Effetcs of Pretreatment and Drying Temperature on Quality of Dried Bamboo Shoots (Dendrocalamus membranaceus Munro)
EFFECTS OF PRETREATMENT AND DRYING
TEMPERATURE ON QUALITY OF DRIED BAMBOO
SHOOTS (
Dendrocalamus membranaceus
Munro)
SKRIPSI
DINI QUEENTASARI
F 24080024
FACULTY OF AGRICULTURAL ENGINEERING AND TECHNOLOGY
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2012
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Effects of Pretreatment and Drying Temperature on Quality of
Dried Bamboo Shoots (
Dendrocalamus membranaceus
Munro)
Dini Queentasari1, Adil Basuki Ahza1, Natthawuddhi Donlao2, and Puwanart Fuggate2
1
Department of Food Science and Technology, Faculty of Agricultural Engineering and Technology, Bogor Agricultural University, Dramaga, Bogor 16002, Indonesia
2
School of Agro-Industry, Mae Fah Luang University Chiang Rai 57100, Thailand
ABSTRACT
Whole bamboo shoots (Dendrocalamus membranaceus Munro) freshly harvested in Doi Tung were blanched at 90-100 ⁰C in various concentrations of sodium metabisulfite solution (0, 0.5%, 1.0%, and 1.5%) for ten minutes, as pretreatment, and then dried at various temperatures (50
⁰C, 60 ⁰C, and 70 ⁰C) using a laboratory scale hot air drier. Effects of both pretreatment and drying temperature on quality of dried bamboo shoots were evaluated. There were seven parameters observed: drying time, aw, color, rehydration ratio, shrinkage, firmness, and total
residual sulfites. Results showed that drying time decreased with increase in the drying temperature (p<0.01) while both pretreatment and drying temperature had no significant effect (p>0.05) on aw and shrinkage of dried bamboo shoots. Moreover, L* value, b* value, and
rehydration ratio increased with increase in concentration of sodium metabisulfite and decrease in drying temperature, whereas a* value increased. The higher b* value and rehydration ratio (p<0.01) were found in samples blanched in 1.5% Na2S2O5 solution and dried at 50 ⁰C and
samples blanched in 1.0% Na2S2O5 solution and dried at 60 ⁰C. It was also observed that total
residual sulfites in dried-sulfited sample was quite high, ranged from 1250 to 3378 ppm SO2 while
the sample blanched in 1.5% Na2S2O5 solution had higher residual sulfites than the other
concentrations. Based on the parameters, sample blanched in 1.0% Na2S2O5 solution and then
dried at 60 ⁰C was chosen to be the best sample. Results of rating hedonic test confirmed that the rehydrated of the best sample was more preferrable than the rehydrated-commercial dried bamboo shoots. It is suggested that blanching in 1.0% Na2S2O5 solution and then drying at 60 ⁰C is a better
drying condition to produce dried bamboo shoots with a desired quality and applicable in Doi Tung.
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Dini Queentasari. F24080024. Effects of Pretreatment and Drying Temperature on Quality of Dried Bamboo Shoots. Advisors: Adil Basuki Ahza (Bogor Agricultural University), Natthawuddhi Donlao and Puwanart Fuggate (Mae Fah Luang University). 2012
SUMMARY
Thailand is the second major world producer and exporter of bamboo shoots and Doi Tung, a mountainous region in Northen Thailand, has tropical bamboos (Dendrocalamus membranaceus
Munro) that produce shoots from May to October with most productions in July to August every year. In Huay Poo Village, Doi Tung, there is a factory that processes freshly harvested bamboo shoots minimally. The factory is owned by Mr. Theraapoong, as a supplier of fresh bamboo shoots for this research. Bamboo shoots are just peeled, boiled, and sliced there. After that, they were packed and transported to secondary factories in Chiang Mai and Lampang for further processing. There is no added value of produced bamboo shoots in the primary factory. Thus, it is a need to improve the existing production of bamboo shoots in the factory.
Bamboo shoot is very seasonal and perishable food. It can be stored for one day at ambient temperature. Hence, it takes a processing method to prolong shelf life of fresh bamboo shoots which is applicable in Doi Tung. Drying is a good alternative processing method that is commonly applied by Thai people. Moreover, China has produced dried bamboo shoots since years ago. In China, bamboo shoots were processed using heat generated from wood burning. This drying method has many disadvantages, such as time consuming, weather dependent, and dust and insects contamination possibility. This study is aimed to overcome such disadvantages. Bamboo shoots were dried using hot air drying method which is more hygienic, controlable, and applicable in Doi Tung. Bamboo shoots were dried until its moisture content reached 10% dry basis which is less than Thai Industrial Standards Institute (14% wet basis for dried products). Prior to drying, bamboo shoots were blanched in sodium metabisulfite solution in various concentrations (0.5%, 1.0%, 1.5%) at 90-100 ⁰C for 10 minutes to prevent browning reaction during drying. Both pretreatment and the drying process may cause many physical, chemical, biochemical, and sensory changes in the bamboo shoots. Hence, it is necessary to develop a better drying condition to produce good quality of dried bamboo shoots. There are many factors influence the quality of dried products, yet this research was just focused on two factors, i.e. concentration of sodium metabisulfite used in blanching solution and drying temperature.
This research was carried out in two stages, i.e. preliminary and main research. Preliminary research included preparation of raw bamboo shoots and adjustment of drying process. Drying process and analyses of dried and rehydrated bamboo shoots were carried out in the main research. There were some quality parameters observed in this study, i.e. drying time, water activity, color, rehydration ratio, dimensional changes (shrinkage), firmness, and total residual sulfites. Sodium metabisulfite of 0, 0.5%, 1.0%, and 1.5%, three different drying temperatures of 50 ⁰C, 60 ⁰C, and 70 ⁰C were studied. Effects of both factors, the pretreatment and the drying temperature, on the parameters of quality of dried bamboo shoots were observed. Both factors had opposites effect on some quality parameters.
