influence of antioxidative hindered phenols on the taste
TRANSCRIPT
Food Sci. Technol. Res., 15 (5), 491–498, 2009
Influence of Antioxidative Hindered Phenols on the Taste of Beverages in
the Presence of Free Chlorine
Tetsuya YaMaMoto1, Minoru inagaki
2* and Yasuo kazuMa1
1 Department of Quality Assurance, Fuji Electric Retail Systems Co., Ltd., Maesuna 160-1, Kounosu, Saitama 369-0198, Japan2 Department of Life Science, Faculty of Bioresources, Mie University, Kurima-machiya 1577, Tsu, Mie 514-8507, Japan
Received September 26, 2008; Accepted May 15, 2009
The taste, as well as odor, of hindered phenols which are commonly used as antioxidants for olefin polymers of cup-type vending machine for beverages was investigated to identify the cause of the in-creasing unpleasant taste of beverages with free chlorine added in the source water for sterilization. The threshold concentration of solutions of mono- and di-substituted hindered phenols were confirmed to de-crease due to free chlorine, while that of tri-substituted hindered phenols with substituents at the 2, 4, and 6 positions were not affected by free chlorine. The magnitude of the decrease in the threshold concentra-tion depended on the number of free 2, 4, and 6 positions on the aromatic ring. The products formed by chlorination, oxidation, ring opening and dimerization of the hindered phenols were identified by GC/MS in the model reaction with free chlorine. Based on the threshold concentrations of some identified prod-ucts, their effects on the increasing unpleasant taste were estimated.
Keywords: hindered phenol, free chlorine, chlorination, threshold concentration, taste, beverage, antioxidant, sensory test
*To whom correspondence should be addressed.
E-mail: [email protected]
IntroductionEnsuring high quality of source water is the most impor-
tant factor for serving tasty beverages in cup-type vending
machines, cold drink dispensers, and water servers. Unpleas-
ant taste, as well as odor, is often the result of problems of
the source water in the water tank or piping of these bever-
age machines, which contain 0.1-0.6 ppm free chlorine for
sterilization. Since chlorine itself lacks taste up to 1.0 ppm,
the cause of unpleasant taste may be result from the organic
materials used in the beverage machines. The chemical sub-
stances eluted from the materials may interact with free chlo-
rine to form the unpleasant taste, thus requiring examination
of these interactions.
In case of free chlorine is incorporated for sterilization in
tap water, phenol and its derivatives from industrial drain-
age are known to cause unpleasant taste through formation
of chlorinated phenols (McGuire et al., 1981; Nyström et al.,
1992). Many studies have reported the relationship between
these reaction products and the concentration of free chlorine
and the reaction time (Eisenhauer, 1964; Ettinger and Ruch-
hoft, 1951; Lee and Morris, 1962; Onodera et al., 1998).
However, hindered phenols, which have bulky alkyl substitu-
ents on their aromatic ring, have yet to be thoroughly exam-
ined for their effects on the taste of beverages. Hindered phe-
nols, especially those having three alkyl substituents on their
aromatic ring, are used as phenolic antioxidants of resin ma-
terials everywhere in food and beverage machines to prevent
heat deterioration during the molding process. Moreover,
such tri-substituted hindered phenols have been reported to
be eluted from the resin materials into drinking water (Fors-
man, 1967; Gordon and Rothstein, 1967; Kawamura et al.,
1997). Therefore, tri-substituted hindered phenols may have
their own unpleasant taste or may form substances having
unpleasant taste in the presence of free chlorine, as found in
other phenols. Furthermore, tri-substituted hindered phenols
may deteriorate to produce less substituted derivatives, that
is, non-, mono- and di-substituted phenols, during heating in
the molding process, leading to derivatives which elute into
the water and react with free chlorine to form substances
with unpleasant taste.
