DAIRY FOODS
Influence of Guar Gum on the Distribution of Some
Flavor Compounds in Acidified Milk Products
C.
G. LO,*gl K. D. LEE,* R. L. RICHTER,t and C. W. DlLLt
'Department of Food Science and Nutrition, University of Minnesota, St Paul 55108
tDepartrnent of Animal Science, Texas A&M University, College Station 77843
ABSTRACT
Acidified milk samples containing 0.1 to 0.5% guar
gum were prepared with concentrations of milk fat
from 0 to 20% and SNF from 6 to 12%. The partition
coefficients of acetaldehyde, ethanol, and diacetyl
were determined by headspace analysis using gas
chromatography in samples that were acidified to pH
4.5 at 30 and 50°C. Guar gum did not affect the
partition coefficients of the flavor compounds under
any experimental condition. At both temperatures,
the partition coefficient of acetaldehyde was affected
by the concentration of acetaldehyde and the interaction of SNF and acetaldehyde concentration. The
lowest partition coefficients of acetaldehyde were observed at 9% SNF under various experimental conditions. The concentration of ethanol and the interaction of milk fat and ethanol concentration affected the
partition coefficient of ethanol at both temperatures.
The partition coefficient of ethanol increased as
ethanol concentration and SNF increased. Milk fat,
concentration of diacetyl, and the interaction of SNF,
fat, and diacetyl concentration affected the partition
coefficient of diacetyl at 30°C. The partition coefficient of diacetyl increased as SNF increased. At 50°C,
concentration of diacetyl was the only significant factor. Partition coefficients for ethanol and diacetyl
were similar at 30°C; however, at 50"C, the partition
coefficient of diacetyl was higher than the partition
coefficient of ethanol. The partition coeficient was
largest for acetaldehyde at both temperatures.
( Key words: guar gum, partition coefficient, acidified milk products)
INTRODUCTION
The rapid development of no fat, reduced fat, and
"lite" acidified milk products, such as yogurt, sour
cream, and buttermilk, has opened new growth areas
for cultured milks. This trend is attributed to changes
in consumption patterns of consumers because of
Received August 7 , 1995.
Accepted July 30, 1996.
'To whom correspondence should be addressed
1996 J Dairy Sci 79:2081-2090
nutritional and health concerns. The development of
these products frequently involves removal of fat or
sugars and the addition of hydrocolloids or starches to
achieve desirable rheological characteristics. The effects of these changes on the flavor of the product and
on the distribution of flavor compounds are unknown.
Factors that might change flavor need to be understood in order to assess the effects of changes in food
formulations on perceived flavors.
Hydrocolloids are the stabilizers most commonly
used in the dairy industry to improve the appearance
and viscosity of products. Use of hydrocolloids at concentrations ranging from 0.1 to 0.5% ( 18) is common
and does not contribute directly to the taste or odor
components of flavor (17, 34). Guar gum, a type of
hydrocolloid, is usually used as a stabilizer for acidified milk products because the viscosity of guar gum
solutions is not affected by the acid levels found in
fermented milk products ( 3 , 10). This neutral polymer, with a molecular mass of about 220,000 ( l o ) ,
can develop appreciable viscosity even at low concentrations because of swelling and dispersion of the
molecular chains in water. In practice, acidified milk
products stabilized with guar gum have a slightly
shorter body and lower viscosity than do products
containing locust bean gum (18).
Acetaldehyde, ethanol, and diacetyl are compounds
that are critical t o the aroma and flavor of fermented
milk products. In proper concentrations, these compounds contribute to the quality of products (11, 121,
but excessive or insufficient quantities of any compound cause a flavor defect ( 22 1. Steam-distillation
techniques, combined with a colorimetric reaction,
have traditionally been used to measure the concentrations of these flavor compounds (2 1, 28). However,
these procedures are tedious, and the determined concentration of the volatiles does not provide information that could be used to evaluate the effect of the
product matrix on the aroma of the product. In contrast, headspace analysis by gas chromatography is a
rapid, uncomplicated procedure that permits quantitation of volatile compounds in the headspace above a
sample. Partition coefficients (14, 24, 25), a ratio of
concentration of the solute in the gas phase to its
concentration in the liquid phase, can be determined
2081
2082
LO ET AL.
to define the distribution of flavor compounds in and
above a product. Knowledge of partition coefficients
would eliminate the requirement of a standard curve
for each compound in a product matrix and make it
possible to calculate the concentration of a flavor
compound in the liquid phase from the concentration
measured in the gas phase.
Because of the complex nature of food products,
most published data about partition coefficients are
limited to a single aqueous phase or to simple model
food systems. For a better understanding of the distribution of the major volatiles in cultured milk products
with reduced fat, the effects of guar gum on the
partition coefficients of acetaldehyde, ethanol, and
diacetyl were investigated and are reported in this
research.
