates c an be normally

2028

KNEIFEL ET AL.

achieved by studying its physicochemical be-

havior as well as its micro)structure 52). As

can be derived from above, the total water held

or

trapped in the structure may

be

and often is

more

than the amount bo un d so tightly t hat it

is no longer available as a solvent. This excess

includes mechanically held water, i.e., capil

lary water, or water absorbed by the swelling

of the protein 36).

this paper, we present a review

of

the

different methods used for determining t he


of

proteins as well as

parameters influencing and contributing to this

property.

FUND MENT LS W TER HOLDING

C P CITY

spite

of

the difficulty to differentiate

exactly the different forms of water bound or

retained in a protein-rich food system, the fol

lowing definition will be made. Generally, the

water held in a protein structure can be divided

in to t wo ma in types: 1) that part b oun d

to

the

molecule and is no longer available as a sol

vent

and 2) the other part trapped i n the pro

tein matrix or a corresponding co-matrix poly

saccharide, fat). The first type can be regarded

as abs orbe d water an d the second as ret ained

water. most cases, the water-holding capac

ity of a protein matrix is determined by both

the amount

of

absorbed and retained water.

The absorbed water, which is more tightly

bound to the protein molecules, will be consid

ered first. This type

of

water is largely influ

enced by the physicochemical parameters that

directly affect the proteins 19, 51, 52, 53) and

the surface properties of the protein molecules

that interact with the dissolving solution 65,

89, 94, 97, 118). This means that the water

holding capacity depends not only on pore and

capillary size but also on the charges of the

protein molecules hydrophobic interactions,

hydrogen bonds, S-S bonds, acids, bases, and

zwitterions) as well as on Van der Waals

forces 14, 5 2, 66, 78, 96, 106).

addition to

these parameters, the surrounding medium may

also affect the protein due

to

ionic strength, ion

species, pH condition, temperature, and the

time

taken for equilibrating the protein with

the water 19, 32, 64, 81).

particular, low

molecular weight substances lactose and min

eral salts such as sodium chloride) are reported

Journal of

D ai ry Sc ie nc e Vol. 7 4,

No 7

1991

to have a significant effect on the water-hold

ing capacity of some proteins 1, 6, 5 3, 103).

Retained water, on the other hand, is influ

enced by different structures that establish net

works that immobilize water. This water

should not be considered as free water. Fr ee

wat er is more c omm on ly associat ed wit h t he

final product and means that it is retained by a

co-matrix that enables or contributes to gel

formation. Several subst ances mai nly pr o

teins, including milk proteins, and polysaccha

rides) are known to be capable of forming such

gels, which can absorb and retain a substantial

amount of water. This special feature may be

added to certain foods such as processed

cheese, cheese analogues, meat and fish prod

ucts, pastries, baked goods, and also to various

nonfood products e.g., pharmaceuticals,

paints, concrete, etc.)

by

incorporating the sub

stances into the matrices of varying degrees of

complexity.

W TER HOLDING C P CITY OF

D IRY PRODUCTS

dairy products, some types

of

caseins,

caseinates, coprecipitates, and whey proteins

can be incorporated into certain food products

and not only increase their water-holding ca

pacity but also improve other features such as

nutritional value, solubility, emulsification ca

pacity, viscosity, organoleptic properties, etc.

Results reported on the water-holding capaci

ties

of

dairy products are summarized in Table

De M oo r a nd Huyghebaert 17) reported

that the overall water-holding capacities of

whey powders and demineralized whey pow

ders are generally low but that the protein

component of these powders has a high water

holding capacity. The opposite effect was

noted for caseinates. Thus, the evaluation of

this parameter depends not only on the proper

ties of th e complete product but also on the

properties of the individual components of the

product. Preheating

of

the base milk prior to

the manufacture

of

sodium caseinate leads to a

concomitant adsorption

of

whey proteins onto

casein, increasing the water-holding capacity

of

the product 68, 131). This effect was

thought to

be

due to thermal denaturation of

the whey proteins creating a sponge-like sur

face on th e casei n, which retai ns more wat er

than a caseinate powder produced from un

heated milk. The water-holding capacity of

regul ar s od ium caseinates c an be normally

8/10/2019 Pi is 0022030291783732

3/15

WATER-HOLDlNG CAPACITY OF MILK PROTEINS; REVIEW

2029

TABLE

1.

Reports

on


of milk

TABLE

continued Reports on water-holding capacity

proteins

in

various products.

of milk

proteins in various products.

Refer

ence

number

Refer

ence

Aulhors number Authors

...;.;..----------------

36eurts et

aI.

1974

RUegg el aI. 1974 114

Tarodo de

la

Fuente and Alais 1974 125

Thompson et aI. 1969 127

Caseinates

and

coprecipitates

Brendl

nd

Klein 1972

10

Comer 1979 15

Delaney 1976 16

De Wit 1988 19

Goldman

and Southward 1974 37

Hermansson 1972 51

Hermansson and Akesson 1975 53

Kneifel et aI. 1990 68

Quinn

and

Paton 1979 109

Southward 1985 121

Thomas

et

aI.

1974 126

Van Geonip 1978 130

Vattula et aI 1979 131

Welsby

el

aI. 1982 134

West 1984 135

Cheese

classified between that of egg white poor and

soybean isolate excellent 135 . In most

studies, heating of whey proteins did not sig

nificantly improve this property compared with

unheated proteins 6, 16, 69, 83 . Only Bech

5 reported enhanced water-holding capacity

by whey proteins after severe heat treatment. It

was apparent from differential scanning calori

metric measurements that in whey protein

Oll-

centrates particularly low molecular weight

components other than lactose are mainly re

sponsible for water-binding 6 .

Increased water-holding capacity

of

casein

derivatives was obtained after polymerization

72 , after modification of sodium caseinate by

the attachment

of

reducing sugars to the

amino lysyl residues in the presence of

cyanoborohydride 12 , with casein acylated in

the presence of acid anhydrides 73 , with

whey protein isolates precipitated

at

low

pH

values 117, 123 , and with coprecipitates 37,

121, 131 . The latter authors also showed that

high Ca coprecipitates exhibit a higher water

bolding capacity than low preparations.

Addition

of

tripolyphosphate during the manu

facture

of

a high Ca coprecipitate led to a

decreased water-holding capacity of the prod-

18

43

70,

71,

72

73

84

89

96

113

continued

Kroll et aI. 1984

Mellon et aI. 1947

Modler 1985

Man 1989

RUegg and Blanc 1976

Skim

milk

and whey beat coagulated

Delaney 1976 16

Kabus 1972 61

Nonfat

dry

milk

Brendl nd Klein 1972

10

Comer 1979 15

Larson et

aI.

1951 75

Smith et aI. 1973 119

Milk proteins including concentrates

BrencH nd Klein 1972

10

Mietsch et aI. 1989 86

Korolczuk 1982 73

Ozimek and Poznanski 1981 103

Van den Hoven 1987 129

- Whey proteins including whey protein concentrate -

Bech 1980 5

Berlin et aI. 1973 6

Burgess and Kelly 1979 11

Cbeftel and Lorient 1982 13

Delaney 1976 16

De

Wit 1988 19

De

Wit and

De

Boer 1975 21

De Wit and Klarenbeek 1988 23

Farrell et aI. 1989 26

Guy et aI 1974 42

Haggett 1976 44

Harper

1984 47

Hermansson 1972 51


Kester and Richardson 1984 62

im

et

aI.

1989 63

Mangino 1984 81

McDonough et

aI.

1974 83

Modler 1985 89

Mon 1980 92

u nn and Paton 1979 109

Schmidt et aI. 1984 117

Short

1980 118

Sternberg et aI. 1976 123


Van

Gennip 1978 130

Welsby et aI. 1982 134

zadow and

Hardbam

1981 144

Caseins including derivatives

Dewan e t aI. 1973

Hagenmaier 1972

Korolczuk 1982, 1984

Journal of Dairy Science Vol. 74, No.7, 1991

WATER-HOLDlNG CAPACITY OF MILK PROTEINS; REVIEW

2029

TABLE

1.

