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Influence of oat gum, guar gum and carboxymethyl cellulose on the perception of sweetness and flavour
Food Hydrocolloids
vei.« no.6 pp.525-532. 1')')3
Influence of oat gum, guar gum and carboxymethyl cellulose on the perception of sweetness and flavour Y.Malkki, R.-L.Heini6 and K.Autio VTT Technical Research Centre of Finland, Food Research Laboratory, P. O. Box 203, SF-02151 Espoo, Finland Abstract. The influence of three pseudoplastic hydrocolloids. oat gum. guar gum and carboxymethyl cellulose (CMC) on sensory perception of sweetness and flavour was studied in model systems at two viscosity levels. The sweeteners studied were sucrose. fructose and aspartame. the flavour substances ethyl caproate. a-pinene and cinnamic acid. Sweetness was best perceived from oat gum solutions and most weakly from guar gum solutions. The effect of the composition of the thickener on the perception of sweetness was greater than that of viscosity. Reduction of sweetness by hydrocolloids was weaker for aspartame than for fructose or sucrose. In the perception of flavours. both the total length of perception and the time-intensity pattern were more dependent on the model aroma substance than on the thickener. Possible explanations for the differences are discussed.
Introduction
Thickeners and gelling agents are known to modify the perception of both sweetness and flavour. This effect is especially noticeable in gels, where the perception is primarily controlled by efficiency of melting or breaking down the gel in the mouth, by the diffusion of the taste giving or flavouring substances to the surface of broken gel particles, and by the evaporation of flavouring substances. As reviewed by Mitchell (1), there is some evidence to show that the masking effect of polysaccharide-induced viscosity on taste intensity is related to the degree of non-Newtonian behaviour, but also specific effects of the polysaccharides have been shown. Other factors, physical, chemical, physiological or psychological, might also be involved, and the total mechanism of modification is not always known. In formulating food products, this effect causes difficulties, since even slight variations in the gel rigidity can substantially alter the taste or flavour perceived. This difficulty might often be overcome by using thickeners which are pseudoplastic in nature instead of gelling substances. Unless interactions between these compounds and the thickener occur, the transfer of the tastegiving substances to taste receptors and the evaporation of volatile substances during chewing of pseudoplastic foods are reduced mainly by the viscosity. Even this effect is reduced by the elevation of the sample temperature in the mouth. In our earlier studies oat gum has shown interesting rheological properties (2), which can indicate possibilities for its use as a thickener in various foods. Its known properties of causing a reduction of serum cholesterol and affecting resorption of sugars indicate a potential for its use in preparations for clinical nutrition. The purpose of the present study is to compare its effects on the perception of sweetness and aroma with the effects of two commonly used pseudoplastic thickeners. 525
Y.Malkki. R.-L.Heinio and K.Autio
Materials and methods The sensory panel consisted of 30 selected panelists trained in sensory evaluation . Extra training was given in the time-intensity technique before the testings. All sensory sessions were carried out in individual booths designed for sensory evaluation . Samples were pre sented coded and in random order. Some of the evaluations were repeated. Stock solutions of sugars were prepared one to three days before sensory evaluations, and stored in a refrigerator at 6 ± 3°e. Stock solutio ns of thickeners as well as sweetened thickeners were prepared in the morning preceding each test session. and stored at room temperature (22 ± 2°C) . Solutions were tempered to 23 ± 1°C for evaluations, which were performed in the afternoon . O at gum was prepared from commercial oat bran in bench scale following the method developed in this laboratory (3). The two lots of isolated gum preparations used in this study had ~-glucan contents of 74.3 and 83.3% in dry matter, as determined according to the method of McCleary and GlennieHolmes (4). The concentrations of oat gum solutions used in the experiments were adjusted to give the ~-glucan content indicated. Guar gum used was No. G4129 from Sigma Chemical Co , St Louis , MO. Carboxymethyl cellulose (CMC) used was Blanose Cellulose Gum Type 7HF, lot No. 259 by Hercules France S.A ., Rueil Malmaison , France . For both of the latter, the concentrations given refer to amounts of these preparations in the solution . Concentrations of hydrocolloids were selected to give as similar viscosity properties as possible on a large range of shear rates around 50 s - I which is in the range operative during oral evaluation of viscosity (5) , and at n oc, the estimated mean temperature in the mouth during mastication. The viscosity levels selected were 230 and 500 mPa s. Viscosity measurements were performed using a Bohlin VOR Rheometer (Bohlin Reologi AB, Lund, Sweden) , at shear rates from 9.25 to 147 S-I . Sweetener