MATERIALS AND METHODS
Conditions of Gas Chromatography
Gas chromatographic analyses were performed
with a Tracor GLC (model 540; Tracor Inc., Austin,
TX) equipped with a flame-ionization detector.
Acetaldehyde, ethanol, and diacetyl were separated
and quantitated using a DB-1 Megabore column (30
m x 0.70 mm 0.d. x 0.53 mm i.d., coated with methylsilicone; J&W Scientific Marketing, Floson, CA).
High purity hydrogen (30 ml/min) and air (300 mV
min) were used for the flame-ionization detector.
Ultra-high purity helium a t 7.65 mVmin was used as
the carrier gas. The column oven temperature was
40°C. Injector and detector temperatures were 150
and 180°C, respectively. Attenuator settings on the
GLC for electrometer input and output were 1. A
computing integrator (model SP 4290; SpectraPhysics Inc., San Jose, CA) was used for monitoring
and quantitating detector output. The integrator
chart speed was 0.5 c d m i n , and attenuation was set
at 0.5.
Apparatus Preparation
A static dilution bottle with a capacity of 2 L
(Tekmar Company, Cincinnati, O H ) was used for
diluting and standardizing the concentration of
acetaldehyde, ethanol, and diacetyl. To minimize surface absorption, the bottle was silanized by careful
washing with detergent, followed by rinsing with 5%
dimethyldichlorosilane (Supelco, Bellefonte, PA) in
toluene. The bottle was then washed with toluene
three times, rinsed with anhydrous methanol, and
air-dried prior to use.
Journal of Dairy Science Vol. 79, No. 12, 1996
Calibration and Identification
of Flavor Compounds
Diacetyl (Sigma Chemical Co., St. Louis, MO) was
fractionally distilled using a Vigreaux column (CMC,
Inc., Houston, TX).The fraction with a boiling point
of 86°C was collected, and the other fractions were
discarded. This sequence was repeated twice to ensure a pure compound. Acetaldehyde and ethanol
were from Eastman Kodak Company (Rochester,
NY) and Midwest Grain Products Co. (Weston, MO),
respectively. Selected amounts (0.02, 0.04, 0.06, and
0.08 pl) of acetaldehyde, ethanol, and diacetyl were
injected into the static dilution bottle and
equilibrated for 10 min in a 30°C incubator (National
Appliance Co., Portland, OR). A 0.5-ml sample was
withdrawn from the headspace with a 1-ml gastight
syringe (Dynamic Precision Sampling, Baton Rouge,
LA) and injected into the GLC. Retention times of the
known compounds were determined a t a constant
helium flow rate. Calibration curves were prepared to
achieve concentrations of 0.004 to 0.016, 0.004 to
0.016, and 0.005 to 0.020 pg/ml of headspace for
acetaldehyde, ethanol, and diacetyl, respectively.
Regression analysis using mass as the independent
variable and peak area as the dependent variable was
used to calculate the calibration curve for each compound. The procedure was replicated to ensure accuracy of the calibration.
Preparation of Milk Sample
Fresh raw cream, raw skim milk, and NDM obtained from the Texas A&M University Dairy
Products Laboratory were used to prepare milk samples. Fat and moisture contents were determined in
triplicate by the Mojonnier method (26). After analysis, milk samples were stored at 5"C, and the NDM
was stored in a plastic container a t room temperature
until used. Samples with milk fat concentrations of 0,
10, or 20% at SNF concentrations of 6, 9, and 12%
with addition of 0.1, 0.3, or 0.5% guar gum were
prepared by mixing calculated amounts of cream,
skim milk, NDM, guar gum, and water. Milk samples
of 350 ml were pasteurized at 85°C for 30 min in a
water bath (Precision Scientific Co., Chicago, I L ) and
homogenized with a hand homogenizer (ChaseLogeman Corp., Hicksville, NY).
Each milk sample was adjusted to pH 5.3 with 85%
lactic acid (Fisher Scientific, Fair Lawn, N J ) .
Glucono-&lactone (Sigma Chemical Co. 1 was introduced at a n amount equivalent to 7% of SNF.
Thereafter, milk samples were kept at 30°C in a
water bath. A Metrohm-Brinkman pH meter (model
pH 104; Brinkmann Instruments, Westbury, NY 1,
2083
2083
GUAR
GUAR GUM
GUM INFLUENCE
INFLUENCE ON
ON FLAVOR
FLAVOR
equipped
equipped with
with an
an electrode
electrode (Broadley-James
(Broadley-James Co.,
Co., the
the gas
gas and liquid phases at
a t the same temperature,
Santa
Ana,
CA),
was
used
to
monitor
the
pH
of
respectively.
