Journal of Food Engineering 96 (2010) 179–184
Contents lists available at ScienceDirect
Journal of Food Engineering
journal homepage: www.elsevier.com/locate/jfoodeng
Ultra-high-temperature processing of chocolate flavoured milk
Sangeeta Prakash, Thom Huppertz 1, Olena Karvchuk, Hilton Deeth *
School of Land, Crop and Food Sciences, University of Queensland, Brisbane 4072, Australia
a r t i c l e
i n f o
Article history:
Received 4 March 2009
Received in revised form 10 June 2009
Accepted 10 July 2009
Available online 15 July 2009
Keywords:
Milk
UHT
Chocolate
Fouling
Carrageenan
a b s t r a c t
Chocolate milk with different carrageenans (jappa and lambda) and sugar concentrations was heat treated indirectly at 145 °C for 6 s using a bench-top UHT plant. The temperature of the milk in the preheating
and sterilizer sections, and the milk flow rate were determined to evaluate the overall heat transfer coefficient (OHTC) for monitoring fouling during UHT processing. Kappa-carrageenan was more effective than
lambda-carrageenan in providing stability against fouling during UHT processing. By optimizing concentrations of j-carrageenan and sugar, fouling could be minimized during UHT processing. The apparent
viscosity and sedimentation of UHT-processed chocolate milk increased with increasing concentration
of carrageenan and sugar.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Ultra-high-temperature processing is the preferred way of heattreating chocolate flavoured milk as it enhances the flavour of the
chocolate without making it harsh or bitter, provides an overall
smoothness and favourable mouth-feel and extends its shelf-life
(Bixler et al., 2001). Chocolate milk is formulated with milk, cocoa
powder, sugar and hydrocolloids. The final composition, physical
and sensory properties of the chocolate milk largely depend on
the levels of the ingredients including fat, the type of cocoa and
type of hydrocolloid (Yanes et al., 2002a). It is common practice
to add a hydrocolloid to all UHT flavoured milk to increase the
creaminess of the final product and impart a more lasting taste
(Anonymous, 2000). The largest dairy application for kappa-carrageenan (j-car) is in hot-processed chocolate milk as it imparts a
favourable mouth-feel to the milk and provides long-term suspension of the cocoa particles (Bixler et al., 2001). The favourable
mouth-feel results from the enhanced apparent viscosity of the
carrageenan–casein network (Bixler et al., 2001).
Heat treatment significantly increases the shelf-life of flavoured
beverages and also aids the hydration of the hydrocolloid. It has
also been shown that heating milk containing carrageenan at
UHT temperatures increases the strength of the carrageenan gels
and improves the long-term stability of the product. This has been
attributed to the displacement of carrageenan complexed to
j-casein by the denatured b-lactoglobulin, thus increasing the
* Corresponding author. Tel.: +61 7 3346 9191; fax: +61 7 3365 1177.
E-mail address: [email protected] (H. Deeth).
1
NIZO food research, P.O. Box 20, 6710 BA, Ede, The Netherlands.
0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2009.07.008
availability of carrageenan for carrageenan–carrageenan interactions which are largely responsible for formation of the weak gel
network (Sedlmeyer and Kulozik, 2007; Tijssen et al., 2007).
However, during sterilization, problems may arise due to the increased viscosity achieved by the hydrocolloids and also due to the
interactions between the constituents of the flavour and milk that
result in flocculation, coagulation and sediment formation
(Ramesh et al., 1993; Tziboula and Horne, 2000). If the amount
and type of stabilizer are not satisfactory, the finished product
can exhibit a number of undesirable characteristics such as flocculation and coagulation (Anonymous, 2000).
Traditionally j-car has been used as a stabilizer in protein systems, particularly dairy applications (Langendorff et al., 2000).
However data from differential scanning calorimetry show that
heat-induced aggregation of b-lactoglobulin (b-Lg) decreases in
solutions containing low amounts of sulfate-containing polysaccharides like k-carrageenan (k-car) (Zhang et al., 2004), suggesting
the potential importance of k-car in dairy processing.