Reports

on


of milk

TABLE

continued Reports on water-holding capacity

proteins

in

various products.

of milk

proteins in various products.

Refer

ence

number

Refer

ence

Aulhors number Authors

...;.;..----------------

36eurts et

aI.

1974

RUegg el aI. 1974 114

Tarodo de

la

Fuente and Alais 1974 125

Thompson et aI. 1969 127

Caseinates

and

coprecipitates

Brendl

nd

Klein 1972

10

Comer 1979 15

Delaney 1976 16

De Wit 1988 19

Goldman

and Southward 1974 37

Hermansson 1972 51


Kneifel et aI. 1990 68

Quinn

and

Paton 1979 109

Southward 1985 121

Thomas

et

aI.

1974 126

Van Geonip 1978 130

Vattula et aI 1979 131

Welsby

el

aI. 1982 134

West 1984 135

Cheese

classified between that of egg white poor and

soybean isolate excellent 135 . In most

studies, heating of whey proteins did not sig

nificantly improve this property compared with

unheated proteins 6, 16, 69, 83 . Only Bech

5 reported enhanced water-holding capacity

by whey proteins after severe heat treatment. It

was apparent from differential scanning calori

metric measurements that in whey protein

Oll-

centrates particularly low molecular weight

components other than lactose are mainly re

sponsible for water-binding 6 .

Increased water-holding capacity

of

casein

derivatives was obtained after polymerization

72 , after modification of sodium caseinate by

the attachment

of

reducing sugars to the

amino lysyl residues in the presence of

cyanoborohydride 12 , with casein acylated in

the presence of acid anhydrides 73 , with

whey protein isolates precipitated

at

low

pH

values 117, 123 , and with coprecipitates 37,

121, 131 . The latter authors also showed that

high Ca coprecipitates exhibit a higher water

bolding capacity than low preparations.

Addition

of

tripolyphosphate during the manu

facture

of

a high Ca coprecipitate led to a

decreased water-holding capacity of the prod-

18

43

70,

71,

72

73

84

89

96

113

continued

Kroll et aI. 1984

Mellon et aI. 1947

Modler 1985

Man 1989

RUegg and Blanc 1976

Skim

milk

and whey beat coagulated

Delaney 1976 16

Kabus 1972 61

Nonfat

dry

milk

Brendl nd Klein 1972

10

Comer 1979 15

Larson et

aI.

1951 75

Smith et aI. 1973 119

Milk proteins including concentrates

BrencH nd Klein 1972

10

Mietsch et aI. 1989 86

Korolczuk 1982 73

Ozimek and Poznanski 1981 103


- Whey proteins including whey protein concentrate -

Bech 1980 5

Berlin et aI. 1973 6

Burgess and Kelly 1979 11

Cbeftel and Lorient 1982 13

Delaney 1976 16

De

Wit 1988 19

De

Wit and

De

Boer 1975 21

De Wit and Klarenbeek 1988 23

Farrell et aI. 1989 26

Guy et aI 1974 42

Haggett 1976 44

Harper

1984 47

Hermansson 1972 51


Kester and Richardson 1984 62

im

et

aI.

1989 63

Mangino 1984 81

McDonough et

aI.

1974 83

Modler 1985 89

Mon 1980 92

u nn and Paton 1979 109

Schmidt et aI. 1984 117

Short

1980 118

Sternberg et aI. 1976 123


Van

Gennip 1978 130

Welsby et aI. 1982 134

zadow and

Hardbam

1981 144

Caseins including derivatives

Dewan e t aI. 1973

Hagenmaier 1972


Journal of Dairy Science Vol. 74, No.7, 1991

8/10/2019 Pi is 0022030291783732

4/15

2030

KNEIFEL

ET

AL.

uct; the highest water absorption was obtained

with an acid coprecipitate subsequently neu

tralized with sodium hydroxide 121). Thomas

et al. 126) have demonstrated that a strong

pH-dependent water-holding behavior by

coprecipitates can be observed in meat sys

tems.

n

acidic milk protein concentrate

produced by cationic exchange treatment prior

to ultrafiltration and spray drying exhibited a

better water-holding capacity than a neutral

milk protein concentrate powder after

ultrafiltration

of

skimmed

milk

71). Hydroly

sates made from milk proteins by enzymatic

treatment with l c a l a s e ~ or e u t r a s e ~ lost

much of

their water-holding capacity, but the

rate of water absorption was enhanced 86).

However, skimmed milk powders receiving

varied heat treatment did not show different

water-holding capacities 69), and milk powder

was not suitable for use as a filler in com

minuted meat products either because of its

poor water absorption characteristics at high

and low temperatures

IS .

Similar results

were obtained by Smith et al. 119) using

nonfat

dry

milk as a protein additive in frank

furters. Geurts et al. 36) showed that an aver

age

of .S5

g

of

water can

be

bound by 1 g

of

pure casein, whereas lower values .10 to .15

gig) were observed with cheese. By applying

ultracentrifugation tests, some authors

12S

127) found a relationship between the hydra

tion behavior

of

casein micelles and the heat

stability at 13S C)

of

the corresponding milks.

ht

principal, from the technological viewpoint

water interactions with proteins are strongly

influenced by the manufacturing process and

mechanical treatment heat treatment, grinding,

etc.) and by the properties of the various sys

tems applied.

ME SUREMENT OF W TER HOLDING

C P CITY

Generally, hydration

or

water-holding ca

paci ty can be defined as the nwnber

of grams

of

water associated with or occluded by 1 g of

dry protein 32). The methods for testing pro

teins for their use in foods are based mainly on

the application of either an external force such

as pressure, centrifugation, and capillary suc

tion

of

a porous material in contact with the

sample 52)

or

on the evaluation

of

swelling

under defmed conditions measuring the

maxi

Journal of Dairy Science Vol. 74, No.7 99

mwn) fluid uptake, expressed as the number of

cm

3

of

solution absorbed by I g

of dry

protein

32, 124). Alternatively, the filtrate volume can

be measured after a standardized mixing and

filtration

procedure

68, liS . Water-holding

capacity can thus be either estimated directly,

as the amount of water which can be bound,

or

indirectly, as the amount

of

water released by

the sample. When considering the various as

say procedures described, tests for the exami

nation

of the water-holding capacity can be

divided into two groups: tests under model

conditions and tests applied in actual food

systems with the final product containing the

protein additives). Presently, most available

methods are arbitrary, empirical, and internal,

and the corresponding results depend

on

the

experimental conditions used. The main prob

lems associated with the measurement

of

this

and of other properties are the transferability of

the data obtained in the laboratory to commer

cial food processing conditions and the com

parability of the results obtained by the differ

ent methods. Practical experience would

indicate a preference for applied tests rather

than testing under model conditions despite the

higher costs. Nevertheless, the latter proce

dures may sometimes offer the advantage

of

rapid and simple estimations; in particular,

producers

of

milk protein products may use

them for controlling defmed specifications.

Methodology and corresponding references

dealing with the testing of the water-holding

capacity are summarized in Table 2

ht

order

to list the various methods currently used, food

combinations more

or

less related

to

dairy

products were included. However, the increas

ing need for methods adapted for

dairy

prod

ucts requires a comprehensive review

of

the

extensive utilization

of

dairy products in vari

ous other food products. Many of the proce

dures used for the assessment

of

the water

holding capacity

of

proteins may measure both

water absorption and retention. The following

section, however, differentiates between the

methods used to measure water absorption and

those used to measure water retention.