solutions were prepared at two concentration levels which each gave equivalent sweetness in plain water solutions tempered to 23°e. The following concentration ratios were found to be equivalent, as verified by paired comparison tests using a panel of 20 members: 10% sucrose equivalent to 9% fructose or to 0.1325 % aspartame , 30% sucrose equivalent to 25.4 % fructose. (At this sweetness level, aspartame gave a bitter taste.) Relative sweetnesses of thickened solutions were determined by using an extended ranking test. Samples studied in each series were ranked according to their sweetness, and in addition scored using the following scale: 0 = not sweet, 1 = slightly sweet, 2 = sweet , 3 = very sweet. The number of panelists varied between 10 and 30. The results were interpreted using the tables of Newell and MacFarlane (6). Perception of flavours was determined from thickened and sweetened solutions by using semi-automatic time-intensity testing equipment, the panelist recording her/his response by moving the lever of a potentiometer. A sample of 10 ml was kept in the mouth for 5 s, after which it was swallowed, and the recording of intensity was continued until the end of sensation . After each 526
Influence of hydrocolloids on sweetness and flavour
sample the mouth was rinsed carefully with water. The time between two samples was at least one minute. The samples were tested by 15 panelists, each of them also repeating the test. The graphically recorded responses from the panelists were digitalized, and averages calculated for recordings at 0.6 s intervals. Each average curve is thus a result of 30 individual tests. From individual records, averages and ranges for the time to reach the maximal intensity, for the total duration of the perception, and for the maximal intensity were calculated. For flavour perception, three flavouring substances were tested, one of terpene type, a-pinene (boiling point 155°C), another of the ester type, ethyl caproate (boiling point 168°C), the third of the aromatic type, cinnamic acid (boiling point 300°C). All of these were tested in 10% sucrose solutions with the higher level of each of the thickeners. Results
Perception of sweetness Equivalent viscosities. Concentrations of thickeners giving equivalent viscosities at the shear rate 50 S-I in the presence of the sweeteners tested are presented in Table I. Viscosities above this shear rate were nearly identical for each of the sweeteners with the same thickener. Guar gum solutions exhibited the highest and oat gum solutions the weakest shear thinning properties. In paired comparison tests with a panel of 20 members it was verified that 10% sucrose solutions of each of the thickeners at the 500 mPa s viscosity level did not differ statistically significantly from each other in the sensory evaluation of the viscosity. Relative sweetness. Results of sensory assessments, divided into eight tests, are presented in Table II. When testing 10% sucrose solutions containing Table I. Concentrations of the thickeners tested giving equal viscosities in sweetener solutions at 27°C and at a shear rate of 50 S-1 Thickener and sweetener
CMC. sucrose CMC. sucrose CMC. fructose CMC, fructose CMC, aspartame Guar gum, sucrose Guar gum, sucrose Guar gum, fructose Guar gum. fructose Guar gum. aspartame Oat gum, sucrose Oat gum, sucrose Oat gum, fructose Oat gum, aspartame
Sweetener concentration %
Thickener concentration 500 mPa s level 230 mPa s level % %
10
0.67 0.60 0.77 0.67 0.80 0.61 0.57 0.65 0.60 0.65 0.81 0.75 0.80 0.85
30 9 25.4 0.1325 10
30 9 25.4 0.1325 10
30 9 0.1325
1.05 0.93 1.07 1.10 0.90 0.85 0.90 0.91 1.02 0.91 1.00 1.07
527
Y.M alkki, Rv-L,Heinie a nd K.Autio
Ta ble II. Ran kin g a nd sco ring (sca le 0-3) of swee tness of th ick en e d so lutio ns Test a nd no o n panel
Thicken er
Visco sity ran ge
Sweetener
1.2U
CMC CMC
Low H igh Low Hi gh Low H igh
Sucrose Sucrose Sucrose Sucrose Sucro se Su cros e
Lo w Low Low Low Low Low
H igh H igh High
Sucrose Suc rose Sucrose
Lo w Lo w Low
G ua r Oat gum
Lo w Lo w Low
Suc rose Su crose Sucrose
CMC CMC CMC CMC CMC
Low Low Low Low Lo w
CMC CMC CMC
G ua r Gu ar Oa t gu m O a t gum
11. 10
CMC
IV .30
V .20
V1.30
VII, 13
V III , 13
Ra nk su m '
66 a
78 a b 85 abc 104 bc 37 ad 50 a bd
Swee t ness , core me a n
s .d .
1.4 \. 2
\. 8
0 .66 0 .66 0.55 0,46 n.65
\.0
U.66
\. 2 0.8
21 ab
U
26 a
\. 1
0,40 0.56
130
1.6
U.6 1
H igh High High
44 47
2.5 2,5 2.3
0.48 0.53 0.56
Suc ro se Fru ct ose As pa rta me Suc rose Fructose
Low Low Low High High
133 a
0 .9 \.0
0,48
Hig h H igh H igh
Sucrose F ructose A spa rt a me
Lo w Low Low
52 a
Gu ar Gua r Guar Gu ar G ua r
Low Low Low Low Low
Sucros e Fru ct ose A spa rt a me Suc rose Fru cto se
Low Lo w Lo w Hi gh Hi gh
132 a 130 a
G ua r Guar G ua r
H igh High H igh
Sucrose Fru ctose Aspa rta me
O at g um Oat gum O at gum
Low Lo w Lo w
Sucro se Fruc tose Aspart am e
G ua r O a t gum
II1.25
Sweetness ra nge
CMC
58
122 ab 103 ab
44 c 47 c 39 ab 29 b
1.5 2.5
2.7
0.67 0.52 0.53 0,43
1.2 1,4 1.9
0.70 0.60
1.1
0,46 0.58 0 .6S 0,45 0,47
1.1
90
1.8
52 b 46 0
2.6
Low Low Lo w
33 a 29 a
1.3 1.3
16
1.8
Lo w Low Low
34 22 3
1.2
22 a
1.7
2.6
\. 8
O.h6
0.60 0.83 0.64 0 .67 0.73 0 .72
• Sta tistic a l sign ifica nce te st ed se pa ra te ly fo r ea ch te st group .