In the present study, unpleasant taste of source water used
for beverages was investigated in the absence and presence
of free chlorine using many kinds of antioxidative hindered
phenols having different numbers of alkyl substituents on
their aromatic ring. The chemical structure of the reaction
products were characterized using model reactions of hin-
dered phenols with free chlorine. The threshold concentra-
tions for taste of some of these products were also deter-
mined to estimate their contribution to unpleasant taste.
Materials and MethodsMaterials Antioxidative hindered phenols, Irganox
1010, 1076, and 1135 were purchased from Chiba Japan
(Tokyo, Japan). 2,2’,6,6’-Tetra-tert-butyl-4,4’-biphenol
was purchased from Apollo Scientific Ltd. (Cheshire, UK).
6-Chloro-2,4-di-tert-butylphenol was synthesized according
to the reported procedure (Tashiro et al., 1981) with some
modifications, and the structural characterization of the ob-
tained compound was performed by 1H- and 13C-NMR and
GC/MS. The other derivatives (Table 1) were purchased
from Wako Pure Chemical Industries, Ltd. (Osaka, Japan).
Solution preparation for sensory test and determination
of compound concentrations Compounds 1-10 were dis-
solved in tap water passed through an activated charcoal
filter, and the other compounds were dissolved in Milli-Q
purified water at room temperature. The concentrations of
compounds 1-3 were 100 mg/L. In the case of poorly soluble
compounds 4-10, the concentrations of the saturated solu-
tions were determined as follows. The saturated solutions
(100 ml) were filtered and extracted by CH2Cl2 (2 × 5 ml).
After evaporation of the solvent of the combined extracts,
the residues were re-dissolved in 10 ml CH2Cl2 using volu-
metric flasks. For volatile compounds 4-8, the concentra-
tions of these CH2Cl2 solutions were determined by GC/MS
using a silicon DB-1 column (0.25 mmf × 30 m), while for
non-volatile compounds 9 and 10, the concentrations were
determined by reversed phase HPLC monitored at 280 nm.
The solutions with fixed concentrations (x) were geometri-
cally diluted with water by five steps and the series of diluted
solutions were submitted to the sensory test. Concentration
x represents the maximum concentration, with a series of of
concentrations geometrically determined using a step factor
of Df: x, x(1/Df), x(1/Df)2, x(1/Df)3, and x(1/Df)4. The range
of concentrations used in sensory test is shown in Table 1.
The dilution factor per step (Df) was 10.0 for phenol (1) and
3.16 for the other compounds. Temperature of the room and
the sample solutions were set at 23℃.
Generation of free chlorine in the solution for sensory
test In solutions of compounds 1-10, 0.3 ppm free chlorine
was generated by electrolysis at a constant current of 400 mA
using a Ti plate electrode sintered with fine particles of Pt
in dozens of nanometers of diameter (Ooe and Kawashima,
1983; Oka et al., 1996), which is used in cup-type vending
machines and drink dispensers.
Sensory test The total taste included taste and odor sen-
sory was measured when a sample solution was placed in the
mouth. The sensory test is based on the method for evaluat-
ing taste differences between the sample solution and the
control water in a plastic cup. The threshold concentrations
of samples were determined using the parameter of best-
estimate threshold (BET) according to the ASTM Practice E
t. YaMaMoto et al.
WMdnuopmoCtnemirepxE
00001-11.49lonehp
03-3.06.821lonehporolhc-2
001-10.361lonehporolhcid-4,2
03-3.00.361lonehporolhcid-6,2
phenol (1 00001-11.49)
2-tert -butylphenol (2 001-12.051)
2-tert -butyl-4-methylphenol (3 001-12.461)
2,4-di-tert -butylphenol (4 00081-0813.602) a
2,6-di-tert -butylphenol (5 051-5.13.602)
3,5-di-tert -butylphenol (6 0001-013.602) a
BHT (7 42-42.04.022) a
Irganox 1135 (8 014-1.40.193) a
Irganox 1076 (9 58-58.09.035) a
Irganox 1010 (10 061-6.17.7711) a
6-chloro-2,4-di-tert 06-6.07.042lonehplytub- a
2,6-di-tert -butyl-1,4-benzoquinone 220.3 0.6-60 a
2,2',6,6'-tetra-tert -butyl-4,4'-biphenol 410.6 3.5-350
aMaximum concentration was the concentration of the saturated solution because of limited solubility to water.
