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INFLUENCE OF PROCESSING ON THE RHEOLOGICAL PROPERTIES
OF ENTERAL NUTRITION PUDDINGS
N. Nunez1, C. Valencia1, P. Partal1, J.M. Franco1,
E. Brito-de la Fuente2, and C. Gallegos1
1
Departamento de Ingeniería Química. Universidad de Huelva.
21071 Huelva (Spain).
and 2Fresenius Kabi Deutschland GmbH.
D-61440 Oberrusel (Germany)
Abstract: Enteral nutrition is defined as oral or tube-delivered caloric sustenance
products for consumers having a disability or disease with significant nutritional
problems that cannot be managed by ordinary or blenderized food. Puddings are a class
of enteral nutrition products that are designed to provide meal replacements. The
rheological properties of puddings are very complex, being dramatically influenced by
processing variables. In this sense, the overall objective of this work was to evaluate the
influence of different processing and compositional variables of puddings, such as final
thermal treatment, high pressure homogenization previous to its final thermal treatment,
nature and concentration of the starch used in pudding formulation, and storage
temperature after processing, on the rheological behavior and droplet size distribution
of the final product. A strong influence of pudding final thermal treatment on pudding
microstructure and rheology has been found. Another key variable is starch
concentration. The results obtained seem to indicate that thermal treatment duration
should be strongly linked to starch concentration in the pudding. On the other hand,
high pressure homogenization treatment decreases mean particle size, and also the
values of the viscous and linear viscoelasticity functions of enteral puddings.
Keywords: enteral nutrition, pudding, starch, rheology, viscosity, viscoelasticity.
1. INTRODUCTION
Enteral nutrition is defined as oral or tube-delivered caloric sustenance products for consumers
demonstrating a disability or life-threatening disease with significant nutritional problems that cannot be
managed by ordinary or blenderized food. Puddings are a class of enteral nutrition products that are
designed to provide meal replacements.
Pudding products are usually milk protein-based starch paste. Milk proteins are alternative ingredients to
dairy proteins in many food products since they are a good source of essential amino acids. Therefore,
selection of proper ingredients becomes very important for the development of a product with desirable
physical and sensory properties. On the other side, starch is a major hydrocolloid ingredient, used as a
thickening agent for the pudding system (Dickinson, 2003). To make desirable pudding paste, starch paste
should be stable to heat and shearing and should give smooth texture, as well as good storage stability
(Lagarrigue & Alvarez, 2001). Enteral nutrition puddings are enteral nutrition emulsions containing
starch as thickening agent.
The rheological properties of puddings are very complex (Lim & Narsimhan, 2005; Anderson et al.,
2006), being dramatically influenced by processing variables. In this sense, the overall objective of this
work was to evaluate the influence of different processing and compositional variables of enteral nutrition
puddings, such as final thermal treatment, high pressure homogenization previous to its final thermal
treatment, nature and concentration of the starch used in pudding formulation, and storage temperature
after processing, on the rheological behavior and droplet size distribution of the final product.
2.
EXPERIMENTAL
2.1. Materials
Standard enteral nutrition emulsions, food native and chemically modified starches refined from tapioca
(both of them used as thickeners) were kindly supplied by Fresenius Kabi. The vanilla flavour
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commercial pudding product (Forticreme, Nutricia), used as a benchmark, was purchased at a local
market.
2.2. Pudding manufacture
Eight pudding formulations containing different starch concentrations (0.8-1.2% w/w) were manufactured
(see Table 1). Specifically, a starch dispersion was added, at room temperature, to an enteral emulsion
previously prepared according to commercial standard procedures (Fresenius Kabi). Then, the pH of the
sample was adjusted to 7.1. Subsequently, samples were submitted to high pressure homogenization
(Microfluidizer Processor, model M-110L, 550 bars, 1 step) and final thermal treatment (Steam Sterilizer,
model RAYPA AES-12, 120ºC, holding time in the range from 35 to 60 min). Enteral puddings samples
were stored in the fridge (4ºC), and at room temperature (25ºC).