Studies related to chocolate milk have mainly concentrated on
its sensory (Folkenberg et al., 1999), rheological and optical properties (Yanes et al., 2002b). The effect of heat treatment on the stability of chocolate milk has revealed three types of instability:
sedimentation of cocoa particles, formation of large flocs and formation of light- and dark-coloured layers (Yanes et al., 2002b) that
arise due to interactions between the ingredients of the chocolate
and milk components (van den Boomgaard et al., 1987). Fouling or
deposit formation is an every-day concern of the dairy industry
and is a very common problem during UHT processing of chocolate
flavoured milk. No work has been reported on fouling that takes
place during UHT treatment of chocolate milk. The main aim of
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S. Prakash et al. / Journal of Food Engineering 96 (2010) 179–184
the present work was to study UHT processing of chocolate milk
with different concentrations of j-car, k-car and sugar.
2. Materials and methods
2.1. Chocolate milk preparation
Reconstituted whole milk was prepared by mixing whole milk
powder into water to a final concentration of 120 g per L at 35 °C
using a heavy duty mixer (van den Boomgaard et al., 1987). Standard chocolate milk was prepared by adding cocoa powder
(1.5%), caster sugar (7%, 9% and 11%) and carrageenan (j-car or
k-car) (0.00%, 0.01%, 0.03%, 0.05% or 0.10%) to the reconstituted
milk. Commercial-grade cocoa powder was supplied by Frutex
Australia (New South Wales, Australia). j-car (WG80 M) was supplied by Woods & Woods Pty Ltd. (NSW, Australia) and k-car (Seakem CM611) was supplied by Swift Company Ltd. (Victoria,
Australia).
2.2. UHT processing
A bench-top UHT plant, similar to the one described by Wadsworth and Bassette (1985), was used in the experimental trials.
The holding times in the preheating and high-temperature sections
were 8 s at 95 °C and 6 s at 145 °C, respectively. After heat treatment the milk was cooled to 6 35 °C in 25 s in a water-jacketed
cooler. The flow rate of the milk was maintained at 120 mL/min.
The Reynolds Number (Re) of the flow was calculated as
4.03 104, which falls in the turbulent flow regime (Holman,
2002).
The bench-top plant was instrumented with thermocouples located at the inlet and outlet of the pre-heater and the outlet of the
sterilizer and high-temperature holding sections. The thermocouple at the outlet of preheater was at the inlet of the sterilizer section. All thermocouples were connected to a data logger (PCLD8115 supplied by Advantech, Company Ltd., Taiwan) which measured and recorded inputs. The system used a PC-based data acquisition system, VISIDAQ, that allowed real-time monitoring of data
and generated data logs which were used for data management
in MS-ExcelÒ. Milk flow rate was determined by measuring the
time required to collect a known volume of milk. Three measurements were recorded for every 5 min of the entire run and their
average represented the flow rate for the 5 min period.
2.3. Fouling measurement
Fouling was monitored by changes in overall heat transfer coefficient (OHTC) which was measured using the following equation
from Kastanas (1996):
GC p Dh
OHTC ¼
ADT lm
ð1Þ
where G = mass flow rate of the milk in kg/s; Cp = specific heat of
chocolate milk in J/(kg°C) – this was calculated taking into account
the specific heat capacity and mass fraction of each component
(milk powder, specific heat capacity = 3750 J/(kg°C) Walstra et al.
(2005)); cocoa powder, specific heat capacity = 1200 J/(kg°C) (personal communication Dr. Ulrich Krause); sugar specific heat capacity = 1250 J/(kg°C), Walstra et al. (2005). The specific heat capacity
of carrageenan was not included as a negligible amount of carrageenan was added to the mixture); Dh = temperature difference between the inlet and outlet of the UHT section, in °C; A = heat
exchanging surface area of the tubing = 1.627 105 m2;
DTlm = logarithm mean temperature difference (LMTD) in °C:
DT lm ¼
ðT o T mo Þ ðT o T mi Þ
ln½ðT o T mo Þ=ðT o T mi Þ
ð2Þ
where To is the temperature of oil in the high-temperature section
in °C; Tmo and Tmi are the temperatures of milk at the inlet and outlet of the high-temperature section, respectively (Kastanas, 1996).
