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Comparison of the steady rheological characterization of normal and light mayonnaises
Food Hydrocolloids Vol.8 no.3-4 pp.389-400, 1994
Comparison of the steady rheological characterization of normal and light mayonnaises M.Pons. M.J.Galotto and S.Subirats AINA, lnstituto Teenol6gieo Agroalimentario, Pare Tecnologic, P.O. Box 103, Paterna, Valencia, Spain
Introduction
There exist a great number of emulsion products in the food industry, among which we highlight: butter, margarine, mayonnaise, salad creams, milk, icecreams, meat emulsions, etc. Due to the importance of these products, food emulsions represent an area of great relevance within the food industry and require special study. Spanish legislation defines mayonnaise and light sauces as products in the form of semi-solid emulsion, basically made up of edible vegetable oils, eggs or egg yolk, vinegar and lemon juice, with the optional addition of various ingredients (salt, spices, stabilizers, aromatizing agents, colouring, etc.). The term mayonnaise is restricted to those sauces which contain a minimum of 65% oil and 5% egg (expressed in technical egg yolk) and which further present a minimum acidity of 0.2% in acetic acid and a pH lower than 4.2 (R.D. 358/ 1984). Hence, this legislation does not clearly define what is now known by the name of light mayonnaise or light sauces. These continue to be emulsions of oil in water in which the decrease in the percentage of oil leads to the necessity for added stabilising agents, generally hydrocolloids and starches, which avoid the separation of the phases which constitute the emulsion, stabilising the product and giving it the mechanical (rheological and textural) properties characteristic of this kind of product. Like most fluid foodstuffs, sauces show complex rheological behaviour. In general, mayonnaise exhibits pseudoplastic behaviour with a flow threshold, and presents thixotropy (shear stress dependence on the time of shear) (1,2). The information from rheological studies is very useful for this kind of product since it conditions the choice and design of the equipment required in the manufacturing process to supply the parameters which allow a more exhaustive quality control, as well as a measurement of the stability of the product during storage. Thus, the analysis and quantification of mayonnaise on the basis of its consistency, its flow threshold value and the dependent nature of the time of these parameters are of vital importance if we want to have precise knowledge of this kind of product. The aim of the present paper is the physico-chemical characterization of normal and light mayonnaise emulsions, studying the variation with temperature of their rheological properties, analysing the influence of the different oil 389
I\t.Pons, I\t.J.Galotto and S.Subirats
contents of the samples on the flow characteristics, in order to determine their qualitative influence on the internal structure of the emulsion. Materials and methods Commercial samples of standard mayonnaise (KN, KO, YN, CN) and light mayonnaise type sauce (KL, KBC, YL, CL) purchased from retail outlets were analysed selecting those brands with the greatest market share. For each of the mayonnaises the same batch was used in order to avoid possible differences between batches. All the samples were refrigerated at 4°C until their analysis. Measurements were taken in triplicate in samples from different jars of each batch.
Chemical analysis Centesimal chemical characterization of each one of the samples was carried out: moisture, fat content, protein, ash, carbohydrate and pH were analysed according to the Official Analytical Methods of the Spanish Health and Consumer Ministry (1985). The a; of mayonnaises was measured at 25°C using a Novasina Humidat-TH2 Thermoconstanter hygrometer (Novasina AG, Zurich, Switzerland) following the procedure of Kitic (3). Measurement of a., of mayonnaises using an electric hygrometer is difficult because the sensor may become contaminated by the volatile acetic acid of the sample. For this reason all a., measurements in mayonnaises were conducted using a filter (Novasina AG, Universal eVC 21) (4). The time required to attain equilibrium within the sensor chamber was almost 5 h when using the filter eVC 21.
Emulsion stability Stability of mayonnaises was assessed by centrifugation in graduated conical tubes of 10 ml capacity. The volume of the lower aqueous separated phase and also the volume of the oil upper phase were determined. Emulsion stability (E5) was expressed as a percentage of total volume against lower aqueous phase volume. E5 =
(VTOTAL -
VSEPARATED PHASEIVTOTAL)
x 100
As spontaneous separation of the different phases was too slow the separation was done by centrifugation at 4600 r.p.m. for 2.5 h at 15°C using a Medifriger centrifuge. Graduated centrifugal tubes with the different mayonnaises were stored at 37 and 60°C for 23 h afterwards analysing the separated volume in all cases.
Rheological characterization Rheological 390
measurements
of
samples
were
made
In
a
rheometer
Rheological compa rison of mayonnaises
(RO T OV ISCO R V 20) equipped with an M5 osc measuring head (Haa ke Inc ., Saddle Brook , NJ) , using a coaxial cylinde r measur e syste m (gap size of 1.45 mm and cylinder height of 19.6 mm ). Sampl es were kept at 20°C for 15 min be fore the mea suremen ts were ob taine d (5,6) . Rh eo logical a na lysis of mayo nnaises was carried out in two steps . In the first step the te mpe rature effect on the flow be hav io ur of eac h one o f the samples was studied . Thi s study was done by compa rison and ana lysis of the different rh eological parameters obtained from the Ostwald and Casson rheological models and at five different temperatures. Afterwards time-d ependence rh eological beh aviou r (thixotropic beh aviour) was studie d according to the Weltm an and Hahn math em at ical mod els at 20°C (1). Th e flow curve of samples was carr ied out with a viscome ter working in a utomatic mode where th e shea r rat e increas ed fro m 0 to 100 S- I in 1 min and then decreased to 0 S- I in 1 min . For each sa mple rheograms were obta ined at 5, 10, 20, 25 and 30°e. Rheological param et er s K (consistency coefficient) and /1 (flow beh aviour index) were determined from the pow er law equation (Equation 1), the most frequently used rh eological equation for describin g the flow behaviour of pse udo plastic foods. T
=
K-y"
(1)
wher e T is the shea r stress (Pa) , -y is th e shea r rat e (S -I) . For those samples which presented yield stress (TO)' the Casson equation ( Equatio n 2) was used to describe their flow behaviour
Th e A rrhe nius equa tion (Equa tion 3) was used to study the effect of te mpe ra ture on th e rhe ological p rop erties of food s 'll a p =
A .eEl/fR oT
(3)
where Ea is the activation ene rgy in Kcal/f'K'mol . R is the gas co nsa nt, T is the te mpe rature in OK and B is a co nsta nt. Kn owing the Ea allows us to determine th e viscosity or consisten cy of that pr oduct at different temperatures. In general , as Ea incre ases the temperature dependence of th e viscosity increases. The activation energy of th e sa mples (Ea) was det ermin ed from linear regression analysis of the apparent viscosity at 100 s- ) and the reciprocal value of the abso lute temperature (OK).