Table 1. Some compositional characteristics, relevant processing variables, and final mean volume
diameter values for the different pudding samples studied
Sample
Starch
Starch
Concentration
(%w/w)
HPH
Holding
time
(min)
Storage
temperature
(ºC)
D4,3(µm)
4ºC 25ºC
A
B
C
D
E
F
G
H
Forticreme
modified
modified
native
modified
modified
modified
modified
modified
1.2
1.2
1.2
0.8
1.0
1.2
1.2
1.2
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
35
35
35
35
35
60
45
40
4, 25
4, 25
4, 25
4, 25
4, 25
4, 25
4, 25
4, 25
35.6 53.3
120.6 142.4
72.8 50.2
33.0 30.8
22.2 25.8
31.6 31.7
95.3 119.1
21.5 28.4
44.0 44.0
2.3. Droplet size distribution characterization
Droplet size distribution (DSD) measurements were made by using a Malvern Mastersizer X-analyser
(MALVERN Mastersizer Hydro 2000MU, UK). Values of the mean volume diameter (d4,3) were obtained
as follows (Orr, 1983):
d4,3 =
where ni is the number of droplets having a diameter di.
2.4. Rheological characterization
The rheological characterization was carried out in a controlled-stress (MARS, HAAKE, Modular
Advanced System) rheometer, at 25ºC. Small amplitude oscillatory shear (SAOS) tests, inside the linear
viscoelasticity region, were carried out in a frequency range comprised between 100 and 0.068 rad/s,
using a serrated plate-and-plate geometry (35 mm diameter, 1 mm gap). Stress sweep tests, at the
frequency of 1 Hz, were previously performed on each sample to determine the linear viscoelasticity
region. Viscous flow measurements were performed, in a shear rate range of 0.01 – 500 s-1. Serrated
plate-plate geometry (35 mm diameter) was used in order to eliminate the wall-slip effects usually
observed during the flow of these materials. All the samples had the same recent past thermal and
mechanical history. At least two replicates of each test were carried out on fresh samples.
3.
RESULTS AND DISCUSSION
3.1. Influence of pudding high pressure homogenization
The influence of the high pressure homogenization step on the rheological properties of pudding
formulations containing 1.2% starch has been characterized.
Table 1 shows mean volume diameter values for samples submitted, or not, to HPH (samples A and B,
respectively), and stored at room or low temperature. Particle size dramatically decreases when the
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sample is submitted to high pressure homogenization (sample A). Thus, the sample that has not been
submitted to HPH shows larger mean volume diameter and wider particle size distribution, no matter
storage temperature is. In addition, HPH yields lower mean particle size, although wider size distribution,
than that obtained for the commercial pudding sample.
Figures 1 and 2 show the viscous flow curves and the frequency dependence of the linear viscoelasticity
functions, respectively, for the same pudding samples. As can be observed, the sample that was not
submitted to HPH shows the largest viscosity and linear viscoelasticity values, in spite of its larger
particle sizes and wider particle distributions. In addition, they are much higher than those obtained for
the commercial pudding sample, no matter storage temperature is. On the contrary, the sample that was
submitted to high pressure homogenization (sample A) shows viscosity values rather similar to those of
the benchmark.
6
6
10
10
o
o
(a) 4 C
(b) 25 C
5
10
5
4
10
3
10
2
10
10
4
10
(Pa·s)
(Pa·s)
3
10
2
10
1
1
10
10
Sample A
Sample B
Forticreme
0
10
0
10
-1
-1
10
10
-3
-2
10
10
-1
10
0
1
10
2
10
. (1/s)
10
3
-3
10
-2
10
10
-1
10
0
10
1
2
10
10
. (1/s)
3
10
4
10
Figure (1). Influence of HPH on the viscous flow behaviour, at 25ºC, of pudding samples stored at room
or low temperature.