Conc. range used insensory test
Verification of sensory test using compounds ofknown threshold concentrations
Estimation of effect of free chlorine on thresholdconcentrations of hindered phenols
Determination of threshold concentration ofidentified reaction products from model reactions ofhindered phenols with chlorine
(µg/L)
Table 1. Compounds used in sensory test and their concentration range.
492
679-04 (ASTM, 2004). The samples were presented to pan-
elists by a three-cup alternative forced choice method (3-AFC
presentations): one cup containing the added sample was
presented along with two identical controls (ANSI, 2002);
samples with the weakest concentrations were presented first.
Among 50 top panelist candidates who had been selected
from 215 employees based on their score on the recognition
sensory test (two-of-five test by Gallagher, 2004) using com-
pounds with five fundamental tastes and chlorophenols, ten
panelists were randomly selected for the sensory test (19-45
years old; average, 28 years old). Selected panelists were
trained periodically by the recognition sensory test using the
five fundamental tastes, chlorophenols, and a water solution
dipped with several kinds of molded resin plates.
Model reactions of hindered phenol and free chlorine
The solution of 2,4-di-tert-butylphenol (4) or 2,6-di-tert-
butylphenol (5) (100 mg) in ethanol (100 ml) was added to
Milli-Q water (1000 mL) and 5% aqueous NaClO (10 mL),
and incubated at 50℃ for 12 h. After the pH of the solution
was adjusted to 4.0 with acetic acid, the acidified solution
was extracted with benzene (2 × 100 mL). The combined
organic phase was dried with Na2SO4 and evaporated in vac-
uum. The obtained products were analyzed by GC/MS (GC:
Shimadzu GC17, MS: Shimadzu QP5050A) using a silicon
DB-1 capillary column (0.32 mmf × 30 m, thickness 0.25
μm, 100-250℃, He 13 mL/min) and a quadrupole electrode
(1.6 kV) in the positive ion mode at m/z 45-500, and by 1H-
and 13C-NMR (JEOL α-500) in CDCl3. Some products were
isolated by silica gel column chromatography (hexane:ethyl
acetate = 10:1 to 4:1). Three products, 6-chloro-2,4-di-tert-
butylphenol (42), 2,6-di-tert-butyl-1,4-benzoquinone (52),
2,2’,6,6’-tetra-tert-butyl-4,4’-biphenol (55), which were
derived from the model reactions, were identified from the
comparison of relative retentions to phenanthrene-d10 and
mass spectra of standard compounds. Other products were
identified by the comparison of relative retentions to phenan-
threne-d10 and mass spectra of similar standard compounds.
Synthesis of 6-chloro-2,4-di-tert-butylphenol (42) Ac-
cording to the reported method (Tashiro et al., 1981), 6-chlo-
ro-2,4-di-tert-butylphenol was prepared by chlorination of
2,4-di-tert-butylphenol, with slight modification. Briefly,
SO2Cl2 (6 ml, 60.1 mmol) in CCl4 (20 ml) was added drop-
wise to a solution of 2,4-di-tert-butylphenol (4.16 g, 20.2
mmol) in CCl4 (40 ml) at room temperature for over 30 min.