Thixotropic behaviou r Th e time dependence observed in some products is due to the structura l modifica tion produced by the shear. Hen ce the application of exte rna l forces influences th e intern al struc ture cau sing distortion of the arra ngeme nt of the dissolving pol ymeri c molecules a nd deflocculation of the particl es of the disperse phase of the emulsion, as in the case of mayonn aise. T he be hav iour of the
391
I\1.Pons, M.J.Galotto and S.Suhirats
system depends on the relationship between the magnitude of the applied forces and that of the interparticle and intermolecular forces which define its structure (7). Quantitative analysis of the time-dependent behaviour of samples can be evaluated from shear stress data obtained at a constant shear rate and fitting them to thixotropic mathematical models (1). In the present study thixograms were recorded at 20°C at a constant shear rate of 10 s I for 20 min, the time necessary for samples to reach equilibrium. Mathematical models used to describe the time-dependence behaviour were Weltman model (Equation 4) and Hahn model (Equation 5) -r
(4) (5)
where the constant A) indicates the stress after a short shearing time. The constant A 2 in the Hahn model indicates initial shear stress whose magnitude is also dependent on the equilibrium shear stress. The coefficients B I and B 2 indicate rate of structural breakdown. Results and discussion
Chemical analysis Table 1 presents the chemical analysis of the different commercial mayonnaises analysed (moisture, fat, protein, ash and carbohydrate, including pH). It can be observed that four of the samples (normal mayonnaise) present a mean oil content of ~ 76%, while the other four (light mayonnaise) present a much lower oil content (35%). The lower oil phase shows a higher moisture content. Excluding sample KL, the protein percentage of light samples is much lower than the protein content of normal mayonnaises, which can be explained due to a reduction in the egg yolk content in the formula. This fact is especially important in the KBC sample with the lowest egg yolk content, which presents a lower cholesterol content. Light samples also present a carbohydrate content higher than normal samples, which could be explained by the use of stabilizers such as hydrocolloids or starch used in these samples in order to increase the consistency lost with the oil reduction. Table II shows the qualitative composition of different hydrocolloids obtained from the labels of the samples. The pH of light samples is also lower than that of normal mayonnaises due to an increase in the acetic acid content in order to avoid spoilage by microorganisms. The observed a; of normal mayonnaise was -0.96 and that of light samples was higher, close to 0.98. This fact could be explained by the higher water content of light samples which increases their vapour equilibrium pressure.
Emulsion stability Results obtained after centrifugation of samples allow us to conclude that light
392
Table I. C he mical composition . pH a nd water activity o f normal and light co mme rcia l mayonnaises
Samp le
Moisture (%)
O il (%)
KN KO YN CN KBC KL YL CL
19.70 ± 19.40 ± 14.92 ± 2 1.69 ± 56.0 1 ± 52.85 ± 54. 13 ± 56.4 4 ±
76.47 75.38 78.8 1 76. 19 33.34 37.67 35.52 33.79
0.64 0.34 0.18 0.1 1 0.20 0. 19 0.28 0.23
± 1.87
± 2.09 ± 0.70 ± 0.53 ± 0.29 ± 0.64 ± 0.12 ± 0.08
Protein (%)
Ash (%)
± ± ± ± ± ±
1.45 1.19 1.45 0.86 1.86 2. 16 1.98 0.90
1.43 1.40 1.21 0.81 0.40 0.86 0.65 0.74
0.01 0.03 0.02 0.0 2 0.03 0.01 ± 0.02 ± 0.02
± 0.01 ± 0.0 1 ± 0.01 ± 0.02 ± 0.01 ± 0.01 ± 0.01 ± 0.02
Not e : Ca rbo hydra te percentage was ca lculated by differ ence . Data ar e exp resses as: X ±
Ca rbohydrate (% )
pH
0.95 2.63 3.61 0.45 8.39 6.46 7.72 8 . 13
3.84 3.93 3.94 3.61 3.02 3.08 3.64 3.54
3 ......
± ± ± ± ± ± ±
±
0.01 0.02 0.0 1 0.0 1 D.OI 0.01 0.03 D.OI
D.973 0.966 0.940 0.980 0.988 0.986 0.982 0.996
± ± ± ± ± ± ± ±
0.002 0.002 0.002 0.003 D.OOI 0.001 D.002 0.001
:e
::r
~ '=-"'
-So ~
3e
., 0;
~.
= ~
.:::,
= :; t,;.)
-o t,;.)
=
0;
1;.'
'"
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Table II. Hydrocolloids used as stabilizers in normal and light commercial mayonnaises Sample
Hydrocolloids
KN
Modified starch. locust bean gum Modified starch. locust bean gum Xanthan gum Starches Starch. xanthan gum, CMC Modified starch Starch. locust bean gum. pectin Starches
KG
YN CN KBC
KL YL
CL
Note: Qualitative hydrocolloids composition has been obtained from the labels of the different samples. CMC: Carboxymethyicellulose.
