Food Technology. Vol. 38, Num. 5.
May 1984. pp. 67-96.
Symposium: Gelation in Food Protein Systems
Analysis of Gelation in Egg Protein Systems
P.W. Gossett, S.S.H. Rizvi, and R.C.
Authors Rizvi and Baker are, respectively, Associate Professor,
Dept. of Food Science, and Professor and Chairmen, Dept. of Poultry
and Avian Sciences, Cornell University Ithaca, NY 14853. Author
Gossett formerly with Cornell, is a Scientist with The Pillsbury Co.
311 Second St. S E., Minneapolis, MN 55414
Based on a paper presented during the symposium, "Gelation in Food
Protein Systems," at the 43rd Annual Meeting of the Institute of
Food Technologists, New Orleans. La., June 19-22, 1984.
An important function of proteins in food systems is gelation.
This phenomenon involves the formation of a three-dimensional matrix
mainly through inter-protein hydrogen bonding and allows the
immobilization of water within the gel structure. The coagulation or
gelation of proteins—in particular, the irreversible,
heat-induced coagulation or gelation of egg proteins—often
controls the success of certain conked food products. It is of
interest to the food scientist to be able to quantitatively monitor
the gelation process to better predict end-product characteristics,
as well as understand the mechanism of network formation. A better
understanding of the gelation process will permit manipulation of
variables to obtain a gel of desired textural characteristics and
Although the coagulation, i.e., denaturation of proteins can be
brought about by heat, high pressure, salts, acids, alkalies,
alcohols, or denaturing agents such as urea (Mirsky and Pauling
1936), this article will concentrate on the quantitative analysis of
heat-induced coagulation or gelation of egg-albumen proteins (Table 1). Factors affecting the kinetic
parameters of gelation and the rheological properties of the gel
will be discussed, as well as methods used to measure gelation.
Table 1-PHYSICAL AND CHEMICAL
PROPERTIES of egg albumen proteinsa
||% in albumen
||Intrinsic viscosity (dL/g)
||Phosphoglycoprotein; denatures easily; has four
||Glycoprotein, complexes iron and other metals
||Glycoprotein, trypsin inhibitor |
||Glycoprotein, fibrous, viscous |
||Spherical protein; four disulfide bonds; lytic
||Inhibits trypsin and chymotrypsin |
||Binds riboflavin |
||Binds biotin |
a Adapted from Osuga and Feeney (1977) and Powrie
(1977); data refer to albumen from chicken eggs
b From Yang (1961)
c From Kuntz and Kauzmann (1974)
d From Vadehra and Nath (1973); ovomucoid pH 3.8-4.6;
ovomacroglobulin: pH 6-9
e From Fasman (1976)
A discussion of gelation necessitates defining some commonly used
terms associated with the phenomenon. At first glance, some of these
terms, may appear to overlap in meaning. However, each has its
particular role in this discussion.
- Denaturation is (1) the process in which a protein or
polypeptide is transformed from an ordered to a disordered state
without rupture of covalent bonds (Scheraga, 1961), or (2) any
process, except chemical modification, not involving rupture of
peptide bonds which causes a change in the three-dimensional
structure of a protein from its "native" in-vivo form (Haschemeyer
end Haschemeyer, 1973). Denaturation involves protein-solvent
interactions and leads to changes in physical properties, such as
loss of solubility of the protein. Sometimes unfolding of the
protein structure is considered part of denaturation.
- Aggregation is a general term referring to
protein-protein Interactions, with formation of complexes of higher
molecular weights Hermansson 1979). Aggregation is usually governed
by a balance between attractive and repulsive forces. Attractive
forces can involve hydrogen bonds, covalent bonds such as disulfide
linkages, and hydrophobic associations, whereas repulsive forces can
involve coloumbic forces which are affected by the net charge of the
protein molecule or the ionic strength of the solution (Egelandsdal,
- Coagulation is the random aggregation of already
denatured protein molecules (Hermansson, 1979), in which
polymer-polymer interactions are favored over polymer-solvent
reactions (Schmidt, 1981). The coagulum is often turbid, and the
formation of the coagulum is usually thermally irreversible (Shimada
and Matsushita, 1981). A coagulum may settle out of solution.