Methods

ommonly

Used Based on

Water

bsorption

Measurement

Application

the Baumann Apparatus. The

Baumann apparatus 4, 21, 142) measures

2030

KNEIFEL

ET

AL.

uct; the highest water absorption was obtained

with an acid coprecipitate subsequently neu

tralized with sodium hydroxide 121). Thomas

et al. 126) have demonstrated that a strong

pH-dependent water-holding behavior by

coprecipitates can be observed in meat sys

tems.

n

acidic milk protein concentrate

produced by cationic exchange treatment prior

to ultrafiltration and spray drying exhibited a

better water-holding capacity than a neutral

milk protein concentrate powder after

ultrafiltration

of

skimmed

milk

71). Hydroly

sates made from milk proteins by enzymatic

treatment with l c a l a s e ~ or e u t r a s e ~ lost

much of

their water-holding capacity, but the

rate of water absorption was enhanced 86).

However, skimmed milk powders receiving

varied heat treatment did not show different

water-holding capacities 69), and milk powder

was not suitable for use as a filler in com

minuted meat products either because of its

poor water absorption characteristics at high

and low temperatures

IS .

Similar results

were obtained by Smith et al. 119) using

nonfat

dry

milk as a protein additive in frank

furters. Geurts et al. 36) showed that an aver

age

of .S5

g

of

water can

be

bound by 1 g

of

pure casein, whereas lower values .10 to .15

gig) were observed with cheese. By applying

ultracentrifugation tests, some authors

12S

127) found a relationship between the hydra

tion behavior

of

casein micelles and the heat

stability at 13S C)

of

the corresponding milks.

ht

principal, from the technological viewpoint

water interactions with proteins are strongly

influenced by the manufacturing process and

mechanical treatment heat treatment, grinding,

etc.) and by the properties of the various sys

tems applied.

ME SUREMENT OF W TER HOLDING

C P CITY

Generally, hydration

or

water-holding ca

paci ty can be defined as the nwnber

of grams

of

water associated with or occluded by 1 g of

dry protein 32). The methods for testing pro

teins for their use in foods are based mainly on

the application of either an external force such

as pressure, centrifugation, and capillary suc

tion

of

a porous material in contact with the

sample 52)

or

on the evaluation

of

swelling

under defmed conditions measuring the

maxi


mwn) fluid uptake, expressed as the number of

cm

3

of

solution absorbed by I g

of dry

protein

32, 124). Alternatively, the filtrate volume can

be measured after a standardized mixing and

filtration

procedure

68, liS . Water-holding

capacity can thus be either estimated directly,

as the amount of water which can be bound,

or

indirectly, as the amount

of

water released by

the sample. When considering the various as

say procedures described, tests for the exami

nation

of the water-holding capacity can be

divided into two groups: tests under model

conditions and tests applied in actual food

systems with the final product containing the

protein additives). Presently, most available

methods are arbitrary, empirical, and internal,

and the corresponding results depend

on

the

experimental conditions used. The main prob

lems associated with the measurement

of

this

and of other properties are the transferability of

the data obtained in the laboratory to commer

cial food processing conditions and the com

parability of the results obtained by the differ

ent methods. Practical experience would

indicate a preference for applied tests rather

than testing under model conditions despite the

higher costs. Nevertheless, the latter proce

dures may sometimes offer the advantage

of

rapid and simple estimations; in particular,

producers

of

milk protein products may use

them for controlling defmed specifications.

Methodology and corresponding references

dealing with the testing of the water-holding

capacity are summarized in Table 2

ht

order

to list the various methods currently used, food

combinations more

or

less related

to

dairy

products were included. However, the increas

ing need for methods adapted for

dairy

prod

ucts requires a comprehensive review

of

the

extensive utilization

of

dairy products in vari

ous other food products. Many of the proce

dures used for the assessment

of

the water

holding capacity

of

proteins may measure both

water absorption and retention. The following

section, however, differentiates between the

methods used to measure water absorption and

those used to measure water retention.

Methods

ommonly

Used Based on

Water

bsorption

Measurement

Application

the Baumann Apparatus. The

Baumann apparatus 4, 21, 142) measures

8/10/2019 Pi is 0022030291783732

5/15

WATER-HOLDING CAPACITY OF MD..K PROTEINS: REVIEW 2031

TABLE 2. Methods for water-holding capacity measurement in foods.

Products tested Authors

Reference

number

22

83

70, 71, 72

18

21

51

131

142

132

49

4

41, 42

69

55

118

88

143

122

125

111

132

43

84

114

36

133

132

3

54

101

138, 139, 140

53

102

125

53

123

15

73

79

109

126

103

continued

Thomas

et

al. 1974

Ozimek and Poznanski 1981

Sternberg et al. 1976

Comer 1979

Kroll et al. 1984

Luther et al. 1983

Quinn and Paton 1979

Whey protein concentrates

Sodium caseinate, whey protein isolates

Coprecipitates

Soybean proteins

of

different maturity

Hydrocolloids

Meal binders

Various powders

Baumann apparatus

De

Wit and De Boer 1975

Hermansson 1972

Vattula et al. 1979

Yao et al. 1988

Wallingford and Labuza 1983

Heinevetter et al. 1986

Baumann 1967

Viscosimetry

McDonough

et

al. 1974



Milk protein concentrate, casein,

casein derivatives

Casein solutions

Milk proteins

Whey protein concentrate in doughs

lk

powder, caseins. caseinates, coprecipitates

Milk powder in dough systems

Whey proteins

Soybean proteins

in

bread

Soybean products

Doughs

Casein

Carrageenan

Hydrocolloids

Blood plasma gels

Soy protein gels

Meat systems

Meat systems

Beef blends

Dewan et al. 1973

Farinographic techniques

Guy e t al. 1967, 1974

Knightbridge and Goldman 1979

Hoffman

et

al. 1948

Short 1980

Mizrahi

et

al. 196

7

Yasumatsu et al. 1972

Stamberg and Merritt 1941

Rehydration test

De

Wit and Klarenbeek 1986

Cryoscopic osmometry

Tarodo de la Fuente and Alais 1975

Rey and Labuza 1981


Equilibration at dermed humidity sorption isotherms

Casein, blood

serum

albumin, egg white, Hagenmaier 1972

plant proteins

Casein

Casein

Cheese

Wafer doughs

Hydrocolloids

Amino acids

Mellon et al. 1974

Rilegg et a l. 1974

Geurts e t al. 1974

Wedzicha and Quine 1983


Anderson and Witter 1982

Net test

HeJIDansson and Lucisano 1982

Ochiai-Yanagi et al. 1978

Wierbicki e t al. 1956, 1957

He=ansson

and Akesson 1975

OckeJIDan and Leon Crespo 1982

Centrifugation tests

Tarodo de la Fuente and

Alais

1975

He=ansson

and Akesson 1975

Casein

Caseinate, whey protein concentrates

in meat systems

Whey protein isolates

Milk powder. caseinate

Casein, plant protein isolates

Milk protein, soybean, yeast protein

Caseinate, whey concentrate, plant proteins,

egg white

Sodium caseinate, soybean isolates

Milk proteins in meat systems

Journal

of

Dairy Science Vol. 74. No.7, 1991

WATER-HOLDING CAPACITY OF MD..K PROTEINS: REVIEW 2031

TABLE 2. Methods for water-holding capacity measurement in foods.

