Factors Affecting Browning and Crystallisation of Palm Sugar Syrup and Palm Sugar Cake Phisut Naknean A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Food Technology Prince of Songkla University 2010 Copyright of Prince of Songkla University i Thesis Title Factors Affecting Browning and Crystallisation of Palm Sugar Syrup and Palm Sugar Cake Author Mr. Phisut Naknean Major Program Food Technology Major Advisor : Examining Committee : ……………………………..... ……………………...……..........Chairperson (Dr. Mutita Meenune) (Assist. Prof. Dr. Suphitchaya Chanthachum) ..…………………………………………...... Co-advisor : (Dr. Mutita Meenune) ……………………………..... .……………………………………………... (Assist.Prof.Dr.Gaëlle Roudaut) (Prof. Dr. Soottawat Benjakul) ……………………………............................ (Assist. Prof. Dr. Ekapan Kaewmaneechai) The Graduate School, Prince of Songkla University, has approved t h iiis thesis as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Food Technology …………………………….......... (Prof. Dr. Amornrat Phongdara) Dean of Graduate School ii Thesis Title Factors Affecting Browning and Crystallisation of Palm Sugar Syrup and Palm Sugar Cake Author Mr. Phisut Naknean Major Program Food Technology Academic Year 2010 ABSTRACT Palm sugar syrup and palm sugar cake are the local products in Songkhla province. These products have not yet been produced industrially. The properties of these products are extremely varied across the samples and within individual local producer. Some factors affecting the properties of these products are harvesting time of palm sap, processing methods, ingredient added and storage condition. Therefore, this research was to study the properties and factors affecting browning and crystallisation of palm sugar syrup and palm sugar cake. Ten palm sap samples were characterised. The pH of all palm sap varied from 4.19 to 5.23 and total acidity ranged from 0.13% to 0.19%. Ethanol was also found in all samples that indicating the fermentation. Commercial ten palm sugar syrup samples were characterised. HMF content was found to vary between 15.35 mg/kg to 96.76 mg/kg. HMF content of three out of ten samples was higher than the maximum limited as recommend by Codex Alimentarious (40 mg/kg). The TSS ranged from 62.97oBrix to 67.50oBrix. TSS of two out of ten samples did not meet the requirements of Thai industrial standards institute ministry of industry. Ten palm sugar cake samples were also characterised. The hardness was ranged from 30.83 N to 69.00 N. Crystallinity of these samples was found in a range of 73.40%-78.56%. HMF content was found to vary between 21.81 mg/kg to 341.80 mg/kg. HMF content of eight out of ten samples was higher than the maximum limited as recommend by Codex Alimentarious. The changes in physical and chemical properties during the production of palm sugar syrup by palm sap at different harvesting times (6 h, 12 h, 18 h and 24 h) were monitored. The highest nonenzymatic browning reactions and inversion reaction iii were found in palm sugar syrup sample which was taken from harvested palm sap at 24 h. Moreover, HMF of a sample that produced by palm sap after harvesting time for 24 h (113.07 mg/kg) was higher than the standard requirement. The effect of storage temperatures (4oC and 30oC) and storage time (0-12 months) on the properties changed of palm sugar syrup that produced by palm sap after harvesting time for 6 h, 12 h, 18 h and 24 h were investigated. Maillard reaction took place in all samples that stored under 4oC lower than those that stored under 30oC as evidenced by lower a* value, IBP, BI and HMF content and higher L* value, fructose, glucose and FAG content (P<0.05). Low temperature (4oC) can be used to retard dark colour and HMF formation in palm sugar syrup during storage. The changes in physical, chemical properties and antioxidant activity during the production of palm sugar syrup by an open pan (110oC) and a vacuum evaporator (70oC and 80oC) were studied. The results showed that the a*, b*, IBP, BI, HMF content, TSS, and reducing sugar as well as glucose and fructose increased with heating time in each heating process. The increase in browning development (IBP, BI and HMF content) with heating time was concomitant with the increase in DPPH radical scavenging activity, FRAP and reducing power in each heating process. Among all heating processes, palm sugar syrup that produced by an open pan rendered the highest browning development and antioxidant activity. The effect of storage temperatures (4oC and 30oC) and storage time (0-12 months) on the properties changed of palm sugar syrup that produced by an open pan and a vacuum evaporator were also investigated. During