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Rate of browning reaction during preparation of coconut and palm sugar
International Congress Series 1245 (2002) 275 – 278
Rate of browning reaction during preparation of coconut and palm sugar Anton Apriyantono*, Astrid Aristyani, Nurhayati, Yeni Lidya, Slamet Budiyanto, Soewarno T. Soekarto Department of Food Technology and Human Nutrition, Bogor Agricultural University, Kampus IPB Darmaga, P.O. Box 220, Bogor 16002, Indonesia
Abstract The objective of this research was to analyse the rate of browning reaction during preparation of palm and coconut sugar. Brown colour formation during preparation of coconut sugar at a laboratory scale followed a zero order reaction with a constant of formation (k) equal to 5.15 10 3 AU min 1 (AU = Absorbance Unit). The amount of glucose, fructose and sucrose decreased during this preparation and the decrease followed a zero order reaction for glucose, first order for fructose, whereas that for sucrose followed neither zero nor first order reaction. After 90 min boiling (when the coconut sugar was formed), the amounts of glucose, fructose and sucrose left were 27.7%, 35.7% and 83.7% of the initial amount, respectively. The relative percentage area of furans and pyrazines increased during the preparation of coconut sugar and this increase followed a first order reaction for both. The palm sap with initial pH adjusted to 8.0 was heated in a closed system at temperatures of 105, 115 and 121 jC for up to 300 min and every 30 min, the brown colour of the sap was measured at 420 nm. The brown colour formation followed a zero order reaction with k equal to 0.87 10 3, 4.46 10 3, 6.58 10 3 AU min 1 for reaction temperatures of 105, 115 and 121 jC, respectively. The activation energy of the brown colour formation was 160.77 J mol 1. In a separate experiment, an aqueous solution containing glucose, fructose and sucrose at a concentration of 3.42%, 1.56% and 7.22%, respectively, with and without addition of 0.01% L-lysine, each was adjusted to pH 8.0 and heated at 121 jC and analysed as above. The rate of brown colour formation that resulted from heating model aqueous solution containing sugars and L-lysine resembled that resulting from heating palm sap. Therefore, the Maillard reaction plays an important role in the formation of brown colour during preparation of palm sugar. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Palm sugar; Coconut sugar; Browning rate
*
Corresponding author. Tel.: +62-251-623363; fax: +62-251-626725. E-mail address: [email protected] (A. Apriyantono).
0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 2 ) 0 0 8 8 2 - 8
276
A. Apriyantono et al. / International Congress Series 1245 (2002) 275–278
1. Introduction Palm (Arenga pinnata Merr.) and coconut sugar are made from each respective sap. The sap is boiled for about 3 h to produce brown solid with a sweet taste and typical flavor. These sugars are used for preparation of many typical Indonesian foods, especially sweet soy sauce (kecap manis). This research was focused on analysis of rate of browning during preparation of these sugars.
2. Materials and method Coconut sugar was obtained from a local market at Bogor, whereas coconut and palm sap were obtained from the coconut sugar industry at Sukabumi and a rural area of Bogor, respectively. The sap was filtered, put in an icebox, brought to the lab and stored in a freezer before analysis and treatment. This work was divided into three separate experiments. The first experiment was performed to analyse the composition of coconut and palm sugar, i.e., total sugar (Anthrone method), organic acids (HPLC with Biorad Aminex HPX-87H column) and volatiles (GC-MS with Carbowax 20 M column). The second experiment was aimed at monitoring the composition of sugars (HPLC with Biorad HPX-87H column), furans and pyrazines (GC-MS) as well as the brown colour intensity (absorbance at 420 nm) during preparation of coconut sugar. The third experiment was done in order to obtain the rate of brown colour formation during heating of 10 ml palm sap, with the pH adjusted at 8.0 in a closed system, at 105, 115 and 121 jC for 300 min. In addition, the rate of brown colour formation during heating at 121 jC for 300 min of model systems containing glucose, fructose and sucrose at concentrations of 3.42%, 1.56%, and 7.22%, respectively, with and without addition of 0.01% L-lysine, was also measured. Analyses were done in duplicate for experiments 1 and 2, and in triplicate for experiment 3. Preparation of coconut sugar involved heating 2500 ml of coconut sap in a wok pan at a temperature of 110 jC for about 90 min. In this heating process, the liquid sap turned into viscous liquid. When the liquid became viscous, it was poured into moulds and the sap was solidified to form coconut sugar.