samples present higher stability than normal samples. This fact could be due to the decrease in the oil content compared with the normal samples. The reduction of the oil phase produces a destabilization of the emulsion. In order to avoid this effect, light samples are normally stabilized with hydrocolloids, the principal characteristic of which is their higher capacity to absorb water, producing an increase in the continuous phase viscosity and increasing the emulsion stability. There was no diffrence in the behaviour of commercial samples and those stored at 37°C for 24 h. In both cases light mayonnaises present a higher stability than normal ones. Samples stored for 24 h at 60°C presented the same behaviour in all cases, where a considerable structure compactation can be observed due to a water evaporation process, so a lower accumulation of the aqueous phase in the bottom of the test tubes can be shown. Rheological characterization Consistency coefficient (K) and flow behaviour index (n). Shear sstress data of normal and light mayonnaises were obtained over the shear rate range of 0-100 S-I. The Ostwald equation described the shear rate-shear stress data of all samples very well, with the exception of sample CN, whose correlation coefficients obtained at SoC were not statistically significative. Table III shows the results of the rheological parameters at the studied temperatures. Statistical analyses (variance analyses) reveal statistical differences (P > 0.01) in the rheological parameters K and n for the different samples studied. Out of all of the mayonnaise samples, KL presented a higher dispersion of the results, which could be explained by the higher consistency of the sample. This fact agrees with the higher dispersion of the results observed in all samples at SoC, which could indicate that the sensor used is not the most appropriate one for measuring rheological properties of samples with a high consistency. The higher dispersion of the values could also be due to the difficulty of placing the sample inside the sensor. Figure 1 shows the consistency coefficient of samples analysed. A high range of values can be observed, the extreme values belonging to light mayonnaises. 394
Table III. Rheological parameters from Ostwald model for the different samples and temperatures studied 5°C Sample
K
KN KO YN CN KL KBC YL CL
152 ± 149 ± 206 ± n.s. 255 ± 141 ± 93 ± 71 ±
10°C K
n
6 6 6 7 7 7 6
0.148 0.127 0.177 n.s. 0.115 0.245 0.208 0.249
± 0.007 ± 0.007 ± 0.007
± ± ± ±
0.008 (J.OO8 0.008 0.007
116 127 181 123 225 132 80 67
Note: Data are expressed by the equation:
20°C K
n
± ± ± ± ± ± ± ±
X±
6 7 6 6 7 7 7 7
0.173 0.138 0.191 0.148 0.142 0.238 0.222 0.245
± ± ± ± ± ± ± ±
A./~ fItv'n.
0.007 (J.OO8 0.007 0.007 0.008 0.008 0.008 O.OOS
lOS ± 102 ± 166 ± 124 ± 219 ± 113 ± 65 ± 62 ±
25°C K
n
6 7 7 7 6 7 7 7
O.l75 0.139 0.187 0.104 0.123 0.245 0.230 0.230
± ± ± ± ± ± ± ±
0.007 0.008 0.008 0.008 0.007 0.008 0.008 (J.OOS
77 101 153 126 213 III 61 59
3WC
K
n
± ± ± ± ± ± ± ±
6 7 7 6 7 7 7 7
O.l78 0.121 0.173 0.080 O.to5 0.242 0.228 0.227
± ± ± ± ± ± ± ±
0.007 O,()08 0.008 0.007 0.008 (l.()O8 (U)08 0.001'
74 97 139 119 200 106 57 58
n
± ± ± ± ± ± ± ±
6 O.l70 ± 0.007 7 0.117 ± (l.()O8 7 0.172 ± (l.()O8 6 0.109 ± 0.007 7 0.110 ± 0.008 7 0.241 ± 0.008 7 0.123 ± 0.001' 7 0.223 ± 0.001'
;tJ
:r
~
:r% ;:;0 ~
8
~0:
a·
e
=
So,
:3
.~
§ ~
~
:;;"
Vl
~
\0
M.Pnns.I\1.J.Galnttn and S.Subirats
300
250
KL'~ :-----~---.
200
150
M~
-_~--
KBC 100
~~~=:=;=:===;
YLL:!---CL
"'""'"x'"
~
50
275
280
285
290
295
300
305
Temperature (OK) Fig. l. Effect of temperature on the consistency coefficient of the different normal and light commercial mayonnaises.
Statistical analyses of the results do not allow us to define differences between normal and light mayonnaises. Figure 2 presents the flow behaviour index (n) for all samples studied. Its value was lower than 0.3, which indicates pseudoplastic behaviour in all cases. The pseudoplastic character can also be observed with the significant decrease in the apparent viscosity of the samples as the shear rate increases, as reported by Tiu and Boger and Elliot and Ganz (2,8). Chang et al. (9) explain this feature as being due to the fact that mayonnaise oil droplets are stabilized in the presence of egg yolk in the interphase, so that their deformation is very small when higher shear rates are applied. Figoni and Shoemaker (10) explain this behaviour as due to a f1occulation-deflocculation process of the oil droplets in the aqueous continuous phase; as the shear rate increases, the equilibrium of this process is directed to the droplets deflocculation, producing a decrease in the apparent viscosity of the product. Mayonnaise pseudoplasticity has also been explained (11) as due to the fact that an increase in the shear rate produces a progressive orientation in the arrangement of the disorganized long chain molecules with a lower resistance against flow.
Yield stress The Casson equation was employed to estimate the yield stress of the samples at five different temperatures. The correlation coefficients for the regression analyses of the square roots of the shear stress-shear rate were >0.93 with the exception of sample CN, for which correlation coefficients were not statistically significative for all temperatures. Figure 3 illustrates the effect of temperature on the magnitude of the yield stress. A decrease in the yield stress with the increase in product temperature can be observed in all samples, although the importance of the effect is different 396
Rheological comparisun of mayonnaises
---------~ -=:;;;;-=
29S
290
;1
YN
KN
305
300
TemperaturerK) Fig. 2. Effect of temperature on the flow behaviour index of the different normal and light commercial mayonnaises. 300
-r.;(Pa) 2SO
KL
YN
200
150
~e-
~~~
YN
__"",,,,=::::::-_-:'-==="""",""",,=::C
x~_=
100
: ~--======::::====:;i:====O-=--=::===X
KN ;o;CL
50
YL
0
275
285
295
300
305
Temperature (OK) Fig. 3. Effect of temperature on Casson yield stress of the different normal and light commercial mayonnaises.
for each sample. It is not very important for CL; however, the temperature dependence is more important for samples KL, KN and YN. It can therefore be concluded that samples studied had varying levels of consistency and yield stress. This wide range in the rheological parameters of n ; K and yield stress is in agreement with Elliot and Ganz (8) and Paredes et al. (1), and it indicates that consumer preferences cover a wide range of rheological properties of mayonnaise. Activation energy of flow
The Arrhenius equation was used to describe the effect of temperature on the 397
l\I.POIIS. I\I.J .Galotto and S.Subirats
"2'
~
'-'
~ ,... 0
0 ,...
