A Tárrega

E Costell

L Durán

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EFFECT OF TEMPERATURE ON STEADY-STATE FLOW BEHAVIOUR OF 
SEMISOLID DAIRY DESSERTS 
A. Tárrega, L. Durán & E. Costell 
 
Laboratory  of Physical and Sensory Properties 
Instituto de Agroquímica y Tecnología de Alimentos. CSIC. 
P.O. Box 73. 46100 Burjassot (Valencia). Spain 
 
Introduction 
The “natillas”, semisolid dairy dessert of wide consumption in Spain, is composed of 
milk, starch, hydrocolloids, sugars, colorants and aromas. The particular characteristics 
of some ingredients, like fat content of milk, type of starch, and/or type and 
concentration of hydrocolloids, and their crossed interactions, will be reflected in 
notable differences in their rheological and sensory properties. Little information is 
available on the differences to be found in commercial samples of this type of  dairy 
desserts [1, 2]. The flow properties of this type of products, e.g. time dependence and 
pseudoplasticity, are due to the resistance to shear of a biphasic structure defined by the 
characteristics of the dispersed phase (starch granules) and by the viscosity of the 
dispersing phase [3, 4]  
 
The objectives of this work are to characterise the steady-state flow behaviour of 
commercial samples of Spanish “natillas” and to study the effect of the consumption 
temperatures (5 and 25ºC) on their flow properties.  
 
Experimental  
Samples 
Seven samples of vanilla dairy desserts (natillas) of different brands and characteristics 
(Fig.1) covering the commercial range, were purchased from the local market (Table 1). 
The samples were stored at 4±1ºC prior to testing and all measurements were performed 
within the shelf-life period of each sample. 
 
 
 
 2
Table 1. Main composition and price level of commercial vanilla cream dairy desserts 
samples 
Sample Dairy ingredients (1) Thickeners (1) pH (2) 
 
Soluble solids (2) 
(º Brix) 
Price(3) 
1 Semi-skimmed milk 
Modified starch 
Carrageenan 
Xanthan gum 
6.81 24.5 1.4 
2 Milk Semi-skimmed milk 
Modified starch 
Carrageenan 
Guar gum 
6.76 23.7 1 
3 
Milk 
Cream 
Semi-skimmed milk 
powder 
Acetylated 
distarch adipate 
Gelatine 
6.61 28.3 2.3 
4 
Milk 
Cream 
Dairy solids 
Modified starch 
Carrageenan 
Fatty acid esters
6.60 26.3 2.5 
5 Milk Cream 
Modified starch 
Carrageenan 
Guar gum 
6.76 23.5 2.5 
6 Milk Cream 
Modified  starch 
Carrageenan 
Guar gum 
6.72 24.5 1.7 
7 
Milk 
Cream 
Dairy solids 
Modified starch 
Carrageenan 
Fatty acid esters
6.75 24.5 1.9 
 
(1) Declared in label. 
(2) Average value of two measurements 
(3) Lower price considered as reference unit 
 
 
Rheological measurements 
The measurements were carried out in a Haake VT 550 viscometer, using concentric 
cylinders sensors (MV1 and MV3, with 1.05 and 1.38 radii ratios, respectively), 
monitored by a Rheowin Job Manager (Haake, 2002). The samples were analysed at 
two temperatures, 5±1 and 25±1ºC. 
Before analysing flow behaviour, the structure responsible for thixotropy was destroyed 
by shearing for five minutes at 300  s-1, as selected in previous experiments. Sample 
flow was measured by registering shear stress values at increasing shear rates from 1 to 
 3
200 s-1 in 60 s. Data obtained were fitted to the Herschel-Bulkley model (σ=σ0+K  n). 
The yield stress (σ0) value, used in the Herschel-Bulkley’s model, was previously 
obtained by fitting the experimental data to the Casson model: σ0.5=σ00.5+K  0.5  This 
was taken as the square of the ordinate intercept in the Casson plot . Apparent viscosity 
values were obtained with the expression: ηap= σ0/   + K  n – 1. 
 
Statistical analysis 
The effect of temperature on the Herschel-Bulkey parameters was analysed by two 
factors (sample and temperature) ANOVA with interactions. The Fisher test (α=0.05) 
was used to calculate the minimum significant differences. All calculations were carried 
out with the Statgraphics Plus 4.1 software. 
 