3. Results and discussion The results of analysis showed that palm and coconut sugar consisted of mainly sugars at amounts of 89.2% and 91.4%, respectively. The main sugars detected were glucose, fructose and sucrose. Volatiles composition of palm and coconut sugar was dominated by browning reaction products, e.g. furans and pyrazines, and lipid degradation products, e.g. fatty acids and ketones. They also contained organic acids, i.e., citric, succinic and lactic acids. Apart from the fact that sugars were present in abundant amount in both sugars, the presence of pyrazines in palm and coconut sugar indicates that not only caramelisation, but also the Maillard reaction took place during preparation of both sugars.
A. Apriyantono et al. / International Congress Series 1245 (2002) 275–278
277
The coconut sap contained nitrogen at an amount of 0.19% (see Table 1); this nitrogen is presumably part of the protein structure, therefore, it is very likely that the Maillard reaction would contribute to the formation of brown colour during preparation of coconut sugar. The involvement of the Maillard reaction was indicated by the fact that relative percentage area of furans and pyrazines increased during the preparation of coconut sugar and this increase followed a first order reaction for both. The formation of furans and pyrazines depend on the amino acids or protein present in the sap, which were a limiting factor in this case. Preparation of coconut sugar involved the heating of coconut sap at boiling temperature until the sap was sticky enough and then solidified in moulds. During heating of the sap, the intensity of brown colour increased, whereas the amount of sucrose, glucose, fructose and nitrogen decreased markedly (Table 1). Besides caramelisation, this again indicates that the Maillard reaction might take place during preparation of coconut sugar. In order to estimate the order of brown colour formation rate and decrease rate of glucose, fructose, as well as sucrose during coconut sugar preparation, absorbance and percentage of each sugar as compared to each initial amount (or each natural logarithm/ln) were plotted against time. The order was determined by choosing the best fit for linear regression of these correlations as expressed by r2 of the linear regression equation (concentration vs. time for zero order, or ln concentration vs. time for first order). Using this criterion, brown colour formation followed a zero order reaction with a constant of formation (k) equal to 5.15 10 3 AU min 1. The decrease of glucose followed zero order and that of fructose followed first order, whereas that of sucrose did not follow either zero or first order, since the r2 for the zero and first order linear regressions was less than 0.9. Analysis of palm sap showed that the sap contained 13.12% total sugar, 4.80% reducing sugar and 0.05% total N. Previous experiments showed that the sugar composition consisted of 3.42% glucose, 1.56% fructose and 7.22% sucrose [1]. Heating of the
Table 1 Change of coconut sap weight, pH, brown colour intensity and composition during preparation of coconut sugar Parameter
Weight (g) pH Brown colour intensity (420 nm)a Moisture content (%) Total N (g) Sucrose (g) Glucose (g) Fructose (g)
Heating time (min) 0
22.5
45
67.5
90
2637.5 6.40 0.127
1926.0 6.35 0.163
1254.4 6.10 0.363
762.3 6.05 0.451
355.4 n.a. 0.562
87.07 0.7 345.0 (100%)b 45.7 (100%)b 35.8 (100%)b
81.39 n.a. 344.2 (99.8%) 41.3 (90.3%) 23.2 (64.9%)
71.12 n.a. 342.9 (99.4%) 32.4 (70.8%) 21.9 (61.2%)
53.69 n.a. 319.8 (92.7%) 20.7 (45.3%) 13.9 (38.8%)
6.95 0.4 288.7 (83.7%) 12.6 (27.7%) 12.8 (35.7%)
a The value of absorbance was adjusted, i.e. recalculated based on the initial volume of the sap, since the volume decreased during heating. b The values in brackets are the percentages of each sugar as compared to each amount present in the sap before heating (0 min heating).