Dried bamboo shoots produced had low moisture content, ranged from 9.33% to 9.51% and low water activity, ranged from 0.398 to 0.411. As expected, the drying time decreased with increase in the drying temperature. Blanching, as a pretreatment, also affected drying time of
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bamboo shoots. The blanched sample needed drying time with a range from 74 hours at 50 ⁰C to 20 hours at 70 ⁰C, while the unblanched sample needed longer drying time with a range from 96 hours at 50 ⁰C to 23 hours at 70 ⁰C. It can be suggested that the blanching had the positive effect on the drying time. Moreover, it was observed that sodium metabisulfite used in blanching solution had a role to retard browning reaction during drying. Generally, the dried bamboo shoots produced in this research had a light-yellow color. Results showed that L* and b* values of dried and rehydrated bamboo shoots increased with the increase in concentration of sodium metabisulfite solution used in blanching solution and with decrease in drying temperature. The yellowness is representated by a positive value of b*. The more positive value, the more yellow color produced. The highest b* value was found in the sample that blanched in 1.5% sodium metabisulfite solution and dried at 50 ⁰C, yet it was not significantly different (p>0.05) with the sample blanched in 1.0% sodium metabisulfite solution and dried at 60 ⁰C.
Besides color of dried and rehydrated bamboo shoots, rehydration ratio is also an important parameter that should be considered. Dried bamboo shoots must be rehydrated before consuming. Dried products should to have a good ability to reconstitute its original shape and properties by absorbing the water during soaking in the water. Rehydration ratio of the dried bamboo shoots ranged from 2.63 to 4.3. Both concentration of sodium metabisulfite in blanching solution and drying temperature had significant effect on this parameter. Results showed that rehydration ratio increased with increase in concentration of sodium metabisulfite and with decrease in drying temperature. The highest rehydration ratio was found in the sample blanched in 1.5% sodium metabisulfite solution and then dried at 50 ⁰C, yet it was not significantly different (p>0.05) with the sample blanched in 1.0% sodium metabisulfite solution and then dried at 70 ⁰C.
Moreover, sample blanched in 1.5% sodium metabisulfite solution and then dried 70 ⁰C had the highest total weighted score. It was considered that the sample was chosen to be the best sample, yet it should be noted that the dried bamboo shoots may not contain more than 2500 ppm SO2. Blanching the sample in 1.5% sodium metabisulfite solution produced the dried bamboo
shoots contained more than 2500 ppm SO2, thus the sample blanched in 1.5% sodium
metabisulfite solution and then dried 70 ⁰C (with the 2nd highest total weighted score) chosen to be the best sample.
Hedonic rating test was carried out to get confirmation about quality of rehydrated bamboo shoots subjectively. The best dried bamboo shoot was compared with commercial dried bamboo shoots purchased in Mae Sai Market. Thirty five untrained panelists were asked to give preference score of the attributes on a scale from 1 (dislike extremely) to 5 (like extremely). Results showed that there was significantly difference (p<0.01) between both samples on all parameters, i.e. color, aroma, taste, and texture. The rehydrated-dried bamboo shoots produced at the lab was more preferable (p<0.01) than the commercial one. Considering the above results, it was suggested that blanching the sample in 1.0% sodium metabisulfite solution and then drying at 60 ⁰C (the 3rd highest total weighted score) was a better condition for production of dried bamboo shoots that is applicable in Doi Tung.
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EFFECTS OF PRETREATMENT AND DRYING TEMPERATURE
ON QUALITY OF DRIED BAMBOO SHOOTS (
Dendrocalamus
membranaceus
Munro)
SKRIPSI
Submitted as a Partial Fulfillment of the Requirements for
the Degree of Sarjana of Agricultural Technology
at the Department of Food Science and Technology
Faculty of Agricultural Engineering and Technology
Bogor Agricultural University
By
DINI QUEENTASARI
F 24080024
FACULTY OF AGRICULTURAL ENGINEERING AND TECHNOLOGY
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
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Title : Effetcs of Pretreatment and Drying Temperature on Quality of Dried Bamboo
Shoots (Dendrocalamus membranaceus Munro)
Name : Dini Queentasari
Student ID : F24080024
Approved by Academic Advisor
(Adil Basuki Ahza, PhD) NIP. 19521021 197903 1 001
Acknowledged by
Head of Department of Food Science and Technology
(Dr. Ir. Feri Kusnandar, M.Sc) NIP. 19680526 199303 1 004
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iii
STATEMENT OF SKRIPSI AND SOURCES OF INFORMATIONS
I declare the truth that this skripsi entitled Effects of Pretreatment and Drying Temperature on Quality of Dried Bamboo Shoots (Dendrocalamus membranaceus Munro) is
my own work with guidance of the advisors and has not been submitted in any form at any college, except Bogor Agricultural University and Mae Fah Luang University. Sources of informations derived or quoted from published and unpublished works of other authors mentioned in the text and listed in the List of References at the end of this skripsi.
Bogor, December 6, 2012 The declarant
Dini Queentasari F24080024
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iv © 2012 Dini Queentasari
All rights reserved
This work may not be translated or copied in whole or in part without the permission of Bogor Agricultural University, except for brief excerpts in connection with reviews or scholarly analysis.
Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is
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VITAE
Dini Queentasari. She was born in Padang, West Sumatera, May 22, 1990, the eldest child of Mr. Edmon Mazdon and Mrs. MHP Hapriwahyuni with two brothers. She had her kindergarten in Pertiwi II, Kodya Padang (1995-1996). In 1996, she and her family migrated to Jakarta and she continued her elementary school, junior high school, and senior high school in SDN Pesanggerahan 08 Petang (1996-2002), SLTPN Plus 177 Jakarta (2002-2005), and SMAN 47 Jakarta (2005-2008). In 2008, the author continued her study in Bogor Agricultural University. She was accepted as a Food Science and Technology student in the Faculty of Agricultural Engineering and Technology. During her study, she joined some organizations actively, such as TELISIK Pangan and HIMITEPA (Student assosiation of Food Science and Technology) as staff of Indonesia Food Concern Department and trusted to be a leader of rural development program (2009-2010). The author had some work experiences as a assistant at Chemistry and Biochemistry Practices (2011) and Sensory Analysis Practices (2012) in Department of Food Science and Technology. She was also a facilitator in SawitA project, a social corporate responsibility program of PT SMART Tbk cooperated with Faculty of Agricultural Engineering and Technology (2012). She joined and won some competitions, such as 4th winner of National Science Paper in INDEX (2012) and Leader of Funded National Student Creativity Program (2012). Gratefully, she was granted a scholarship in MIT Student Mobility Program to do research in Food Technology, School of Agro-Industry, Mae Fah Luang University, for 4 months. In June 2012, she started her research entitled, “Effects of Pretreatment and Drying Temperature on Quality of Dried Bamboo Shoots” with Aj. Natthawuddhi Donlao, B.Sc, M. Eng as advisor and Dr. Puwanart Fuggate, B.Sc, M.Sc as co-advisor, also Adil Basuki Ahza, PhD, as her academic advisor in Bogor Agricultural University.
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vi
PREFACE
Praise to ALLAH SWT for the mercy, the graciousness, and the guidance throughout the research and skripsi completion. The research entitled Effects of Pretreatment and Drying Temperature on Quality of Dried Bamboo Shoots (Dendrocalamus membranaceus Munro) that was carried out in Mae Fah Luang University from June to October 2012.
By completion of this research and skripsi, the author would like to express great appreciations and sincere thanks to:
1. Lovely Mama, Papa, Yogie W, and Yoga AN for their endless loves, cares, and supports. 2. Adil Basuki Ahza, PhD, as academic advisor, for his time, correction, input, concern, and all
forms of the guidance during study in Bogor Agricultural University.
3. Ajarn Nattawuddhi Donlao, B.Sc, M.Eng as advisor for his time, patient, care, and knowledge in guiding the author to complete the research in Mae Fah Luang University.
4. Dr. Puwanart Fuggate, B.Sc, M.Sc as co-advisor and all lecturers in School of Agro-Industry who have helped solving the problems during the research in Mae Fah Luang University. 5. Mr. Theerapong who has provided the fresh bamboo shoots from Doi Tung for the research. 6. Prof. Dr. Ir. Slamet Budijanto, M.Agr and Dr. Ir. Muhammad Arpah, MS, as examiners, for
their time, corrections, inputs, and helps.
7. Pakde Wahyu and Bude Tri, Ayahanda Ahnaf Hamzah, Ibunda Martini Boer, Pak Oyong, Aviandari Lestari and her family for their cares, concerns, and helps.
8. DITJEN DIKTI for full financial support during the research and Committee of MIT Mobility Program for a chance to do research in Mae Fah Luang University.
9. International Affairs Division of Mae Fah Luang University, Ms. Warunee Kaewbunruang as a coordinator in MIT Program 2012, all friends in School of Agro Industry, and other friends who can not be mentioned one by one for great memories during stay in Thailand.
10.MIT Students 2012: Pradhini, Ariesta, Annisa, and Taufiq for togetherness, cooperations, and helps during the research.
11.All staffs at Scientific Lab 4, Scientific Lab 3, and Scientific and Technological Instrument Center for their helps during the research.
12.Eka Tjipta Foundation and PKS (Persatuan keluarga silungkang) for the scholarships. 13.Mas Yogi Karsono for his time, help, care, and support.
14.“Crayon” friends: Andini Sekar, Herly Andina, Gita Tiara L, Devy Arie F, Purahpu, Risha Aisyah, Niear Rindy A, Syifa Maulia, Febrianto, Panji Aria L, Shahwin A, Septi Purnamasari, Yosy Faradila, Ismi Wahyuniati, and Frena Yulyani for great friendship, helps, and supports. 15.All friends: Derry R, Susilawati, Icin T, Rista D, Yufi S, Hafiz F, Raudhatussa’adah,
Ahmadun, Arum Marya, Eka J, Nurul HA, Hesty S, Diah Ayu, Mbak Nur Sofia WY, Yunita SM, Budyawan S, Suba SW, Misran, Annisa NH, Euis F, Tri Novita, and other friends who can not be mentioned one by one for their helps and supports.
16.All lecturers and partners in Bogor Agricultural University, especially in Department of Food Science and Technology and all people who helped to complete the research.
Last but not least, hopefully this skripsi is useful for the readers and gives a real contribution in food science development, particularly in the manufacture of dried bamboo shoots.
