Milk Reactivity of Gum and Milk Protein Solutions1
K. A. SCHMIDT and D. E. SMITH2
Department of Food Science and Nutrition
University of Minnesota
St. Paul 55108
ABSTRACT
INTRODUCTION
Milk reactivity, defined as the ability
of a gum to produce significantly higher
viscosity in milk than in water, was determined for three gums--carrageenan,
guar, and xanthan-at .05, .1, and .2% in
both NOM and whey protein concentrate
(reconstituted to 11 % solids). Batch
(69·C for 30 min) and HTST (80·C for
25 s) heat treatments were also studied.
Milk reactivity was demonstrated in
batch-heated solutions as follows. The
apparent viscosities of carrageenan-NOM
and carrageenan-whey protein concentrate solutions were higher than those of
carrageenan-water solutions I;'t all three
gum concentrations. Guar at .1 % was
more viscous in whey protein concentrate than in water. For HTST, carrageenan exhibited milk reactivity with NOM
and whey protein concentrate at .1 and
.2%. Guar exhibited milk reactivity with
NOM at .2% and with whey protein
concentrate at all three gum concentrations. Xanthan exhibited milk reactivity
with whey protein concentrate at .05%.
(Key words: proteins, gums, milk reactivity, viscosity)
At equal concentrations, gums exhibit milk
reactivity by producing significantly higher
viscosities in milk than in water. Because the
viscosity increase is greater than the viscosity
difference between water and milk, the increase is attributed to the interactions between
the hydrocolloid and dairy proteins (4). Milk
reactivity may be an important criterion in
choosing stabilizers in frozen dairy desserts or
for new dairy-based "value added" foods. By
definition, milk reactivity can be easily evaluated using statistics, i.e., statistically significant higher viscosities in milk than in water at
equal gum concentrations.
In 1%1, Loewenstein (8) received a patent
to produce a dairy protein powder using
hydrocolloids. The process involved reacting a
hydrocolloid with milk or skim milk, collecting the precipitate, and producing a milk powder with unique functional properties. Hansen
(5) reported the interaction between l(carrageenan (CGN) and as-casein protein.
Other researchers looked at this interaction and
at interactions involving different hydrocolloids and dairy proteins. Using electrophoresis,
Hansen (6) showed that CGN could stabilize
the as-casein fraction against precipitation because of the interaction between the hydrocolloid and casein.
Grindrod and Nickerson (4) used PAGE to
study interactions among hydrocolloids and
dairy proteins and showed that CGN and furcellaran reacted with as-casein.
In 1977, Magsam (9) studied interactions
between dairy proteins and guar, xanthan, and
guar-xanthan blends. Gums were dispersed in
NOM, whey protein concentrates (WPC), or
water; apparent and basic viscosities of the
solutions were measured to determine milk
reactivity. Results showed that guar and xanthan had high milk reactivity with NOM and
WPC; WPC solutions were more viscous than
the corresponding NOM solutions.
Cottrell et al. (1) reported on the CGNcasein interaction by comparing relative vis-
=
Abbreviation key: CGN carrageenan, WPC
protein concentrate.
= whey
Received September 16, 1991.
Accepted July 15, 1992.
lPublished as Paper Number 18,792 of the Scientific
Journal Series of the Minnesota Agricultural Experiment
Station on research conducted under Minnesota Agricultural Experiment Station Project Number 18-24. The
University of Minnesota Computer Center and Minnesota
South Dakota Dairy Center also supplied funding for the
research.
2To whom correspondence should be addressed.
1992 J Dairy Sci 75:3290-3295
3290
MILK REACTIVITY
cosities of ice cream mixes. Relative viscosity
is the ratio of the viscosity of the solution to
the viscosity of the solvent. Of the five gums
studied, only CGN appeared to interact with
the casein fraction.
Because alternative milk bases and gums
are utilized in the dairy foods industry, it is
important to study the interactions of other
gums with whey and with casein proteins.
Therefore, this study was undertaken to determine whether I) guar or xanthan could exhibit
milk reactivity similar to that of CGN gum,
and 2) CGN, guar, and xanthan gums could
exhibit milk reactivity with WPC that had a
similar gross composition to NOM. Both batch
and HTST pasteurization systems were considered.