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Fig. 1. Rate of brown colour reaction during heating of palm sap, Model-1 (containing 3.42% glucose, 1.56% fructose and 7.22% in water) and Model-2 (containing sugars as in Model-1 and 0.01% L-lysine). All solutions were adjusted to pH 8.0.
palm sap is therefore likely to produce brown colour compounds, either by caramelisation or the Maillard reaction. Palm sap model system containing 3.42% glucose, 1.56% fructose and 7.22% water (Model-1), and model system containing sugars as in Model-1 plus 0.01% L-lysine (Model-2) were all adjusted to pH 8.0 and heated at 121 jC for 300 min in a closed system. The rate of brown colour formation resulted from heating of Model-2 was similar to that from heating palm sap as compared to that of Model-1 (Fig. 1). Therefore, the Maillard reaction plays an important role on the formation of brown colour during preparation of palm sugar, since Model-2 contained amino acid, whereas Model-1 contained only sugar (caramelisation reaction only). The palm sap with initial pH adjusted to pH 8.0 was heated in a closed system at temperatures of 105, 115 and 121 jC for up to 300 min, and every 30 min, the colour of the sap was measured at 420 nm. The brown colour formation followed a zero order reaction with k equal to 0.87 10 3, 4.46 10 3, 6.58 10 3 AU min 1 for reaction temperatures of 105, 115 and 121 jC, respectively. This is in line with general phenomena that brown colour formation either in foods or model systems follow zero order reaction [2,3]. The activation energy of the brown colour formation as calculated by using Arrhenius equation was 160.77 J mol 1.
References [1] I.N.K., Putra, Study on thermal browning during preparation of palm sugar from palm sap. Master thesis. Bogor Agricultural University, 1990. [2] T.P. Labuza, M. Saltmarch, Kinetics of browning and protein quality loss in whey powder during steady state and non steady state storage conditions, J. Food Sci. 47 (1981) 92 – 96. [3] W.M. Baisier, T.P. Labuza, Maillard browning kinetics in a liquid model system, J. Agric. Food Chem. 40 (1992) 707 – 713.
Rate of browning reaction during preparation of coconut and palm sugar Anton Apriyantono*, Astrid Aristyani, Nurhayati, Yeni Lidya, Slamet Budiyanto, Soewarno T. Soekarto Department of Food Technology and Human Nutrition, Bogor Agricultural University, Kampus IPB Darmaga, P.O. Box 220, Bogor 16002, Indonesia
Abstract The objective of this research was to analyse the rate of browning reaction during preparation of palm and coconut sugar. Brown colour formation during preparation of coconut sugar at a laboratory scale followed a zero order reaction with a constant of formation (k) equal to 5.15 10 3 AU min 1 (AU = Absorbance Unit). The amount of glucose, fructose and sucrose decreased during this preparation and the decrease followed a zero order reaction for glucose, first order for fructose, whereas that for sucrose followed neither zero nor first order reaction. After 90 min boiling (when the coconut sugar was formed), the amounts of glucose, fructose and sucrose left were 27.7%, 35.7% and 83.7% of the initial amount, respectively. The relative percentage area of furans and pyrazines increased during the preparation of coconut sugar and this increase followed a first order reaction for both. The palm sap with initial pH adjusted to 8.0 was heated in a closed system at temperatures of 105, 115 and 121 jC for up to 300 min and every 30 min, the brown colour of the sap was measured at 420 nm. The brown colour formation followed a zero order reaction with k equal to 0.87 10 3, 4.46 10 3, 6.58 10 3 AU min 1 for reaction temperatures of 105, 115 and 121 jC, respectively. The activation energy of the brown colour formation was 160.77 J mol 1. In a separate experiment, an aqueous solution containing glucose, fructose and sucrose at a concentration of 3.42%, 1.56% and 7.22%, respectively, with and without addition of 0.01% L-lysine, each was adjusted to pH 8.0 and heated at 121 jC and analysed as above. The rate of brown colour formation that resulted from heating model aqueous solution containing sugars and L-lysine resembled that resulting from heating palm sap. Therefore, the Maillard reaction plays an important role in the formation of brown colour during preparation of palm sugar. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Palm sugar; Coconut sugar; Browning rate
*
Corresponding author. Tel.: +62-251-623363; fax: +62-251-626725. E-mail address: [email protected] (A. Apriyantono).