Products tested Authors

Reference

number

22

83

70, 71, 72

18

21

51

131

142

132

49

4

41, 42

69

55

118

88

143

122

125

111

132

43

84

114

36

133

132

3

54

101

138, 139, 140

53

102

125

53

123

15

73

79

109

126

103

continued

Thomas

et

al. 1974

Ozimek and Poznanski 1981

Sternberg et al. 1976

Comer 1979

Kroll et al. 1984

Luther et al. 1983

Quinn and Paton 1979


Sodium caseinate, whey protein isolates

Coprecipitates

Soybean proteins

of

different maturity

Hydrocolloids

Meal binders

Various powders

Baumann apparatus

De

Wit and De Boer 1975

Hermansson 1972

Vattula et al. 1979

Yao et al. 1988


Heinevetter et al. 1986

Baumann 1967

Viscosimetry

McDonough

et

al. 1974



Milk protein concentrate, casein,

casein derivatives

Casein solutions

Milk proteins

Whey protein concentrate in doughs

lk

powder, caseins. caseinates, coprecipitates

Milk powder in dough systems

Whey proteins

Soybean proteins

in

bread

Soybean products

Doughs

Casein

Carrageenan

Hydrocolloids

Blood plasma gels

Soy protein gels

Meat systems

Meat systems

Beef blends

Dewan et al. 1973

Farinographic techniques

Guy e t al. 1967, 1974

Knightbridge and Goldman 1979

Hoffman

et

al. 1948

Short 1980

Mizrahi

et

al. 196

7

Yasumatsu et al. 1972

Stamberg and Merritt 1941

Rehydration test

De

Wit and Klarenbeek 1986

Cryoscopic osmometry

Tarodo de la Fuente and Alais 1975

Rey and Labuza 1981


Equilibration at dermed humidity sorption isotherms

Casein, blood

serum

albumin, egg white, Hagenmaier 1972

plant proteins

Casein

Casein

Cheese

Wafer doughs

Hydrocolloids

Amino acids

Mellon et al. 1974

Rilegg et a l. 1974

Geurts e t al. 1974

Wedzicha and Quine 1983


Anderson and Witter 1982

Net test

HeJIDansson and Lucisano 1982

Ochiai-Yanagi et al. 1978

Wierbicki e t al. 1956, 1957

He=ansson

and Akesson 1975

OckeJIDan and Leon Crespo 1982

Centrifugation tests

Tarodo de la Fuente and

Alais

1975

He=ansson

and Akesson 1975

Casein

Caseinate, whey protein concentrates

in meat systems

Whey protein isolates

Milk powder. caseinate

Casein, plant protein isolates

Milk protein, soybean, yeast protein

Caseinate, whey concentrate, plant proteins,

egg white

Sodium caseinate, soybean isolates

Milk proteins in meat systems

Journal

of

Dairy Science Vol. 74. No.7, 1991

8/10/2019 Pi is 0022030291783732

6/15

8/10/2019 Pi is 0022030291783732

7/15

WATER-HOLDING CAPACITY OF MILK PROTEINS: REVIEW

2033

quantitatively the fluid uptake by powdery

substances and consists

of

a thermostated un-

nel accomplished by a water bath jacket con

nected to a horizontal graduated, cal ibrated

capillary fixed around the top

of

the funnel. A

20- to 500-mg sample

of

protein is dusted on a

wetted filter paper fastened to a fritted glass

filter placed

on

top

of

the funnel filled with

water. The uptake of water by the sample at

equilibrium is read from the graduated capil

lary and expressed on a dry basis. Results are,

therefore, expressed as milliliters

of

water up

take per 1 g

of

dry matter. Under normal

conditions, the powder is dried before the test.

Although a glass lid set on the filter paper is

used to minimize evaporative losses, a blank

value should be examined and finally sub

tracted from the results.

Facultatively, the wetting process can be

followed thereby optically by coloring the flu

id. The testing procedure is influenced by

moisture content and particle size

of

the pow

der as well as by the temperature

of

the liquid.

Additionally, the occurrence

of

air bulbs in the

liquid must be avoided. In 1933, the basic

principle

of

the method was described for the

first time by Enslin 25 . The apparatus was

originally developed for the characterization

of

three parameters

of

different biological and

nonbiological substances: 1 measurement

of

soaking properties, 2 measurement

of

total

pore volume

of

porous substances and pow

ders, and 3 velocity measurement

of

powder

hydration. Because

of

obtaining widely scat

tered results when examining powders, Bau

mann 4 later modified the Enslin methodol

ogy as well as the equipment. The application

of

the Baumann apparatus has proven to be

useful, particularly for the prediction

of

the

spontaneous water uptake

of

hydrocolloids in

low fat meat emulsions 132 and has been

also used for the assessment

of

pharmaceutical

powders. The water-binding values

of

gums

derived from Baumann apparatus measure

ments correlate well with rheological values

such as viscosity, pseudoplastic flow behavior,

and consistency coefficients 132 . However,

problems

of

repeatability may arise from the

very small amounts

of

sample mainly within

the milligram range used for the test. Further

more, it should

be

taken into consideration that

the value obtained by the Baumann apparatus

is a relative one and cannot be taken as abso

lute.

Measurement Increased Viscosity

Strength

When protein solutions are hydrated,

the proteins occlude a certain amount

of

sol

vent. This solvent behaves as a part

of

the

dispersed phase and needs to be included as

such 112 . The hydration

of

the protein will

increase the intrinsic viscosity by the same

factor by which it increases the volume frac

tion.

indirect viscosimetric method was

described using a Brookfield LVT Brookfield

Eng. Lab., Inc., Stoughton, MA viscosimeter

3 rpm, spindle crosspiece length

of

1.1 cm

for estimating the degree

of

water entrapment

after controlled heating of the protein 83 .

Increased viscosity is used as a measure

of

water uptake.

To

prevent the creation

of

a

channel in the gel tube measured by the rotat

ing spindle, the viscosimeter is mounted on a

heliopath stand that lowers the spindle in a

helical path through the test material to ensure

that the rotor always measures undisturbed ma

terial.

The water-holding capacity

of

casein

micelles has also been estimated from the in

crease in volume, based on viscosity measure

ments 18 . Korolczuk 70, 71, 72 used a

defmed formula to calculate the water-holding

capacity from the data obtained by viscosi ty

measurements.

arinographic Techniques Although the

Brabender farinograph technique 41, 42, 55,

69, 75 is widely used

to

measure water ab

sorption by wheat flours, doughs, and soybean

products, few reports

of

its use in testing the


of

flour and milk pro

tein blends have been published. The proce

dure described by Knightbridge and Goldman

69 i s based on the constant dough weight

method, which allows the calculation of sev

eral farinograph characteristics such as the per

centage water absorbed by 30-g samples, sta

bility time difference n time to the nearest

half minute between the point where the curve

first reaches the 500 Brabender Units, i.e.,

development time, and the point where the

curve leaves the 500-Brabender Unit line , and

the tolerance index the difference in Bra

bender Units from the top

of

the curve at the

peak to the top

of

the curve measured 5

m n

after the peak is reached . With some pow

dered milk products, jagged farinograph pro

files will

be

obtained, leading to errors in

interpretation. Nevertheless, as reported by the

Journal

of

Daily Science Vol. 74,

No 7

1991


2033

quantitatively the fluid uptake by powdery

substances and consists

of

a thermostated un-

nel accomplished by a water bath jacket con

nected to a horizontal graduated, cal ibrated

capillary fixed around the top

of

the funnel. A

20- to 500-mg sample

of

protein is dusted on a

wetted filter paper fastened to a fritted glass

filter placed

on

top

of

the funnel filled with

water. The uptake of water by the sample at

equilibrium is read from the graduated capil

lary and expressed on a dry basis. Results are,

therefore, expressed as milliliters

of

water up

take per 1 g

of

dry matter. Under normal

conditions, the powder is dried before the test.

Although a glass lid set on the filter paper is

used to minimize evaporative losses, a blank

value should be examined and finally sub

tracted from the results.

Facultatively, the wetting process can be

followed thereby optically by coloring the flu

id. The testing procedure is influenced by

moisture content and particle size

of

the pow

der as well as by the temperature

of

the liquid.

Additionally, the occurrence

of

air bulbs in the

liquid must be avoided. In 1933, the basic

principle

of

the method was described for the

first time by Enslin 25 . The apparatus was

originally developed for the characterization

of

three parameters

of

different biological and

nonbiological substances: 1 measurement

of

soaking properties, 2 measurement

of

total

pore volume

of

porous substances and pow

ders, and 3 velocity measurement

of

powder

hydration. Because

of

obtaining widely scat

tered results when examining powders, Bau

mann 4 later modified the Enslin methodol

ogy as well as the equipment. The application

of

the Baumann apparatus has proven to be

useful, particularly for the prediction

of

the

spontaneous water uptake

of

hydrocolloids in

low fat meat emulsions 132 and has been

also used for the assessment

of

pharmaceutical

powders. The water-binding values

of

gums

derived from Baumann apparatus measure

ments correlate well with rheological values

such as viscosity, pseudoplastic flow behavior,

and consistency coefficients 132 . However,

problems

of

repeatability may arise from the

very small amounts

of

sample mainly within

the milligram range used for the test. Further

more, it should

be

taken into consideration that

the value obtained by the Baumann apparatus

is a relative one and cannot be taken as abso

lute.