In
this
research,
Santa Ana, CA), was used t o monitor the
research, the mass of acetaldeacetaldeethanol,
and
diacetyl
hyde,
samples
until
pH
4.5
±
0.1
was
reached.
The
samples
samples until pH 4.5 0.1 was reached. The samples hyde, ethanol,
diacetyl in the liquid matrix was
calculated
of
were
5°C until
until used.
used.
were stored
stored at
at 5°C
calculated by the difference between the quantity of
the
compounds
added
into
the
vials
and
the
quantity
the compounds added
in
the headspace.
headspace.
Equilibrium
Determination
Equilibrium Determination
for
Headspace
Analysis
for Headspace Analysis
Statistical
Statistical Analysis
Analysis
Storage
Storage hypo-vials
hypo-vials (165
(165 ml;
ml; Pierce,
Pierce, Rockford,
Rockford, IL)
IL)
The experiment was repeated twice for the three
were
were used
used as
as sample
sample containers.
containers. Each
Each vial was
concentrations of each compound.
compound. All of the data were
silanized
as described
described earlier.
earlier. Ten
Ten and
and 20
20 gg of disdis- concentrations
silanized as
27 ) ;
tilled
at 30°C
30°C were
were each
each put into
into three storage
storage split by temperature using a split-plot design ((27);
tilled water
water at
ConSNF, fat,
fat, and guar gum were whole-plot factors. Convials,
vials, covered
covered with
with aa septum
septum constructed
constructed of teflon and SNF,
silicon,
silicon, and
and sealed
sealed with
with aluminum
aluminum crimp-on
crimp-on seals
seals centration was aa subplot factor. Data were analyzed
analysis of variance, and contrast was used for
(Pierce).
(Pierce). Acetaldehyde,
Acetaldehyde, ethanol,
ethanol, and
and diacetyl
diacetyl were by analysis
(30),
1, and followintroduced
at 0.06,
0.06, 0.06,
0.06, and 0.05
0.05 fLI,
p1, respectively,
respectively, separation of means using the SAS (30
introduced at
ing
model:
model:
using
using aa 0.5-fLl
0.5-p1 7000
7000 series
series syringe
syringe (Hamilton
(Hamilton ComCompany,
pany, Reno,
Reno, NV).
NV). The
The final
final concentration
concentration of each
Yijklm = fL + Ei + Sj + Fk + (SF)jk + Gl
compound
(micrograms per
compound in
in water was
was 55 ppm (micrograms
gram). The
The vials
vials were
were then agitated
agitated by shaking
shaking and
gram).
+ (SG )jl + (FG)kl + (SFG )jkl + eijkl
The concentration
concentration of
placed into
into incubators
incubators at 30°C. The
placed
+ Cm + (SC)jm + (FC)km + (GC)lm
acetaldehyde, ethanol,
ethanol, and diacetyl
diacetyl in the headspace
acetaldehyde,
+
(SFC)jkm + (SGC )jlm + (FGC)klm
l-h intervals.
intervals.
was determined
determined by GLC
GLC analysis
analysis at 1-h
was
+ (SFGC)jklm + Vijklm
Equilibration requirements
requirements were satisfied when the
Equilibration
concentration of the
the compound in the headspace
headspace did
concentration
change with time.
time. The time required for each where
not change
compound to
to reach equilibrium was determined
determined in
compound
p
= overall mean,
fL =
duplicate for
for each
each sample.
sample. Similar
Similar analysis was conconduplicate
of experiment (i
(i = 1
1 and 21,
2),
E
= effect of
9% SNF,
SNF, 0%
0% fat,
fat, and 0.3%
0.3%
ducted using milk with 9%
ducted
of SNF ((jj = 6, 9, and 12%),
12%),
S = effect of
gum as
as aa liquid matrix.
matrix.
guar gum
of fat ((kk =
= 0, 10,
10, and 20%),
20%),
F
F = effect of
+
=
Determination of the Partition
Partition
Determination
Coefficient
Coefficient
Partition coefficients
coefficients were determined
determined for each
at
concentrations
compound
in
milk
samples
compound
samples
concentrations of 3, 6,
30 and 50°C.
50°C. Temperatures
Temperatures of 30 and
and 99 ppm at 30
50°C were
were selected to ensure efficient liberation of the
50°C
volatiles from
from the liquid phase during incubation.