5
5
10
10
o
(c) 4 C
o
(d) 25 C
4
10
4
3
10
2
10
10
G´; G´´ (Pa)
2
10
1
G´; G´´ (Pa)
3
10
1
10
G´
10
G´´
Sample A
Sample B
Forticreme
0
0
10
10
-2
10
-1
10
0
10
1
10
(rad/s)
2
10
-2
10
-1
10
0
10
1
10
(rad/s)
2
10
3
10
Figure (2). Influence of HPH on the frequency dependence of the storage and loss moduli, at 25ºC, of
pudding samples stored at room or low temperature.
3.2. Influence of starch nature and concentration
Figures 3 and 4 show the viscous flow curves and the frequency dependence of the linear viscoelasticity
functions, respectively, for samples containing native (sample C) or chemically modified starch (sample
A), stored at room or low temperature. As can be observed, samples containing native starch show larger
viscosities and linear viscoelasticity functions values at both storage temperatures. This suggests that the
chemically modified starch is less shear sensitive as compared to the native one. In addition, native
starch-containing sample rheological functions are higher than those obtained for the commercial pudding
sample, no matter storage temperature is.
3
6
6
10
10
o
(e) 4 C
o
(f) 25 C
5
10
5
4
10
3
10
2
10
10
4
10
3
(Pa·s)
(Pa·s)
10
2
10
1
1
10
10
Sample A
Sample C
Forticreme
0
10
0
10
-1
-1
10
10
-3
10
-2
-1
10
10
0
1
10
10
. (1/s)
2
3
10
10
-3
10
-2
-1
10
10
0
10
.
1
10
2
3
10
10
4
10
(1/s)
Figure (3). Influence of starch nature on the viscous flow behaviour, at 25ºC, of pudding samples stored
at room or low temperature.
5
5
10
10
o
(g) 4 C
o
(h) 25 C
4
10
4
3
10
2
10
3
10
G´, G´´ (Pa)
G´, G´´ (Pa)
10
2
10
1
1
10
G´
10
G´´
Sample A
Sample C
Forticreme
0
10
-2
10
-1
0
10
10
1
2
10
(rad/s)
0
10
-2
10
10
-1
0
10
10
1
2
10
(rad/s)
3
10
10
Figure (4). Influence of starch nature on the frequency dependence of the storage and loss moduli, at
25ºC, of pudding samples stored at room or low temperature.
The influence of starch concentration on pudding rheology has also been considered. Figures 5 and 6
show the viscous flow curves and the frequency dependence of the linear viscoelasticity functions,
respectively, for samples containing 0.8% (sample D), 1.0% (sample E), and 1.2% (sample A) modified
starch, stored at room or low temperature. Samples containing 0.8% starch show the largest viscosities
and linear viscoelasticity functions values at both storage temperatures, displaying a continuous decrease
in the rheological functions as starch concentration increases. These results are quite unexpected.
However, taking into account that all the samples were submitted to the same final thermal treatment, it is
apparent that the final rheological properties are strongly linked to both final thermal treatment and starch
concentration in the pudding. Data not shown here suggest that protein aggregation play a major role in
explaining this anomalous rheological behaviour. In addition, the rheological functions values for the
most concentrated sample are similar to those obtained for the commercial pudding, whilst the differences
increase as starch concentration decreases.
6
6
10
10
o
o
(i) 4 C
(j) 25 C
5
10
5
4
10
3
10
2
10
1
10
10
4
10
3
(Pa·s)
(Pa·s)
10
2
10
1
10
Sample A
Sample D
Sample E
Forticreme
0
10
0
10
-1
-1
10
10
-3
10
-2
10
-1
10
0
10
.
1
10
(1/s)
2
10
3
10
-3
10
-2
10
-1
10
0
10
.
1
10
(1/s)
2
10
3
10
4
10
4
Figure (5). Influence of modified starch concentration on the viscous flow behaviour, at 25ºC, of pudding
samples stored at room or low temperature.