storage, Maillard reaction took place in a sample that stored under 4oC lower than those that stored under 30oC. This was shown by lower a* value, IBP, BI and HMF content, and higher L* value, fructose, glucose and FAG content during storage for 12 months (P<0.05). Only the sample produced by an open pan and stored under 30oC contained higher HMF content (50.58 mg/kg) than the permitted maximum limit. The effect of sucrose (30%, 40%, and 50%) and glucose syrup (10% and 20%) addition on properties of palm sugar cake that produced from palm sugar syrup with either using an open pan or a vacuum evaporator were investigated. It was found iv that an increase in hardness and crystallinity was found in all samples with increasing sucrose content (P<0.05). There was a decrease in hardness and crystallinity with increasing glucose syrup content (P<0.05). The highest dark colour and lowest hardness was observed in a sample that produced from 100% palm sugar syrup as indicated by the lowest L* and hardness and the highest a*, IBP, BI and HMF content. Furthermore, the highest overall acceptability score was found in samples that produced from 50% palm sugar syrup, 40% sucrose and 10% glucose syrup. Thus, this formulation was selected to study the effect of storage temperature (4oC and 30o) and storage time (12 months for 11% of RH and 4 weeks for 75% of RH) on properties changes of palm sugar cake that produced from palm sugar syrup with either using an open pan or a vacuum evaporator. During storage, Maillard reaction took place in samples stored under 4oC lower than those stored under 30oC in both RHs. This was shown by lower a* value, BI and higher L* value at the end of storage (P<0.05). Storage temperature did not affected on hardness and crystallinity of all samples that stored in both RHs. Continuous decrease in hardness and crystallinity was found in all samples stored under 75% of RH during storage (P<0.05). Thus, storage condition under 30oC and 75% of RH is improper to store palm sugar cake due to these conditions greatly promote the decrease in hardness and increase in dark colour of palm sugar cake. The effect of storage temperature (20oC and 30oC) on MSI characteristic, EMC and Tg of palm sugar cake that produced from palm sugar syrup with either using an open pan or a vacuum evaporator was investigated. It was found that MSI for all palm sugar cake samples that stored under both temperatures was Type-III isotherms. Storage temperature did not affect on EMC when a sample stored under 11-75% of RH (P0.05). The EMC of all samples that stored under 20oC was higher than those stored under 30oC and 85% of RH (P<0.05). Storage temperature did not affect on Tg of all samples. There was no significant difference in Tg of all samples that stored under 11-51% RH (P0.05). However, the Tg of all samples decreased with increasing RH in a range of 75-85%. In addition, a decrease in crystallinity and increase in IBP and BI during storage was detected in a sample that stored under high RH (75-85%). v CONTENTS Page Abbreviation…………………………………………………………………… vii Contents…………………………………………………………………….….. viii List of Tables…………………………………………………………………... xiii List of Figures……………………………………………………………..…… xvii List of Appendix Figure……………………………………………………….. xxiv Chapter 1. Introduction and Review of Literature 1.1 Introduction………………………………………………………... 1 1.2 Review of Literature..…………………………………………….... 3 1.2.1 Palmyra palm………………………………………………… 3 1.2.2 Palm sap and its quality……………………………………… 4 1.2.3 Plant syrup…………………..……………………………….. 6 1.2.3.1 Plant syrup production………………………………. 7 1.2.3.2 Quality of plant syrup after processing and during storage……………………………………………… 9 1.2.4 Sugar cake……………………………………………………. 10 1.2.4.1 Sugar cake production……………………………… 1 1 1.2.3.1 Quality of sugar cake……………………………….. 11 1.2.5 Inversion reaction……………………………………………. 14 1.2.6 Nonenzymatic browning reaction…………………………… 1 4 1.2.6.1 Maillard reaction……………………………………. 14 1.2.6.2 Formation of colour in the Maillard reaction……….. 17 1.2.6.3 Formation of flavour in the Maillard reaction……… 19 1.2.6.4 Factors affecting on the Maillard reaction………….. 21 1.2.6.5 Caramelisation……………………………………… 21 1.2.6.6 Antioxidant activity of Maillard reaction product (MRPS) and Caramelisation product (CPs)………... 22 viii CONTENTS (Continued) Page 1.2.7 Sugar crystallisation…………………………………………. 2 3 1.2.7.1 Crystallisation in solution…………………………... 24 1.2.7.2 Factors affecting on the sugar crystallisation……….. 25 1.2.8 MSI and phase-transition in sugar-based product…………… 26 1.2.8.1 MSI of crystalline and amorphous sugar…………….. 26 1.2.8.2 Glass transition temperature…………………………. 28 1.2.8.3 Crystallisation of amorphous sugar………………….. 