Then the mixture was heated with stirring at 85℃ overnight
and poured onto ice water (200 ml). The CCl4 layer was
separated, dried over Na2SO4, and evaporated to give a crude
oily residue (4.97 g). The residue was chromatographed on
silica gel (Silica gel 60N, Kanto Chemical Co., 63-210 μm)
eluting with hexane:CH2Cl2 = 3:1, to afford a colorless syrup
(4.04 g, 83%). 1H NMR (CDCl3, 500 MHz) d = 1.28 and 1.41
(18H, s, tert-butyl), 5.69 (1H, s, OH), and 7.19 and 7.20 (1H,
d, J = 1.83 Hz, H-3 and 5); 13C NMR (CDCl3, 125 MHz) d =
29.39, 31.43, 34.44, 35.40, 120.30, 122.80, 123.20, 136.62,
143.07, and 147.21; GC/MS (1.6 kV) m/z (relative intensity
%) 240 (M+, 17), 242 ([M+2]+, 5), 225 (100), 227 (33), and
57 (53).
Results and DiscussionEstablishment of the sensory test method for determina-
tion of threshold concentrations of hindered phenols In the
present study, a sensory test was designed and its appropri-
ateness was evaluated by comparing the values of threshold
concentration for phenols and chlorophenols determined
by the test with those previously reported. The threshold
concentrations for taste were determined for phenol, 2-chlo-
rophenol, 2,4-dichlorophenol, and 2,6-dichlorophenol based
on the evaluation of differences in taste including odor of
the sample from the control water when the solutions were
placed in the mouth. Taste and odor were undesirable for
these samples, although these should not have been distin-
guishable in the present sensory test. The threshold concen-
trations of phenol and chlorophenols were represented using
the values of BET, and compared with those previously re-
ported (Burttschel et al., 1959) (Table 2). The aqueous sam-
ple solutions were diluted 4 times with the control water us-
Taste of Hindered Phenols in Beverages
Best-estimatethreshold (BET)
log10 BET Standard logdeviation From the literaturea
7.05.2023lonehp ＞ 1000
2-chlorophenol 2.4 0.4 0.8 4
2,4-dichlorophenol 7.7 0.9 0.6 8
2,6-dichlorophenol 1.4 0.1 0.8 2
a Burttschell et al ., 1959.
Compound
Thereshold concentration (µg/L)
Table 2. Threshold concentrations of phenol and chlorophenols.
493
t. YaMaMoto et al.
Fig. 1. Hindered phenols 1-10 used in the sensory test in the presence and absence of free chlorine.Phenols were classified into four groups: non-substituted, phenol (1); mono-substituted, 2-tert-butylphenol (2); di-substituted, 2-tert-butyl-4-methylphenol (3), 2,4-di-tert-butylphenol (4), 2,6-di-tert-butylphenol (5), and 3,5-di-tert-butylphenol (6); and tri-substituted, 2,6-di-tert-butyl-4-methylphenol (7), Irganox 1135 (8), Irganox 1076 (9), and Irganox 1010 (10).
OH OH OH OH
OHOH OH
HO
O
O C18H37
HO
O
O C8H17
1 23
4
5 67
8 9
10
O
OH
O
O
OH
O
O
O
O
O
O
O
ing fixed dilution factors (Df) (Table 1). The series of diluted
samples were presented to ten panelists by 3-AFC presenta-
tions, where the samples were presented in the order from
smaller to larger concentrations. The BET values for each
panelist was determined by calculating the average between
the concentration at which the last incorrect choice was
made and the next higher concentration at which a correct
choice was made, and the BET value of the compound and
its standard log deviation was statistically calculated from
log10BET values of all panelists to allow the individual varia-
tion in sensitivity of preferences and strength of taste. Table
2 showed that phenol was almost tasteless (BET = 320 μg/L),
and that the chlorinated derivatives, especially 2,6-dichloro-
phenol, had a very strong taste (BET = 1.4 μg/L). Absolute
BET values and their magnitude of difference between the
samples were quite consistent with those previously reported
(Burttschel et al., 1959). Consequently, the present sensory
test method was confirmed to be effective and appropriate.