1
:1
~ :.----
'VJ
0 en
7,8
"E
7,6
0-
7,4"';
U
:> ~
§'
.5
7,2
.r
0.0033
0,00335
0,0034
0,00345
0,0035
0,00355
0,0036
Fig. 4. Arrhenius plot of the apparent viscosity of the different normal and light commercial mayonnaises.
apparent viscosity of mayonnaise at 100 S-1 (Figure 4). This shear rate was selected in order to compare data to previous studies and because it is a shear rate commonly encountered during stirring and oral evaluations (12,13), The regression analysis shows that the Arrhenius equation fits the experimental results very well in all the samples (r 2 > 0.92). The range of calculated Ea was 1.9 to 4.0 Kcal/mol. The effect of temperature on the apparent viscosity of the samples in ascending order was: KL < KBC < CL < YN < YL < KO < KN. From these results, it can be asserted that the oil content affects the Ea of the samples, since normal mayonnaises with a higher oil content are more dependent on temperature,
Thixotropic behaviour The thixotropic behaviour of fluid products produces a decrease in the apparent viscosity of the sample over time. This is due to a restructural change which leads to a gradual decrease in the shear stress that product can support and thus a lower flow resistance (10). Table IV presents the constant of the Weltman and Hahn equations. Both rheological models describe the structural degradation of mayonnaises although the Weltman model fits best (r 2 > 0.87). These results are in agreement with those obtained by Paredes et al. (14) with salad dressings. Parameter Al obtained from the Weltman equation, which represents the shear needed to initiate the structural degradation responsible for the thixotropic behaviour of the product, ranged from 88 to 226 Pa, both values corresponding to light mayonnaises. These results were also in accordance with the Casson yield stress values obtained at 20°C (the correlation coefficient of the regression analysis of the Casson yield stress and the initial shear stress A 1 was 0,89). 398
Rheological romparlson of mayonnaises
Table IV. Rheological parameters from the Weltman and Hahn models for the different normal and light commercial mayonnaises Sample
Tc(Pa)
AWe!tman
KG
88 ± 6 7fi, ± 5 190 ± 13 141 ± 2 90 ± 2 fi,1 ± 3
100 126 226 157.7 98.8 fi,fi,
CN KL KBC YL CL
±7 ±9 ± 20 ± 1.2 ± 1.8 ±3
Note: Data are expressed by the equation:
"Weltman 13.5 46 28 16.9 8.8 7.5
X±
± 1.4 ±7 ±6 ± 1.2 ± 0.5 ± 0.1
AHahn 1.17 1.92 1.73 1.35 1.05 0.9fi,
± 0.09 ± 0.06 ± 0.05 ± 0.07 ± 0.02 ± o.oi
"Hahn 0.15 0.16 0.091 0.150 0.133 0.14
± 0.02 ± 0.01 ± 0.012 ± 0.005 ± 0.009 ± o.m
cr.
Parameter B I measures the extent of structural breakdown over a given period of time, and hence, the rate of thixotropic breakdown. Values obtained range from 7.5 to 46.0 Pas. For light mayonnaise a direct relationship can be observed between the rate of structural breakdown and the consistency coefficient of the samples. Those samples with higher consistency present a higher rate of structural breakdown. Conclusions This study has shown the dependence of the decrease in the oil content of mayonnaise on their rheological parameters. Firstly it should be stressed that the wide range in the rheological parameters n, K and yield stress reflects that consumers are unconcerned about these rheological properties of mayonnaises. The Ostwald model can be used to describe the rheological behaviour of light and normal mayonnaises, which presented in all cases, a pseudoplastic behaviour. Thixotropic behaviour can be described using the Weltman model in normal and light mayonnaises. Acknowledgements The authors wish to thank the Spanish Ministry of Education and Science, for the grant awarded to one of them. References I. Paredes,M.D.e., Rao,M.A. and Bourne,M.e. (1988) Rheological characterization of salad dressings. 1: Steady shear, thixotropy and effect of temperature. J. Text. Stud., 19, 247-258. 2. Tiu.C, and Boger,D.v. (1974) Complete characterization of time-dependent food products. J. Text. Stud., 5, 329-338. 3. Kitic.D.; Favetto,G.J., Chirife.J, and Resnik,S.L. (1986) Measurements of water activity in the intermediate moisture range with the Novasina Thermoconstanter Humidity Meter. Lebensm. Wiss Und Technol., 19, 297. 4. Chirife.L, vigo,M.S., Gomez,R.G. and Favetto,G.J. (1989) Water activity and chemical composition of mayonnaises. J. Food Sci., 54, 165fi,-1659. 5. Barbosa,G.v. and Peleg,M. (1983) Flow parameters of selected commecial semi-liquid food products. J. Text. Stud., 14, 213-234. 6. Lewis.Ll. and Shoemaker,Ch.F. (1984) A method for measurement of the transit response of semisolid foods under steady shear. J. Food Sci., 49, 741-743; 755. 7. Rha,e. (1978) Rheology of fluid foods. Food Teclznol., 32, 7; 77-82.
399
M.Pons. I\I.J.Gaiotto and S.Suhirats
8. ElIiot,J.H. and Ganz.A.J. (1977) Salad dressing-preliminary rheological characterization. J. Text. Stud., 8. 359-371. 9. Chang,e.M., Powrie,W.D. and Fennerna.O. (1972) Electron microscopy of mayonnaise. 1. Can. lnst. Food Sci. Technol., 5,134-139. 10. Figoni,P.1. and Shoemaker,Ch.F. (1983) Characterization of time dependent flow properties of mayonnaise under steady shear. J. Text. Stud .. 14. 431-442. 11. Holdsworth,S.D. (1971) Applicability of rheological models to the interpretation of flow and processing behaviour of fluid food products. J. Text. Stud.. 2,394-418. 12. Sharna.F.. Parkinson.C, and Sherrnan.P. (1973) Identification of stimuli controlling the sensory evaluation of viscosity. I. Non-oral methods. [I. Oral methods. J. Text. Stud .• 4, 102-118. 13. Speers.R.A. and Tung,M.A. (1986) Concentration and temperature dependence of flow behaviour of xanthan gum dispersions. J. Food Sci., 51, I; 96-98; 103. 14. Paredes,M.D.e.. Rao,M.A. and Bourne,M.e. (1989) Rheological characterization of salad dressings. 2; Effect of storage. 1. Text. Stud., 20, 235-250.