0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 2 ) 0 0 8 8 2 - 8
276
A. Apriyantono et al. / International Congress Series 1245 (2002) 275–278
1. Introduction Palm (Arenga pinnata Merr.) and coconut sugar are made from each respective sap. The sap is boiled for about 3 h to produce brown solid with a sweet taste and typical flavor. These sugars are used for preparation of many typical Indonesian foods, especially sweet soy sauce (kecap manis). This research was focused on analysis of rate of browning during preparation of these sugars.
2. Materials and method Coconut sugar was obtained from a local market at Bogor, whereas coconut and palm sap were obtained from the coconut sugar industry at Sukabumi and a rural area of Bogor, respectively. The sap was filtered, put in an icebox, brought to the lab and stored in a freezer before analysis and treatment. This work was divided into three separate experiments. The first experiment was performed to analyse the composition of coconut and palm sugar, i.e., total sugar (Anthrone method), organic acids (HPLC with Biorad Aminex HPX-87H column) and volatiles (GC-MS with Carbowax 20 M column). The second experiment was aimed at monitoring the composition of sugars (HPLC with Biorad HPX-87H column), furans and pyrazines (GC-MS) as well as the brown colour intensity (absorbance at 420 nm) during preparation of coconut sugar. The third experiment was done in order to obtain the rate of brown colour formation during heating of 10 ml palm sap, with the pH adjusted at 8.0 in a closed system, at 105, 115 and 121 jC for 300 min. In addition, the rate of brown colour formation during heating at 121 jC for 300 min of model systems containing glucose, fructose and sucrose at concentrations of 3.42%, 1.56%, and 7.22%, respectively, with and without addition of 0.01% L-lysine, was also measured. Analyses were done in duplicate for experiments 1 and 2, and in triplicate for experiment 3. Preparation of coconut sugar involved heating 2500 ml of coconut sap in a wok pan at a temperature of 110 jC for about 90 min. In this heating process, the liquid sap turned into viscous liquid. When the liquid became viscous, it was poured into moulds and the sap was solidified to form coconut sugar.
3. Results and discussion The results of analysis showed that palm and coconut sugar consisted of mainly sugars at amounts of 89.2% and 91.4%, respectively. The main sugars detected were glucose, fructose and sucrose. Volatiles composition of palm and coconut sugar was dominated by browning reaction products, e.g. furans and pyrazines, and lipid degradation products, e.g. fatty acids and ketones. They also contained organic acids, i.e., citric, succinic and lactic acids. Apart from the fact that sugars were present in abundant amount in both sugars, the presence of pyrazines in palm and coconut sugar indicates that not only caramelisation, but also the Maillard reaction took place during preparation of both sugars.