Decrease in threshold concentrations of hindered phenol
by reaction with free chlorine To test the situation within
the water tank of the beverage machines, taste of phenol
(1) and hindered phenols 2-10 (Fig. 1) combined with free
chlorine (0.3 mg/L) was examined by the sensory test. The
494
phenols having bulky substituents 2-10 corresponded to the
hindered phenols, and tri-substituted hindered phenols 7-10
having substituents on the 2,4,6 positions, are widely used
as antioxidants for resin materials. To begin with the test,
the control water was tested to confirm it had no taste in the
absence and presence of free chlorine (0.3 mg/L). Tap water
rather than deionized or distilled water was needed in this
experiment, because some degree of electric conductivity
was required to generate free chlorine by electrolysis.
The BET values of each phenol solution before and af-
ter treatment with free chlorine are shown in Table 3. The
parameters calculated by log[BET(+Cl2)/BET(-Cl2)] were
the logarithmic ratio of threshold concentrations in the BET
value, and were used for estimation of the magnitude of the
change in the BET by free chlorine. For example, the value
-3.0 for phenol (1) indicated that the threshold concentration
of phenol solution remarkably decreased in three logarithmic
orders (10-3) by free chlorine addition. In the cases of solu-
tions with non-, mono-, and di-substituted phenols 1-6, the
threshold concentrations decreased in one logarithmic order
by free chlorine addition. This is the first experimental proof
that hindered phenols generate compounds having more in-
tense taste by free chlorine treatment. However, in the case
of solutions with tri-substituted phenols 7-10, the threshold
concentrations did not change after free chlorine treatment.
Figure 2 clearly shows that the number of free 2, 4, and 6
positions on the aromatic ring is strongly correlated with the
magnitude of decrease in threshold concentrations, shown by
log[BET(+Cl2)/BET(-Cl2)]. This correlation is attributable
to the fact that the ortho and para positions (2, 4, and 6) of
phenols are susceptible to electrophilic substitution rather
than the meta position (3 and 5). Antioxidative hindered phe-
nols having alkyl substituents to protect these positions were
unaffected by free chlorine treatment. The bulky tert-butyl
substituent partly contributed to the suppressed reactivity,
because less reactivity observed for 3,5-di-tert-butylphenol
(6) than the non-substituted phenol (1).
Taste of Hindered Phenols in Beverages
Starting hindered phenol
log10 BET Standard logdeviation
log10 BET Standard logdeviation
phenol (1) none-substituted 320 2.5 0.7 0.3 -0.5 0.7 -3.0
2-tert -butylphenol (2) mono-substituted 50 1.7 0.8 2.0 0.3 0.8 -1.4
2-tert -butyl-4-methylphenol (3) 75 1.9 0.5 10 1.0 1.2 -0.9
2,4-di-tert -butylphenol (4) 4400 3.6 0.3 290 2.5 1.3 -1.2
2,6-di-tert -butylphenol (5) 30 1.5 0.8 7.5 0.9 1.1 -0.6
3,5-di-tert -butylphenol (6) 1300 3.1 0.7 100 2.0 1.2 -1.1
BHT (7) 13 1.1 0.8 13 1.1 0.8 0.0
Irganox 1135 (8) 52 1.7 1.3 41 1.6 1.1 -0.1
Irganox 1076 (9) 54 1.7 0.8 43 1.6 0.8 -0.1
Irganox 1010 (10) 140 2.2 0.9 300 2.5 0.4 0.3
log10
[BET(+Cl2)
/BET(-Cl2)]
Before treatment (-Cl 2 lC+(tnemtaertretfA) 2)
Best-estimatethreshold (BET)
Best-estimatethreshold (BET)
Classification
Thereshold concentration (µg/L)
di-substituted
tri-substituted
-4
-3
-2
-1
0
1
2
0 1 2 3
Number of free 2,4,6 positionson the aromatic ring
)/B
ET
(-C
l)] 2
Lo
g[B
ET
(+C
l 2
Table 3. Threshold concentrations of hinderd phenol solutions before and after treatment with free chlorine.