Measurement Increased Viscosity

Strength

When protein solutions are hydrated,

the proteins occlude a certain amount

of

sol

vent. This solvent behaves as a part

of

the

dispersed phase and needs to be included as

such 112 . The hydration

of

the protein will

increase the intrinsic viscosity by the same

factor by which it increases the volume frac

tion.

indirect viscosimetric method was

described using a Brookfield LVT Brookfield

Eng. Lab., Inc., Stoughton, MA viscosimeter

3 rpm, spindle crosspiece length

of

1.1 cm

for estimating the degree

of

water entrapment

after controlled heating of the protein 83 .

Increased viscosity is used as a measure

of

water uptake.

To

prevent the creation

of

a

channel in the gel tube measured by the rotat

ing spindle, the viscosimeter is mounted on a

heliopath stand that lowers the spindle in a

helical path through the test material to ensure

that the rotor always measures undisturbed ma

terial.

The water-holding capacity

of

casein

micelles has also been estimated from the in

crease in volume, based on viscosity measure

ments 18 . Korolczuk 70, 71, 72 used a

defmed formula to calculate the water-holding

capacity from the data obtained by viscosi ty

measurements.

arinographic Techniques Although the

Brabender farinograph technique 41, 42, 55,

69, 75 is widely used

to

measure water ab

sorption by wheat flours, doughs, and soybean

products, few reports

of

its use in testing the


of

flour and milk pro

tein blends have been published. The proce

dure described by Knightbridge and Goldman

69 i s based on the constant dough weight

method, which allows the calculation of sev

eral farinograph characteristics such as the per

centage water absorbed by 30-g samples, sta

bility time difference n time to the nearest

half minute between the point where the curve

first reaches the 500 Brabender Units, i.e.,

development time, and the point where the

curve leaves the 500-Brabender Unit line , and

the tolerance index the difference in Bra

bender Units from the top

of

the curve at the

peak to the top

of

the curve measured 5

m n

after the peak is reached . With some pow

dered milk products, jagged farinograph pro

files will

be

obtained, leading to errors in

interpretation. Nevertheless, as reported by the

Journal

of

Daily Science Vol. 74,

No 7

1991

8/10/2019 Pi is 0022030291783732

8/15

2034

KNEIFEL ET AL.

authors 69), the suitability of various dried

m il k products for u se i n different food prod

ucts can be selectively estimated with this

method.

Rehydration Test o Milk Protein Products

This method 22) was originally developed for

examining the dispersion behavior of milk pro

teins rather than for the assessment of the

water-holding capacity. It is based on spec

trophotometrical measurements

of

the change

in transmission density

of

the dispersed protein

as a function of time. The device consists of a

cylindrical tube with a fritted glass bottom, on

which a known amount of the sample is

placed.

The

gl as s tube is co nnecte d t o a spec

trophotometer set at 600

nm

equipped with a

flow-through cell and an

X-Y

recorder. A de

fined volume of water is then circulated by

means of a peristaltic pump. n optical index

is calculated that defines a kinetic relationship

between the reconstitution properties and the

characteristics of the protein powder. n this

procedure, two steps can be distinguished: 1)

the powdered product is rewetted and 2 then

dispersed or dissolved. n a recently published

modification, samples

of

the protein-water

mixture are taken out discontinuously from the

tube using a syringe and are sequentially trans

ferred into the cuvette

of

a spectrophotometer

for transmittance measurements 20).

ryoscopic Osmometry

T hi s method was

used for characterizing the water-binding prop

erties

of

carrageenan and other hydrocolloids,

b as ed o n wa te r activity measurements 111,

125, 132). This technique does not measure the

water activity directly but measures t he so

called colligative property of freezing point

utilizing the ability of a substance to depress

the freezing point of a solution, b as ed on t he

Raoult s Law. The freezing point is internally

converted into an effective osmotic concentra

tion given in milliosmoles p er kilogram

of

water

111 .

One drawback of the use of

cryoscopic osmometry for predicting the wa

ter-holding capacity is that the results obtained

are not comparable with those of the Baumann

apparatus 132).

Equilibration

t

a Defined Relative Humidi-

ty Wat er-hold ing is measured as the wei ght

uptake after exposure of the dry protein sample

to

an atmosphere at defined relative humidity

e.g., over saturated

KC1

NaCl, Ca026H20

according

to

the sorption isotherms. As can be

Journal of Dairy S cience Vol. 74, No.7 1991

deducted from the work

of

Mel lon e t al. 84),

water absorption studies have been contribut

ing to the basic knowledge about t he water

binding of casein structures. n many proteins,

a moisture equilibrium is mainly achieved

within 24 h 43).

n

contrast, for the examina

tion of ground cheese and para-casein, 4 d

were necessary to equilibrate the samples 36);

sigmoid types

of

sorption is oth erms we re

achieved with cheese. Similar trials were car

ried out with various hydrocolloids pectins,

gums, etc.) by Wallingford and Labuza 132)

at a defined water activity of .98 a nd also wit h

wafer biscuits in a water activity range of .14

to

.53 133).

Methods Commonly Used Based

on Water Retention Measurement

Net Test

The net 54, 138, 139, 140) is a

combined filtration and centrifugation proce

dure that is mainly used for the examination of

meat and related products. It is carried out with

special pyrex glass or plexiglass equipment

consisting of three parts: 1 a tu be i n which t he

g el is formed, 2) a filter p ap er t o be placed on

t he net, and 3) the mi ddl e sect ion wi th the n et

and an O-ring between the middle and bottom

sections. The description

of

the procedure uses

the dimensions outlined by Hermansson and

Lucisano 54); the original dimensions as

given by Wierbicki et al. 138, 139, 140) are

slightly different. After preparing the gel with

the substance to be tested in the upper tube, the

gel is cooled, the bottom rubber stopper is

removed, and the test t ube is a ttached to the

middle section. This section has a 200-llm

nylon mesh net in the bottom

to

allow drainage

of water to the bottom section. For work with

protein gels, a filter paper is placed

on

top of

the net.

n

O-ring is placed between the mid

dle and bottom section in order to prevent

leakage during centrifugation. The bottom has

an inner diameter of

11

mID. The whole assem

bly is

put

into a centrifuge tube and gently

centrifuged. St an da rd condit ions are 3 g of

sample and centrifugation at 790 x

g

235

rpm). For the assessment of soybean proteins,

Ochiai-Yanagi et al. 101 used a modified

procedure involving less sample material and a

lower centrifugation speed. Moisture loss can

be determined by weighing the gel before cen

trifugation and the released liquid after centri-

2034

KNEIFEL ET AL.

authors 69), the suitability of various dried

m il k products for u se i n different food prod

ucts can be selectively estimated with this

method.

Rehydration Test o Milk Protein Products

This method 22) was originally developed for

examining the dispersion behavior of milk pro

teins rather than for the assessment of the

water-holding capacity. It is based on spec

trophotometrical measurements

of

the change

in transmission density

of

the dispersed protein

as a function of time. The device consists of a

cylindrical tube with a fritted glass bottom, on

which a known amount of the sample is

placed.