After
the
compounds reached equilibrium,
equilibrium, a 0.5-ml
Mter
compounds
headspace
sample
was
withdrawn
from the vials with
headspace sample
from
a
l-ml
gastight
syringe,
without
removing
the sample
a 1-ml
syringe,
vial
from
the
incubator,
and
injected
into
the GLC.
vial from
incubator,
GLC.
analyses were made for each vial. The
Duplicate analyses
syringe was flushed
flushed with air between each injection.
syringe
A partition coefficient was calculated as
A
Kd =
CG
-
CL
[1]
111
where Kd is the partition coefficient of the compound
compound
between gas and liquid phases, and CG
CG and CL are
concentrations of the compound
the equilibrium concentrations
compound in
G = effect of
guar gum (1
0.3, and 0.5%),
ofguar
(l = 0.1,
0.1,0.3,
0.5%),
of concentration ((nn = 3, 6, and 9
C =
= effect of
ppm),
PPm),
eijkl =
= error term denoting variations within
of which
guar gum, the means squares of
were used to test guar gum effect and all
guar gum interactions,
interactions, and
Vijklm
Vijklm = error term denoting variations within concentration, the mean squares of
of which
were used to test concentration effect and
all concentration interactions.
RESULTS AND DISCUSSION
Compound Identification
Identification
and Calibration
Calibration
Purified compounds were added tto
o storage vials,
vials,
and the headspace in the vials was analyzed by
by GLC
GLC
to determine retention times. The retention
retention times
times of
of
acetaldehyde, ethanol, and diacetyl were 1.05, 1.34,
and 2.46 min, respectively; only a single peak
peak was
was
detected for each compound.
compound. Linear regression
regression equaequa).
tions were calculated for calibration (Table l1).
Journal of
of Dairy Science
Science Vol.
Vol. 79,
79, No.
No. 12,
12, 1996
1996
2084
LO ET AL.
TABLE 1. Regression equations and coefficients of determination
for the major flavor compounds over a range of concentrations
tested.
Compound
Regression equation1
r2
Acetaldehyde
Ethanol
Diacetyl
Y = -191.33 + 156043.43X
Y = -44.89 + 142847.34X
Y = 26.29 + 174540.51X
0.96
0.99
0.99
ethanol concentration and of SNF, fat, and ethanol
concentration affected the partition coefficients of
ethanol at 30°C ( P < 0.05). Except for the interaction
of SNF, fat, and ethanol concentration, these same
A
18.0 1
'Y = Peak area of GLC response; X = mass x 10-3
Equilibrium and Sample
Weight Determination
Water and milk with 9% SNF, 0% milk fat, and
0.3% guar gum were utilized to determine the
equilibration times of acetaldehyde, ethanol, and diacetyl (Figure 1). No difference was found either for
water or milk between equilibration times for the
partition coefficients of the three volatile compounds
when incubation time exceeded 1 h. Therefore, 1 h
was chosen as the minimum time required for the
samples to reach equilibrium. Partition coefficients
were lower for milk than for water, which indicates
that the compounds interacted with milk constituents
(e.g., protein, milk fat, carbohydrate, or milk salts)
and were retained in the milk matrix.
The partition coefficients of acetaldehyde, ethanol,
and diacetyl in 10 and 20 g of water are compared in
Figure 2. The partition coefficients of the three flavor
compounds were not affected ( P > 0.05) by the weight
of the water. Smith and Van Ness ( 3 1 ) stated that
equilibrium time should increase with sample weight,
but that was not the case in the current study. Possibly, differences between the sample weights or the
amounts of flavor compounds used in this study were
not great enough to reflect a difference in equilibration times. Based on these results, a sample size of 10
g was selected for further study.
27.0
Statistical Analysis
24.0
21.0
Results from the analysis of variance of the data
are shown in Table 2. Because partition coefficients
were dependent on temperature, as they were in
studies by Friant (14) and Kieckbusch and King
( 191, the model was split by temperature for appropriate analyses. At 30"C, concentration of
acetaldehyde and interactions of SNF and acetaldehyde concentration and of SNF,fat, and acetaldehyde
concentration affected ( P < 0.05) the partition coefficient of acetaldehyde. The effects of acetaldehyde concentration and the interaction of SNF and acetaldehyde concentration were significant at 50°C.
Concentration of ethanol and interactions of fat and
Journal of Dairy Science Vol. 79, No. 12, 1996
0.0
1.o
gA
2.0
3.0
Time (h)
B
21.0
18.0
0.0
30.0
1.o
2.0
3.0
2.0
3.0
Time (h)
-I
18.0
15.0
12.0
9.0
6.0
3.0
0.0
0.0
1 .o
Time (h)
Figure 1. Equilibration of acetaldehyde ( A ) , ethanol ( B ) , and
diacetyl ( C 1 a t 5 ppm in water w ) and in milk ( A) with 9% SNF,
0% fat, and 0.3% guar gum a t 30°C. Kd = Partition coefficient.