MATERIALS AND METHODS
Preparation of Solutions
Low heat NOM (Mid-America Dairy,
Springfield, MO), 34% protein WPC (Foremost Whey Products, Plover, WI), and doubledistilled, deionized water were the three bases
of the solutions. Double-distilled, deionized
water was included to determine milk reactivity. Milk powders were rehydrated at room
temperature to 22% (wtIvol) with doubledistilled, deionized water using an Osterizer
blender (Sunbeam Corp., Milwaukee, WI) and
left overnight at 4·C to allow for full hydration. Guar, sodium salts of lC-CGN, and xanthan were from Sigma Chemical Co. (St.
Louis, MO). Gums were dispersed at room
temperature in double-distilled, deionized water with rapid agitation to make a 1.2% (wt/
vol) solution. Gums were rehydrated overnight
at 4·C.
The following day, gum-milk protein solutions were prepared as follows. The WPC or
NOM solutions were heated on a magnetic stir
plate to 40·C with constant agitation and
diluted to 11 % solids with the appropriate
amount of gum solution and water. The desired
gum concentrations were .05, .1, and .2% wt/
vol. If the sample was batch pasteurized, the
solution continued to be heated until it reached
67·C and then was placed in a 70·C water
bath; once the solution reached 69·C, it was
held for 30 min. The HTST pasteurized solutions were heated to 64·C on a magnetic stir
3291
plate with constant agitation and then heated
(80·C for 25 s) in a laboratory-scale HTST
system. Immediately following batch or HTST
pasteurization, solutions were cooled to less
than 20·C in 1.5 min in a laboratory-scale
cooling system, and samples were collected
and stored at 4·C. Solutions without gums
were run for controls as described.
Viscosity Measurements
Apparent viscosities of the solutions were
determined the following day. Samples were
analyzed at 4·C using a Haake Rotovisco Viscometer fitted with a MVI sensor system and
an MK 50 measuring head (Haake Buchler,
Saddle Brook, NJ); a Haake 86A refrigerated
water bath (Haake Buchler) was used to maintain a constant temperature throughout testing.
Shear stress was determined over a shear rate
range of 1 to 865/s using a Haake PG 142
programmer (Haake Buchler) to increase shear
rate. A plotter (model 7040A; HewlettPackard, San Diego, CA) recorded the shear
stress and shear rate curve for each solution.
Apparent viscosity was then calculated for
each solution at a shear rate of 250/s (7, 12).
Apparent viscosities were reported in centipoise.
Experimental Design
The experimental design was a split plot:
gum type was the whole-plot treattnent; gum
concentration and solution base were split-plot
treattnents. All solutions were split-plot treatments. All solutions were random (all proteinconcentration combinations), so there was no
structure within the split plot. Analysis of variance was performed to determine significant
effects at P = .05 using SAS (10). All significant effects and interactions were further analyzed with the Bonferonni mean comparison
test to determine differences among treattnent
means using P = .05. Three replications were
done. Heat treattnents were analyzed
separately.
For the relative viscosities, analyses of variance were performed to determine the significant effects at P = .05 using SAS (10). To
determine milk reactivity, Dunnet's test was
run to compare each solution with the corresponding water-gum concentration.
Journal of Dairy Science Vol. 75, No. 12, 1992
3292
SCHMIDT AND SMITH
TABLE 1. Analysis of variance of log viscosity for gum x protein (Prot) x concentration (Cone) for batch and HTST
heat treatments.
Heat treatment l
df
MS
Batch
Replicate
Gwn
Between error
Prot
Cone
Prot x Cone
Gum x Prot
Gum x Cone
Gum x Prot x Cone
Within error
2
2
4
2
2
4
4
4
8
48
.008
.307
.010
1.505
1.689
.007
.493
.024
.008
.003
HTST2
Replicate
Gum
Between error
Prot
Cone
Prot x Cone
Gum x Prot
Gum x Cone
Gum x Prot x Cone
Within error
2
2
4
2
2
4
4
4
8
48
.004
.077
.002
2.608
1.587
.062
.409
.019
.040
.005
.Coefficient of variation
2Coefficient of variation
= 5.60;
= 6.81;
MS error
MS error
F
.809
30.7
P
.424
<.001
488.7
548.44
2.43
160.23
7.79
2.73
<.001
<.001
.05
<.001
<.001
.047
2.0
38.5
.25
<.001
652.0
317.4
12.4
81.8
3.8
8.0
<.001
<.001
<.001
<.001
<.001
<.001
= .0036.