The

gl as s tube is co nnecte d t o a spec

trophotometer set at 600

nm

equipped with a

flow-through cell and an

X-Y

recorder. A de

fined volume of water is then circulated by

means of a peristaltic pump. n optical index

is calculated that defines a kinetic relationship

between the reconstitution properties and the

characteristics of the protein powder. n this

procedure, two steps can be distinguished: 1)

the powdered product is rewetted and 2 then

dispersed or dissolved. n a recently published

modification, samples

of

the protein-water

mixture are taken out discontinuously from the

tube using a syringe and are sequentially trans

ferred into the cuvette

of

a spectrophotometer

for transmittance measurements 20).

ryoscopic Osmometry

T hi s method was

used for characterizing the water-binding prop

erties

of

carrageenan and other hydrocolloids,

b as ed o n wa te r activity measurements 111,

125, 132). This technique does not measure the

water activity directly but measures t he so

called colligative property of freezing point

utilizing the ability of a substance to depress

the freezing point of a solution, b as ed on t he

Raoult s Law. The freezing point is internally

converted into an effective osmotic concentra

tion given in milliosmoles p er kilogram

of

water

111 .

One drawback of the use of

cryoscopic osmometry for predicting the wa

ter-holding capacity is that the results obtained

are not comparable with those of the Baumann

apparatus 132).

Equilibration

t

a Defined Relative Humidi-

ty Wat er-hold ing is measured as the wei ght

uptake after exposure of the dry protein sample

to

an atmosphere at defined relative humidity

e.g., over saturated

KC1

NaCl, Ca026H20

according

to

the sorption isotherms. As can be

Journal of Dairy S cience Vol. 74, No.7 1991

deducted from the work

of

Mel lon e t al. 84),

water absorption studies have been contribut

ing to the basic knowledge about t he water

binding of casein structures. n many proteins,

a moisture equilibrium is mainly achieved

within 24 h 43).

n

contrast, for the examina

tion of ground cheese and para-casein, 4 d

were necessary to equilibrate the samples 36);

sigmoid types

of

sorption is oth erms we re

achieved with cheese. Similar trials were car

ried out with various hydrocolloids pectins,

gums, etc.) by Wallingford and Labuza 132)

at a defined water activity of .98 a nd also wit h

wafer biscuits in a water activity range of .14

to

.53 133).

Methods Commonly Used Based

on Water Retention Measurement

Net Test

The net 54, 138, 139, 140) is a

combined filtration and centrifugation proce

dure that is mainly used for the examination of

meat and related products. It is carried out with

special pyrex glass or plexiglass equipment

consisting of three parts: 1 a tu be i n which t he

g el is formed, 2) a filter p ap er t o be placed on

t he net, and 3) the mi ddl e sect ion wi th the n et

and an O-ring between the middle and bottom

sections. The description

of

the procedure uses

the dimensions outlined by Hermansson and

Lucisano 54); the original dimensions as

given by Wierbicki et al. 138, 139, 140) are

slightly different. After preparing the gel with

the substance to be tested in the upper tube, the

gel is cooled, the bottom rubber stopper is

removed, and the test t ube is a ttached to the

middle section. This section has a 200-llm

nylon mesh net in the bottom

to

allow drainage

of water to the bottom section. For work with

protein gels, a filter paper is placed

on

top of

the net.

n

O-ring is placed between the mid

dle and bottom section in order to prevent

leakage during centrifugation. The bottom has

an inner diameter of

11

mID. The whole assem

bly is

put

into a centrifuge tube and gently

centrifuged. St an da rd condit ions are 3 g of

sample and centrifugation at 790 x

g

235

rpm). For the assessment of soybean proteins,

Ochiai-Yanagi et al. 101 used a modified

procedure involving less sample material and a

lower centrifugation speed. Moisture loss can

be determined by weighing the gel before cen

trifugation and the released liquid after centri-

8/10/2019 Pi is 0022030291783732

9/15


2035

fugation, and water-holding capacity can be

calculated after the determination of the pro

tein or

dry

content of the gel plug before and

after centrifugation. The result must be cor

rected for water uptake by the filter paper. The

drip collected in the bottom section can also be

analyzed. For the examination

of

the moisture

losses

of

blood plasma gels, a standard devia

tion ranging from .5 to 1.5 (wt/wt, absolute)

was reported (54). One advantage

of

this

method is that low speed centrifugation limits

the degree

of

structural breakdown, and only

water, but not the gel structure, passes through

the net. This is a prerequisite for obtaining

reliable results that can

be

transferred to an

industrial setting. Hitherto, no experiences

have been reported on the application of the

net test to

milk

protein products.

Centrifugation Tests

A variety

of

condi

tions are described, ranging from high speed

ultracentrifugation to low speed centrifugation,

which are carried out according to internally

applied standard methods (8, 46, 53, 54, 82,

87, 105, 120, 123, 126, 127), e.g., the assay

conditions from Hermansson and Lucisano

(54) are 50-ml centrifugation tubes (27 in

diameter) filled with 10 g

of

sample and cen

trifuged at 20,200 x

g

(13,000 rpm) for 30

min.

After centrifugation, the amount of liquid

released is weighed. Other authors (73, 109,

119, 123) centrifuged

at lower speeds (1000 or

2000

x

g

following an incubation period of

10 min at 97 C (subject to slight modification)

of

the protein solution. After centrifugation,

the released water is absorbed by a filter paper

on which the tubes have been inverted (123).

The wetted filter paper is then weighed. Alter

natively (109), the supernatant is discarded,

and the protein with the remaining water is

weighed. Such centrifugation procedures, ei

ther to estimate cold or hot water absorption

(depending on preparation conditions), are

commonly used for the examination

of

cereals

(2,

15).

Capillary Volumeter Method

This appara

tus was specifically invented by Hofmann (56)

for the examination

of

meat and is based on

the manometric measurement of the

air

volume

in a capillary repressed by the fluid absorbed

or by the loss of weight by the sample tested.

The device consists of a porous gypsum corpus

that is pressed onto the sample in a volumetric

beaker with constant pressure. The fluid

released by the sample displaces the

ir

of an

overflow pipe directly connected to the plaster.

The results can be expressed either as mil-

liliters of fluid per square centimeter of sample

surface or as milligrams

of

fluid per gram

of

sample. Hitherto, no experiences have been

reported with the application of this method

(57) for the examination of

milk

proteins. In

the case of meat samples, a maximum devia

tion

of

6 was observed (56).

Measurement

Capillary Suction Poten-

tial This method is rather similar to the capil

lary volumeter test and was specifically deve

loped for the examination of moist foods and

gels that easily deform under pressure. The

material to be measured is placed in a special

polypropylene cup, layered with a filter paper

with a predetermined moisture content, sealed

with a rubber stopper with a glass capillary (.3

rom

inner diameter) inserted, and held at 6 C

for 72 h. The glass capillary prevents pressure

build-up

in

the stoppered container. From the

change in moisture content of the filter paper

after equilibration as measured by weighing,

the suction potential in

N/cm

of

the measured

material is read off a standard curve. This

curve has to be determined by measuring the

water lost from a filter paper in a standard soil

test cell as a function of applied pressure.

Based on this, the suction pressure as a func

tion

of

moisture content can be estimated at

very high water contents. A large contact sur

face and a thin gel layer must

be

ensured to

achieve fast movement

of

water from the gel

to the filter paper. The measurement is affected

by initial gel concentration, initial water con

tent of filter paper, and temperature of equili

bration (74). As reported by those authors, the

time of h at 6 C was appropriate to attain

equilibrium at the highest suction potential

differential. A coefficient of variation

of

2.5 was calculated based on measurements

of

a

series of three different gels.

Pressure Methods Some authors I 76)

make a distinction between expressible fluid,

free-type water, and bound-type water. For

examining these parameters, a Universal Test

ing Machine Instron 1122 (lnstron Ltd., Bucks,

England) was used for compression of the

samples along the vertical axis. The released

fluid is collected on 10 sheets

of

preweighed,

dried filter paper, and the expressible fluid is

determined by measuring the weight gain

of



2035

fugation, and water-holding capacity can be

calculated after the determination of the pro

tein or

dry

content of the gel plug before and

after centrifugation. The result must be cor

rected for water uptake by the filter paper. The

drip collected in the bottom section can also be

analyzed. For the examination

of

the moisture

losses

of

blood plasma gels, a standard devia

tion ranging from .5 to 1.5 (wt/wt, absolute)

was reported (54). One advantage

of

this

method is that low speed centrifugation limits

the degree

of

structural breakdown, and only

water, but not the gel structure, passes through

the net. This is a prerequisite for obtaining

reliable results that can

be

transferred to an

industrial setting. Hitherto, no experiences

have been reported on the application of the

net test to

milk

protein products.