- Gelation. is an orderly aggregation of proteins, which
may or may not be denatured, forming a three-dimensional network
(Hermansson 1979). Polymer-polymer and polymer-solvent interactions,
as well as attractive and repulsive forces, are balanced such that a
well-ordered matrix can be formed (Schmidt, 1981). The gel may be
turbid or translucent; in the latter case, the gel may be
thermoreversible (Shimada and Matsushita, 1981). The term gelation
is also used in another context with respect to egg-yolk proteins.
The phenomenon of egg-yolk gelation refers to the formation of an
irreversibly gelled product upon freezing of the yolk (Cotterill,
1977). However, in this article, the term gelation will refer to the
former definition only.
Theory of Gelation
Attempts to describe the mechanism and theory of gel network
formation are numerous. The classic explanation of heat induced
aggregation of protein molecules is the following two-step process
Native protein -> denatured protein (long chains) ->
aggregated protein (associated network)
The first step is considered a denaturation process and the
second step an aggregation process. Comparison of the rate of the
denaturation step vs that of the aggregation step helps determine
gel characteristics. For example, Ferry (1948) suggested that for a
given rate of denaturation the rate of aggregation will be slow if
the attractive forces between the denatured protein chain are small.
The resulting gel will be a finer network of protein chains, will be
less opaque, and will exhibit less syneresis than one with a faster
rate of aggregation. A coarser network of protein chains yields an
opaque gel with large interstices capable of holding solvent which
is easily expressed from the matrix. Hermansson (1979) suggested
that conditions favoring denaturation, such as high or low pH, have
the opposite effect on aggregation of globular proteins, possibly
due to the fact that at high net charge, protein-solvent
interactions such as denaturation are favored, rather than
protein-protein interactions such as aggregation. A gel network with
a certain degree of order can be attained if the aggregation step
occurs more slowly than the denaturation step. thus giving the
denatured protein molecule, time to orient themselves before
aggregation; this is lower in opacity and higher in elasticity then
one where aggregation is not suppressed. Schmidt (1981) suggested
that if aggregation occurs simultaneously with denaturation, an
opaque. less elastic gel results.
Since the kinetics of the denaturation step relative to the
aggregation step appear to he important in determining the type of
gel produced, it is useful to review some kinetic terms that aid in
describing the gelation process:
l. Reaction Rate Constant. The first is the reaction rate
constant k (min -1), which is obtained from the
first-order relationship (Land, 1975):
- -- = kc
where c=concentration and -dc/dt=the rate at which concentration
decreases. Integrating between limits et at time l=U and c et time t
A plot of ln c vs t gives a line of slope -k.
The rate constant may be temperature dependent, end this
dependence of reaction rate constant on temperature can best be
described by the Arrhenius equation:
k=S exp (-Ea/RT)
where s=frequency factor (min -1), e.=activation
energy (cal/mole). r=gas constant (1.987 cal/mole.°K), and
t=absolute temperature (°K). A plot of In k vs 1/T gives e
straight line of slope -Ea/R.