thickeners , both ranking and sco ring indicated that the sweetness intensity was the highe st in oat gum soluti on s and the lowest in guar gum so lutions. This result was obt ained at both viscosity levels tested (Tests 1 and II) . Although all differences were not statistically significant, In the scores of sweetness the tendency was clear. Wh en comparing the sweetn ess of 10% sucrose solutions at both viscosity levels and with all of th e thick eners of the models, the following ranking order of swee tness can be deri ved fro m the result s (Tes ts I and II) : oat gum/low > oat gum/high > CMC/low > CMC/high > guar gum/low > gua r gum/high . Thi s ranking order indicates that the effect of the composition of the thickener was grea ter th an that of viscosity .
528
Influence of hydrocolloids on sweetness and flavour
At the higher sweetener concentrations, the differences in the effect of hydrocolloids were not statistically significant (Tests III, IV and VI). When the three sweeteners were compared in thickened solutions (Tests IV to VIII), it was found, that the sweetness of aspartame was least and sucrose the most affected by all of the thickeners. The effect of the thickeners was dissimilar in respect of fructose and sucrose, especially in the case of oat gum, in solutions of which fructose was as sweet as aspartame (Test VIII). The results at the lower sweetness level can be summarized as follows:
Thickener and level
Ranking order of sweetness
CMC/low: CMC/high:
aspartame > fructose ~ sucrose aspartame > fructose > sucrose
guar gum/low: guar gum/high:
aspartame > fructose = sucrose aspartame > fructose = sucrose
oat gum/low:
aspartame
=
fructose > sucrose
Perception of flavour The perception of flavours from thickened solutions was found to be more dependent on the flavouring substance than on the thickener (Figure 1 and Table III). In all thickener solutions a-pinene gave a very similar time-intensity pattern. It also had the shortest total duration of perception among the flavour substances tested. For cinnamic acid, after the initial rapid rise the maximal intensity was reached later and the total length of perception was on average longer than with the two other flavouring substances. For ethyl caproate, a second intensity peak was observable in guar gum and CMC, but not in oat gum solutions. Indications for a similar behaviour were observable also in cinnamic acid solutions thickened with guar gum. Among the thickeners, there was an indication that the total length of perception would be shortest with oat gum solutions, and the total intensity highest from CMC and lowest from oat gum solutions. However, there was a great variation in the individual responses, which was not balanced in averaging sets of observations. Thus the statistical significance of the perception intensity data is evidently weak. Discussion The difference between the thickeners in the effect on the perception of sweetness can be based on physical, chemical or physiological reasons. In comparison to CMC and guar gum solutions, solutions of oat gum gave similar results as starch in the studies of Vaisey et al. (6). The fact that sweetness was better released even from the higher viscosity level of oat gum solutions than from the lower viscosity level of the other thickeners tested gives reason to assume some kind of chemical bonding or adsorption between sucrose and CMC or guar gum. This would be an obvious explanation, since l3-glucan, the principal component of oat gum, consists of glucose units only, and has only a few charged
529
Y.Miilkki, R.-L.Heiniii and K.Autio
ALPHA-PINENE
% of full scale
80 70 60 50 40 30
20 10
I'"M.
I/- ~ l". ,, ,~\ ~ .~~~ t' ,~ I
.
o~ o
-,
"
15
30
\\ 60
45
75
90
75
90
time (sec) ETHYL CAPROATE
% of full scale
80 70 60 50 40 30
20 10
o
,(\
1/." ~ II' .~\
r--. f\
~.\-
f
~.,
I II
"
r"
v.
~
o
t-.