2085
GUAR GUM INFLUENCE ON FLAVOR
factors were significant when determinations were
made at 50°C. Fat, concentration of diacetyl, and the
interaction of SNF, fat, and diacetyl concentration
affected the partition coefficient of diacetyl at 30°C (P
A
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0 - f - - - - - - - r - - - - - - . - - - - - - ,
0.0
2.0
1.0
3.0
Time (h)
44.0
B
40.0
36.0
32.0
28.0
24.0
20.0
16.0
12.0
8.0
4.0
0.0 +-------,,..-------r----.,
0.0
1.0
2.0
3.0
Time (h)
135.0
c
120.0
105.0
90.0
75.0
60.0
45.0
30.0
15.0
0.0
-+-----~=====-'--~----­
0.0
1.0
2.0
3.0
< 0.05). However, diacetyl concentration was the only
factor that significantly affected the partition coefficient of diacetyl at 50°C.
Higher temperature increased (P < 0.05) the partition coefficient of the flavor compounds. To escape
from the liquid phase, volatile molecules must possess
a minimum kinetic energy. The higher the temperature is, the greater is the fraction of molecules possessing at least that minimum energy required to
escape from the solution (36). Therefore, as temperature increased, molecules in the headspace of a sample also increased. Differences in the binding of flavor
compounds by milk components or the solubility of
flavor compounds in the water or lipid phase are
other possible causes of the differences that were
observed at 30 and 50°C (9). The increased volatility
of flavor compounds at 50°C might be the reason that
the interaction of SNF, fat, and concentration was
significant at 30°C but not at 50°C.
Saleeb and Pickup (29) reported that the variation
of headspace concentration of a given volatile compound is governed by the nature and energy of the
interaction of that particular compound with the substrate. Arnold (1) demonstrated that, for nonfood
systems, the magnitude of heat of adsorption was the
main factor in determining which volatile molecules
would be preferentially adsorbed. In our study, the
behavior of three flavor compounds was not consistent. For real food systems consisting of various ingredients, different solubilities for different flavor compounds, competition for surface sites, and interactions
among absorbents would be expected to have more
influence on the distribution of flavor compounds in
foodstuffs and headspace.
The partition coefficients were dependent on the
concentration of the flavor compounds (Table 2). The
concentrations used in this research mimicked the
concentrations found III real products, which corresponded to the ideal state of infinite dilution at
which point Henry's law should be valid. Henry's law
states that the partial pressure of the solute in the
equilibrium vapor above the solution was directly
proportional to the solute concentration in the liquid.
Friant (14) and Buttery et al. (6) found that partition coefficients did not change consistently as concentration of volatile compounds changed. In contrast,
dependency of the partition coefficient on concentration also was reported (16, 20) as a Freundlich-type
behavior (1); at low compound concentration, the
primary mechanism is chemisorption on proteins and,
at high concentration, solubility in fat.
Time (h)
Partition Coefficients of Acetaldehyde
Figure 2. Comparison of partition coefficients for acetaldehyde
(A), ethanol (B), and diacetyl (C) at 5 ppm in 10 g (.) and 20 g
(It.) of water at 30°C. Kd = Partition coefficient.
Results of the effects of SNF, milk fat, and concentration of acetaldehyde on the partition coefficients at
Journal of Dairy Science Vol. 79, No. 12, 1996
2086
LO ET AL.
TABLE 2. Analysis of variance for the effect on the partition coefficients for acetaldehyde, ethanol, and
diacetyl in acidified milk.
Acetaldehyde
Source1
~
S
F
G
SF
SG
FG
SFG
C
sc
FC
SFC
GC
SGC
FGC
SFGC
~
df
~
30°C
~
2
2
2
4
4
4
8
2
4
4
8
4
8
8
16
~
0.055
0.828
0.971
0.965
0.979
0.977
0.999
<0.001*
0.015*
0.456
<0.001*
0.653
0.998
0.637
0.824
Ethanol
50°C
~~
30°C
~
0.376
0.493
0.998
0.972
0.976
0.715
0.994
<0.001*
0.035*
0.073
0.058
0.966
0.432
0.345
0.959
Diacetyl
50°C
~~
0.830
0.212
0.682
0.191
0.508
0.831
0.815
<0.001*
0.217
0.004*
<0.001*
0.287
0.134
0.267
0.305
~
30°C
~
0.997
0.306
0.770
0.616
0.997
0.991
0.998
<0.001*
0.101
0.004*
0.070
0.513
0.732
0.769
0.727
50°C
~
0.856
0.008*
0.344
0.058
0.530
0.819
0.972
<0.001*
0.206
0.250
0.003*
0.582
0.515
0.299
0.682
~
0.407
0.267
0.428
0.317
0.471
0.563
0.586
0.001*
0.416
0.438
0.300
0.363
0.545
0.383
0.435
1s = SNF a t 6, 9, and 12%; F = fat a t 0, 10, and 20%; G = p a r gum at 0.1, 0.3, and 0.5%; and C =
concentration a t 3, 6, and 9 ppm.