Bogor, December 6,2012
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vii
LIST OF CONTENTS
Page
PREFACE ... vi
LIST OF TABLES ... ix
LIST OF FIGURES ... x
LIST OF APPENDIXES ... xi
I. INTRODUCTION ... 1
1.1 BACKGROUND ... 1
1.2 OBJECTIVES ... 2
1.3 SCOPE ... 2
1.4 EXPECTED OUTCOME ... 2
II. LITERATURE REVIEW ... 3
2.1 BAMBOO SHOOTS ... 3
2.2 DEHYDRATION ... 4
2.2.1 Drying ... 4
2.2.2 Hot Air Drying ... 5
2.3 PRETREATMENT ... 6
2.3.1 Blanching ... 6
2.3.2 Sulfiting ... 7
2.4 PREVIOUS STUDIES AND REAL CONDITION ... 8
2.4.1 Previous Studies ... 8
2.4.2 Real Condition ... 9
III.MATERIALS AND METHODS ... 11
3.1 TIME AND PLACE ... 11
3.2 MATERIALS AND INSTRUMENTS ... 11
3.3 METHODS ... 11
3.3.1 Preliminary Research ... 11
3.3.1.1 Sample Preparation ... 12
3.3.1.2 Adjustment of Drying Procedure ... 13
3.3.2 Main Research ... 13
3.3.2.1 Drying Procedure ... 13
3.3.2.2 Physical, Chemical, and Sensory Analyses ... 14
3.3.2.2.1 Determination of Moisture Content (AOAC 1995) ... 14
3.3.2.2.2 Water Activity Measurement ... 14
3.3.2.2.3 Color Measurement (Hunter Lab) ... 15
3.3.2.2.4 Determination of Rehydration Ratio (Doymaz 2008, modified) ... 15
3.3.2.2.5 Determination of Dimensional Changes (Shrinkage) (Dehkordi 2010, modified)... 15
3.3.2.2.6 Texture Analysis ... 16
3.3.2.2.7 Determination of Total Residual Sulfites (AOAC 1970; FAO JECFA 2006) ... 16
3.3.2.2.8 Determination of The Best Sample (Zaboj 2002; DFPNI 2010, modified) ... 17
3.3.2.2.9 Sensory Analysis... 19
3.3.3 Experimental Design ... 19
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viii
IV.RESULTS AND DISCUSSION ... 21
4.1 PRELIMINARY RESEARCH... 21
4.2 MAIN RESEARCH ... 22
4.2.1 Moisture Content and Water Activity ... 22
4.2.2 Drying Time ... 24
4.2.3 Color of Dried and Rehydrated Bamboo Shoots ... 25
4.2.4 Rehydration Ratio... 27
4.2.5 Dimensional Changes (Shrinkage) ... 29
4.2.6 Texture of Dried and Rehydrated Bamboo Shoots ... 30
4.2.7 Total Residual Sulfites ... 32
4.2.8 Best Sample ... 32
4.2.9 Sensory Analysis of The Best Sample of Bamboo Shoot ... 33
V. CONCLUSION AND RECOMMENDATIONS ... 36
5.1 CONCLUSION ... 36
5.2 RECOMMENDATIONS ... 37
REFERENCES ... 38
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ix
LIST OF TABLES
Page
Table 1. Macronutrients of Dendrocalamusmembranaceus (Chongtham et al. 2011) ... 4
Table 2. TA.XTPlus settings ... 16
Table 3. Weighted factors ... 18
Table 4. Category scales for rating hedonic test ... 19
Table 5. Treatment combinations ... 20
Table 6. Mean moisture content of bamboo shoots before drying ... 23
Table 7. Mean moisture content of dried bamboo shoots ... 23
Table 8. Mean water activity (aw) of dried bamboo shoots ... 24
Table 9. Mean L*, a*, b* values of dried bamboo shoots ... 26
Table 10. Mean L*, a*, b* values of rehydrated bamboo shoots ... 27
Table 11. Mean shrinkage of bamboo shoots ... 29
Table 12. Total weighted scores of dried bamboo shoots ... 33
Table 13. Results of a 5-scales of rating hedonic test between rehydrated-dried bamboo shoots produced at the lab and rehydrated-commercial dried bamboo shoots .... 35
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x
LIST OF FIGURES
Page
Figure 1. Freshly harvested bamboo shoots ... 3
Figure 2. Drying curve (Brennan et al. 1990) ... 5
Figure 3. Minimal processing of bamboo shoots in Huay Poo Factory ... 9
Figure 4. One of production site for drying whole bamboo shoots in China ... 10
Figure 5. (a) peeled bamboo shoots; (b) drying process; (c) dried bamboo shoots; (d) packed dried bamboo shoots, produced in China ... 10
Figure 6. Stages of the research ... 12
Figure 7. Sample preparation ... 13
Figure 8. Weighting method to determine the best sample ... 17
Figure 9. Fresh bamboo shoots purchased in Chiang Mai ... 21
Figure 10. Peeled bamboo shoots (left) and dried bamboo shoots (right) ... 22
Figure 11. Dried untreated bamboo shoots ... 22
Figure 12. Chemical and biochemical rates as functions of water activity (Chen 2008) .... 24
Figure 13. Mean drying time of untreated and treated bamboo shoots ... 25
Figure 14. Dried bamboo shoots (left-right: blanched in 0, 0.5%, 1.0%, 1.5% of Na2S2O5 solution); a) dried at 50 ⁰C, b) dried at 60 ⁰C, and c) dried at 70 ⁰C ... 26
Figure 15. Rehydrated bamboo shoots (left-right: blanched in 0, 0.5%, 1.0%, 1.5% of Na2S2O5 solution); a) dried at 50 ⁰C, b) dried at 60 ⁰C, and c) dried at 70 ⁰C .... 27
Figure 16. Mean rehydration ratio of dried bamboo shoots ... 28
Figure 17. Mean firmness dried bamboo shoots ... 31
Figure 18. Mean firmness rehydrated bamboo shoots ... 31
Figure 19. Mean total residual sulfites in dried bamboo shoots ... 32
Figure 20. Age of panelists attended sensory test ... 34
Figure 21. Frequency of bamboo shoots consumption ... 34
Figure 22. Form of bamboo shoots regularly consumed by panelists ... 34
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xi
LIST OF APPENDIXES
Page
Appendix 1. Solutions for total residual sulfites ... 44
Appendix 2. Worksheet for sensory analysis ... 45
Appendix 3. Scoresheet for sensory analysis (English) ... 46
Appendix 4. Scoresheet for sensory analysis (Thai)... 47
Appendix 5. Data of drying time of bamboo shoots ... 48
Appendix 6. Result of ANOVA of drying time of bamboo shoots... 48
Appendix 7. Data of moisture content of bamboo shoots before drying... 49
Appendix 8. Data of moisture content of bamboo shoots after drying ... 53
Appendix 9. Result of one-way ANOVA of initial moisture content ... 56
Appendix 10. Result of ANOVA of final moisture content ... 56
