The Malaysian Journal of Analytical Sciences, Vol 12, No 3 (2008): 513 - 519
MINIMIZATION OF SUCROSE LOSSES IN SUGAR INDUSTRY BY pH
AND TEMPERATURE OPTIMIZATION
Kornvalai Panpae1*, Wasna Jaturonrusmee1, Withawat Mingvanish1 , Chantana Nuntiwattanawong2, Surapon
Chunwiset 2 , Kittisak Santudrob1 and Siriphan Triphanpitak1
1
Department of Chemistry , Faculty of Science , King’s Mongkut’s
University of Technology Thonburi, Bangkok 10140, Thailand
2
Chaimongkol Refined Sugar Company, Limited.( U-Thong Factory ),
Supanburi Province 72160, Thailand
* Corresponding author: kornvalai.pan@kmutt.ac.th
Abstract
Invert sugar has several disadvantage properties that play an important role in many food applications. It has a high affinity
for water and is the cause of making products retain moisture.Invert sugar also affects the caramelization process , producing
a browning effect. In this study, the possibility of minimization of sucrose inversion during the industrial production of
sugar cane was investigated by the variation of the important parameters, i.e. temperature and pH of sugar cane juice for
each of samples. The amounts of sucrose and reducing sugar alerting during the sucrose inversion process were determined
by the values of % Pol and % reducing sugar (% RS), respectively. Starting with the study of temperature and pH effects of
the sucrose solution with the concentration of 16 Brix, used as a sample model, it was found that no change in amounts of
reducing sugar and sucrose was observed at room temperature (34oC) in the pH range of 5-11.
At pH 3, the amounts of reducing sugar increased and the amount of sucrose decreased as the time increased. These
indicated that the process of sucrose inversion should better occur in more acidic solutions. Compared to the room
temperature, it was found that the increment of temperature led to enhance the process of sucrose inversion. This was
depicted by higher values of %RS and lower value of % Pol as the temperatures were elevated. The experiments were also
done with real sugar cane juice, i.e. first, last, and mixed juice. The tendency of changes of the amounts of reducing sugar
and sucrose in sugar cane samples by varying temperature and pH were found to resemble to those for the sample model.
The increment of temperatures have also affected on a reduction of amounts of sucrose in each sugar cane juice. In addition,
it could be concluded that the acidity of the solution affects sucrose easier to be broken down to glucose and fructose
molecules.
Keywords : Sugar industry , Sugar cane juice , Sucrose inversion , Reducing sugar,Inverted sucrose
Introduction
Industrial processes aim at maximizing their production capacities while simultaneously improving the product
quality and reducing operating costs. Usually, there exists a trade off between these requirements. This is
particularly true in the production of high quality sugar from sugar cane crushing factory where high
productivity at minimizing invert sugar is the most important issue. Sugar cane must be crushed to extract the
juice. The crushing process must break up the hard nodes off the cane and flatten the stems. The juice is
collected, filtered and sometimes treated and then boiled to drive off the excess water. In the process of juice
treatment, juice should be filtered through a cloth before boiling in order to remove any solids such as dirt or
particles of cane. The juice is neutralized with lime (Ca(OH)2) and then is boiled. After removal from the heat,
the pans of juice are usually stirred rapidly to incorporate air and promote an even crystallization. For those
with access to simple sugar measuring devices, this usually corresponds to a Brix (sugar content) of 90-95%.
The schematic representating process of sugar production is shown in Figure 1.
Monitoring of total reducing sugar (reducing sugars plus hydrolyzed sucrose (Alves et al., 2006)) is very
important in relation to the sugar cane agro-industry, as it may provide information for evaluation of the raw
matter and for quality control of the sugar manufacturing process. The inversion reaction is shown in Figure 2.
Invert sugar syrup, an equimolecular mixture of glucose and fructose, is a valuable sweetener and is require by
the food and pharmaceutical industries. High fructose syrups are in great demand as food and soft drink
sweeteners. However, inversion of sucrose, an irreversible reaction, and thus the reaction rate is not influenced
by the product accumulation, is, therefore, a major problem on sucrose losses, across unit processes in the sugar
industry.
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Kornvalai Panpae et al: MINIMIZATION OF SUCROSE LOSSES IN SUGAR INDUSTRY BY pH AND
TEMPERATURE OPTIMIZATION
Figure 1 The process diagram of sugar production.
Fig. 1: The process diagram of sugar production.
Fig. 2: The inversion of sucrose.