'4J
'., J
~
... 1\\\ . \ •
15
30
45
"
\
f\
60
\
time (sec) Fig. 1. Time-intensity response (% of full scale) curves for perception of 0.08% a-pinene, 0.08% ethyl caproate, and 0.2% cinnamic acid in 10% sucrose solutions of three thickeners at concentrations giving 500 mPa s viscosity. Each curve is an average from 30 individual recordings. ( - - ) = CMC, ( - - ) = guar guam, (- - - -) = oat gum.
groups in the molecules (7), whereas CMC and guar gum are more complex in their structure. It is also possible that some rheological properties not determined in this study might have influenced perception. Since oat gum is very sticky in nature, it could adhere a longer time on the taste buds than the other thickened solutions tested, and thus enhance and prolong the sweet sensation. Although the thickeners tested have differing temperature coefficients of the viscosity, this is an improbable cause due to the fact that the differences in the viscosities at 27°C between the higher level of oat gum and the lower level of other thickeners were great. In comparison of the effect of the thickeners on flavour perception, oat gum solutions had a tendency to give the lowest maximal intensity of the flavourings. 530
Influence of hydrocolloids on sweetness and flavour
CINNAMIC ACID
% of full scale
80 70 60 50
.
JV I',"
40
30 20 10
N6.
IV'
~M¥"
I
I
I
•
I.~
I
oI
o
I!' , . ..
~'~'il ;~ ~
_r-••
\ f\..\
•
I
15
30
45
60
\ t\
.
'"
\\
75
90
time (sec) Fig. I. Continued.
Table III. Perception of flavours from 10% sucrose solutions with thickeners at 500 mPa (Means and ranges of 30 individual judgements)
5
level
CMC
Guar gum
Oat gum
Ethyl caproate (0.08%) Time [5] to maximum Total duration [sl Max. intensity (%) of scale
9.1 (2-20) 30.8 (15-67) 83.1 (51-100)
8.5 (1-14) 28.4 (II-59) 75.0 (29-100)
9.2 (2-22) 27.3 (13-49) 71.9 (25-100)
a-pinene (0.08%) Time [5] to maximum Total duration [s] Max. intensity (%) of scale
11.4 (5-23) 29.0 (10-56) 70.0 (39-100)
11.8 (3-22) 29.0 (II-57) 62.3 (20-99)
10.7 (2-23) 24.9 (13-50) 52.8 (25-85)
Cinnamic acid (0.2%) Time [s] to maximum Total duration [5] Max. intensity (%) of scale
14.1 (4-43) 33.9 (8-83) 57.8 (24-100)
11.8 (1-37) 29.3 (11-80) 56.2 (17-100)
12.2 (1-43) 29.3 (8-68) 54.2 (13-100)
Also the duration of perception was the shortest with oat gum. On the other hand, CMC tended to give the highest maximum intensities and also the longest total durations. Since viscosities were adjusted to the same level, diffusivities according to Wilke-Chang prediction equation (9) should be similar. Thus the differences caused by the thickeners can only be explained by some kind of bonding between the flavouring substance and the molecules of the thickening agent. Effects similar to those known for cyclodextrin cannot be excluded. The time-intensity method used gave interesting information on the phenomena, but in its interpretation the greatest difficulty encountered was the great variation in the recordings from the different panelists. In addition to the large ranges indicated in Table III, the shape of the individual recording curves often varied, sometimes having two or several peaks. A part of this variation
531
Y.Mlilkki. R.-L.Heiniii and K.Autio
might be caused by the novelty of the method for the panelists, and evidently by a more extended training than that now applied, more uniformity in the recording of perception could be achieved. However, the differences in the recordings of panelists might also indicate important properties not observed or reacted to by all panelists, and thus by merely calculating means of some basic parameters, a part of the information could easily be lost. Although the timeintensity method is no longer new. it evidently is in need of standardization and rules for interpreting the results. Conclusions The results have shown that in pseudoplastic solutions there are distinct differences between thickeners in respect of perception of sweetness and flavour from the solutions. In a comparison of solutions of CMC, guar gum and oat gum, the sweetness is best perceived from oat gum solutions. Different sweeteners are affected differently by the thickening agents. For the time-intensity of flavour perception, the flavouring component has more influence than the thickening agent. There is also an indication that the flavour perception from ~-glucan solutions is shorter in duration and slightly less intensive than from CMC or guar gum solutions. which give nearly similar responses. References l. Mitchell.Lk. (1979) In Mitchell,J.R. and Blanshard,J.M.V. (eds). Polysaccharides in Foods. Butterworth, London. p. 64. 2. Autio,K., Myllyrnaki.O. and Malkk i.Y. (1987) J. Food Sci., 52,1364-1366. 3. Autio.K.; Malkki.Y, and Virtanen,T. (1992) Food Struct., 11,47-54. 4. McCleary.B. and Glennie-Holmes.M, (1985) J. lnst. Brewing, 91. 285-295. 5. Sherman,P. (1988) In Blanshard,J.M.V. and Mitchell,J.R. (eds), Food Structure, its Creation and Evaluation. Butterworths, London, pp. 417-432. 6. Newell,G.J. and MacFarlane,J.D. (1987) J. Food Sci., 52.1721-1725. 7. Vaisey.M .. Brunon.R, and Cooper.J. (1969) J. Food Sci.. 34, 397-400. 8. Varum,K.M. and Srnidsred.O. (1988) Carbohydr. Polym., 9.103-117. 9. Wilke.CR. and Chang.P. (1955) A.l.Ch.E.J.. 1,264-270.