400
Comparison of the steady rheological characterization of normal and light mayonnaises M.Pons. M.J.Galotto and S.Subirats AINA, lnstituto Teenol6gieo Agroalimentario, Pare Tecnologic, P.O. Box 103, Paterna, Valencia, Spain
Introduction
There exist a great number of emulsion products in the food industry, among which we highlight: butter, margarine, mayonnaise, salad creams, milk, icecreams, meat emulsions, etc. Due to the importance of these products, food emulsions represent an area of great relevance within the food industry and require special study. Spanish legislation defines mayonnaise and light sauces as products in the form of semi-solid emulsion, basically made up of edible vegetable oils, eggs or egg yolk, vinegar and lemon juice, with the optional addition of various ingredients (salt, spices, stabilizers, aromatizing agents, colouring, etc.). The term mayonnaise is restricted to those sauces which contain a minimum of 65% oil and 5% egg (expressed in technical egg yolk) and which further present a minimum acidity of 0.2% in acetic acid and a pH lower than 4.2 (R.D. 358/ 1984). Hence, this legislation does not clearly define what is now known by the name of light mayonnaise or light sauces. These continue to be emulsions of oil in water in which the decrease in the percentage of oil leads to the necessity for added stabilising agents, generally hydrocolloids and starches, which avoid the separation of the phases which constitute the emulsion, stabilising the product and giving it the mechanical (rheological and textural) properties characteristic of this kind of product. Like most fluid foodstuffs, sauces show complex rheological behaviour. In general, mayonnaise exhibits pseudoplastic behaviour with a flow threshold, and presents thixotropy (shear stress dependence on the time of shear) (1,2). The information from rheological studies is very useful for this kind of product since it conditions the choice and design of the equipment required in the manufacturing process to supply the parameters which allow a more exhaustive quality control, as well as a measurement of the stability of the product during storage. Thus, the analysis and quantification of mayonnaise on the basis of its consistency, its flow threshold value and the dependent nature of the time of these parameters are of vital importance if we want to have precise knowledge of this kind of product. The aim of the present paper is the physico-chemical characterization of normal and light mayonnaise emulsions, studying the variation with temperature of their rheological properties, analysing the influence of the different oil 389
I\t.Pons, I\t.J.Galotto and S.Subirats
contents of the samples on the flow characteristics, in order to determine their qualitative influence on the internal structure of the emulsion. Materials and methods Commercial samples of standard mayonnaise (KN, KO, YN, CN) and light mayonnaise type sauce (KL, KBC, YL, CL) purchased from retail outlets were analysed selecting those brands with the greatest market share. For each of the mayonnaises the same batch was used in order to avoid possible differences between batches. All the samples were refrigerated at 4°C until their analysis. Measurements were taken in triplicate in samples from different jars of each batch.
Chemical analysis Centesimal chemical characterization of each one of the samples was carried out: moisture, fat content, protein, ash, carbohydrate and pH were analysed according to the Official Analytical Methods of the Spanish Health and Consumer Ministry (1985). The a; of mayonnaises was measured at 25°C using a Novasina Humidat-TH2 Thermoconstanter hygrometer (Novasina AG, Zurich, Switzerland) following the procedure of Kitic (3). Measurement of a., of mayonnaises using an electric hygrometer is difficult because the sensor may become contaminated by the volatile acetic acid of the sample. For this reason all a., measurements in mayonnaises were conducted using a filter (Novasina AG, Universal eVC 21) (4). The time required to attain equilibrium within the sensor chamber was almost 5 h when using the filter eVC 21.
Emulsion stability Stability of mayonnaises was assessed by centrifugation in graduated conical tubes of 10 ml capacity. The volume of the lower aqueous separated phase and also the volume of the oil upper phase were determined. Emulsion stability (E5) was expressed as a percentage of total volume against lower aqueous phase volume. E5 =
(VTOTAL -
VSEPARATED PHASEIVTOTAL)
x 100
As spontaneous separation of the different phases was too slow the separation was done by centrifugation at 4600 r.p.m. for 2.5 h at 15°C using a Medifriger centrifuge. Graduated centrifugal tubes with the different mayonnaises were stored at 37 and 60°C for 23 h afterwards analysing the separated volume in all cases.
Rheological characterization Rheological 390
measurements
of
samples
were
made
In
a
rheometer
Rheological compa rison of mayonnaises
(RO T OV ISCO R V 20) equipped with an M5 osc measuring head (Haa ke Inc ., Saddle Brook , NJ) , using a coaxial cylinde r measur e syste m (gap size of 1.45 mm and cylinder height of 19.6 mm ). Sampl es were kept at 20°C for 15 min be fore the mea suremen ts were ob taine d (5,6) . Rh eo logical a na lysis of mayo nnaises was carried out in two steps . In the first step the te mpe rature effect on the flow be hav io ur of eac h one o f the samples was studied . Thi s study was done by compa rison and ana lysis of the different rh eological parameters obtained from the Ostwald and Casson rheological models and at five different temperatures. Afterwards time-d ependence rh eological beh aviou r (thixotropic beh aviour) was studie d according to the Weltm an and Hahn math em at ical mod els at 20°C (1). Th e flow curve of samples was carr ied out with a viscome ter working in a utomatic mode where th e shea r rat e increas ed fro m 0 to 100 S- I in 1 min and then decreased to 0 S- I in 1 min . For each sa mple rheograms were obta ined at 5, 10, 20, 25 and 30°e. Rheological param et er s K (consistency coefficient) and /1 (flow beh aviour index) were determined from the pow er law equation (Equation 1), the most frequently used rh eological equation for describin g the flow behaviour of pse udo plastic foods. T
=
K-y"
(1)
wher e T is the shea r stress (Pa) , -y is th e shea r rat e (S -I) . For those samples which presented yield stress (TO)' the Casson equation ( Equatio n 2) was used to describe their flow behaviour
Th e A rrhe nius equa tion (Equa tion 3) was used to study the effect of te mpe ra ture on th e rhe ological p rop erties of food s 'll a p =
A .eEl/fR oT
(3)
where Ea is the activation ene rgy in Kcal/f'K'mol . R is the gas co nsa nt, T is the te mpe rature in OK and B is a co nsta nt. Kn owing the Ea allows us to determine th e viscosity or consisten cy of that pr oduct at different temperatures. In general , as Ea incre ases the temperature dependence of th e viscosity increases. The activation energy of th e sa mples (Ea) was det ermin ed from linear regression analysis of the apparent viscosity at 100 s- ) and the reciprocal value of the abso lute temperature (OK).