In the sugar refinery, determination of reducing sugars commonly relies on the Lane-Eynon titration or on the
Somogyi-Nelson spectrophotomatric procedure, both relying on sugar oxidation by Cu2+ ion (Alves et al.,
2006). There are a number of publications focusing on the determination and/or preventation of “sucrose
inversion” (Khan and Rahman, 1996 ; Wienen and Shalleuberger, 1988 ; Eggleston et al.,2002 ; Eggleston and
Monge, 2005 : Alves et al.,2006) as well as using enzymatic reactions (Almeida et al.,2005 ; Kurup et al.,2005).
However, most of the investigations are based on single objective optimization, incorporating several objectives
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The Malaysian Journal of Analytical Sciences, Vol 12, No 3 (2008): 513 - 519
with some weight factor. Single objective function optimization approach is not efficient and also has the
drawback of possibly losing certain optimal solution. Sometimes it is very difficult to ensure for more complex,
real-life problems.
In this study, an attempt has been made to establish the optimum conditions to reduce invert sugar of sugar cane
juice in U-Thong Sugar Industry Factory by optimizing pH and temperature compared with pure cane sugar.
Materials and Methods
Materials
Mixed juice, limed juice and clear juice samples were obtained from an industrial sugar cane process line. The
experiments were performed at the factory laboratory. Mixed juice was the first crushed juice mixed with juice
from 4 crushings without chemical was added. Limed juice was the mixed juice which pH adjusted to neutral by
lime. Other chemical : dry lead subacetate (Pb(CH3COO)2Pb(OH)2) ; Analytical grade, pure cane sugar
(sucrose, C12H22O11); Analytical grade and methylene blue indicator solution C16H18N3SCl.2H2O) were obtained
from Asia Pacific Specialty Chemicals Co. Copper sulfate (CuSO4.5H2O) ; Analytical grade and Rochelle salt,
sodium potassium tartate (COOK(CHOH)2COONa.4H2O) ; analytical grade were purchased from Ajax
Chemical Co.
Apparatus
A polarimeter with sodium-vapor lamp, thermostat and circulating pump was use to determine % Pol of the
samples. The mean Brix of triplicate samples was measured using a Leica Abbe Mark II refractometer with a
crosshair reticule. Brix is total dissolved solid in juice solution. The concentration (C) of sucrose in solution
(g/100cm3) can be obtained by measuring brix of solution and value of C from “Table of brix and grammes of
sucrose per 100 cm3 of sugar solutions” of Bureau of Sugar Experiment Stations (1970).
Methods
The pH of standard sucrose solution (16 Brix) and raw juice samples (pH 5.53) were adjusted from 3.0 to 11.0
with 10% HNO3 and 20% lime solution at the same temperature. The thermal stability of standard sucrose was
studied by heating and stirring at 34 (room temperature), 60, 70, 80 and 90 °C. For the juice, it was heated to 80
°C only.
Quality evaluation
After the experiments, the standard sucrose and the juice samples were characterized base on their Brix, % Pol,
% RS (reducing sugar), TSS (total suspended solid) and TDS (total dissolved solid). All experiments were
repeated three times and the average value were used.
Results and Discussion
Analytical data of non-pH and temperature controlled sugar cane juice
Physical and Chemical characteristics of the non-pH and temperature controlled juice are presented in Table 1.
Table 1: Analytical data of mixed, lime and clear juice samples
Technical data
mixed juice
lime juice
clear juice
TS
TSS
TDS
86.36
10.45
64.26
270.04
4.60
280.04
131.01
1.48
104.46
(mgL-1)
After neutralization, TS and TDS values of lime juice were rather high since adding lime, for neutralization,
increases in total solids in sugar cane solution.
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Kornvalai Panpae et al: MINIMIZATION OF SUCROSE LOSSES IN SUGAR INDUSTRY BY pH AND
TEMPERATURE OPTIMIZATION
Effects of pH and temperature on the cane sugar (concentration 16 Brix)
% RS and % Pol of the standard sucrose was studied at various pH (3.0, 5.0, 7.0 and 11.0) and temperatures at
34, 60, 70, 80 and 90 °C. The selected results (at temperature 30, 70 and 80 °C) are shown in Figure 3-8.