Appendix 11. Data of water activity (aw) of dried bamboo shoots ... 57
Appendix 12. Result of ANOVA of aw of dried bamboo shoots ... 58
Appendix 13. Data of L* value of dried bamboo shoots ... 59
Appendix 14. Data of a* value of dried bamboo shoots ... 60
Appendix 15. Data of b* value of dried bamboo shoots ... 61
Appendix 16. Result of ANOVA of L* value of dried bamboo shoots ... 62
Appendix 17. Result of ANOVA of a* value of dried bamboo shoots ... 63
Appendix 18. Result of ANOVA of b* value of dried bamboo shoots ... 64
Appendix 19. Data of L* value of rehydrated bamboo shoots ... 65
Appendix 20. Data of a* value of rehydrated bamboo shoots... 66
Appendix 21. Data of b* value of rehydrated bamboo shoots ... 67
Appendix 22. Result of ANOVA of L* value of rehydrated bamboo shoots ... 68
Appendix 23. Result of ANOVA of a* value of rehydrated bamboo shoots ... 69
Appendix 24. Result of ANOVA of b* value of rehydrated bamboo shoots ... 70
Appendix 25. Data of rehydration ratio of dried bamboo shoots ... 71
Appendix 26. Result of ANOVA of rehydration ratio of dried bamboo shoots ... 73
Appendix 27. Data of shrinkage of bamboo shoots ... 74
Appendix 28. Result of ANOVA of shrinkage of bamboo shoots... 78
Appendix 29. Data of firmness of dried bamboo shoots ... 79
Appendix 30. Result of ANOVA of firmness of dried bamboo shoots ... 81
Appendix 31. Data of firmness of rehydrated bamboo shoots ... 82
Appendix 32. Result of ANOVA of firmness of rehydrated bamboo shoots ... 84
Appendix 33. Total residual sulfites in dried bamboo shoots ... 85
Appendix 34. Result of ANOVA of total residual sulfites ... 87
Appendix 35. Scores of rating hedonic test given by the panelists ... 88
Appendix 36. Results of t-Test: two-sample assuming equal variances for rating hedonic test of rehydrated bamboo shoots ... 89
Appendix 37. Total weighted scores of dried bamboo shoots ... 92
Appendix 38. Total weighted scores of dried bamboo shoots (regardless of firmness of dried and rehydrated bamboo shoots) ... 93
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I.
INTRODUCTION
1.1
BACKGROUND
Bamboo shoot is one of most socioeconomically important products. Every year, over two million bamboo shoots are consumed around the world. It supply a rapidly expanding export market, with China as the major world producer and exporter, followed by Thailand, with minor quantities from Indonesia, Vietnam, and Malaysia (Russo et al. 2000; ERG 2004). At the present, it is largerly sold in the fresh form. However, bamboo shoot is a very seasonal and perishable product, it can be stored just for one day at ambient temperature. Thus, to meet export demands, it needs to be processed and preserved properly.
Doi Tung, a mountainous region in Northen Thailand, produces 6000-7000 kg fresh bamboo shoots every week during the season (Halbreich et al. 2012). Fresh bamboo shoots (Dendrocalamus membranaceus Munro) are minimally processed there. They are just boiled and sliced specifically and then sent to secondary factories in Chiang Mai and Lampang for futher processing. At the secondary factories, the sliced bamboo shoots are canned to increase its shelf life. Yet, the canned products have perceived minus points, such as loss of flavor and crunchiness, poor shape and size, and should be consumed within three to four days after the container opened. Hence, it takes other processing method to increase the shelf life of fresh bamboo shoots which is applicable in Doi Tung, i.e. drying.
Drying is a good alternative processing method that is often applied by Thai people. It can prolong shelf life of bamboo shoots. Dried bamboo shoots can be a good alternative to canned bamboo shoots or even fresh bamboo shoots that remain available in off-season. Moreover, dried bamboo shoots have been produced traditionally in China. There bamboo shoots were processed using heat generated from wood burning. This drying method has many disadvantages, i.e. time consuming, weather dependent, and dust and insects contamination possibility. This study is aimed to overcome such disadvantages. Bamboo shoots were dried using hot air drying method, which is more hygienic, controlable, and applicable in Doi Tung, until its moisture content reached 10% dry basis which is less than Thai Industrial Standards Institute (14% wet basis for dried products).
Prior to drying bamboo shoots were also subjected to prtreatment, blanching using sodium metabisulfite solution, to prevent browning reaction during drying with regard to total residual sulfites. Moreover, it should be noted that total residual sulfites in the product should be less than maximum level regulated by Thailand FDA which is 2500 ppm SO2 for dried fruits and
vegetables. Both pretreatment and drying process may cause many physical, chemical, biochemical, and sensory changes in the bamboo shoots. Hence, it is nesessary to develop the availability of high quality dried bamboo shoots with acceptable color and shape, good rehydration, texture properties, and total residual sulfites which is less than Thailand FDA maximum level, to be produced in Doi Tung largerly.
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2
1.2
OBJECTIVES
Objectives of this study are:
1.2.1 To examine main effects of pretreatment and drying temperature on quality of dried and rehydrated bamboo shoots.
1.2.2 To determine drying conditions of fresh bamboo shoots (Dendrocalamus membranaceus
Munro), i.e. concentration of sodium metabisulfite used in blanching solution and drying temperature.