Fig. 2. Relationship between the magnitude of decrease in threshold concentrations of hindered phenols by free chlorine and the number of free 2,4,6 positions on the aromatic ring.
BET(-Cl2): Threshold concentrations before the addition of free chlorine, BET(+Cl2): Threshold concentrations after the addition of free chlorine, ■: phenol (1), ●: 2-tert-butylphenol (2), □: 2-tert-butyl-4-methylphenol (3), ○: 2,4-di-tert-butylphenol (4), ◆: 2,6-di-tert-butylphenol (5), ×: 3,5-di-tert-butylphenol (6), ◇: 2,6-di-tert-butyl-4-methylphenol (7), △: Irganox 1135 (8), —: Irganox 1076 (9), ▲: Irganox 1010 (10).
495
Structural characterization and threshold concentration
of reaction products of hindered phenols with free chlorine
Among hindered phenols with decreased threshold concen-
trations by free chlorine treatment, 2,4-di-tert-butylphenol
(4) and 2,6-di-tert-butylphenol (5) were further subjected to
the model reaction with free chlorine derived from sodium
hypochlorite (equivalent to 0.5 mg/L free chlorine). The re-
sulted reaction mixtures were analyzed by GC/MS. Various
reaction products were produced through chlorination (42-45,
51, 53), ring-opening (41, 43, 45, 54), oxidation (44, 52, 55),
and dimerization (55), as summarized in Table 4. Chlorina-
tion was estimated based on the presence and intensity of
the peaks for [M+2]+ and [M+4]+ in the mass spectra. Ring-
opening, oxidation, and dimerization were estimated by the
t. YaMaMoto et al.
Reactionproduct
Adjusted retention time (min）
Relative retention to phenanthrene-d10
Compound M+ (m/z)TIC
Intensityb
41 -)gninepo-gnir(nwonknu36.08.6 ++
42f 8.5 0.79 6-chloro-2,4-di-tert -butylphenol 240 ++
43 9.4 0.88 unknown (chlorination, ring-opening) - +++
44e,h 9.9 0.92 4-chloro-2.6-di-tert -butylphenol 240 ++
45 10.7 1.00 unknown (chlorination, ring-opening) - ++
51e,g 5.7 0.53 2-tert -butyl-6-chlorophenol 184 +
52c,f 8.2 0.76 2,6-di-tert -butyl-1,4-benzoquinone 220 +++
53e,h 9.9 0.92 4-chloro-2,6-di-tert -butylphenol 240 +
54 -)gninepo-gnir(nwonknu70.15.11 ++
55d,f 17.4 1.62 2,2',6,6'-tetra-tert -butyl-4,4'-biphenol 410 +++
a GC/MS conditions: Shimadzu GC-17, Column Silicon DB-1 (ID 0.32 mm, 0.25 mm, 30 m),Injection oven, 250°C; column oven, 100°C (kept for 5 min) to 250°C (15°C/min).
Carrier gas He (13 mL/min), Shimadzu QP5050A, 1.6 kV, Mass range < 500.b Intensity of total ion chlomatogram; +++: strong, ++: medium, +: weak.c
3, 500 MHz) d = 1.28 (18H, s, tert-butyl), and 6.51 (2H, s, H-3 and 5).d 1H NMR (CDCl3, 500 MHz) d = 1.37 (36H, s, tert -butyl), 4.12 (2H, s, OH), and 7.71 (4H, s, H-3, 3’, 5, 5’)
13C NMR (CDCl3, 125 MHz) d = 29.40, 35.58, 130.16, 157.93, 187.82, and 189.12.e The structures were tentatively identified with MS.f The relative retention of the compounds were confirmed by comparing with those of the standard compounds.g This compound showed a similar mass spectrum, but a different relative retention with the standard compound 4-chloro-2- tert -butylphenol.h This compound showed a similar mass spectrum, but a different relative retention with the standard compound 6-chloro-2,4-di- tert -butylphenol.