5
5
10
10
o
(k) 4 C
o
(l) 25 C
4
10
4
3
10
2
10
10
3
G´, G´´ (Pa)
G´, G´´ (Pa)
10
2
10
G´
1
10
G´´
1
10
Sample A
Sample D
Sample E
Forticreme
0
0
10
10
-2
-1
10
0
10
10
1
2
10
(rad/s)
-2
10
-1
10
0
10
10
1
2
10
(rad/s)
3
10
10
Figure (6). Influence of modified starch concentration on the frequency dependence of the storage and
loss moduli, at 25ºC, of pudding samples stored at room or low temperature.
3.3. Influence of final thermal treatment
Figures 7 and 8 show the viscous flow curves the frequency dependence of the linear viscoelasticity
functions, respectively, for samples submitted to different thermal treatment times. As can be observed,
thermal treatment times longer than 35 min yield relatively similar viscosity and linear viscoelasticity
functions values, higher than those obtained for the commercial enteral pudding. It is worth mentioning
that sample G (45 min thermal treatment) shows the highest consistency. Similarly to the results obtained
with sample B (not submitted to HPH), its larger mean particle size and wider distribution may be
probably due to a bad performance during sample high pressure homogenization. In any case, the results
confirm that the final thermal treatment time is related to the consistency of enteral puddings. In this
sense, a longer time is necessary to obtain higher consistency as starch concentration increases.
6
6
10
10
o
(m) 4 C
o
(n) 25 C
5
10
5
4
10
3
10
10
4
10
3
(Pa·s)
(Pa·s)
10
2
10
2
10
1
1
10
10
Sample F
Sample G
Sample H
Sample A
Forticreme
0
10
-1
0
10
-1
10
10
-3
10
-2
10
-1
10
0
10
.
1
10
(1/s)
2
10
3
10
-3
10
-2
10
-1
10
0
10
.
1
10
2
10
3
10
4
10
(1/s)
Figure (7). Influence of final thermal treatment time on the viscous flow behaviour, at 25ºC, of pudding
samples stored at room or low temperature.
5
5
5
10
10
o
(a) 4 C
o
(b) 25 C
4
10
4
3
10
2
10
10
3
G´, G´´ (Pa)
G´, G´´ (Pa)
10
2
10
G´
1
G´´
10
1
10
Sample F
Sample g
Sample H
Sample A
Forticreme
0
10
-2
10
-1
10
0
10
1
10
(rad/s)
2
10
0
10
-2
10
-1
10
0
10
1
10
(rad/s)
2
10
3
10
Figure (8). Influence of final thermal treatment time on the frequency dependence of the storage and loss
moduli, at 25ºC, of pudding samples stored at room or low temperature.
4.
CONCLUSIONS
From the experimental results obtained, we may conclude that the mean volume diameter of enteral
puddings dramatically decreases when samples are submitted to high pressure homogenization. Samples
with identical composition that are not submitted to high pressure homogenization show the largest
viscosity and linear viscoelasticity values, in spite of its larger particle sizes and wider particle
distributions.
Starch nature has a significant influence on the rheology of pudding samples. Thus, native starchcontaining samples, submitted to HPH, show larger values of the viscous and linear viscoelaticity
functions. In addition, starch concentration has a marked influence on the rheology of puddings.
Finally, the results obtained confirm that the final thermal treatment time is related to the consistency of
enteral puddings. In this sense, a longer time is necessary to obtain higher pudding consistency as starch
concentration increases.
REFERENCES
Anderson, M.C., Shoemaker, C.F. & Singh R.P. (2006). Rheological characterization of aseptically
packaged pudding. Journal of Texture Studies, 37, 681-695.
Dickinson, E. (2003). Hydrocolloids at interfaces and the influence on the properties of dispersed
systems. Food Hydrocolloids, 17(1), 25–39.
Lim, H.S. & Narsimhan, G. (2005). Pasting and rheological behavior of soy protein-based pudding. LWT,
39, 343-349.
Lagarrigue, S., & Alvarez, G. (2001). The rheology of starch dispersions at high temperatures and high
shear rates: a review. Journal of Food Engineering, 50(4), 189–202.
Orr, C. (1983). In P. Becher (Ed.), Emulsion droplet size (Vol. 1) (pp. 369–404). Encyclopedia of
emulsion technology, New York: Marcel Dekker.
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