= .0048.
RESULTS AND DISCUSSION
To analyze the data correctly, the apparent
viscosity values were transformed to the log
scale (base 10), which is the standard method
for analyzing viscosity data (3). Log increases
in viscosity corresponded to linear increases in
gum concentration (3). The analyses of variance of batch and HTST treatments are shown
in Table 1. All main effects, two-factor interactions, and the three-factor interaction were significant.
When different gums were simultaneously
compared at more than one concentration in
different protein solutions, a significant threefactor interaction in the ANOVA indicated
milk reactivity. Only the three-factor interaction showing milk reactivity is discussed
herein. Other significant interactions are discussed more fully elsewhere (11).
Transformed (1oglO) apparent viscosities are
shown in Table 2. Bonferonni mean comparisons were used to compare the same gum at
the same concentration in different base solutions. Milk reactivity results are summarized in
Table 3.
Journal of Dairy Science Vol. 75. No. 12. 1992
For batch heat treatment, only CGN showed
milk reactivity at all three gum concentrations
with NDM and WPC. Guar exhibited milk
reactivity with WPC at .1%. These results
differ from those of Magsam (9), who found
milk reactivity with guar and xanthan gums in
both NDM and WPC. These differences could
be attributed to the differences in the study
design and analysis. The results in this study
suggest that gum concentration and protein
source are important parameters for milk reactivity. Perhaps conditions such as gum and
protein concentration need to be optimized to
allow for maximum interaction between the
hydrocolloid and protein. If the gum to protein
concentration is
not optimized, then
hydrocolloid-hydrocolloid or protein-protein
interactions may predominate, thus affecting
milk reactivity.
The HTST results differed from the batch
heat treatment. The CGN exhibited milk reactivity only with NDM and WPC at .1 and .2%.
Guar exhibited milk reactivity with WPC at all
three gum concentrations, whereas xanthan exhibited milk reactivity with WPC at .05%.
These results suggest that gum concentration
3293
MILK REACTIVITY
and protein source are important parameters to
optimize milk reactivity properties of gums.
Milk reactivity has also been determined by
evaluating the relative viscosities of the solutions (l). Relative viscosity is the ratio of the
apparent viscosity of the solution to the apparent viscosity of the solvent. In this case, the
solvent is NOM, WPC, or double-distilled,
deionized water. Analyses of variances were
performed on these data. To interpret these
data, relative viscosities of solutions with proteins are compared with the corresponding solutions containing water. High relative viscosities indicate that solvent-solute interactions are
occurring. Therefore, Dunnet's test was conducted on the mean relative viscosities to de-
TABLE 2. Apparent viscosities (loglO) (centipoise) for
batch and HTST heat treatments of solutions of selected
gums with water, NDM. and whey protein concentrate
(WPC).I
Heat
treatment
Guar
Xanthan
.478
.648
.853
.561
.773
1.138
.745
.943
1.146
1.335*
1.608*
1.950*
1.009
1.009
1.346
1.003
1.003
1.261
.933*
1.331 *
1.625*
.850
1.078*
1.409
.957
1.126
1.336
.439
.483
.721
.543
.777
1.040
.441
.851
1.022
NDM
.05%
.1%
.2%
1.031
1.502*
1.891 *
.754*
.900*
1.332*
.786
.985
1.312
WPC
.05%
.1%
.2%
1.045
1.209*
1.617*
1.265*
1.363*
1.549*
1.125*
1.169
1.289
Batch2
Water
.05%
.1%
.2%
NDM
.05%
.1%
.2%
WPC
.05%
.1%
.2%
HTST3
Water
.05%
.1%
.2%
Carrageenan
INDM and WpC reconstituted to 11% solids.
2MS Error = .0036.
3MS Error = .0052.
*Means are significantly different from the corresponding water-gum concentrations (P ~ .05).
TABLE 3. Milk reactivity for batch and HTST heat treatments.
Heat
treatment
Batch
Carrageenan, .05, .1, and .2%.
Guar, .1%
HTST
Carrageenan, .1 and .2%
Guar, .05, .1, and .2%
Xanthan, .05%
Reactivity
NDM > water
Wpcl > water
WPC> water
NDM >
WPC >
WPC>
WPC>
WPC >
water
water
water
water
water
Iwpc = Whey protein concentrate.
termine which protein-gum-concentration exhibited milk reactivity. Results are shown in
Table 4.