*Significant ( P < 0.05).
different milk fat concentrations at 30°C are shown in
Table 3. At 50°C (Table 4), a mean partition coefficient was calculated that corresponded to each
acetaldehyde concentration at each concentration of
SNF because the only significant interaction was between SNF and acetaldehyde concentration.
The effect of SNF on the partition coefficients of
acetaldehyde at each concentration of milk fat was
consistent but unique. The partition coefficient of
acetaldehyde was lowest at 9% SNF under every experimental condition. Three types of flavor interactions are possible in mixtures: synergism, addition,
and suppression. Every constituent in the aqueous
phase, especially lactose, protein, and hydrocolloids,
can affect the results. Lactose and some proteins have
been shown to act as a carrier and to bind flavors
physically and chemically ( 2 3 ) . However, differences
might be explained with a mixed effect that could
vary according to the amount, composition, physical
state, and the degree of SNF dispersion in other
constituents (4,15). In addition, the current system
comprised air, fabricated acidified milk, and three
different ligands. At the 9% SNF concentration, some
specific change in conformation probably increased
the number of binding sites, which caused acetaldehyde to remain in the liquid phase.
Partition Coefficients
of Ethanol
Table 5 contains the results of the effects of SNF,
ethanol concentration, and milk fat at 0, 10, and 20%
on the partition coefficients of ethanol at 3 , 6, and 9
ppm at 30°C. The partition coefficients for ethanol
increased as SNF concentrations increased within
each concentration of ethanol. This trend was observed at each concentration of milk fat. The effects of
TABLE 3. Effects of SNF, milk fat, and acetaldehyde concentration on the partition coefficients ( K d ) of acetaldehyde a t 3, 6, and 9 ppm at
30°C.
0% Milk fat
10% Milk fat
20% Milk fat
SNF
3 PPm
6P P ~
9 PPm
3 PPm
6 P P ~
9 PPm
3 PPm
6 PPm
9 PPm
6
9
12
4.75a
4.04*
4.09a
2.79a
2.05a
3.64a
3.45a
1.79a
2.93a
4.75a
2.78b
3.68ab
4.01a
2.54a
3.49a
3.89a
1.05b
4.79a
4.90a
3.71a
4.W
4.628
2.75b
4.07ab
4.13a
2.81a
3.89a
a,bMeans ( n = 6) in the same column without a common superscript differ ( P < 0.05); degrees of freedom of error terms = 54; standard
error = 0.503.
Journal of Dairy Science Vol. 79, No. 12, 1996
2087
GUAR GUM INFLUENCE ON FLAVOR
TABLE 4. Effects of SNF and acetaldehyde concentration on the
partition coefficients ( K d ) of acetaldehyde a t 50°C.
SNF
3 PPm
6 PPm
9 PPm
10.3ga
8.25a
10.36a
Kd (xlO-3)
8.30a
7.47a
8.88a
8.48a
5.45h
7.52ah
(%a)
6
9
12
~
a,bMeans ( n = 1 8 ) in the same column without a common superscript differ ( P < 0.05); degrees of freedom of error term = 54;
standard error = 0.882.
milk fat on the partition coefficients of ethanol at 3, 6,
and 9 ppm at 50°C are shown in Table 6. The effect of
SNF concentration was not included because the interaction of SNF, fat, and ethanol concentration on
the partition coefficients was not significant ( P >
0.05). Partition Coefficients of ethanol increased as
milk fat concentrations increased. Also, partition
coefficients increased as concentration of ethanol increased at each concentration of milk fat.
Because lactose and protein are major components
in the SNF fraction of milk, effects of their physical
and chemical interactions with volatiles on flavor
retention should be addressed. Wientjes ( 3 7 1 found
that the addition of sugar in a dilute aqueous system
produced increased partial vapor pressure for a number of compounds; partial pressure for others
decreased markedly. From the results of the current
study, we suspected that lactose enhanced the vapor
pressure of ethanol, which was more pronounced as
the concentration of ethanol increased. Lactose, which
is soluble in water, could compete with ethanol for
water because ethanol also binds water with a hydrogen bond. A decreased solubility of volatiles in sugar
solutions is probably caused by a salting-out effect,
which would increase the vapor pressure of flavor
compounds.
Interactions of flavor compounds with proteins can
involve mechanisms such as physical and chemical
adsorption by van der Waals interactions, covalent
and electrostatic interactions, or penetration into the
food interior by diffusion. Even though polar compounds such as alcohols are bound via hydrogen linkages, hydrophobic interactions with nonpolar amino
acid residues are considered to be predominant in the
binding of volatile compounds of low molecular mass.