1H NMR (CDCl
Table 4. Summary of characterization of GC/MS analysis of reaction products of hindered phenols 4 and 5 with free chlorinea.
OH
Cl
O
O
OH
OH
42 52
55
Fig. 3. Compounds determined by their threshold concentrations to be reaction products of hindered phenols 4 and 5 with free chlorine: 6-chloro-2,4-di-tert-butylphenol (42), 2,6-di-tert-butyl-1,4-benzoquinone (52), 2,2’,6,6’-tetra-tert-butyl-4,4’-biphenol (55).
496
fragment ions in the mass spectra. The products reasonably
identified by mass spectrometry and the relative retention to
phenanthrene-d10 in gas chromatography are listed by name
in Table 4.
The threshold concentrations of three compounds,
6-chloro-2,4-di-tert-butylphenol (42), 2,6-di-tert-butyl-1,4-
benzoquinone (52), 2,2’,6,6’-tetra-tert-butyl-4,4’-biphenol
(55), showing relatively strong intensity in the TIC of the
resulting reaction mixtures, were determined by the sensory
test (Fig. 3, Table 5). These compounds were formed by dif-
ferent reaction pathways, including chlorination, oxidation,
and dimerization (Table 4). The significance of contribution
of each compound could be estimated, when the BET values
of the compounds were smaller than those of the resulting
reaction mixture of 4 and 5 with free chlorine. The logarith-
mic values of BET for compounds 42 (1.0), 52 (0.0), and 55
(0.4) were significantly smaller compared to those for 4 (2.5)
and 5 (0.9). The values of log[BET(compound)/BET(starting
material + Cl2)] ranged from -1.5 to -0.5, thus confirming the
individual contribution of compounds 42, 52, and 55 to the
increasing taste of solution 4 and 5 after treatment with free
chlorine.
The present study confirmed for the first time that hin-
dered phenols with substitutions at the 2, 4, and 6 positions
generate compounds having more intense taste when reacted
with free chlorine. The less substitutions at 2, 4, and 6 po-
sitions (0 to 3) on the phenolic aromatic ring, the greater
magnitude of decrease in the threshold concentrations in the
presence of free chlorine. Thus, the magnitude of decrease in
the threshold concentrations for the antioxidative hindered
phenols was very small in the presence of free chlorine. Ac-
cordingly, the antioxidative hindered phenols themselves
showed almost no contribution to the unpleasant taste caused
by free chlorine. However, it has been recognized that resin
materials containing antioxidative hindered phenols which
had reacted with free chlorine resulted in unpleasant taste
after heating during the molding process (Yamamoto et al.,
unpublished data). If less substituted phenols were derived
from antioxidative hindered phenols by heating, they may
generate compounds having more intense taste under the
influence of free chlorine. Further studies are thus needed to
investigate the effect of heating on taste of antioxidative hin-
dered phenols.
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52 2,6-di-tert -butyl-1,4-benzoquinone 5 1.1 0.0 1.6 -0.8 +
55 2,2',6,6'-tetra-tert -butyl-4,4'-biphenol 5 2.4 0.4 1.3 -0.5 +
a The thereshold concentrations of the starting material after the reaction with free chlorine were 290 µg/L for 4 and 7.5 µg/L for 5 (see Table 3).b Compounds 52 and 55 were commercially available. Compound 42 was synthesized by chemical reaction of 2,4-di-tert -butylphenol with SO2Cl2 (Tashiro et al ., 1981).
c The logarithmic ratio of threshold concentration of starting compound with free chlorine and that of the reaction product. A small value indicates a large free chlorine effect on the threshold concentration of the identified reaction product.
d The contributiuon of the compound to taste was estimated when the threshold concentraion of the compound was smaller than that of the starting material after the reation with free chlorine.
Thereshold concentration (µg/L)b
Contribution of reaction
products to tasted
Table 5. Threshold concentrations of identified reaction products of hinderd phenol with free chlorine.
Taste of Hindered Phenols in Beverages 497
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