532
vei.« no.6 pp.525-532. 1')')3
Influence of oat gum, guar gum and carboxymethyl cellulose on the perception of sweetness and flavour Y.Malkki, R.-L.Heini6 and K.Autio VTT Technical Research Centre of Finland, Food Research Laboratory, P. O. Box 203, SF-02151 Espoo, Finland Abstract. The influence of three pseudoplastic hydrocolloids. oat gum. guar gum and carboxymethyl cellulose (CMC) on sensory perception of sweetness and flavour was studied in model systems at two viscosity levels. The sweeteners studied were sucrose. fructose and aspartame. the flavour substances ethyl caproate. a-pinene and cinnamic acid. Sweetness was best perceived from oat gum solutions and most weakly from guar gum solutions. The effect of the composition of the thickener on the perception of sweetness was greater than that of viscosity. Reduction of sweetness by hydrocolloids was weaker for aspartame than for fructose or sucrose. In the perception of flavours. both the total length of perception and the time-intensity pattern were more dependent on the model aroma substance than on the thickener. Possible explanations for the differences are discussed.
Introduction
Thickeners and gelling agents are known to modify the perception of both sweetness and flavour. This effect is especially noticeable in gels, where the perception is primarily controlled by efficiency of melting or breaking down the gel in the mouth, by the diffusion of the taste giving or flavouring substances to the surface of broken gel particles, and by the evaporation of flavouring substances. As reviewed by Mitchell (1), there is some evidence to show that the masking effect of polysaccharide-induced viscosity on taste intensity is related to the degree of non-Newtonian behaviour, but also specific effects of the polysaccharides have been shown. Other factors, physical, chemical, physiological or psychological, might also be involved, and the total mechanism of modification is not always known. In formulating food products, this effect causes difficulties, since even slight variations in the gel rigidity can substantially alter the taste or flavour perceived. This difficulty might often be overcome by using thickeners which are pseudoplastic in nature instead of gelling substances. Unless interactions between these compounds and the thickener occur, the transfer of the tastegiving substances to taste receptors and the evaporation of volatile substances during chewing of pseudoplastic foods are reduced mainly by the viscosity. Even this effect is reduced by the elevation of the sample temperature in the mouth. In our earlier studies oat gum has shown interesting rheological properties (2), which can indicate possibilities for its use as a thickener in various foods. Its known properties of causing a reduction of serum cholesterol and affecting resorption of sugars indicate a potential for its use in preparations for clinical nutrition. The purpose of the present study is to compare its effects on the perception of sweetness and aroma with the effects of two commonly used pseudoplastic thickeners. 525
Y.Malkki. R.-L.Heinio and K.Autio
Materials and methods The sensory panel consisted of 30 selected panelists trained in sensory evaluation . Extra training was given in the time-intensity technique before the testings. All sensory sessions were carried out in individual booths designed for sensory evaluation . Samples were pre sented coded and in random order. Some of the evaluations were repeated. Stock solutions of sugars were prepared one to three days before sensory evaluations, and stored in a refrigerator at 6 ± 3°e. Stock solutio ns of thickeners as well as sweetened thickeners were prepared in the morning preceding each test session. and stored at room temperature (22 ± 2°C) . Solutions were tempered to 23 ± 1°C for evaluations, which were performed in the afternoon . O at gum was prepared from commercial oat bran in bench scale following the method developed in this laboratory (3). The two lots of isolated gum preparations used in this study had ~-glucan contents of 74.3 and 83.3% in dry matter, as determined according to the method of McCleary and GlennieHolmes (4). The concentrations of oat gum solutions used in the experiments were adjusted to give the ~-glucan content indicated. Guar gum used was No. G4129 from Sigma Chemical Co , St Louis , MO. Carboxymethyl cellulose (CMC) used was Blanose Cellulose Gum Type 7HF, lot No. 259 by Hercules France S.A ., Rueil Malmaison , France . For both of the latter, the concentrations given refer to amounts of these preparations in the solution . Concentrations of hydrocolloids were selected to give as similar viscosity properties as possible on a large range of shear rates around 50 s - I which is in the range operative during oral evaluation of viscosity (5) , and at n oc, the estimated mean temperature in the mouth during mastication. The viscosity levels selected were 230 and 500 mPa s. Viscosity measurements were performed using a Bohlin VOR Rheometer (Bohlin Reologi AB, Lund, Sweden) , at shear rates from 9.25 to 147 S-I . Sweetener solutions were prepared at two concentration levels which each gave equivalent sweetness