2. Z Value. Another useful kinetic quantity in describing
the temperature dependency of the reaction rate is the Z value,
which a defined as the necessary rise in heating temperature
(°C) needed for a 10-fold increase in the reaction rate
(Dagerskod, 1977). If some parameter of the gelation process is
measured, say heating time to reach a certain gel strength, then the
Zc value is the temperature rise needed to increase the
heating time or reaction rate 10-fold, This value is useful in
calculating the cook value, which is the time required at
temperature T for a sample with a certain Zc value to
receive a heat treatment equivalent to 1 min at 100°C
(Dagerskod, 1977). To quantitate gelation, it in useful to coagulate
samples to equal cook values to ensure equivalent heat treatment
Factors Affecting Gelation
Many researchers have tried to identify the factors which effect
aggregation of proteins, since altering the rate of aggregation
relative to the rate of denaturation appears to affect gel
characteristics. The following are some of the factors which have
- Electrostatic Charge is one of the must commonly
investigated factors. The pH as well as the ionic strength of the
protein environment can alter the charge distribution among the
amino acid side chains and can either decrease or increase the
protein-protein interaction,. Nakamura et al. (1978) concluded that
the main factor contributing to the heat-induced aggregation of
ovalbumin (pI 4.5-4.6) is the degree of electrostatic repulsion
among the denatured protein molecules. When the heat-denatured
protein concentration is high (>0.5%), the aggregate size
decreases as the pH increases from 5.8 to 10.0; this is due to
increased repulsive forces among the protein molecules at the
alkaline pH levels. Conversely, decreasing the pH or adding cations
decreases the negative charge end accelerates aggregate formation,
as does increasing the ionic strength.
Shimada end Matsushita (1980a; 1981) found that the turbidity of
a 4.5% protein solution (3.6% ovalbumin, 0.9% conalbumin) heated
for 15 min at 80°C decreases as the pH increases from 8 to 11,
after which no turbidity is observed. Hardness of the gel is a
maximum at pH 8.5 and decreases on either side of this pH. The
turbidity increases upon addition of cations (Ca++
>> Li+ > Na+
Cs+) to a 2.8% albumin solution heated for 30 min at
80°C. Anions increase the turbidity in the alkaline pH regions
(SO4= > Cl- > Br-
> I- > SCN-). Salts shift the critical pH for
coagulant formation to alkaline pH levels as ionic strength
increases, perhaps by decreasing the amount of water bound to the
albumin and making it less soluble (Bull and Breese, 1970) or by
decreasing water protein interactions and increasing protein-protein
Holme (1963) observed that the rate of aggregation of heated l.8%
ovalbumin solutions is higher at pH 5.5 and 8.5 then at pH 7.0.
However, at pH 5.5 the development of turbidity is rapid, with
actual precipitation of the protein and slight increases in the
levorotation and intrinsic viscosity of the supernatant, while at pH
8.5 there is slight turbidity and marked increases in levorotation
and viscosity of the clarified solution.
Hegg et al. (1979) found from differential scanning calorimetry
measurements that the denaturation temperature for a 4.4% ovalbumin
solution increases from 62°C at pH 3 to 79°C at pH 6-10 but
decreases to 77°C al pH 11. The aggregation temperature, defined
as the temperature at which 10% of the protein has aggregated, was
found to be 65-70°C at pH 4.0-5.5. The fact that aggregation
only occurs around the isoelectric point implies that aggregation
behavior is determined by the number of net charges on the ovalbumin
molecule. When 1% NaCl is added to the ovalbumin, aggregation occurs
at conditions ranging from 53°C at pH 3 to over 85°C at pH
11. The relationship between denaturation temperature TD
and aggregation temperature TA determines the quality of
the thermal aggregates; if TA is 6 -7°C lower than
TD, precipitates of over 13% dry matter result; if
TA is 4-6°C lower than TD, gel-like
precipitates of 9-13% dry matter appear: if
TD-TA is 2-4°C, opaque gels of 5-9 % dry
matter form; and if TD-TA is 1-2°C or
negative, transparent gels of less than 5% dry matter are found.
Unlike Ferry (1948), Hegg et al. (1979) implied that aggregation
takes place prior to denaturation, at all pH levels except pH 11,
but that TD-TA decreases as pH is increased.
At pH 10.5, denaturation and aggregation are predicted to occur
simultaneously. Hegg and Lofqvist (1974) hypothesized that at
extreme pH values or upon addition of anionic detergents the greater
number of charged groups of the same sign repel each other and cause
the protein to expend. The expanded molecules also repel each ether
and thus hinder aggregation.