Several researchers ( 1 3 , 3 3 ) have found that the
concentration of volatile compounds was lowered in
headspace as concentrations of proteins in the aqueous phase increased. Solms et al. ( 3 3 1 and Solms and
Guggenbuehl ( 3 2 1 reported that the binding sites
and the amount of bound flavor compound increased
as the denaturation of protein increased because more
hydrophobic regions were then available for further
binding. However, the number of volatile molecules
bound per mole of protein could also decrease as the
oligomeric protein concentration increased, which
might be a result of interactions among proteins ( 8 ).
This postulation supported the results of this study,
which demonstrated that partition coefficients increased as concentration of SNF increased in a sample matrix.
Partition Coefficients of Diacetyl
The effects of SNF, milk fat, and concentration on
the partition coefficient of diacetyl at 30°C are shown
in Table 7. The partition coefficients of diacetyl increased as percentage of milk fat increased at every
SNF concentration. At 50°C, mean values of partition
coefficients were taken at different concentrations of
diacetyl because only the concentration of diacetyl
affected partition Coefficients ( P < 0.05). The means
of partition coefficients at 3, 6, and 9 ppm of diacetyl
were 1.54, 3.50, and 4.82, respectively.
Buttery et al. ( 5 ) developed a model system to
compare the volatilities of some flavor compounds in
model systems using oil or water and oil. Those
researchers stated that flavor compounds in those
model systems were distributed between the fat and
the aqueous phase, following the physical laws of
solubility partition ( 33 ) . Fat-soluble compounds had
TABLE 5 . Effects of SNF, milk fat, and ethanol concentration on the partition coefficients ( K d ) of ethanol at 3, 6, and 9 ppm a t 30°C.
0% Milk fat
10% Milk fat
20% Milk fat
SNF
3 PPm
6 PPm
9 PPm
3 PPm
6 PPm
9 PPm
3 PPm
6 PPm
9 PPm
6
9
12
0.36a
0.4P
0.49a
0.66a
0.69a
0.70a
0.80a
0.85a
1.02a
0.36a
0.54a
0.62a
0.57a
0.65"
0.73a
0.69h
0.93ah
1.22a
0.45a
0.51a
0.55"
0.62"
0.73"
0.74"
0.84b
1.15h
1.79"
a,bMeans ( n = 6 ) in the same column without a common superscript differ ( P < 0.05): degrees of freedom of error term = 54; standard
error = 0.091.
Journal of Dairy Science Vol. 79, No. 12, 1996
2088
LO ET AL.
TABLE 6. Effects of milk fat and ethanol Concentration on the
partition coefficients ( K d ) of ethanol a t 50°C.
gum from 0.1 to 0.5% (data not shown) (Table 2 ) .
Samples with 0.310 guar gum were used for the following comparisons. Partition coefficients for
Fat
3 PPm
6 PPm
9 PPm
acetaldehyde, ethanol, and diacetyl in milk with and
Kd (x1O-3)
( 9% )
0.3% gum using 9% SNF and 0% fat a t 30
without
0
0.92a
1.52"
2.06b
10
1.05a
1.58a
2.28h
and 50°C are shown in Table 8 . No significant differ20
1.00a
1.67a
2.82a
ences were detected. Burger (4) studied changes in
a,bMeans ( n = 181 in the same column without a common super- volatile headspace concentrations in systems of air
script differ ( P < 0.05); degrees of freedom of error term = 54; and water upon addition of hydrocolloids. Most
standard error = 0.098.
hydrocolloids decreased the concentration of a volatile
in headspace; however, a decrease was not observed
with some hydrocolloids, especially when the concenless volatility in those systems. The acidified milk tration of a flavor compound was low. Mechanisms
samples in the current system were composed of three proposed for these effects were restricted diffusion
phases with oil, water, and air; the increase in parti- and inhibition of bulk mixing. At high concentrations
tion coefficients as milk fat concentration increased of flavor compounds, polymer entanglement was sugwas expected. However, recent work by Ulberth ( 35 1 gested to be the dominant effect that inhibited
showed that milk fat content (0.6 to 32.1%) did not replenishment of surface depletion. Direct binding of
significantly affect the volatility of fat-soluble aroma flavor molecules to polymers is another possible
substances. Because the present system was more mechanism, especially when the formation of struccomplicated than the model system reported by But- tured zones is possible. These zones can be stabilized
tery et al. (71, combinations of phase partition, by hydrogen bonds, electrostatic forces, van der Waals
specific binding, or transfer effects were likely to oc- forces, and hydrophobic interactions. For many polycur and to affect retention of flavor compounds.