The bench-top UHT plant was operated and cleaned as described by Kastanas (1996). The experiment was stopped when
the temperature at the outlet of the high-temperature section
dropped below 120 °C or earlier if deposits blocked the channel
or if the back-pressure could not be maintained at 0.4 MPa. The
indicator of the pressure gauge fluctuated from its set point of
0.4 MPa with fouling, and the fluctuation became more pronounced as deposit built up on the walls of the tubes. All the experimental trials were carried out in duplicate.
2.4. Apparent viscosity
The apparent viscosity of the UHT-processed chocolate milk
was measured at room temperature using a Brookfield Viscometer
(Model DV-I Viscometers, Brookfield Engineering Laboratories,
INC., USA) fitted with a UL adaptor. A spindle speed of 30 rpm
was used.
2.5. Sediment measurement
Sedimentation in chocolate milk is defined as the settling of
particles, including cocoa particles, under gravity. Sediment in
the sterilized chocolate milk was measured estimated by a centrifugation method, using calibrated centrifuge tubes (50 mL). The
weight of the centrifuge tubes was recorded and milk was weighed
(40 ± 0.1 g) into them. The samples were placed in a centrifuge
(Model 5702 R, Eppendorf) at 3000g for 15 min. After centrifugation, the solid sediment was separated from the supernatant by
decanting. The tubes were then placed in an oven at 120 °C for
36 h and the dry weight of the sediment was measured. For each
sample, duplicate analyses were carried out. The results were expressed as g/100 g of milk.
2.6. Statistical analysis
All statistical analyses were performed using MINITABÒ 15 statistical software (Minitab Inc., Chicago, USA, 2007). The general linear model analysis was performed with the GLM ANOVA tests
procedure. When the main ANOVA tests were significant, multiple
comparisons of treatments were further conducted with the Tukey
test implemented in the procedure. The p-values of specific comparisons are reported in the text.
3. Results
3.1. Effect of j-car, k-car and sugar concentration on UHT processing
of chocolate milk
The variation in OHTC with time of operation for chocolate milk
with 1.5% cocoa powder, 7% sugar and different concentrations of
j-car (0%, 0.01%, 0.03%, 0.05% and 0.1%) is shown in Fig. 1. The control sample, i.e. the sample to which no j-car was added, showed
considerable fluctuation in temperature and back-pressure right
from the start which became more pronounced towards the end
of the run. The cocoa particles settled to the bottom of the balance
tank and interfered with the running of the bench-top UHT plant as
the back-pressure could not be maintained. The OHTC dropped
rapidly with time of operation. The fluctuation in OHTC is a result
of the fluctuation in temperature.
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S. Prakash et al. / Journal of Food Engineering 96 (2010) 179–184
5000
1000
0.03%
0.01%
600
400
0.10%
0.05%
0%
0.01%
0.03%
0.05%
0.10%
0%
200
1000
2000
3000
4000
3000
2000
1000
0
0
κ-carrageenan
α-carrageenan
4000
Average run-time (s)
20
OHTC (kW/m C)
800
0
5000
0.00
0.02
0.04
Time of operation (s)
0.06
0.08
0.10
Carrageenan concentration (%)
Fig. 1. Variation in OHTC with time of operation during UHT processing of
chocolate milk with different concentrations of added j-car.
UHT processing of chocolate milk with 0.01% added j-car
showed an improvement in run-time (average run-time, 4020 s)
(SD = 60 s); however there was fluctuation in both temperature
and back-pressure, and towards the end of the runs the fluctuation
was so severe that the bench-top UHT plant had to be shut down.