Thixotropic behaviou r Th e time dependence observed in some products is due to the structura l modifica tion produced by the shear. Hen ce the application of exte rna l forces influences th e intern al struc ture cau sing distortion of the arra ngeme nt of the dissolving pol ymeri c molecules a nd deflocculation of the particl es of the disperse phase of the emulsion, as in the case of mayonn aise. T he be hav iour of the
391
I\1.Pons, M.J.Galotto and S.Suhirats
system depends on the relationship between the magnitude of the applied forces and that of the interparticle and intermolecular forces which define its structure (7). Quantitative analysis of the time-dependent behaviour of samples can be evaluated from shear stress data obtained at a constant shear rate and fitting them to thixotropic mathematical models (1). In the present study thixograms were recorded at 20°C at a constant shear rate of 10 s I for 20 min, the time necessary for samples to reach equilibrium. Mathematical models used to describe the time-dependence behaviour were Weltman model (Equation 4) and Hahn model (Equation 5) -r
(4) (5)
where the constant A) indicates the stress after a short shearing time. The constant A 2 in the Hahn model indicates initial shear stress whose magnitude is also dependent on the equilibrium shear stress. The coefficients B I and B 2 indicate rate of structural breakdown. Results and discussion
Chemical analysis Table 1 presents the chemical analysis of the different commercial mayonnaises analysed (moisture, fat, protein, ash and carbohydrate, including pH). It can be observed that four of the samples (normal mayonnaise) present a mean oil content of ~ 76%, while the other four (light mayonnaise) present a much lower oil content (35%). The lower oil phase shows a higher moisture content. Excluding sample KL, the protein percentage of light samples is much lower than the protein content of normal mayonnaises, which can be explained due to a reduction in the egg yolk content in the formula. This fact is especially important in the KBC sample with the lowest egg yolk content, which presents a lower cholesterol content. Light samples also present a carbohydrate content higher than normal samples, which could be explained by the use of stabilizers such as hydrocolloids or starch used in these samples in order to increase the consistency lost with the oil reduction. Table II shows the qualitative composition of different hydrocolloids obtained from the labels of the samples. The pH of light samples is also lower than that of normal mayonnaises due to an increase in the acetic acid content in order to avoid spoilage by microorganisms. The observed a; of normal mayonnaise was -0.96 and that of light samples was higher, close to 0.98. This fact could be explained by the higher water content of light samples which increases their vapour equilibrium pressure.
Emulsion stability Results obtained after centrifugation of samples allow us to conclude that light
392
Table I. C he mical composition . pH a nd water activity o f normal and light co mme rcia l mayonnaises
Samp le
Moisture (%)
O il (%)
KN KO YN CN KBC KL YL CL
19.70 ± 19.40 ± 14.92 ± 2 1.69 ± 56.0 1 ± 52.85 ± 54. 13 ± 56.4 4 ±
76.47 75.38 78.8 1 76. 19 33.34 37.67 35.52 33.79
0.64 0.34 0.18 0.1 1 0.20 0. 19 0.28 0.23
± 1.87
± 2.09 ± 0.70 ± 0.53 ± 0.29 ± 0.64 ± 0.12 ± 0.08
Protein (%)
Ash (%)
± ± ± ± ± ±
1.45 1.19 1.45 0.86 1.86 2. 16 1.98 0.90
1.43 1.40 1.21 0.81 0.40 0.86 0.65 0.74
0.01 0.03 0.02 0.0 2 0.03 0.01 ± 0.02 ± 0.02
± 0.01 ± 0.0 1 ± 0.01 ± 0.02 ± 0.01 ± 0.01 ± 0.01 ± 0.02
Not e : Ca rbo hydra te percentage was ca lculated by differ ence . Data ar e exp resses as: X ±
Ca rbohydrate (% )
pH
0.95 2.63 3.61 0.45 8.39 6.46 7.72 8 . 13
3.84 3.93 3.94 3.61 3.02 3.08 3.64 3.54
3 ......
± ± ± ± ± ± ±
±
0.01 0.02 0.0 1 0.0 1 D.OI 0.01 0.03 D.OI
D.973 0.966 0.940 0.980 0.988 0.986 0.982 0.996
± ± ± ± ± ± ± ±
0.002 0.002 0.002 0.003 D.OOI 0.001 D.002 0.001
:e
::r
~ '=-"'
-So ~
3e
., 0;
~.
= ~
.:::,
= :; t,;.)
-o t,;.)
=
0;
1;.'
'"
'I.Pons. 'I.J.Gulotto dill! S.Subirats
Table II. Hydrocolloids used as stabilizers in normal and light commercial mayonnaises Sample
Hydrocolloids
KN
Modified starch. locust bean gum Modified starch. locust bean gum Xanthan gum Starches Starch. xanthan gum, CMC Modified starch Starch. locust bean gum. pectin Starches
KG
YN CN KBC
KL YL
CL
Note: Qualitative hydrocolloids composition has been obtained from the labels of the different samples. CMC: Carboxymethyicellulose.