When the relative viscosity method is
evaluated, gum-protein interactions occur in
the following solutions. For batch-heated samples, CGN showed milk reactivity in NOM at
all three concentrations and with WPC at .1
and .2%. For HTST samples, CGN showed
milk reactivity at all three concentrations with
NOM and WPC. Guar in WPC exhibited milk
reactivity at all three gum concentrations,
whereas xanthan exhibited milk reactivity with
WPC at .05%.
Overall, the results of the two methods
agree (statistical analysis of three-factor interaction and relative viscosity analysis). Only the
statistical analysis indicates that milk reactivity
occurs in the batch-WPC-guar-.l % solution,
whereas results of the relative viscosity approach does not indicate milk reactivity. This
discrepancy between the methods may be due
to the risk that is taken with a stated P value,
i.e., the risk of reporting a significant difference when none exists.
These results are in agreement with previous research. The CGN requires high temperatures and long periods to achieve maximal
hydration and reactivity. Batch heat treatment
is an excellent time and temperature combination for CGN (4, 5, 6). When the casein-CGN
interaction was investigated, previous research
emphasized heat treatments similar to batch
pasteurization. Guar gum is more compatible
with HTST processing than with batch
Journal of Dairy Science Vol. 75, No. 12, 1992
3294
SCHMIDT AND SMITIi
processing conditions because guar decomposes and loses some of its viscosity-building
effects when exposed to high temperatures for
long periods (13). These changes could account for the ability of guar to have greater
milk reactivity in HTST solutions than in batch
solutions. The viscosity of xanthan gum is
relatively independent of temperature treat·
ments but more sensitive to solute composition.
Some dairy proteins are also heat sensitive;
for example, whey proteins denature at 80'C
(2). Denaturation causes conformational
changes in the protein that may alter the viscosity and may expose additional or alternate
binding sites, which may have occurred in the
TABLE 4. Relative viscosity for balch and mST heat
treatments.
Heat
treatment
Guar
Xanthan
1.612
2.383
3.819
1.950
3.176
7.359
2.978
4.708
7.493
NOW
.05%
.1%
.2%
5.56010.56022.910-
1.562
2.625
5.702
1.982
2.589
4.686
WPO·3
.05%
.1%
.2%
2.203
5.50910.841-
1.820
3.077
6.599
2.329
3.434
5.573
Batch l
Water
.05%
.1%
.2%
mST"
Water
.05%
.1%
.2%
Carrageenan
1.473
1.628
2.817
1.869
3.203
5.870
1.478
3.797
5.635
NOM
.05%
.1%
.2%
2.7618.16720.000-
1.457
2.041
5.522
1.571
2.483
5.272
WPC
.05%
.1%
.2%
2.8514.15910.643-
4.7335.9309.100-
3.4273.792
5.000
lMS Error = 11.87.
2NDM and WPC reconstituted to 11 % solids.
3WPC = Whey protein concentrate.
4MS Error = 10.36.
-Means are significantly different from the corresponding water-gum concentration (P S .05).
Journal of Dairy Science Vol. 75. No. 12, 1992
HTST-guar-WPC solutions with higher viscosities. Caseins are less sensitive to heat treatments, and this protein behavior appeared to be
important for milk reactivity when the HTST
treatment of WPC exposed additional binding
sites and thus enhanced the milk reactivity
properties of guar and xanthan gums.
CONCLUSIONS
This study showed that all three gumsCON, guar, and xanthan gum-possessed milk
reactivity with both NOM and WPC, suggesting that both the whey proteins and casein
proteins have the ability to interact with
hydrocolloids. However, the reactivity appeared to be highly dependent on gum concentration and on heat treatment. Optimization of
the protein:gum ratio may be necessary to
maximize the reaction between the hydrocolloids and proteins to produce viscous solutions.
Whey proteins were able to interact with
CON, guar, and xanthan gum. This interaction
may have implications in frozen dairy desserts
or dairy-based, value added foods in which
high viscosities may be required for products
to enhance product stabilization.
A comparison between a statistical approach and relative viscosity approach to determine milk reactivity of gums showed agreement.
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Journal of Dairy Science Vol. 75, No. 12, 1992