The amount of cocoa particles settling to the bottom of the balance
tank was also less than in the run with no added carrageenan.
Processing chocolate milk with 0.03% j-car greatly improved
the run-time (average run-time 5000 s) (SD = 20 s) of the plant
compared with that obtained with 0 and 0.01% j-car. The fluctuations in temperature and back-pressure were minimal and the
amount of cocoa particles that settled at the bottom of the balance
tank was also less than in the runs with 0% and 0.01% j-car.
Addition of 0.05% and 0.1% of j-car markedly reduced the runtime of the plant (Fig. 1). There was no induction period but a steep
drop in OHTC. The back-pressure was constant throughout the run;
however the temperature at the outlet of the sterilizer section
dropped rapidly. Fouling was very severe with 0.1% added j-car
and the tubes were almost blocked before the run could be
terminated.
The run-times obtained with UHT processing of chocolate milk
with 1.5% cocoa powder, 7% sugar and different concentrations
(0.01%, 0.03%, 0.05% and 0.1%) of k-car are shown in Fig. 2.
Fig. 3. Interaction plot for run-times at various concentrations of j- and kcarrageenan (SE = 37.26 s).
The run-times at the lower concentrations of k-car (0.01% and
0.03%) were shorter than those with similar concentrations of jcar (Fig. 3) (P < 0.001).
There was no significant difference in the run-times of chocolate milk with 0%, 0.01% and 0.03% k-car. An observation made during processing which is also evident in Fig. 2 was the fluctuation in
temperature and back-pressure even at 0.03% k-car which was not
observed at similar concentrations of j-car. At higher concentrations (0.05% and 0.1%) the run-times were short, as was observed
with similar concentrations of j-car (Fig. 3).
The interaction plot of run-time at 0–0.1% concentrations of jcar and k-car is presented in Fig. 3. Tukey simultaneous tests were
performed for all pair-wise comparisons of j-car and k-car. The results showed that the run-times for k-car were significantly shorter
than those for j-car at 0.01%, 0.03% and 0.05% (P < 0.05), with no
significant difference at 0.1% k-car and j-car.
The UHT-processed chocolate milk, when collected in a glass
beaker, showed distinct dark and light layers with 0.05% and
0.1% j-car and k-car but not with 0%, 0.01% and 0.03% j-car and
k-car. The appearance of these layers is often associated with the
type of cocoa powder, the sterilization time or percentage of stabilizers (van den Boomgaard et al., 1987). Considering the same cocoa powder and the same sterilization time were used for all the
trials in our study, the layers are attributable to the higher percentages of j-car and k-car.
1200
0%
0.01%
0.03%
0.05%
0.10%
1000
7%
800
800
20
OHTC (kW/m C)
20
OHTC (kW/m C)
1000
600
0.03%
400
0.05%
0.01% 0%
0.10%
200
600
400
7%
9%
11%
9%
200
11%
0
0
0
500
1000
1500
2000
2500
3000
3500
Time of operation (s)
Fig. 2. Variation of time of operation of the UHT system with different concentrations of added k-car.
0
500
1000 3500
4000
4500
5000
Time of operation (s)
Fig. 4. Variation of time of operation of the UHT system with different concentrations of added sugar.
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S. Prakash et al. / Journal of Food Engineering 96 (2010) 179–184
Standard chocolate milk has a sugar concentration of 7% (van
den Boomgaard et al., 1987). The role of sugar during UHT processing of chocolate milk was investigated by increasing the concentration to 9 and 11% and keeping the concentrations of carrageenan
(0.03%) and cocoa powder (1.5%) constant. j-Car at 0.03% was used
as it gave the longest run-time. The variation of OHTC with time of
operation is shown in Fig. 4 (some data points between 1000 and
3500 s have been omitted in the graph to facilitate display of the
short and long runs). Higher sugar concentration (9% and 11%) fouled the plant very quickly.
of carrageenan (P < 0.001). However there was no significant difference in amount of sediment obtained at similar concentrations in
the range 0.01–0.03% of the different types of carrageenan.