samples present higher stability than normal samples. This fact could be due to the decrease in the oil content compared with the normal samples. The reduction of the oil phase produces a destabilization of the emulsion. In order to avoid this effect, light samples are normally stabilized with hydrocolloids, the principal characteristic of which is their higher capacity to absorb water, producing an increase in the continuous phase viscosity and increasing the emulsion stability. There was no diffrence in the behaviour of commercial samples and those stored at 37°C for 24 h. In both cases light mayonnaises present a higher stability than normal ones. Samples stored for 24 h at 60°C presented the same behaviour in all cases, where a considerable structure compactation can be observed due to a water evaporation process, so a lower accumulation of the aqueous phase in the bottom of the test tubes can be shown. Rheological characterization Consistency coefficient (K) and flow behaviour index (n). Shear sstress data of normal and light mayonnaises were obtained over the shear rate range of 0-100 S-I. The Ostwald equation described the shear rate-shear stress data of all samples very well, with the exception of sample CN, whose correlation coefficients obtained at SoC were not statistically significative. Table III shows the results of the rheological parameters at the studied temperatures. Statistical analyses (variance analyses) reveal statistical differences (P > 0.01) in the rheological parameters K and n for the different samples studied. Out of all of the mayonnaise samples, KL presented a higher dispersion of the results, which could be explained by the higher consistency of the sample. This fact agrees with the higher dispersion of the results observed in all samples at SoC, which could indicate that the sensor used is not the most appropriate one for measuring rheological properties of samples with a high consistency. The higher dispersion of the values could also be due to the difficulty of placing the sample inside the sensor. Figure 1 shows the consistency coefficient of samples analysed. A high range of values can be observed, the extreme values belonging to light mayonnaises. 394
Table III. Rheological parameters from Ostwald model for the different samples and temperatures studied 5°C Sample
K
KN KO YN CN KL KBC YL CL
152 ± 149 ± 206 ± n.s. 255 ± 141 ± 93 ± 71 ±
10°C K
n
6 6 6 7 7 7 6
0.148 0.127 0.177 n.s. 0.115 0.245 0.208 0.249
± 0.007 ± 0.007 ± 0.007
± ± ± ±
0.008 (J.OO8 0.008 0.007
116 127 181 123 225 132 80 67
Note: Data are expressed by the equation:
20°C K
n
± ± ± ± ± ± ± ±
X±
6 7 6 6 7 7 7 7
0.173 0.138 0.191 0.148 0.142 0.238 0.222 0.245
± ± ± ± ± ± ± ±
A./~ fItv'n.
0.007 (J.OO8 0.007 0.007 0.008 0.008 0.008 O.OOS
lOS ± 102 ± 166 ± 124 ± 219 ± 113 ± 65 ± 62 ±
25°C K
n
6 7 7 7 6 7 7 7
O.l75 0.139 0.187 0.104 0.123 0.245 0.230 0.230
± ± ± ± ± ± ± ±
0.007 0.008 0.008 0.008 0.007 0.008 0.008 (J.OOS
77 101 153 126 213 III 61 59
3WC
K
n
± ± ± ± ± ± ± ±
6 7 7 6 7 7 7 7
O.l78 0.121 0.173 0.080 O.to5 0.242 0.228 0.227
± ± ± ± ± ± ± ±
0.007 O,()08 0.008 0.007 0.008 (l.()O8 (U)08 0.001'
74 97 139 119 200 106 57 58
n
± ± ± ± ± ± ± ±
6 O.l70 ± 0.007 7 0.117 ± (l.()O8 7 0.172 ± (l.()O8 6 0.109 ± 0.007 7 0.110 ± 0.008 7 0.241 ± 0.008 7 0.123 ± 0.001' 7 0.223 ± 0.001'
;tJ
:r
~
:r% ;:;0 ~
8
~0:
a·
e
=
So,
:3
.~
§ ~
~
:;;"
Vl
~
\0
M.Pnns.I\1.J.Galnttn and S.Subirats
300
250
KL'~ :-----~---.
200
150
M~
-_~--
KBC 100
~~~=:=;=:===;
YLL:!---CL
"'""'"x'"
~
50
275
280
285
290
295
300
305
Temperature (OK) Fig. l. Effect of temperature on the consistency coefficient of the different normal and light commercial mayonnaises.
Statistical analyses of the results do not allow us to define differences between normal and light mayonnaises. Figure 2 presents the flow behaviour index (n) for all samples studied. Its value was lower than 0.3, which indicates pseudoplastic behaviour in all cases. The pseudoplastic character can also be observed with the significant decrease in the apparent viscosity of the samples as the shear rate increases, as reported by Tiu and Boger and Elliot and Ganz (2,8). Chang et al. (9) explain this feature as being due to the fact that mayonnaise oil droplets are stabilized in the presence of egg yolk in the interphase, so that their deformation is very small when higher shear rates are applied. Figoni and Shoemaker (10) explain this behaviour as due to a f1occulation-deflocculation process of the oil droplets in the aqueous continuous phase; as the shear rate increases, the equilibrium of this process is directed to the droplets deflocculation, producing a decrease in the apparent viscosity of the product. Mayonnaise pseudoplasticity has also been explained (11) as due to the fact that an increase in the shear rate produces a progressive orientation in the arrangement of the disorganized long chain molecules with a lower resistance against flow.
Yield stress The Casson equation was employed to estimate the yield stress of the samples at five different temperatures. The correlation coefficients for the regression analyses of the square roots of the shear stress-shear rate were >0.93 with the exception of sample CN, for which correlation coefficients were not statistically significative for all temperatures. Figure 3 illustrates the effect of temperature on the magnitude of the yield stress. A decrease in the yield stress with the increase in product temperature can be observed in all samples, although the importance of the effect is different 396
Rheological comparisun of mayonnaises
---------~ -=:;;;;-=
29S
290
;1
YN
KN
305
300
TemperaturerK) Fig. 2. Effect of temperature on the flow behaviour index of the different normal and light commercial mayonnaises. 300
-r.;(Pa) 2SO
KL
YN
200
150
~e-
~~~
YN
__"",,,,=::::::-_-:'-==="""",""",,=::C
x~_=
100
: ~--======::::====:;i:====O-=--=::===X
KN ;o;CL
50
YL
0
275
285
295
300
305
Temperature (OK) Fig. 3. Effect of temperature on Casson yield stress of the different normal and light commercial mayonnaises.
for each sample. It is not very important for CL; however, the temperature dependence is more important for samples KL, KN and YN. It can therefore be concluded that samples studied had varying levels of consistency and yield stress. This wide range in the rheological parameters of n ; K and yield stress is in agreement with Elliot and Ganz (8) and Paredes et al. (1), and it indicates that consumer preferences cover a wide range of rheological properties of mayonnaise. Activation energy of flow
The Arrhenius equation was used to describe the effect of temperature on the 397
l\I.POIIS. I\I.J .Galotto and S.Subirats
"2'
~
'-'
~ ,... 0
0 ,...