in plain water solutions tempered to 23°e. The following concentration ratios were found to be equivalent, as verified by paired comparison tests using a panel of 20 members: 10% sucrose equivalent to 9% fructose or to 0.1325 % aspartame , 30% sucrose equivalent to 25.4 % fructose. (At this sweetness level, aspartame gave a bitter taste.) Relative sweetnesses of thickened solutions were determined by using an extended ranking test. Samples studied in each series were ranked according to their sweetness, and in addition scored using the following scale: 0 = not sweet, 1 = slightly sweet, 2 = sweet , 3 = very sweet. The number of panelists varied between 10 and 30. The results were interpreted using the tables of Newell and MacFarlane (6). Perception of flavours was determined from thickened and sweetened solutions by using semi-automatic time-intensity testing equipment, the panelist recording her/his response by moving the lever of a potentiometer. A sample of 10 ml was kept in the mouth for 5 s, after which it was swallowed, and the recording of intensity was continued until the end of sensation . After each 526
Influence of hydrocolloids on sweetness and flavour
sample the mouth was rinsed carefully with water. The time between two samples was at least one minute. The samples were tested by 15 panelists, each of them also repeating the test. The graphically recorded responses from the panelists were digitalized, and averages calculated for recordings at 0.6 s intervals. Each average curve is thus a result of 30 individual tests. From individual records, averages and ranges for the time to reach the maximal intensity, for the total duration of the perception, and for the maximal intensity were calculated. For flavour perception, three flavouring substances were tested, one of terpene type, a-pinene (boiling point 155°C), another of the ester type, ethyl caproate (boiling point 168°C), the third of the aromatic type, cinnamic acid (boiling point 300°C). All of these were tested in 10% sucrose solutions with the higher level of each of the thickeners. Results
Perception of sweetness Equivalent viscosities. Concentrations of thickeners giving equivalent viscosities at the shear rate 50 S-I in the presence of the sweeteners tested are presented in Table I. Viscosities above this shear rate were nearly identical for each of the sweeteners with the same thickener. Guar gum solutions exhibited the highest and oat gum solutions the weakest shear thinning properties. In paired comparison tests with a panel of 20 members it was verified that 10% sucrose solutions of each of the thickeners at the 500 mPa s viscosity level did not differ statistically significantly from each other in the sensory evaluation of the viscosity. Relative sweetness. Results of sensory assessments, divided into eight tests, are presented in Table II. When testing 10% sucrose solutions containing Table I. Concentrations of the thickeners tested giving equal viscosities in sweetener solutions at 27°C and at a shear rate of 50 S-1 Thickener and sweetener
CMC. sucrose CMC. sucrose CMC. fructose CMC, fructose CMC, aspartame Guar gum, sucrose Guar gum, sucrose Guar gum, fructose Guar gum. fructose Guar gum. aspartame Oat gum, sucrose Oat gum, sucrose Oat gum, fructose Oat gum, aspartame
Sweetener concentration %
Thickener concentration 500 mPa s level 230 mPa s level % %
10
0.67 0.60 0.77 0.67 0.80 0.61 0.57 0.65 0.60 0.65 0.81 0.75 0.80 0.85
30 9 25.4 0.1325 10
30 9 25.4 0.1325 10
30 9 0.1325
1.05 0.93 1.07 1.10 0.90 0.85 0.90 0.91 1.02 0.91 1.00 1.07
527
Y.M alkki, Rv-L,Heinie a nd K.Autio
Ta ble II. Ran kin g a nd sco ring (sca le 0-3) of swee tness of th ick en e d so lutio ns Test a nd no o n panel
Thicken er
Visco sity ran ge
Sweetener
1.2U
CMC CMC
Low H igh Low Hi gh Low H igh
Sucrose Sucrose Sucrose Sucrose Sucro se Su cros e
Lo w Low Low Low Low Low
H igh H igh High
Sucrose Suc rose Sucrose
Lo w Lo w Low
G ua r Oat gum
Lo w Lo w Low
Suc rose Su crose Sucrose
CMC CMC CMC CMC CMC
Low Low Low Low Lo w
CMC CMC CMC
G ua r Gu ar Oa t gu m O a t gum
11. 10
CMC
IV .30
V .20
V1.30
VII, 13
V III , 13
Ra nk su m '
66 a
78 a b 85 abc 104 bc 37 ad 50 a bd
Swee t ness , core me a n
s .d .
1.4 \. 2
\. 8
0 .66 0 .66 0.55 0,46 n.65
\.0
U.66
\. 2 0.8
21 ab
U
26 a
\. 1
0,40 0.56
130
1.6
U.6 1
H igh High High
44 47
2.5 2,5 2.3
0.48 0.53 0.56
Suc ro se Fru ct ose As pa rta me Suc rose Fructose
Low Low Low High High
133 a
0 .9 \.0
0,48
Hig h H igh H igh
Sucrose F ructose A spa rt a me
Lo w Low Low
52 a
Gu ar Gua r Guar Gu ar G ua r
Low Low Low Low Low
Sucros e Fru ct ose A spa rt a me Suc rose Fru cto se
Low Lo w Lo w Hi gh Hi gh
132 a 130 a
G ua r Guar G ua r
H igh High H igh
Sucrose Fru ctose Aspa rta me
O at g um Oat gum O at gum
Low Lo w Lo w
Sucro se Fruc tose Aspart am e
G ua r O a t gum
II1.25
Sweetness ra nge
CMC
58
122 ab 103 ab
44 c 47 c 39 ab 29 b
1.5 2.5
2.7
0.67 0.52 0.53 0,43
1.2 1,4 1.9
0.70 0.60
1.1
0,46 0.58 0 .6S 0,45 0,47
1.1
90
1.8
52 b 46 0
2.6
Low Low Lo w
33 a 29 a
1.3 1.3
16
1.8
Lo w Low Low
34 22 3
1.2
22 a
1.7
2.6
\. 8
O.h6
0.60 0.83 0.64 0 .67 0.73 0 .72
• Sta tistic a l sign ifica nce te st ed se pa ra te ly fo r ea ch te st group .