The addition of sugar at 9% and 11% increased the apparent viscosity of the milk and markedly reduced the run-time of the system (Fig. 4). There was no significant difference in run-time of
the plant during UHT processing of chocolate milk with 9% and
11% added sugar but these run-times were significantly different
from those with 7% added sugar (P < 0.001) (Fig. 4). The observed
viscosities and processing parameters, as shown in Table 2, suggest
that the higher apparent viscosity resulting from the higher sugar
contents caused shorter run-times and more sedimentation. There
was no observable induction period and the decline phase was
steep for the two higher sugar levels (Fig. 4).
Analysis was performed on the log-transformed data for the
amount of sediment and apparent viscosity obtained with different
concentrations of sugar. There was a significant difference in the
apparent viscosity and amount of sediment obtained between 7%
and 9% added sugar (P < 0.001 and 0.05), between 7% and 11%
added sugar (P < 0.001 and 0.01), and between 9% and 11% added
sugar (P < 0.01 and 0.01). The results (Tables 1 and 2) suggest that
sediment and apparent viscosity both increase with increasing carrageenan concentration.
3.2. Effect of j-car, k-car and sugar on apparent viscosity and
sedimentation
The initial OHTC and product outlet temperature (OHTC and
outlet temperature at commencement of the experiment), apparent viscosity and sediment data of UHT-processed samples of chocolate milk with different concentrations of j-car and k-car are
shown in Table 1.
The addition of j- and k-car significantly influenced the apparent viscosity of the processed chocolate milk (P < 0.001). There was
a steady increase in apparent viscosity with increase in j- and kcar concentration with 0.1% markedly increasing the apparent viscosity of the UHT-processed chocolate milk. The increase in apparent viscosity at 0.05% and 0.1% was accompanied by a reduction in
run-time of the plant, with 0.1% fouling the plant in less than 9 min
(Figs. 1 and 2). The decreased initial product outlet temperature
and OHTC at higher j- and k-car concentration could be due to
increasing apparent viscosity (thus decreasing turbulence in the
tubular heat exchangers) during heating (Table 1). A similar increase in viscosity was observed by Kastanas (1996) during fouling
of concentrated milk.
A Tukey simultaneous test was performed for all pair-wise comparisons of apparent viscosity. The apparent viscosity of UHT-treated chocolate milk at 0.1% carrageenan was significantly different
from the apparent viscosity obtained at lower concentration
(0.01–0.05%) with a significant difference (P < 0.05) in apparent
viscosity obtained with similar concentrations of different
carrageenans.
Analysis was performed on log-transformed data for the
amount of sediment obtained from UHT-processed samples of
chocolate milk with different concentration of carrageenan. There
was a significant difference in the amount of sediment obtained
with j- and k-car (P < 0.001) and with the different concentrations
4. Discussion
In this study UHT processing of chocolate milk without added
hydrocolloid was practically impossible with the bench-top UHT
system. The dispersed cocoa particles in the milk interfered with
the processing causing constant fluctuation in temperature and
back-pressure. Addition of j-car stabilized the chocolate milk formulation to UHT processing with 0.03% j-car giving the best results, that is, the maximum run-time. This concentration is the
critical gelling concentration for j-car. The sulfated linear polysaccharide j-car behaves as an adsorbing polymer and forms complexes with the proteins in milk. The complex is primarily based
on electrostatic interactions between j-casein and j-car (Snoeren
et al., 1975). At elevated temperatures, caseins micelles in the presence of j-car form into clusters or ‘‘microdomains” which exclude
the j-car; on cooling, the carrageenan strands associate with the
casein on the periphery of the clusters and with other carrageenan
molecules in solution via a double helix structure to form a strong
gel network (Spagnuolo et al., 2005). The dispersed cocoa particles
Table 1
Effect of j- and k-carrageenan concentration on processing parameters, apparent viscosity and sedimentation of UHT-processed chocolate milk (average values, n = 2).