 Results  
On registering shear stress variation with shear rate, all samples showed non-Newtonian 
shear-thinning behaviour with an apparent initial resistance to flow. Experimental data 
fitted well to the Herschel-Bulkley model (Fig. 3) with R2 values ranging between 0.993 
and 0.998 for measurements at 5ºC and between 0.990 and 0.999 for those at 25ºC. The 
yield stress values, obtained for all samples at both temperatures, were important - 
higher than 7.77 Pa at 5ºC and higher than 5.76 Pa at 25ºC- indicating plastic behaviour.  
Since the parameter K values depend on n values, apparent viscosity at 1 s-1 (η1) values 
were used in the analysis of variance performed to study the effects of sample and 
temperature on flow properties. ANOVA results showed that sample-temperature 
interactions were significant for σ0 (Fint = 5.40, p=0.005) and for (Fint = 6.63, p=0.002). 
Both the yield stress and the apparent viscosity values were lower at 25ºC, this 
difference being significant for all samples but for sample 1. The effect of temperature 
on flow index was significant but of low entity (Fig. 4). Differences among samples for 
the flow parameters were always higher at 5ºC. At this temperature, sample 1 exhibited 
lower initial resistance to flow, lower consistency and lower pseudoplasticity than the 
rest of samples.  
Similar results to those obtained here for “natillas” have been reported for starch pastes 
by other authors. Recently, Nayouf et al [5] studied the rheological properties of 
crosslinked waxy corn starch and concluded that, except for the lower concentration 
γ 
γ 
γ 
γ
 4
(2% starch) pastes, experimental data fitted well to the Herschel-Bulkley’s model.  
Acquarone et al [6] also used this model to characterise the flow of waxy corn starch 
dispersions with added sucrose.  
 
Conclusions 
Though quantitatively different, all samples of “natillas”, after eliminating thixotropy 
by shearing, showed shear-thinning properties with measurable initial resistance to 
flow, e.g., a plastic behaviour that fitted well to the Herschel-Bulkley model. Although 
the extent of the differences varied among samples, in general, time dependence, 
plasticity and consistency were lower and pseudoplasticity was slightly higher at the 
higher temperature (25 vs. 5ºC) 
 
Acknowledgements 
 
To McyT of Spain for financial support (Project AGL 2000-1590), and for the 
fellowship awarded to author Tárrega. 
 
References 
 
1. Wijk, R. A., van Gemert, L. J., Terpstra, M. E. J. & Wilkinson, C. L.(2003). Food 
Quality and Preference, 14, 305-307 
2. Wischmann, B., Norsker, M. & Adler-Nissen, J. (2002). Nahrung  Food, 46, 167-
173. 
3. Nguyen, Q. D., Jensen, C. T. B. & Kristensen P. G. (1998). Chemical Engineering 
Journal, 70, 165-171. 
4. Thebaudin, J. Y., Lefebvre, A. C. & Doublier, J. L (1998). Lebensmitttel 
Wissenschaft und Thecnologie, 31, 354-360 
5. Nayouf, M., Loisel, C. & Doublier, J. L. (2003). Journal of Food Engineering, 59, 
209-219. 
6. Acquarone , V. M. & Rao, M. A. (2003). Carbohydrate Polymers, 51, 451-458. 
 
 5
 
 
 
 
 
 
 
 
 
 
0
50
100
150
200
250
0 50 100 150 200
Shear Rate (1/s)
S
he
ar
 S
tre
ss
 (P
a)
Figure 2. Hysteresis loop obtained at 5ºC for sample 4  without previous shearing (x) 
and after shearing at  300s-1 during 5 minutes (x). 
Figure 1. Samples of vanilla dairy dessert analysed. 
 6
 
 
 
 
 
 
0
20
40
60
80
100
120
140
160
180
200
0 50 100 150 200
Shear rate (1/s)
Sh
ea
r s
tr
es
s 
( P
a)
b
0
20
40
60
80
100
120
140
160
180
200
0 50 100 150 200
Shear rate (1/s)
Sh
ea
r s
tr
es
s 
( P
a)
a
Figure 3. Steady-state flow curves obtained for dairy dessert samples at 5ºC (a) and 
25ºC (b). Experimental values (∀) 1, (∀) 2, (∀) 3, (∀) 4, (∀) 5, (∀) 6, (∀) 72, and fits 
to Herschel-Bulkey model (—). Identification of samples in table 1 
 
 
 
 
 
 
0
5
10
15
20
25
30
35
1 2 3 4 5 6 7
samples
a
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7
samples
b
0.5
0.55
0.6
0.65
0.7
0.75
0.8
1 2 3 4 5 6 7
samples
c
η 1
(P
a.
s)
σ 0
(P
a)
n 
Figure 4.  Values of Yield strees (a), apparent viscosity at 1 s-1(b) and flow index (c) obtained for dairy dessert samples at 5ºC (a) and 25ºC (b). 
Identification of samples in table 1 
 


EFFECT OF TEMPERATURE ON STEADY-STATE FLOW BEHAVIOUR OF SEMISOLID DAIRY DESSERTS

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EFFECT OF TEMPERATURE ON STEADY-STATE FLOW BEHAVIOUR OF SEMISOLID DAIRY DESSERTS

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