1.3
SCOPE
Scope of this study is determination of good drying temperature and concentration sodium metabisulfite used in blanching solution to produce dried bamboo shoots (Dendrocalamus membranaceus Munro) which is good in physical properties (color, rehydration ratio, and firmness); chemical properties (total residual sulfites); and sensory properties (color, taste, texture, and aroma).
1.4
EXPECTED OUTCOME
This study would provide a better drying condition which is applicable in Doi Tung, Chiang Rai, Thailand.
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II.
LITERATURE REVIEW
2.1
BAMBOO SHOOTS
Bamboo shoot is one of non-wood forest products in Thailand. It is also one of important raw materials for making traditional delicacy of many countries in Eastern Asia. Bamboo shoot, as shown in Figure 1, is edible portion of bamboo plant that have emerged from the ground and harvested before significant fibre development. Bamboo shoot is protected by many sheaths of overlapping, brown husk covered in fine, and sharp hairs. Freshly harvested shoot has conical shape, creamy color inside, a strong smell, sweet taste, and crunchy texture. It also has a length of 20-30 cm and weighs almost to a pound. However, the size and the weight depend on its growth location; depth, fertility, pH, and nutrition of the soil; temperature; watering and drainage conditions (Winarno 1992; ERG 2004).
Figure 1. Freshly harvested bamboo shoots
Based on climate, bamboo is categorized into two groups, i.e. monopodial (sub-tropical) bamboos and sympodial (tropical) bamboos. Sub-tropical bamboos produce three types of shoots, i.e. spring or summer shoots, winter shoots, and rhizome shoots, while tropical bamboos produce only summer shoots. Thailand has sympodial bamboos that produce shoots from May to October with most productions in July to August every year (INBAR 2006). There are many species of bamboo shoots growing in Thailand, such as Bambusa edulis, Bambusa oldhamii, Bambusa pallida, Dendrocalamus asper, Thryrsostachys siamensis, Dendrocalamus giganteus,
Dendrocalamus merrillianus, and Dendrocalamus membranaceus Munro (Winarno 1992; Scurlock et al. 2000; ERG 2004). Dendrocalamus membranaceus Munro or white bamboo grows well in Doi Tung, Northen Thailand. It is one of the most promising species for bamboo shoots in Doi Tung. It is smooth and easy to handle. It also has a hole at the center and a lighter weight.
Bamboo shoots are very nutritious food. Nutritional content of bamboo shoots,
Dendrocalamus membranaceus, was shown in Table 1. They are rich in protein that produces eight essential amino acids. They are also low in cholesterol and saturated fat contents, and high in dietary fibers. Although the fat content is comparatively low, it is still higher than many other vegetables and the shoots contain rich essential fatty acids. They also contain active materials, such as antioxidants (flavones, phenols, and steroids). They are valuable in pharmaceutical and food processing industries and can be processed either into beverages, medicines, additives, or health foods. Bamboo shoots also contain flavones and glycosides which have excellent
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anti-4 microbial property; dietary flavonoids which have anti-proliferative activity; lysine which is known as a limited amino acid; and Germaclinum which is known to carry anti-aging properties (Middleton et al. 2000; Zagrobelny et al. 2004; NMBAb 2009).
Table 1. Macronutrients of Dendrocalamusmembranaceus (Chongtham et al. 2011)
Nutrient Content (g/100 g fresh weight)
Moisture 89.30 ± 1.34
Carbohydrate 5.40 ± 0.03
Protein 3.38 ± 0.10
Amino acids 3.46 ± 0.02
Ash 0.63 ± 0.04
Dietary fibre 2.91 ± 0.06
Fat 0.43 ± 0.05
Starch 0.23 ± 0.04
Vitamin C 1.58 ± 0.06
Vitamin E 0.65 ± 0.10
Despite its benefits, many tropical shoots contain high level of anti-nutrient as cyanogens (FAO 2012). A survey (2008-2009) that has been conducted in Thailand by Bureau of Quality and Safety of Food cooperated with Regional Medical Sciences Centers and Provincial Public Health Offices reported that the highest mean level of cyanide was found in fresh bamboo shoot at the level of 167 mg/kg and the lower quantity was detected in fermented bamboo shoot and boiled bamboo shoot at the levels of 41.1 mg/kg and 19.2 mg/kg, respectively (Teerapapthamkul et al.
2011). The results showed that cyanide content may be reduced by boiling or fermentation process. Some studies have also reported that cyanide content from bamboo shoots as Taxiphyllin can be reduced by boiling, steaming, soaking in water, superheated steam drying, or fermentation (Ferreira et al. 1995; Tripathi 1998; Bhargava et al. 1996; Wongsakpairod 2000; Bhatt et al.
2003).
2.2
DEHYDRATION
2.2.1
Drying
Drying is a major process for preserving food. It is one of the oldest that commonly applied in food processing. Drying is defined as a process of moisture removal due to simultaneous heat and mass transfer (Brennan and Grandison 2012). Terms “drying” and “dehydration” are used interchangeably in process engineering. However, in food science and technology, the term “drying” is traditionally used for thermal removal of water to about 15-20% moisture in dry basis, which is approximately equilibrium moisture content of dried product at ambient air conditions, while the term “dehydration” is traditionally used for drying foods down to about 2-5% (Saravacos and Maroulis 2011).
The main aim of drying is to extend food shelf life without requiring a refrigerated transport and storage by reducing water activity to a level which inhibits the growth and multiplication of spoilage or pathogenic microorganisms; reducing moisture content and enzyme activity which lead to undesirable chemical changes (Brennan and Grandison
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5 2012). Drying may also reduce weight and volume of the products that lead to substantial savings in packaging, transport, and storage cost (Sivasankar 2002). Drying is a complex process requiring precise process control. There are some factors that must be considered in drying process, including drying temperature and drying time which depend on composition, moisture content, size, and shape of the raw materials; airflow velocity; and relative humidity.