When liquid egg white is heated at 58°C for 5, 15, 30, and 60
min, the optical density decreases as the pH increases from 6.0 to
10.0 (Seideman at al., 1963); this agrees with analogous work using
dilute albumin solutions. Egg white containing 50% sucrose requires
a higher temperature for coagulation, which is also pH
- Protein Concentration is also a factor affecting
aggregation. Nakamura et al. (1978) found that almost all of the
protein aggregates, regardless of concentration, when ovalbumin is
heated at 80°C. About 80% of the protein (pH 6.2) heated at
75°C for 5 min aggregates, regardless of albumin concentration;
but at 70°C, a concentration of at least 1% is required for
aggregation. A higher protein concentration is probably needed to
allow a closer association of molecules for aggregate formation at
the lower temperatures.
Shimada and Matsushita (1980a; b) observed that as albumin
concentration increases from 0.09%, to 12.5%, turbidity of the
solutions heated at 80°C for 15 min is observed over a wider pH
range. The pH required for equal turbidity increases as the protein
concentration increases on the alkaline side of the isoelectric
point from pH 6 to 11, and decreases on the acidic side from pH 4.5
- The Formation of Disulfide Bonds and the exposure of
hydrophobic amino acid residues are thought to be involved in the
first step of coagulation (Shimada and Matsushita, 1980a; b).
Proteins with higher percentages of hydrophobic amino acids are
classified as coagulation-type proteins and concentration dependent,
while proteins with a lower percentage are gelation-type proteins
and concentration independent. Further heating causes egg albumin to
polymerize by intermolecular sulfhydryl-disulfide, exchange, forming
a network (Buttkus, 1974; Shimada and
Matsushita, 1980b). However, Hegg (1982)
has indicated that many globular proteins with differing sulfhydryl
convents can form heat induced gels and that no correlation between
disulfide or sulfhydryl .content and gel-forming ability can be
- The Composition of the albumin mixture also
affects the aggregation of the proteins. Denaturation temperatures
of conalbumin, globulins, ovalbumin, and lysozyme are 57.3, 72.0,
71..5, and 81.5°C, respectively, while ovomucin and ovomucoid do
not coagulate (Johnson and Zabik. 1981). The gel strength of the
lysozyme gel is the highest, followed by that of globulin.
Conalbumin gels exhibit the most drainage. In binary mixtures of
albumin proteins, aggregation occurs near the denaturation
temperature of the least-heat-stable protein. The lysozyme-globulin
gel is the firmest, while the ovomucoid-ovalbumin gel is the least
firm. Ovomucoid combinations exhibit high drainage.
Table 2-APPARENT VISCOSITY
AND YIELD FORCE (20°C) for albumen at pH 9.0 heated at various
temperatures and for albumen at different pH levels heated at
||Heating temperature (°C)
||Apparent viscosity (Poise)
||Yield force (dynes x 106 |
||80 ± 12b
||3.6 ± 0.9b |
||156 ± 59bc
||7.5 ± 0.1c |
||230 ± 13cd
||7.7 ± 1.3c |
||235 ± 15d
||11.6 ± 1.4d |
||333 ± 29e
||10.2 ± 1.6d |
||117 x 39b
||5.1 ± 1.1b |
||128 ± 39bc
||6.3 ± 1.5b |
||156 ± 59bc
||7.5 ± 0.1b |
||278 ± 29cd
||12.2 ± 2.4bc |
||330 ± 122de
||19.7 ± 9 3c |
||476 ± 153e
||18.5 ± 8.4c |
Measurement of Heat-Induced Gelation
Many methods for measuring gelation involve testing individual
samples after discrete time intervals of heating until coagulation
or gelation is completed. Some of the methods which have been used
are discussed below:
- Gel Strength. A common method is to measure gel
strength or firmness of the gel after various heating times. The
rigidity of heat-induced 8.2% ovalbumin gels, as in measured by the
initial slope of a force-distance curve given by a compression test
on the Instron Universal Testing Machine, varies with the pH of the
solution, with maximum gel strength exhibited an either side of the
isoelectric point (Egelandsdal, 1980). Using the Instron force
applied to a probe when the surface yield point of a gel is reached