thickeners , both ranking and sco ring indicated that the sweetness intensity was the highe st in oat gum soluti on s and the lowest in guar gum so lutions. This result was obt ained at both viscosity levels tested (Tests 1 and II) . Although all differences were not statistically significant, In the scores of sweetness the tendency was clear. Wh en comparing the sweetn ess of 10% sucrose solutions at both viscosity levels and with all of th e thick eners of the models, the following ranking order of swee tness can be deri ved fro m the result s (Tes ts I and II) : oat gum/low > oat gum/high > CMC/low > CMC/high > guar gum/low > gua r gum/high . Thi s ranking order indicates that the effect of the composition of the thickener was grea ter th an that of viscosity .
528
Influence of hydrocolloids on sweetness and flavour
At the higher sweetener concentrations, the differences in the effect of hydrocolloids were not statistically significant (Tests III, IV and VI). When the three sweeteners were compared in thickened solutions (Tests IV to VIII), it was found, that the sweetness of aspartame was least and sucrose the most affected by all of the thickeners. The effect of the thickeners was dissimilar in respect of fructose and sucrose, especially in the case of oat gum, in solutions of which fructose was as sweet as aspartame (Test VIII). The results at the lower sweetness level can be summarized as follows:
Thickener and level
Ranking order of sweetness
CMC/low: CMC/high:
aspartame > fructose ~ sucrose aspartame > fructose > sucrose
guar gum/low: guar gum/high:
aspartame > fructose = sucrose aspartame > fructose = sucrose
oat gum/low:
aspartame
=
fructose > sucrose
Perception of flavour The perception of flavours from thickened solutions was found to be more dependent on the flavouring substance than on the thickener (Figure 1 and Table III). In all thickener solutions a-pinene gave a very similar time-intensity pattern. It also had the shortest total duration of perception among the flavour substances tested. For cinnamic acid, after the initial rapid rise the maximal intensity was reached later and the total length of perception was on average longer than with the two other flavouring substances. For ethyl caproate, a second intensity peak was observable in guar gum and CMC, but not in oat gum solutions. Indications for a similar behaviour were observable also in cinnamic acid solutions thickened with guar gum. Among the thickeners, there was an indication that the total length of perception would be shortest with oat gum solutions, and the total intensity highest from CMC and lowest from oat gum solutions. However, there was a great variation in the individual responses, which was not balanced in averaging sets of observations. Thus the statistical significance of the perception intensity data is evidently weak. Discussion The difference between the thickeners in the effect on the perception of sweetness can be based on physical, chemical or physiological reasons. In comparison to CMC and guar gum solutions, solutions of oat gum gave similar results as starch in the studies of Vaisey et al. (6). The fact that sweetness was better released even from the higher viscosity level of oat gum solutions than from the lower viscosity level of the other thickeners tested gives reason to assume some kind of chemical bonding or adsorption between sucrose and CMC or guar gum. This would be an obvious explanation, since l3-glucan, the principal component of oat gum, consists of glucose units only, and has only a few charged
529
Y.Miilkki, R.-L.Heiniii and K.Autio
ALPHA-PINENE
% of full scale
80 70 60 50 40 30
20 10
I'"M.
I/- ~ l". ,, ,~\ ~ .~~~ t' ,~ I
.
o~ o
-,
"
15
30
\\ 60
45
75
90
75
90
time (sec) ETHYL CAPROATE
% of full scale
80 70 60 50 40 30
20 10
o
,(\
1/." ~ II' .~\
r--. f\
~.\-
f
~.,
I II
"
r"
v.
~
o
t-.
'4J
'., J
~
... 1\\\ . \ •
15
30
45
"
\
f\
60
\
time (sec) Fig. 1. Time-intensity response (% of full scale) curves for perception of 0.08% a-pinene, 0.08% ethyl caproate, and 0.2% cinnamic acid in 10% sucrose solutions of three thickeners at concentrations giving 500 mPa s viscosity. Each curve is an average from 30 individual recordings. ( - - ) = CMC, ( - - ) = guar guam, (- - - -) = oat gum.
groups in the molecules (7), whereas CMC and guar gum are more complex in their structure. It is also possible that some rheological properties not determined in this study might have influenced perception. Since oat gum is very sticky in nature, it could adhere a longer time on the taste buds than the other thickened solutions tested, and thus enhance and prolong the sweet sensation. Although the thickeners tested have differing temperature coefficients of the viscosity, this is an improbable cause due to the fact that the differences in the viscosities at 27°C between the higher level of oat gum and the lower level of other thickeners were great. In comparison of the effect of the thickeners on flavour perception, oat gum solutions had a tendency to give the lowest maximal intensity of the flavourings. 530
Influence of hydrocolloids on sweetness and flavour
CINNAMIC ACID
% of full scale
80 70 60 50
.