29 1.2.8.4 Nonenzymatic browning in glassy system…………... 3 1 1.3 Objectives of study………………………………………………… 33 2. Characterisation of palm sap, palm sugar syrup and palm sugar cake 2.1 Abstract…………………………………………………………….. 34 2.2 Introduction………………………………………………………... 36 2.3 Materials and Methods…………………………………………….. 38 2.4 Results and Discussion…………………………………………….. 47 Physical properties…………………………………………………. 47 Chemical properties………………………………………………... 57 Microbiological properties………………………………………… 77 Relationship among palm sap properties…………………………... 79 Relationship among palm sugar syrup properties………………….. 81 Relationship among palm sugar cake properties…………………... 83 2.5 Conclusion………………………………………………………… 85 3. Effect of harvesting time of palm sap and storage condition on the properties changes of palm sugar syrup 3.1 Abstract…………………………………………………………….. 87 ix CONTENTS (Continued) Page 3.2 Introduction………………………………………………………... 88 3.3 Materials and Methods…………………………………………….. 90 3.4 Results and Discussion…………………………………………….. 96 Changes in physical properties during the production of palm sugar syrup produced by palm sap at different harvesting times….. 96 Changes in chemical properties during the production of palm sugar syrup produced by palm sap at different harvesting times….. 102 Changes in physical properties during storage of palm sugar syrup produced by palm sap at different harvesting times……………….. 110 Changes in chemical properties during storage of palm sugar syrup produced by palm sap at different harvesting times……………….. 117 Changes in microbiological properties during storage of palm sugar syrup produced by palm sap at different harvesting times….. 127 3.5 Conclusion………………………………………………………..... 133 4. Effect of processing method and storage condition on the properties changes of palm sugar syrup 4.1 Abstract…………………………………………………………….. 134 4.2 Introduction………………………………………………………... 135 4.3 Materials and Methods…………………………………………….. 137 4.4 Results and Discussion…………………………………………….. 146 Changes in physical properties during the production of palm sugar syrup produced by an open pan and a vacuum evaporator….. 146 Changes in chemical properties during the production of palm sugar syrup produced by an open pan and a vacuum evaporator….. 152 Changes in physical properties during storage of palm sugar syrup produced by an open pan and a vacuum evaporator……………….. 166 x CONTENTS (Continued) Page Changes in chemical properties during storage of palm sugar syrup produced by an open pan and a vacuum evaporator……………….. 173 Changes in microbiological properties during storage of palm sugar syrup produced by an open pan and a vacuum evaporator….. 182 4.5 Conclusion………………………………………………………... 187 5. Effect of sucrose and glucose syrup addition on the properties of palm sugar cake and its changes during storage 5.1 Abstract…………………………………………………………….. 189 5.2 Introduction………………………………………………………... 190 5.3 Materials and Methods…………………………………………….. 192 5.4 Results and Discussion…………………………………………….. 201 Effect of sucrose and glucose syrup addition on the physical properties of palm sugar cake……………………………………… 201 Effect of sucrose and glucose syrup addition on the chemical properties of palm sugar cake……………………………………… 211 Effect of sucrose and glucose syrup addition on sensory evaluation of palm sugar cake…………………………………………………. 223 Effect of storage temperature and storage time on the physical properties of palm sugar cake during storage in different relative humidities (RHs)…………………………………………………... 225 Effect of storage temperature and storage time on the chemical properties of palm sugar cake during storage in different relative humidities (RHs)…………………………………………………… 239 5.5 Conclusion………………………………………………………..... 255 xi CONTENTS (Continued) Page 6. Moisture adsorption isotherm and glass transition temperature of palm sugar cake 6.1 Abstract…………………………………………………………….. 256 6.2 Introduction………………………………………………………... 257 6.3 Materials and Methods…………………………………………….. 258 6.4 Results and Discussion…………………………………………….. 262 Natural of moisture adsorption isotherm…………………………... 262 Glass transition temperature……………………………………….. 264 Changes in crystallinity of palm sugar cake during storage in different relative humidities………………………………………... 266 Changes in intermediate browning product and browning intensity of palm sugar cake during storage in different relative humidities... 267 6.5 Conclusion…………………………………………………………. 268 7. Summary and future works 7.1 Summary…………………………………………………………… 270 7.2 Future works……………………………………………………...... 272 References………………………………………………………………… 273 Vitae………………………………………………………………………. 302 Appendix………………………………………………………………….. 304 xii