Product quality plays a major role in food drying process. Drying causes both desirable and undesirable physical, biochemical, and sensory changes. In many cases, improper drying may lead to irreversible change to product quality. However, it should be noted that free water which is removed from the product should easily be rehydrated to reconstruct structure of the product (Ahmed 2011).
2.2.2
Hot Air Drying
Most of drying processes are carried out in convective drying, in which air used for heating product and removing evaporated water. The heat is mainly transferred by convection from the air to the surface of wet product and by conduction within the product. It is assumed that all heat is transferred to the product surface from the air by convection and that process occurs from one large surface only (Brennan and Grandison 2012). If the rate of moisture content change is plotted against time, as shown in Figure 2, the drying curve for a wet product in hot air at constant temperature, relative humidity, and airflow velocity, consists of three periods as follows:
ZZZZZ
1. A-B: equilibration period. Wet surface of the product goes into equilibrium with the air. All heat provided in the air is used to heat up the product to a predetermined drying temperature.
2. B-C: constant rate period. Surface of the product is saturated with free water. Water on the surface evaporates and free water within the product moves to the surface that maintain the surface in a saturated state. Drying rate remains constant during this period.
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6 3. C-D: falling rate period. Temperature on the product surface increases and
almost reaches dry bulb temperature of the air as drying goes to completion. Hence, it is towards end of the process that any heat damage may occur to the product. Most of the drying takes place in falling rate period (Ahmed 2011; Brennan and Grandison 2012).
Cabinet (tray) drier is commonly used in hot air drying of solid food piece. It is a multipurpose and batch operated drier. Cabinet drier consists of an insulated cabinet, equipped with a fan, an air heater, and a space occupied by trays of food. Heating may be by an air flowing throughout trays, by conduction from heated trays, or by radiation from heated surfaces. The drier can vary in size from a bench-scale unit holding one or two small trays of food to large unit taking stacks of large trays. Cabinet drier has low capital and maintenance cost (Sudheer and Indira 2007; Brennan and Grandison 2012).
2.3
PRETREATMENT
2.3.1
Blanching
Prior to futher processing such as drying, canning, or freezing, most vegetables and some fruits are blanched. Blanching is defined as a process of heating food rapidly to a predetermined temperature, holding for a specified time, and then either cooling rapidly or passing immediately to the further processing. Blanching is a pretreatment usually applied between preparation and main processing. The main aim of blanching is enzyme inactivation. It is important to inactivate enzyme, that is enzymes would lead to discoloration, softening, production of off odours and flavours, or breakdown of nutrients (Brennan and Grandison 2012). Most raw materials are subjected to blanch prior to drying as temperature associated with drying process are insufficient to inactivate enzymes within the product and enzyme activity can not be reduced by decreasing moisture content (Sudheer and Indira 2007). Blanching also acts a final cleaning and microbiological reduction process, which is useful in dried food to prevent surviving organisms multiplication during rehydration (Brennan and Grandison 2012). It should be noted that drying does not destroy microorganisms, it only inhibits their growth, thus it is essential to make sure that materials are not contaminated with microorganisms before drying.
Two methods of blanching are commonly applied, i.e. hot water blanching and steam blanching. Hot water blanching is most common method that the raw materials are immersed in hot water usually at 75-95 ⁰C for 1-10 minutes, while steam blanching utilizes saturated steam at atmospheric or low pressure (150 kPa). Steam blanching is more able to keep thermo-sensitive nutrients and water-soluble compounds in products than hot water blanching (De Ancos et al. 2012; Zheleva and Kamburova 2009).
There are some factors that must be considered for determining time and temperature of blanching in order to keep quality of the raw material and avoid over-processing, i.e. food characteristics, size and shape of raw materials, method of heating, and desired effects of blanching in the product. However, time and temperature combinations for different food and different processes are specific. Generally, it is applied blanching time of 1-15 minutes at 70-100 ⁰C (Brennan and Grandison 2012). Blanching, as thermal treatment, causes reduction on quality of the products, yet most of the quality attributes are less sensitive to thermal treatments than the quality-changing enzymes within the products.
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7 It would be good suggestion that blanching at higher temperature and shorter time can keep quality attributes of the products (Sudheer and Indira 2007).
2.3.2
Sulfiting
Sulfites, as sulfur dioxide (SO2) or inorganic sulfites (SO32-), are commonly used to
inhibit and control both enzymatic and nonenzymatic browning or microbial growth, or as bleaching and antioxidant agents. The main purpose of sulfiting is to prevent discoloration or preserving of fruits and vegetables (Brennan and Grandison 2012). The following sulfiting agents listed in current Codex GSFA are sulfur dioxide (INS 220), sodium sulfite (INS 221), sodium hydrogen sulfite (INS 222), sodium metabisulfite (INS 223), potassium metabisulfite (INS 224), potassium sulfite (INS 225), calcium hydrogen sulfite (INS 227), potassium bisulfite (INS 228), and sodium thiosulfate (INS 539) (WHO 2009).
Mechanisms of enzymatic browning inhibition by sulfites become complicated, yet it was reported that active form of the sulfiting agents is undissociated sulfurous acid
(H2SO3), thus the sulfiting is more effective at low pH (≥4) (Brennan and Grandison
2012). There are several mechanisms as follows: 1) sulfites may directly inhibit polyphenol oxidase which is responsible to enzymatic browning reaction on the surface of cut fruits and vegetables; 2) they may also bind carbonil intermediate products, such as quinones, formed during browning reaction, which can cyclize, oxidize, and condense to form brown pigments; 3) they also act as reducing agents that promote the conversion of the quinones back to the original phenols. Moreover, sulfites also inhibit nonenzymatic browning by binding reducing sugar (Taylor et al. 2003).