Amount of j-car (%)
0
0.01
0.03
0.05
0.1
Sediment (g/100 g of milk)
Apparent viscosity (mPa s)
Initial product outlet temperature (°C)
Initial OHTC (kW/m2°C)
j-car
k-car
908
904
905
807
731
903
904
907
816
729
j-car
k-car
j-car
k-car
j-car
1.73
1.63
1.50
2.63
6.70
1.60
1.58
1.60
5.15
8.20
3.29
3.76
4.08
5.27
>20
3.26
3.87
4.90
5.82
>20
145.19
145.12
145.15
143.02
141.04
(0.03)
(0.01)
(0.01)
(007)
(0.27)
(0.04)
(0.03)
(0.03)
(0.16)
(0.21)
(0.10)
(0.08)
(0.11)
(0.10)
(0.37)
(0.27)
(0.14)
(0.06)
k-car
(0.12)
(0.08)
(0.13)
(0.06)
(0.13)
145.17
145.19
145.19
143.83
142.62
(0.04)
(0.09)
(0.02)
(0.14)
(0.21)
(1.41)
(2.12)
(2.85)
(2.83)
(2.12)
(2.12)
(2.83)
(1.41)
(2.83)
(3.54)
Standard deviation shown in parenthesis.
Table 2
Effect of sugar concentration on sedimentation, apparent viscosity and run-time during UHT processing of chocolate milk containing 0.03% of j-car (average values, n = 2).
Amount of sugar (%)
Sediment (g/100 g of milk)
Apparent viscosity(mPa s)
Initial product outlet temperature (°C)
Initial OHTC (kW/m2°C)
Run-time (s)
7
9
11
1.50 (0.01)
8.73 (0.18)
11.48 (0.38)
4.08 (0.11)
>20
>20
145.2 (0.11)
142.7 (0.18)
140.2 (0.16)
905 (2.1)
805 (2.8)
701 (6.4)
5000 (28.3)
480 (42.4)
420 (28.3)
Standard deviation shown in parenthesis.
S. Prakash et al. / Journal of Food Engineering 96 (2010) 179–184
in chocolate milk become incorporated into the casein–carrageenan gel network and as a result the cocoa particles are immobilized. The immobility is advantageous as it reduces the fluctuation
in temperature and back-pressure and also sedimentation of cocoa
particles in the balance tank as observed in this study. However
there needs to be enough carrageenan in the system to cover the
particle surfaces and provide sufficient free polymer for the development of a network that withstands the gravitational forces acting on the dispersed particles (Langendorff et al., 1997). This was
evident in the present study as below a minimum concentration
of added j-car (0.03%), the chocolate milk was unstable to UHT
processing with fluctuation in temperature and back-pressure.
Apart from keeping the cocoa particles in suspension, the j-carrageenan–protein interaction provides stabilization of the milk
against precipitation by Ca2+ by shielding the calcium-sensitive
caseins, as- and b-caseins, from contact with Ca2+ (Lin and Hansen,
1970; Lin et al., 1972). Studies have revealed that j-car does not
influence the denaturation (unfolding) of b-Lg (Tziboula and
Horne, 1999) but accelerates the aggregation of denatured b-Lg
molecules (Capron et al., 1999). Grijspeerdt et al. (2004) have suggested that the shorter the unfolded form is present in the UHT
plant the longer the run-time. Therefore, the longer run-times with
0.01% and 0.03% of j-car in chocolate milk could be associated with
the quicker aggregation of denatured b-Lg molecules.
k-Car forms complexes with caseins similar to those with j-car
(Spagnuolo et al., 2005) but in this study was unable to impart stability when added to chocolate milk at 0.01–0.1% during UHT processing. Although it cannot be confirmed from this study, the
fluctuations in temperature and back-pressure suggest the inability of the k-car–casein network to hold the cocoa particles in suspension. This is supported by the fact that k-car is less effective in
stabilizing as-casein against calcium-induced precipitation (Lin
and Hansen, 1970). Studies have also shown that k-car lowers
the degree of heat-induced aggregation of b-Lg. All these factors
would contribute towards the shorter run-times obtained during
UHT processing of chocolate milk with added k-car compared with
those with added j-car.