JV I',"
40
30 20 10
N6.
IV'
~M¥"
I
I
I
•
I.~
I
oI
o
I!' , . ..
~'~'il ;~ ~
_r-••
\ f\..\
•
I
15
30
45
60
\ t\
.
'"
\\
75
90
time (sec) Fig. I. Continued.
Table III. Perception of flavours from 10% sucrose solutions with thickeners at 500 mPa (Means and ranges of 30 individual judgements)
5
level
CMC
Guar gum
Oat gum
Ethyl caproate (0.08%) Time [5] to maximum Total duration [sl Max. intensity (%) of scale
9.1 (2-20) 30.8 (15-67) 83.1 (51-100)
8.5 (1-14) 28.4 (II-59) 75.0 (29-100)
9.2 (2-22) 27.3 (13-49) 71.9 (25-100)
a-pinene (0.08%) Time [5] to maximum Total duration [s] Max. intensity (%) of scale
11.4 (5-23) 29.0 (10-56) 70.0 (39-100)
11.8 (3-22) 29.0 (II-57) 62.3 (20-99)
10.7 (2-23) 24.9 (13-50) 52.8 (25-85)
Cinnamic acid (0.2%) Time [s] to maximum Total duration [5] Max. intensity (%) of scale
14.1 (4-43) 33.9 (8-83) 57.8 (24-100)
11.8 (1-37) 29.3 (11-80) 56.2 (17-100)
12.2 (1-43) 29.3 (8-68) 54.2 (13-100)
Also the duration of perception was the shortest with oat gum. On the other hand, CMC tended to give the highest maximum intensities and also the longest total durations. Since viscosities were adjusted to the same level, diffusivities according to Wilke-Chang prediction equation (9) should be similar. Thus the differences caused by the thickeners can only be explained by some kind of bonding between the flavouring substance and the molecules of the thickening agent. Effects similar to those known for cyclodextrin cannot be excluded. The time-intensity method used gave interesting information on the phenomena, but in its interpretation the greatest difficulty encountered was the great variation in the recordings from the different panelists. In addition to the large ranges indicated in Table III, the shape of the individual recording curves often varied, sometimes having two or several peaks. A part of this variation
531
Y.Mlilkki. R.-L.Heiniii and K.Autio
might be caused by the novelty of the method for the panelists, and evidently by a more extended training than that now applied, more uniformity in the recording of perception could be achieved. However, the differences in the recordings of panelists might also indicate important properties not observed or reacted to by all panelists, and thus by merely calculating means of some basic parameters, a part of the information could easily be lost. Although the timeintensity method is no longer new. it evidently is in need of standardization and rules for interpreting the results. Conclusions The results have shown that in pseudoplastic solutions there are distinct differences between thickeners in respect of perception of sweetness and flavour from the solutions. In a comparison of solutions of CMC, guar gum and oat gum, the sweetness is best perceived from oat gum solutions. Different sweeteners are affected differently by the thickening agents. For the time-intensity of flavour perception, the flavouring component has more influence than the thickening agent. There is also an indication that the flavour perception from ~-glucan solutions is shorter in duration and slightly less intensive than from CMC or guar gum solutions. which give nearly similar responses. References l. Mitchell.Lk. (1979) In Mitchell,J.R. and Blanshard,J.M.V. (eds). Polysaccharides in Foods. Butterworth, London. p. 64. 2. Autio,K., Myllyrnaki.O. and Malkk i.Y. (1987) J. Food Sci., 52,1364-1366. 3. Autio.K.; Malkki.Y, and Virtanen,T. (1992) Food Struct., 11,47-54. 4. McCleary.B. and Glennie-Holmes.M, (1985) J. lnst. Brewing, 91. 285-295. 5. Sherman,P. (1988) In Blanshard,J.M.V. and Mitchell,J.R. (eds), Food Structure, its Creation and Evaluation. Butterworths, London, pp. 417-432. 6. Newell,G.J. and MacFarlane,J.D. (1987) J. Food Sci., 52.1721-1725. 7. Vaisey.M .. Brunon.R, and Cooper.J. (1969) J. Food Sci.. 34, 397-400. 8. Varum,K.M. and Srnidsred.O. (1988) Carbohydr. Polym., 9.103-117. 9. Wilke.CR. and Chang.P. (1955) A.l.Ch.E.J.. 1,264-270.
532