Centrifugation Tests

A variety

of

condi

tions are described, ranging from high speed

ultracentrifugation to low speed centrifugation,

which are carried out according to internally

applied standard methods (8, 46, 53, 54, 82,

87, 105, 120, 123, 126, 127), e.g., the assay

conditions from Hermansson and Lucisano

(54) are 50-ml centrifugation tubes (27 in

diameter) filled with 10 g

of

sample and cen

trifuged at 20,200 x

g

(13,000 rpm) for 30

min.

After centrifugation, the amount of liquid

released is weighed. Other authors (73, 109,

119, 123) centrifuged

at lower speeds (1000 or

2000

x

g

following an incubation period of

10 min at 97 C (subject to slight modification)

of

the protein solution. After centrifugation,

the released water is absorbed by a filter paper

on which the tubes have been inverted (123).

The wetted filter paper is then weighed. Alter

natively (109), the supernatant is discarded,

and the protein with the remaining water is

weighed. Such centrifugation procedures, ei

ther to estimate cold or hot water absorption

(depending on preparation conditions), are

commonly used for the examination

of

cereals

(2,

15).

Capillary Volumeter Method

This appara

tus was specifically invented by Hofmann (56)

for the examination

of

meat and is based on

the manometric measurement of the

air

volume

in a capillary repressed by the fluid absorbed

or by the loss of weight by the sample tested.

The device consists of a porous gypsum corpus

that is pressed onto the sample in a volumetric

beaker with constant pressure. The fluid

released by the sample displaces the

ir

of an

overflow pipe directly connected to the plaster.

The results can be expressed either as mil-

liliters of fluid per square centimeter of sample

surface or as milligrams

of

fluid per gram

of

sample. Hitherto, no experiences have been

reported with the application of this method

(57) for the examination of

milk

proteins. In

the case of meat samples, a maximum devia

tion

of

6 was observed (56).

Measurement

Capillary Suction Poten-

tial This method is rather similar to the capil

lary volumeter test and was specifically deve

loped for the examination of moist foods and

gels that easily deform under pressure. The

material to be measured is placed in a special

polypropylene cup, layered with a filter paper

with a predetermined moisture content, sealed

with a rubber stopper with a glass capillary (.3

rom

inner diameter) inserted, and held at 6 C

for 72 h. The glass capillary prevents pressure

build-up

in

the stoppered container. From the

change in moisture content of the filter paper

after equilibration as measured by weighing,

the suction potential in

N/cm

of

the measured

material is read off a standard curve. This

curve has to be determined by measuring the

water lost from a filter paper in a standard soil

test cell as a function of applied pressure.

Based on this, the suction pressure as a func

tion

of

moisture content can be estimated at

very high water contents. A large contact sur

face and a thin gel layer must

be

ensured to

achieve fast movement

of

water from the gel

to the filter paper. The measurement is affected

by initial gel concentration, initial water con

tent of filter paper, and temperature of equili

bration (74). As reported by those authors, the

time of h at 6 C was appropriate to attain

equilibrium at the highest suction potential

differential. A coefficient of variation

of

2.5 was calculated based on measurements

of

a

series of three different gels.

Pressure Methods Some authors I 76)

make a distinction between expressible fluid,

free-type water, and bound-type water. For

examining these parameters, a Universal Test

ing Machine Instron 1122 (lnstron Ltd., Bucks,

England) was used for compression of the

samples along the vertical axis. The released

fluid is collected on 10 sheets

of

preweighed,

dried filter paper, and the expressible fluid is

determined by measuring the weight gain

of


8/10/2019 Pi is 0022030291783732

10/15

2036

KNEIFEL

ET

AL.

the filter paper after sample compression and

reported in terms

of

percentage

of

expressible

fluid based on the weight

of

unpressed sam

ples. Moisture in expressed fluid is calculated

after drying the wet filter paper containing the

expressed fluid and is referred to as free-type

water. Moisture in the pressed sample is calcu

lated as the percentage of moisture left in the

sample after fluid was expressed by the Instron

machine. After drying the pressed samples,

moisture is calculated as the difference in

weight between wet pressed samples and dried

pressed samples and referred to as bound-type

water. Another pressure method originally de

veloped for the testing

of

meat 39, 40 was

adapted to milk protein products 61 . The

sample is weighed on a filter paper or cotton

sheet and pressed between two solid plates

with a force

of

400 N for 5 min. The assembly

is covered with aluminum foil to prevent water

evaporation during the procedure. The results

are expressed as weight measurements. Pohja

and Niinivaara 107 used an analogous princi

ple for the examination of meat and noticed

that the sensitivity

of

the test decreases with an

increasing force.

Differential Scanning alorimetry Thermal

analysis techniques 1, 7, 114, 141 such as

differential thermal analysis and differential

scanning calorimetry DSC are of potential

value for assessing the changes in the physical

state

of

foods.

The

purpose

of

these methods is

to record the difference between an enthalpy

change that occurs

in

a very small sample

around 10 mg and

some reference materi

als during heat treatment. In the classical ther

mal analysis, a single heating source is used,

whereas in DSC the sample and reference are

each provided with independent heaters.

In

food analysis, DSC was primarily used for

studying the protein denaturation 113

or

the

phenomenon

of

gelatinization

of

starches

141 . RUegg et al. 113 demonstrated that

this technique can be also applied for observ

ing the hydration behavior

of

different caseins.

Furthermore, based

on

microcalorimetric

measurement it was shown by these authors

that the heat fusion

of

water in aqueous casein

systems reveals four different states of water:

nonfreezable water, freezable water with

both

heat and temperature of fusion different from

the bulk liquid, freezable water with tempera

ture of fusion different from bulk water, and

Journal

of

Dairy Science Vol. 74, No.7 1991

freezable water indistinguishable by DSC from

ordinary water. Berl in et al. 6, 7 used

DSC

equipment for the examination

of

nonfreezable

water in whey protein concentrates. Similar

DSC applications were described for assessing

the freezable water in other foods 104 .

Filtration Procedure This method 68 was

used for the examination

of

caseinates and is

applied as a rapid internal method by

producers

of

process cheese. After equilibra

tion

of

the powder with excess water, the

volume

of

released water is measured. The

caseinate dispersion has to be prepared accord

ing to a standardized mixing procedure. An

aliquot

of

the sample is then pipetted into a

funnel containing a folded filter set

on

a mea

suring cylinder. The process is timed with a

stop watch, and after 5

min

water-holding ca

pacity can be indirectly calculated by subtract

ing the filtrate volume from the whole volume

pipetted. A rehydration index described by

Rustad and Nesse 115 is derived by a similar

process: a I g sample

of

protein is allowed to

swell in 50

ml of

water for 1 min. Surplus

water

is

removed by a filter funnel with a

sintered glass plate under moderate suction,

and the weight

of

the ftlter cake is determined.

The rehydration index

is

defined as the ratio of

sample weight after swelling to sample weight

before swelling.

ther Testing rinciples

ooking Test

During heating, food is

af-

fected in many ways, including development

of

textural changes.

In

general, some proteins

coagulate or degrade when heated; but other

proteins gel upon cooling. Cooking procedures

for the assessment

of

water-holding are mainly

applied for examining meat products. We

found no corresponding reports concerning

cooking tests for milk proteins, but for the

examination of meat this test can be of value.

A very simple procedure described is to cook

the sample under defined conditions and to

weigh it before and after cooking 128 . An

other cooking method has also

been

demon

strated for chicken meat 35 .