as an indicator of gel strength, Dunkerley and Hayes (1980) showed
that the gel strength of egg white at pH 7.0 is at a maximum of 2.3
Newtons (N) at 85°C; 1.3 N at pH 7 and 90°C; and 8.5 N at pH
9.3 end 92-95°C. Beveridge et el. (1980) measured firmness of
albumen coagulum as the maximum force required to shear a sample in
a shear compression cell; they found that coagulant shearing force
increases by approximately 0.1 kg of force/min of heating (0-60 min)
and with temperature (77-90°C). The increase in firmness is not
a linear function of temperature; the higher temperatures produce
gels considerably firmer then those at lower temperatures. Hickson
et al. (1982) used an annular back-extrusion device attached to an
Instron machine to measure the penetration force, viscosity index,
and apparent elasticity of egg albumen gels heated at 80°C. They
found that the penetration force and viscosity index increase at the
rate of 0.0625 N/min and 8.75 Poise/min, respectively, up to 80 min
of heating, after which decreases are observed. Elasticity increased
from 0 to 30 N/cm2 after 120 min of heating. Shimada ad
Matsushita (1980,) determined hardness of albumin gels from profile
analysis of the first chew as measured on a Texturometer using a
"visco-type" plunger and a 24-mm-diameter cup; they found that
coagulum begins to form 3 min after heating at 80°C and that
hardness reaches 300 kg of force after 12 min.
Using a capillary extrusion apparatus fitted to an Instron
machine, Gossett (1983) and Gossett et
al. (1983a) measured the apparent viscosity and yield force of
albumen gels at various pH levels and heating temperatures; they
found that gel strength increases with increasing pH and with
increasing heating temperature (Table 2).
- Solubility. The change in solubility of a heated
protein system has also been monitored as an indicator of the
coagulation or gelation process. Upon heating at 80°C, the
turbidity, measured as absorbance at 600 nm, of a 4.5% solution of
egg albumin was shown to increase rapidly within the first minute,
then slowly (Shimada and Matsushita, 1980a). Seideman et al. (1963)
found that the optical density of egg white at 550 nm increases with
time of heating (58°C, 0-60 min) and increases more rapidly with
decreasing pH (8.0-10.5).
- Gravimetric Analysis. Gravimetric analysis of the
coagulum or the supernatant after centrifugation has been another
method of following the coagulation process. Recovering or
separating the precipitate or coagulum from the solution can be
difficult because the precipitates can vary from rapidly sedimenting
flocculates to nonsedimenting, sol-like opaque aggregates (Hegg et
al., 1978). To follow thermal precipitation of protein solutions,
Hegg et al (1978; 1979) removed volumes of solution at various time
or temperature intervals of heating, centrifuged the solution, and
calculated the percentage of aggregated protein as the decrease in
absorbance of the supernatants at 380 mm. For slower-sedimenting
plateaus, absorbance at 340 nm (opalescence) of the supernatants was
measured (Hegg et al., 1978).The weight of the aggregate can also be
monitored and the dry matter content DM calculated by the following
equation (Hegg et al., 1979):
where, C0 =initial protein concentration,
V0 =initial solution volume, a= percent aggregation and
Wa = weight of the aggregate. Nakamura et a1. (1978) have
measured the amount of aggregated proteins as the difference between
the soluble protein concentration before and after heat treatment
- Formation of Disulfide Linkages. Chemical
properties such as the formation of disulfide linkages can be
determined as coagulation proceeds. Shimada and Matsushita (1980a)
measured the number of free sulfhydryl groups with
5,5'-dithiobios(2-nitrobenzoic acid) (DTNB) on solutions of
dissolved albumin coagulums formed by heating 4.5% solutions at
80°C; the number of moles of SH groups/105 g of
protein decreased from 5 to 3.5 after 1 min of heating and reached a
plateau of 3 after 5 min.