1
:1
~ :.----
'VJ
0 en
7,8
"E
7,6
0-
7,4"';
U
:> ~
§'
.5
7,2
.r
0.0033
0,00335
0,0034
0,00345
0,0035
0,00355
0,0036
Fig. 4. Arrhenius plot of the apparent viscosity of the different normal and light commercial mayonnaises.
apparent viscosity of mayonnaise at 100 S-1 (Figure 4). This shear rate was selected in order to compare data to previous studies and because it is a shear rate commonly encountered during stirring and oral evaluations (12,13), The regression analysis shows that the Arrhenius equation fits the experimental results very well in all the samples (r 2 > 0.92). The range of calculated Ea was 1.9 to 4.0 Kcal/mol. The effect of temperature on the apparent viscosity of the samples in ascending order was: KL < KBC < CL < YN < YL < KO < KN. From these results, it can be asserted that the oil content affects the Ea of the samples, since normal mayonnaises with a higher oil content are more dependent on temperature,
Thixotropic behaviour The thixotropic behaviour of fluid products produces a decrease in the apparent viscosity of the sample over time. This is due to a restructural change which leads to a gradual decrease in the shear stress that product can support and thus a lower flow resistance (10). Table IV presents the constant of the Weltman and Hahn equations. Both rheological models describe the structural degradation of mayonnaises although the Weltman model fits best (r 2 > 0.87). These results are in agreement with those obtained by Paredes et al. (14) with salad dressings. Parameter Al obtained from the Weltman equation, which represents the shear needed to initiate the structural degradation responsible for the thixotropic behaviour of the product, ranged from 88 to 226 Pa, both values corresponding to light mayonnaises. These results were also in accordance with the Casson yield stress values obtained at 20°C (the correlation coefficient of the regression analysis of the Casson yield stress and the initial shear stress A 1 was 0,89). 398
Rheological romparlson of mayonnaises
Table IV. Rheological parameters from the Weltman and Hahn models for the different normal and light commercial mayonnaises Sample
Tc(Pa)
AWe!tman
KG
88 ± 6 7fi, ± 5 190 ± 13 141 ± 2 90 ± 2 fi,1 ± 3
100 126 226 157.7 98.8 fi,fi,
CN KL KBC YL CL
±7 ±9 ± 20 ± 1.2 ± 1.8 ±3
Note: Data are expressed by the equation:
"Weltman 13.5 46 28 16.9 8.8 7.5
X±
± 1.4 ±7 ±6 ± 1.2 ± 0.5 ± 0.1
AHahn 1.17 1.92 1.73 1.35 1.05 0.9fi,
± 0.09 ± 0.06 ± 0.05 ± 0.07 ± 0.02 ± o.oi
"Hahn 0.15 0.16 0.091 0.150 0.133 0.14
± 0.02 ± 0.01 ± 0.012 ± 0.005 ± 0.009 ± o.m
cr.
Parameter B I measures the extent of structural breakdown over a given period of time, and hence, the rate of thixotropic breakdown. Values obtained range from 7.5 to 46.0 Pas. For light mayonnaise a direct relationship can be observed between the rate of structural breakdown and the consistency coefficient of the samples. Those samples with higher consistency present a higher rate of structural breakdown. Conclusions This study has shown the dependence of the decrease in the oil content of mayonnaise on their rheological parameters. Firstly it should be stressed that the wide range in the rheological parameters n, K and yield stress reflects that consumers are unconcerned about these rheological properties of mayonnaises. The Ostwald model can be used to describe the rheological behaviour of light and normal mayonnaises, which presented in all cases, a pseudoplastic behaviour. Thixotropic behaviour can be described using the Weltman model in normal and light mayonnaises. Acknowledgements The authors wish to thank the Spanish Ministry of Education and Science, for the grant awarded to one of them. References I. Paredes,M.D.e., Rao,M.A. and Bourne,M.e. (1988) Rheological characterization of salad dressings. 1: Steady shear, thixotropy and effect of temperature. J. Text. Stud., 19, 247-258. 2. Tiu.C, and Boger,D.v. (1974) Complete characterization of time-dependent food products. J. Text. Stud., 5, 329-338. 3. Kitic.D.; Favetto,G.J., Chirife.J, and Resnik,S.L. (1986) Measurements of water activity in the intermediate moisture range with the Novasina Thermoconstanter Humidity Meter. Lebensm. Wiss Und Technol., 19, 297. 4. Chirife.L, vigo,M.S., Gomez,R.G. and Favetto,G.J. (1989) Water activity and chemical composition of mayonnaises. J. Food Sci., 54, 165fi,-1659. 5. Barbosa,G.v. and Peleg,M. (1983) Flow parameters of selected commecial semi-liquid food products. J. Text. Stud., 14, 213-234. 6. Lewis.Ll. and Shoemaker,Ch.F. (1984) A method for measurement of the transit response of semisolid foods under steady shear. J. Food Sci., 49, 741-743; 755. 7. Rha,e. (1978) Rheology of fluid foods. Food Teclznol., 32, 7; 77-82.
399
M.Pons. I\I.J.Gaiotto and S.Suhirats
8. ElIiot,J.H. and Ganz.A.J. (1977) Salad dressing-preliminary rheological characterization. J. Text. Stud., 8. 359-371. 9. Chang,e.M., Powrie,W.D. and Fennerna.O. (1972) Electron microscopy of mayonnaise. 1. Can. lnst. Food Sci. Technol., 5,134-139. 10. Figoni,P.1. and Shoemaker,Ch.F. (1983) Characterization of time dependent flow properties of mayonnaise under steady shear. J. Text. Stud .. 14. 431-442. 11. Holdsworth,S.D. (1971) Applicability of rheological models to the interpretation of flow and processing behaviour of fluid food products. J. Text. Stud.. 2,394-418. 12. Sharna.F.. Parkinson.C, and Sherrnan.P. (1973) Identification of stimuli controlling the sensory evaluation of viscosity. I. Non-oral methods. [I. Oral methods. J. Text. Stud .• 4, 102-118. 13. Speers.R.A. and Tung,M.A. (1986) Concentration and temperature dependence of flow behaviour of xanthan gum dispersions. J. Food Sci., 51, I; 96-98; 103. 14. Paredes,M.D.e.. Rao,M.A. and Bourne,M.e. (1989) Rheological characterization of salad dressings. 2; Effect of storage. 1. Text. Stud., 20, 235-250.
400