time (hours)
Fig. 3: % RS of standard sucrose at 34 °C
Fig. 4: % Pol of standard sucrose at 34 °C
time (hours)
time (hours)
Fig. 5: % RS of standard sucrose at 70oC
Fig. 6: % Pol of standard sucrose at 70 °C
time (hours)
Fig. 7: % RS of standard sucrose at 80 °C
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time (hours)
time (hours)
Fig. 8: % Pol of standard sucrose at 80 °C
The Malaysian Journal of Analytical Sciences, Vol 12, No 3 (2008): 513 - 519
Sucrose is dextrorotatory, but the resulting mixture of glucose and fructose is slightly levorotatory, because the
levorotatory fructose has s greater molar rotation than the dextrorotatory glucose. As the sucrose is used up and
the glucose-fructose mixture is formed, the angle of rotation to the right (as the observer looks into the
polarimeter tube) becomes less and less, and finally the light is rotated to the left (Scheme 1).
Scheme 1
At the temperature of higher 80 °C, it was found that the caramelization occurred to a significant extent as the
thermal degradation of sugars. Under heat, caramelization transforms sugars from colourless, sweet compounds
into substances ranging in brown colour.
pH effects on the sucrose inversion of mixed juice
Table 2 shows analytical data of mixed juice at 34 (room temperature) and 70 °C and pH at
5.35 (non-pH controlled), 6.0, 7.0 and 8.0
Table 2: Analytical data of pH and temperature controlled mixed juice.
pH
data
% RS
Brix
Pol
% Brix
% Pol
%Pur
34oC
1.39
15.17
47.90
15.17
11.75
77.44
5.35
70oC
1.87
17.37
55.63
17.37
13.53
77.89
34oC
1.35
15.48
48.20
15.48
11.81
76.27
6.0
70oC
1.56
16.78
54.32
16.78
13.24
78.91
34oC
1.52
15.24
48.18
15.24
11.81
77.52
7.0
70oC
1.56
16.80
53.62
16.80
13.07
77.79
34oC
1.35
15.11
48.61
15.11
11.93
78.92
8.0
70oC
2.24
16.27
53.34
16.27
13.03
80.07
Data based on three replications.
Temperature effects on the sucrose inversion of sugar cane juice
Thermal stability of sucrose, measured in % RS and % Pol, was summarized in Table 3. It is found that the
percentage of inversion of % RS and % Pol values at 80 °C were significant extent, especially for the last juice
in the time period of 40 min.
Increasing solid content resulted in lower % Pol during heating at 80 °C. All
of the juice are more susceptible to temperature elevation during heating than during storage at room
temperature.
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Kornvalai Panpae et al: MINIMIZATION OF SUCROSE LOSSES IN SUGAR INDUSTRY BY pH AND
TEMPERATURE OPTIMIZATION
Table 3: Effect of temperature on % inversion of RS and Pol of first, last and mixed juice Samples
temperature
sample
data
first juice
% RS
% Pol
last juice
% RS
% Pol
mixed juice
% RS
% Pol
34oC
20 min
9.76
0.72
15.33
-0.37
0.56
0.08
80oC
40 min
8.64
12.90
23.03
-1.29
4.92
0.13
20 min
6.98
14.72
6.77
5.59
9.11
40 min
9.80
-62.96
25.30
11.12
17.39
21.80
Conclusion
The measurement of sucrose inversion across unit processes in the sugar industry is notoriously difficult and
has meant that very limited diagnosis of process problems contributing to sucrose losses has occurred. Sucrose
concentrations are traditionally measured at the factory using polarization or optical rotation purity
measurements. Results from this study showed that sucrose inversion in various sugar cane juice samples
strongly depended on pH, temperature and also solid content. Increasing solid content (lime juice) , pH and
temperature during both heating and storage at room temperature, increased the rate of sucrose inversion. The
tendency of changes of the amounts of reducing sugar and sucrose in sugar cane samples by varying
temperature and pH were found to resemble to those for the sample model. To minimize the total reducing
sugar, we recommended that temperature was a critical factor controlling sucrose inversion whereas the anion
(OH - from lime) at the higher pH had a slightly influence on physical and chemical properties of the juice
compared to the high stability and purity of pure cane sugar.
Acknowledgements
This research was supported by Industrial Cooperative Learning Research, Faculty of Science, King Mongkut’s
University of Technology Thonburi, Bangkok 10140, Thailand. Many helpful information and sugar cane juice
samples provided by Chaimongkol Refined Sugar Co. Ltd. and providing of factory laboratory spaces as well as
the necessary instruments, from U-Thong Sugar Industry Factory, Supanburi Province,Thailand are high
appreciated.
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