The viscosity of milk is between 2.2 and 2.5 mPa s and milk is a
Newtonian fluid (Yanes et al., 2002a,b). The difference in apparent
viscosity between milk and chocolate milk is evident in this study
and can be attributed to the concentration of hydrocolloid, the possible interactions between hydrocolloid and casein micelles and
the sugar added. The increase in apparent viscosity with addition
of carrageenan is due to the linear macromolecular structure and
polyelectrolytic nature of carrageenan. The mutual repulsion of
the many negatively charged half-ester sulfate groups along the
polymer chain causes the molecule to be highly extended, while
its hydrophilic nature causes it to be surrounded by a sheath of
immobilized water molecules. Both of these factors contribute to
the resistance to flow (Yanes et al., 2002a,b). This resistance reduces the turbulence in flow so that the product close to the wall
of the tube moves slowly, becomes overheated and facilitates the
formation of a permanent fouling layer. Also higher carrageenan
concentrations increase the size of casein micelles aggregates (Michon et al., 2005) which renders them more likely to contribute to
the rapid fouling observed at higher concentration of j-car.
Apart from increasing the apparent viscosity, higher concentrations of sugar reduce the solvent quality and cause the collapse of
the j-casein hairy brush on the surface of the micelles (Schorsch
et al., 1999, 2002). This leads to aggregation of the casein micelles
making them more susceptible to coagulation when exposed to
heat. This may explain the shorter run-time at higher concentrations of sugar (9% and 11%).
The sedimentation results show higher sediment formation at
higher concentrations of sugar and carrageenan that could be associated with aggregation of casein at higher sugar and carrageenan
183
concentrations. There was no significant difference in sediment
values at low carrageenan concentrations.
The chocolate milk was stable to UHT processing up to a critical
j-car concentration, 0.03%, above which the excess carrageenan
remains in solution and flocculates the carrageenan-coated micelles by depletion causing sedimentation (Spagnuolo et al.,
2005). The small increase in apparent viscosity at low concentrations of carrageenan (0.01–0.03%) did not affect the run-time as
the flow of the chocolate milk was similar to that of aqueous solutions of carrageenan without any intermolecular bonds which form
at higher j-car concentrations in milk due to formation of carrageenan–casein micelle aggregates (Yanes et al., 2002a).
5. Conclusions
This study found that fouling of heat exchangers during UHT
processing of chocolate milk can be minimized by adding optimal
concentrations of j-carrageenan and sugar. The effect of carrageenan at the optimal concentration can be attributed to the formation of a complex between it and casein which only
marginally increases the apparent viscosity and effectively holds
the cocoa particles in suspension, preventing them from interfering
with the operation of the UHT plant. The results also indicate that
j-car is more effective in providing stability against fouling during
UHT processing than k-car. This can be attributed to the abilities of
j-car to accelerate the aggregation of denatured b-Lg molecules
and stabilize casein against calcium-induced precipitation more
effectively than k-car.
The results suggest that while whey proteins and calcium are
important, caseins play a significant role in fouling during chocolate milk processing. This is particularly evident when excessive
concentrations of sugar or carrageenan are added. Furthermore,
the higher concentrations of sugar and carrageenan contribute to
increased sediment formation due to coagulation of caseins in
the UHT-processed milks. Both the fouling and sediment formation
observed with higher sugar and carrageenan levels are associated
with very high viscosities after heat treatment. It is apparent that
excessive fouling and sediment formation only occur after the
apparent viscosity reaches some critical value. This value should
be determined to ensure optimum efficiency in UHT processing
of chocolate milk.
Acknowledgement
The authors wish to thank Dairy Australia for their financial
support of this work.
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