Fig. I -Typical Plots of electrobalance force vs
time of heating for egg albumen (PH 9.0) at various temperatures of
hearing. Plots shown terminate at or shortly after maximum force
- Electrophoresis. The disappearance or appearance
of different polyacrylamide gel electrophoretic (PAGE) bands of
proteins with different heating time and temperatures has been
observed. Matsuda et al. (1981a) found that the intensity of bands
for ovalbumin (at pH 7 and 9), ovotransferrin (pH 7), globulins Al,
A2, and G3A (pH 7 and 9), and flavoprotein (pH 7 and 9) decreases
with heating time (0-60 min) but for ovotransferrin (pH 9) and
ovomucoid (pH 7) remains constant. At pH 7, bands of ovotransferrin
disappear at around 60°C; globulin G3A, 65°C; ovalbumin,
80°C; globulins A1 and A2, 84°C; and flavoprotein, 85°C;
ovomucoid does not disappear. Shimada and Matsushita (1980a) used
sodium dodecyl sulfate PAGE to show that the relative amount of
monomeric ovalbumin decreases rapidly after 5 min of heating and
continues to slowly decrease up to 15 min, with the amounts of
polymerized proteins increasing with heating time.
- Structural Changes. The denaturation step of the
gelation process has been studied by observing structural changes of
egg protein solutions upon heating. The reduced viscosity of a 1.8%
ovalbumin solution increases with temperature of heating above
65°C and with time of heating (Holme, 1963). Removal of the
aggregate by centrifugation yields supernatants with reduced
viscosities and levorotation similar to those of the native,
unheated solutions; this indicates that the intermediate denatured
species of ovalbumin is rapidly converted to aggregates upon
heating, since only aggregated and native molecules are present in a
headed solution. Matsuda et al. (1981b) used circular dichroism at
222 nm and ultraviolet absorption at 287 nm to study heat induced
structural changes and unfolding in ovomucoid, a very heat-resistant
egg protein. Denaturation of egg white has also been studied using
differential scanning calorimetry (Donavan et al., 1975); egg white
(at pH 7) heated at 10°C/min exhibits two endotherms-one at
65°C (conalbumin) and the other at 84°C (ovalbumin).
New Method Developed
The above methods for measuring heat-induced coagulation do have
certain limitations, one of which is the need to make single-point
measurements on many samples at different time intervals throughout
the process to obtain a continuous view of the phenomenon. These
samples must be [cooled?] instantly; otherwise the coagulation
process con[tinues?] another limitation of some gel-strength or
gravimetric measurements is that the sample is destroyed during the
measurement. Yet another limitation is that for some turbidity
measurements, once the sample becomes opaque, no further change is
registered by the spectrophotometer despite continuing changes in
gel characteristics. Furthermore, a gel can be clear end still
exhibit increasing gel strength with time.
With these limitations in mind, we devised a new method to
quantitate, the gelation process (Gossett et al., (1983b). This
nondestructive technique requires only one sample to observe the
total process. It involves continuous monitoring of the force
exerted by the gel as coagulation takes place and can be used to
obtain kinetic data on the heat-induced gelation of egg albumen.
The technique uses a recording electrobalance from which a wire
probe is suspended into a jacketed cylinder containing the albumen
sample. The cylinder is connected to a water bath maintained at the
appropriate temperature, and, as coagulation occurs with time, the
force exerted by the gel on the probe as the matrix forms is
recorded on e linear recorder.
Typical electrobalance force-vs-time curves (Fig.
1) for albumen heated at temperatures from 60 to 95°C show
that the force increases until a maximum force is observed. For some
treatments, however, there are decreases in force after the maximum
force is attained; this is thought to be due to expansion of the gel
once the gel coagulates—the expansion may have raised the
probe and caused a decrease in observed force.