A. Apriyantono et al. / International Congress Series 1245 (2002) 275–278
277
The coconut sap contained nitrogen at an amount of 0.19% (see Table 1); this nitrogen is presumably part of the protein structure, therefore, it is very likely that the Maillard reaction would contribute to the formation of brown colour during preparation of coconut sugar. The involvement of the Maillard reaction was indicated by the fact that relative percentage area of furans and pyrazines increased during the preparation of coconut sugar and this increase followed a first order reaction for both. The formation of furans and pyrazines depend on the amino acids or protein present in the sap, which were a limiting factor in this case. Preparation of coconut sugar involved the heating of coconut sap at boiling temperature until the sap was sticky enough and then solidified in moulds. During heating of the sap, the intensity of brown colour increased, whereas the amount of sucrose, glucose, fructose and nitrogen decreased markedly (Table 1). Besides caramelisation, this again indicates that the Maillard reaction might take place during preparation of coconut sugar. In order to estimate the order of brown colour formation rate and decrease rate of glucose, fructose, as well as sucrose during coconut sugar preparation, absorbance and percentage of each sugar as compared to each initial amount (or each natural logarithm/ln) were plotted against time. The order was determined by choosing the best fit for linear regression of these correlations as expressed by r2 of the linear regression equation (concentration vs. time for zero order, or ln concentration vs. time for first order). Using this criterion, brown colour formation followed a zero order reaction with a constant of formation (k) equal to 5.15 10 3 AU min 1. The decrease of glucose followed zero order and that of fructose followed first order, whereas that of sucrose did not follow either zero or first order, since the r2 for the zero and first order linear regressions was less than 0.9. Analysis of palm sap showed that the sap contained 13.12% total sugar, 4.80% reducing sugar and 0.05% total N. Previous experiments showed that the sugar composition consisted of 3.42% glucose, 1.56% fructose and 7.22% sucrose [1]. Heating of the
Table 1 Change of coconut sap weight, pH, brown colour intensity and composition during preparation of coconut sugar Parameter
Weight (g) pH Brown colour intensity (420 nm)a Moisture content (%) Total N (g) Sucrose (g) Glucose (g) Fructose (g)
Heating time (min) 0
22.5
45
67.5
90
2637.5 6.40 0.127
1926.0 6.35 0.163
1254.4 6.10 0.363
762.3 6.05 0.451
355.4 n.a. 0.562
87.07 0.7 345.0 (100%)b 45.7 (100%)b 35.8 (100%)b
81.39 n.a. 344.2 (99.8%) 41.3 (90.3%) 23.2 (64.9%)
71.12 n.a. 342.9 (99.4%) 32.4 (70.8%) 21.9 (61.2%)
53.69 n.a. 319.8 (92.7%) 20.7 (45.3%) 13.9 (38.8%)
6.95 0.4 288.7 (83.7%) 12.6 (27.7%) 12.8 (35.7%)
a The value of absorbance was adjusted, i.e. recalculated based on the initial volume of the sap, since the volume decreased during heating. b The values in brackets are the percentages of each sugar as compared to each amount present in the sap before heating (0 min heating).
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Fig. 1. Rate of brown colour reaction during heating of palm sap, Model-1 (containing 3.42% glucose, 1.56% fructose and 7.22% in water) and Model-2 (containing sugars as in Model-1 and 0.01% L-lysine). All solutions were adjusted to pH 8.0.
palm sap is therefore likely to produce brown colour compounds, either by caramelisation or the Maillard reaction. Palm sap model system containing 3.42% glucose, 1.56% fructose and 7.22% water (Model-1), and model system containing sugars as in Model-1 plus 0.01% L-lysine (Model-2) were all adjusted to pH 8.0 and heated at 121 jC for 300 min in a closed system. The rate of brown colour formation resulted from heating of Model-2 was similar to that from heating palm sap as compared to that of Model-1 (Fig. 1). Therefore, the Maillard reaction plays an important role on the formation of brown colour during preparation of palm sugar, since Model-2 contained amino acid, whereas Model-1 contained only sugar (caramelisation reaction only). The palm sap with initial pH adjusted to pH 8.0 was heated in a closed system at temperatures of 105, 115 and 121 jC for up to 300 min, and every 30 min, the colour of the sap was measured at 420 nm. The brown colour formation followed a zero order reaction with k equal to 0.87 10 3, 4.46 10 3, 6.58 10 3 AU min 1 for reaction temperatures of 105, 115 and 121 jC, respectively. This is in line with general phenomena that brown colour formation either in foods or model systems follow zero order reaction [2,3]. The activation energy of the brown colour formation as calculated by using Arrhenius equation was 160.77 J mol 1.
References [1] I.N.K., Putra, Study on thermal browning during preparation of palm sugar from palm sap. Master thesis. Bogor Agricultural University, 1990. [2] T.P. Labuza, M. Saltmarch, Kinetics of browning and protein quality loss in whey powder during steady state and non steady state storage conditions, J. Food Sci. 47 (1981) 92 – 96. [3] W.M. Baisier, T.P. Labuza, Maillard browning kinetics in a liquid model system, J. Agric. Food Chem. 40 (1992) 707 – 713.