Nuclear Magnetic Resonance The nuclear

magnetic resonance NMR technique 26 has

increasingly contributed fundamental informa

tion to the understanding

of

the molecular

hydration behavior

of

colloidal biological sys-

2036

KNEIFEL

ET

AL.

the filter paper after sample compression and

reported in terms

of

percentage

of

expressible

fluid based on the weight

of

unpressed sam

ples. Moisture in expressed fluid is calculated

after drying the wet filter paper containing the

expressed fluid and is referred to as free-type

water. Moisture in the pressed sample is calcu

lated as the percentage of moisture left in the

sample after fluid was expressed by the Instron

machine. After drying the pressed samples,

moisture is calculated as the difference in

weight between wet pressed samples and dried

pressed samples and referred to as bound-type

water. Another pressure method originally de

veloped for the testing

of

meat 39, 40 was

adapted to milk protein products 61 . The

sample is weighed on a filter paper or cotton

sheet and pressed between two solid plates

with a force

of

400 N for 5 min. The assembly

is covered with aluminum foil to prevent water

evaporation during the procedure. The results

are expressed as weight measurements. Pohja

and Niinivaara 107 used an analogous princi

ple for the examination of meat and noticed

that the sensitivity

of

the test decreases with an

increasing force.

Differential Scanning alorimetry Thermal

analysis techniques 1, 7, 114, 141 such as

differential thermal analysis and differential

scanning calorimetry DSC are of potential

value for assessing the changes in the physical

state

of

foods.

The

purpose

of

these methods is

to record the difference between an enthalpy

change that occurs

in

a very small sample

around 10 mg and

some reference materi

als during heat treatment. In the classical ther

mal analysis, a single heating source is used,

whereas in DSC the sample and reference are

each provided with independent heaters.

In

food analysis, DSC was primarily used for

studying the protein denaturation 113

or

the

phenomenon

of

gelatinization

of

starches

141 . RUegg et al. 113 demonstrated that

this technique can be also applied for observ

ing the hydration behavior

of

different caseins.

Furthermore, based

on

microcalorimetric

measurement it was shown by these authors

that the heat fusion

of

water in aqueous casein

systems reveals four different states of water:

nonfreezable water, freezable water with

both

heat and temperature of fusion different from

the bulk liquid, freezable water with tempera

ture of fusion different from bulk water, and

Journal

of

Dairy Science Vol. 74, No.7 1991

freezable water indistinguishable by DSC from

ordinary water. Berl in et al. 6, 7 used

DSC

equipment for the examination

of

nonfreezable

water in whey protein concentrates. Similar

DSC applications were described for assessing

the freezable water in other foods 104 .

Filtration Procedure This method 68 was

used for the examination

of

caseinates and is

applied as a rapid internal method by

producers

of

process cheese. After equilibra

tion

of

the powder with excess water, the

volume

of

released water is measured. The

caseinate dispersion has to be prepared accord

ing to a standardized mixing procedure. An

aliquot

of

the sample is then pipetted into a

funnel containing a folded filter set

on

a mea

suring cylinder. The process is timed with a

stop watch, and after 5

min

water-holding ca

pacity can be indirectly calculated by subtract

ing the filtrate volume from the whole volume

pipetted. A rehydration index described by

Rustad and Nesse 115 is derived by a similar

process: a I g sample

of

protein is allowed to

swell in 50

ml of

water for 1 min. Surplus

water

is

removed by a filter funnel with a

sintered glass plate under moderate suction,

and the weight

of

the ftlter cake is determined.

The rehydration index

is

defined as the ratio of

sample weight after swelling to sample weight

before swelling.

ther Testing rinciples

ooking Test

During heating, food is

af-

fected in many ways, including development

of

textural changes.

In

general, some proteins

coagulate or degrade when heated; but other

proteins gel upon cooling. Cooking procedures

for the assessment

of

water-holding are mainly

applied for examining meat products. We

found no corresponding reports concerning

cooking tests for milk proteins, but for the

examination of meat this test can be of value.

A very simple procedure described is to cook

the sample under defined conditions and to

weigh it before and after cooking 128 . An

other cooking method has also

been

demon

strated for chicken meat 35 .

Nuclear Magnetic Resonance The nuclear

magnetic resonance NMR technique 26 has

increasingly contributed fundamental informa

tion to the understanding

of

the molecular

hydration behavior

of

colloidal biological sys-

8/10/2019 Pi is 0022030291783732

11/15

WATER-HOLDING CAPACTIY OF

M LK

PROTEINS: REVIEW

2037

terns.

n

addition, NMR was demonstrated to

be a valuable tool for exploring the molecular

structure

of

the casein micelles 26). As shown

by

these authors, the hydration water, non

freezable or mobile water as influenced by

interactions with macromolecules, can be in

vestigated by using this method. Although the

hydration water seems to have little or no

influence on the total water-holding properties

of products, the NMR technique enables the

characterization of other important properties

that partially determine water and protein in

teractions; e.g., the pore size distribution can

be regarded as one of these parameters 52).

i Nola and Brosio 24) tried to calculate

bound and free water in various powders from

the results obtained by pulsed NMR. However,

despite NMR, which enabled the detection

of

nonfreezable water within a defined matrix, the

water-binding results obtained by the pulsed

NMR technique were not sufficiently compa

rable with those results from other methods,

possibly due to different methods

of

data anal

ysis.

ON LUSIONS

Water is a major component of food, com

prising about 75 to 95 of many food prod

ucts. Apart from its influence upon organolep

tic properties, several microbiological and

physicochemical reactions are affected by this

constituent 66). Knowledge

of

the different

forms of water in food as well as of the

different possibilities

of

assessing it is still

incomplete. The way water affects the physical

nature of foods is complicated because of the

interactions between water and the medium,

which involve the physical structure and the

chemical components such as various solutes,

including polymers and colloidally dispersed

particles 90). Water in foods has been divided

into different classes and described in many

different terms. Physically, water content helps

to determine mechanical strength, elasticity,

plasticity, and flow of

food materials 74).

Therefore, in complex food matrices, these

parameters can be directly influenced by using

additives that promote or inhibit water-bind

ing. Because an increase in water-holding ca

pacity is one of the advantages arising from

the incorporation of certain milk: proteins in

food products, the use of these substances is on

the rise where they are legally permitted.

It is essential for both producers and users

of these substances to have methods available

that not only allow them to determine

their

products conform to established specifications

but also to determine the usefulness of their

products for the food manufacturing industry.

Testing under model conditions does not al

ways allow direct transferability

of

the data

obtained, but to a certain extent it can be

of

value. Nevertheless, one must be careful in

interpreting the data obtained by the different

tests when considering the methods used e.g.,

pressure methods and centrifugation tests), be

cause it may not be known whether water loss

is entirely due to the force applied

or

if it

originates in part from an alteration in the

internal structure of the material tested Fur

thermore, elastic samples may undergo defor

mation without losing water and can therefore

only be tested with difficulty. n such a case,

methods based on capillary suction measure

ments might offer some advantages. Hitherto,

no results using these methods with milk: pro

teins have been reported. Another problem of

the tests commonly applied is that the results

are often relative and expressed in different

units due to different principles of measure

ment.

To

circumvent this disadvantage, the

expression of the water-holding capacity

should be standardized in derIDed phys

icochemical units so that producers and users

will have comparable test results based on the

same units of measurement.

For the assessment of

milk:

proteins, appro

priate collaborative studies should be planned

in the future to compare the various methods

and to determine their applicability. Finally,

past experience has demonstrated the useful

ness of having two kinds

of

reliable standar

dized methods at one s disposal: a rapid initial

testing procedure using elementary laboratory

equipment and an in-depth test to be applied to

the final food mixture.

R F R N S

1A1jawad, L. S., and J. A. Bowers . 1988. Wat er

binding capacity

of ground Jamb-soy mixtures with

different levels of water and salt a

pi is 0022030291783732

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