Table 3-FIRST-ORDER RATE
CONSTANTS for heat coagulation or albumen under various
||Water bath temperature (°C)
||k1 (min -1 )
||k2 (min -1 )
||Timeb (min) |
||0.037 -± 0.008d
||4.83 ± 1.36 |
||0.377 ± 0.150d
||0.036 ± 0.006d
||5.44 ± 1.88 |
||0.421 ± 0.143de
||0.046 ± 0.012d
||4.42 ± 1.11 |
||0.051 ± 0.011d
||4.54 ± 1.51 |
||0.617 ± 0.083ef
||0.064 ± 0.026
||3.01 ± 0.49 |
||0.662 ± 0.04f
||0.067 ± 0.021
||3.09 v 0.14 |
||0.157 ± 0.010e
||2.04 ± 0.33 |
||1.223 v 0.12g
||0.231 ± 0.089f
||1.59 ± 0.45 |
|Ave. r2 for regression
||0.347 ± 0.145d
||0.102 ± 0.021 d
||4.42 ±1.13 |
||0.434 ± 0.056d
||0.071 ± 0.020e
||3.69 ± 0.69 |
||0.617 ± 0.083de
||0.064 ± 0.026 e
||3.01 ±0.49 |
||0.923 ± 0 419ef
||0.049 ± 0.020 e
||1.80 ± 0.23 |
||0.983 ± 0.328ef
||0.044 ± 0 0.015 e
||1.76 ± 0.41 |
||0.820 ± 0.175'f
||0.036 ± 0.018 e
||2.02 ± 0.20 |
|Ave. r2 for regression
||0 93 |
a Quadruplicate determinations. From Gossett )1983),
Gossett et al. (1983b)
b Time at which first step "ends" and second step
defg Means in the same column within a set that are
followed by different superscripts are significantly different (P
Fig. 2-PLOT OF ln FORCE VS TIME showing rate
constants k1 and k2 and the time t where the
first step "stops" and the second step "starts." From Gossett at al.
Rate constants for albumen (at pH 9) heated at 60-9.5°C and
for albumen (pH 7.0-11.0) heated at 80°C are shown in Table 3. First-order kinetics and the existence
of two reactions during the heat-coagulation of the albumen, as
su[illegible] by the broken-line curve in Figure
2, yielded rate [constants] k1 and k2 and
were obtained by best r2 fit If k1 is
interpreted to be the rate constant for the denaturation process and
k2 the rate constant for the aggregation process, then
the data suggest that the denaturation end aggregation rates both
increase with increasing heating temperatures. The time at which the
first step "ends" and the second step "starts" is found to decrease
with increasing heating temperature; this suggests that at higher
temperatures, denaturation occurs faster and the onset of
aggregation is expedited. With increase in pH, rate constants for
denaturation increase but those for aggregation decrease; the
results agree with those of Nakamura et al. (1978) and Hermansson
(1979), who suggested that aggregation is decelerated at higher pH
Fig 3-ARRHENIUS PLOTS for rate constants
k1 (r=0.94) and k2 r=0.931) From Gossett et
Activation energies for the rate constants were calculated using
the Arrhenius relationship; Figure 3 shows
Ea to be 8.7 kcal/mole for the denaturation step and 14.4
kcal/mole for the aggregation step (Dwek and Navon, 1972, estimated
Ea for the denaturation of egg albumen to be
approximately 24 kcal/mole). In addition, a Zc value of
41.7°C was calculated by plotting the ln of the heating time
required to reach a certain force value vs the heating
Although this method offers the advantage of using just one a
ample to continuously observe the gelation process, there are
presently some limitations to the technique. The true source and
physical meaning of the measured force are not yet understood and
should be a topic of future research. Change. in the geometry of the
gelling apparatus need to be explored to differentiate between the
contribution of gelation and that of thermal expansion to the force.
Lastly, optimization of probe design for various gel types would be
The gelation of food proteins is important to textural and
rheological characteristics of a food product. Future, research
should be directed toward finding quick, reliable methods that
quantitate the gelation phenomenon so that food scientists can
better manipulate the process to obtain desirable, high-quality
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Bull, H.B. and Breese, K. 1970. Water and solute
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the nature of the chemical and physical bonds which contribute to
some structural properties of protein foods: A hypothesis. J.
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