saccharides, the formation of structures zones is well
Moisture content of the acidified milk samples known in relation to the gel-forming properties of the
might have influenced the partition coefficients if the polysaccharides, and these zones can further interact
solubility of the compounds was affected. As the con- with flavor molecules. Recent data ( 2 1 described a
centration of milk fat increased, less water would be marked decrease of flavor concentration in the headavailable in the milk to solubilize the flavor com- space with increasing coil overlap and entanglement
pounds, causing a higher partition coefficient. Also, in flavored aqueous guar gum systems; those results
the free fatty acid content of milk possibly increased were an indication of the occurrence of binding efas milk fat concentration increased. Free fatty acids
fects. However, those results were obtained when a
would lower the surface tension between the aqueous
high concentration of the flavor compound was used
and air phases, causing a high vapor pressure in the
in the system. The comparatively low concentrations
headspace. This phenomenon would result in increased concentrations of the volatile compounds in of flavor compounds that were used in the complicated milk system might explain the difference that
the headspace.
was noted in our study.
Partition coefficients of acetaldehyde were higher
Effect of Guar Gum
than partition coefficients of ethanol and diacetyl. At
on Partition Coefficients
30"C, partition coefficients of ethanol and diacetyl
No differences between partition coefficients were were similar but lower than the partition coefficient
0.05) with concentrations of guar of acetaldehyde. However, at 50"C, the effect of temsignificant ( P
~~~~~
~
TABLE 7. Effects of SNF, milk fat, and diacetyl concentration on the partition coefficients of diacetyl at 3, 6, and 9 ppm a t 30°C.
~
~
10% Milk fat
0% Milk fat
SNF
3 PPm
6 PPm
9 PP*
3 PPm
(%)
6
9
12
0 31a
0 34a
0 33.1
0 56"
0 86"
0 75"
1 07'3
1 188
1103
O38a
0 35a
0 456
2 0 4 Milk fat
6 PPm
9 PPm
3 PPm
6 PPm
9 PPm
Kd (x10 3 )
0 65"
0 92a
0 77"
128ah
0 43.1
056.1
0 48"
154'3
0 99b
2 14"
1501,
0 84b
1 67b
120b
1 62a
",bMeans ( n = 6 ) in the same column without a common superscript differ ( P < 0.05); degrees of freedom of error term
error = 0.124.
Journal of Dairy Science Vol. 79, No. 12, 1996
=
54; standard
2089
GUAR GUM INFLUENCE ON FLAVOR
TABLE 8. Partition coefficients of acetaldehyde ( A ) , ethanol ( E ), and diacetyl ( D 1 without and with
0.39 guar gum using 9% SNF and 0% milk fat as liquid phase a t 30 and 5O"C.l
Concentration
of volatiles
(PPm)
3
6
9
"one
0.051.
30°C
Gum
A
E
D
5.17
6.38
2.39
2.35
1.72
1.66
0.25
0.29
0.71
0.71
0.83
0.80
Kd ( ~ 1 0 - 3 )
0.22
11.77
0.21
10.06
0.82
5.38
0.84
5.35
1.27
3.47
1.31
3.29
(%i)
0
0.3
0
0.3
0
0.3
50°C
A
E
D
0.60
0.64
1.22
1.41
1.68
1.52
0.92
0.86
3.21
3.23
4.03
3.99
of the means of partition coefficients comparing with and without guar gum differed ( P >
perature on partition coefficients was greater with
diacetyl than with ethanol. The partition coefficient of
diacetyl increased fourfold, but the partition coefficient of ethanol only increased about twofold, suggesting that the binding of ethanol was probably stronger
than the binding of diacetyl in acidified milk systems.
CONCLUSIONS
Guar gum did not affect the partition coefficients of
acetaldehyde, ethanol, or diacetyl; concentrations approximated those encountered in acidified milk
products. These results indicated that guar gum in a
commercial concentration range of 0.1 t o 0.5% could
be used in fermented milk products without changing
the distribution of these flavor compounds from that
in products without guar gum. The percentage of milk
ingredients in acidified milk products can affect the
distribution of flavor compounds between the product
matrix and the headspace above the product. The
effect of milk components was complex, and each
flavor compound was affected differently. Interactions
between the concentration of the flavor compounds
and milk components were significant. These results
demonstrate that the effect of milk product composition on the partition coefficients of flavor compounds
is dependent upon the physical properties of the
flavor compound and on the interactions with the
different phases in a milk system. In general, increased temperature of analysis reduced the effect of
milk components on the partition coefficients, which
must be considered when the purpose of the analysis
is to determine the distribution of flavor compounds
under the conditions at which the foods will be consumed.
ACKNOWLEDGMENT
This research was supported by a research grant
from Dairy Management, Inc.
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