Sodium metabisulfite is commonly applied in food processing. In wine making, it serves several functions, i.e. as a antimicrobial agent, an antibrowning agent, and an acetaldehyde binder. Naturally, sulfite always exists in a fermentation medium. Acetaldehyde, pyruvic acid, and -ketoglutaric acid bind SO2 and act to control level of
free SO2, which has antimicrobial properties, in the fermentation medium. Moreover,
sodium metabisulfite is more often used in pretreatment of dried products than the others due to its highest theoretical yield of SO2 (67.39%) and its good solubility (54% at 20 ⁰C)
(Taylor et al. 1986). It is also possible to accomplish the sulfuring by one of several methods. In England, blanching is applied by immersion in hot water, it is relatively easy to incorporate the sulfiting treatment by merely adding sulfite salts into blanching bath and maintaining the desired concentration by addition of salts at fairly frequent intervals (AIC 1944).
Despite many beneficial functions of sulfites, residual sulfur dioxide within sulfited products contributes to adverse reaction in sub-population sulfite sensitive asthmatics. Yet, the sulfite level of use typically does not reflect the level remaining in a food at the time of ingestion. The sulfite level decreases during processing and storage of the sulfited products (WHO 1999). Thailand FDA has regulated that maximum sulfite residue is 2500 ppm, calculated as SO2, for dried fruits and vegetables. According to GSFA (general standard for
food additives), dried vegetables which contain up to 5000 ppm sulfites are usually rehydrated and cooked before consumption (CAC 2011).
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8
2.4
PREVIOUS STUDIES AND REAL CONDITION
2.4.1
Previous Studies
Kleinhenz et al. (2002) reported that freshly harvested bamboo shoots can be stored for one day under traditional storage at ambient temperature (20-25 ⁰C) without packaging. At temperatures above 1-2 ⁰C (i.e. 8 ⁰C), discoloration occured and fungal growth reduced shelf life of bamboo shoots to not more than 10 days. The bamboo shoots can be stored for 21 days at 1-2 ⁰C with LDPE bags as packaging.
Muchtadi and Adawiyah (1996) reported that pre-cooking (blanching in antibrowning agents) significantly affected quality of dried bamboo shoot (Dendrocalamus asper). In that study, fresh bamboo shoots was trimmed, sliced longitudinally, and then dried using cabinet drier at 60 ⁰C for 7-8 hours. Prior to drying, the sliced bamboo shoots were subjected to two different pretreatments (pre-cooking), i.e. blanching at 90-100 ⁰C for 5 minutes and autoclaving with pressure of 0.8 bar for 10 minutes. Both pretreatments were carried out in solutions of antibrowning agents. There are three different antibrowning agents used in this study, including sodium metabisulfite (2000 ppm), sodium chloride (2%), and ascorbic acid (0.05%). Results showed that the unpretreated bamboo shoots needed a longer time, about 90 minutes, to reach a maximum rehydration capacity than the pretreated bamboo shoots that only needed 30 minutes. Rehydration ratio of the pretreated shoots were higher than the unpretreated shoots, while the highest rehydration ratio was found in the bamboo shoots subjected to blanch in sodium metabisulfite solution. Among the antibrowning agents, sodium metabisulfite (2000 ppm) was the most effective agent to prevent browning during the process. Brine (2%) and plain water, although not as effective as sodium metabisulfite, gave a lighter color to dried bamboo shoots compared with ascorbic acid.
Trongpanich et al. (1993) also did a bamboo shoots research. There were three different treatments to produce dried bamboo shoots, i.e. 1) bamboo shoots were dried after cutting; 2) the cut bamboo shoots were soaked in 1% sodium metabisulfite solution for 20 minutes before drying; 3) the bamboo shoots were blanched in boiling water for 10 minutes, cut, and soaked in 1% sodium metabisulfite for 20 minutes, and then dried. The bamboo shoots were cut into thickness of 0.3 cm for all treatments. The samples were dried using two different driers, i.e. conventional drier and dehumidified drier, at the same temperature, 55 ⁰C. It was reported that blanching for 10 minutes and then soaking in 1.0% sodium metabisulfite solution prior to drying produced a better quality and highest acceptance of dried bamboo shoots after storing for 6 months compared with non-treatment and treatment with only soaking in 1.0% sodium metabisulfite solution. Soaking in 1% sodium metabisulfite solution may only retard the browning reaction within the products for 3 months of storage. The study also reported that the unblanched sample [treatment 1) and treatment 2)] had higher rehydration ratio than the blanched sample [treatment 3)].
Halbreich et al. (2012) observed Huay Poo Factory, a bamboo shoots factory in Huay Poo Village, Doi Tung, Northen Thailand. The factory is owned by Mr. Theraapoong (as a supplier of fresh bamboo shoots in this reseach) and his wife. Freshly harvested bamboo shoots were minimally processed there. After processing, bamboo shoots were packed and then transported to secondary factories in Chiang Mai and Lampang, Thailand, by truck. The production process can be seen in Figure 3. At the secondary factories, the
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9 bamboo shoots were canned. Yet, there were several minus of canned product, i.e. bulky, poor shape (shredded and sliced), loss of aroma and crunchiness, and should be used within 3 to 4 days after opening the container. There was no added value of the bamboo shoots produced in Doi Tung. The authors also reported that there was a need to suggest how to improve and add value to the existing production of bamboo shoots in the factory (e.g. how to dry properly). There are also two important considerations to improve the product, i.e. convenience to use and availability (ERG 2004). Based on the global R&D needs in drying, dried bamboo shoot can be considered as new product that has not been developed before (Mujummdar and Huang 2010).
2.4.2
Real Condition
China is the largest world producer and exporter of bamboo shoots. Dried bamboo shoots have been produced in China. On August 31, 2011, Mr. Theerapong, supplier of bamboo shoots in this study, study visited to a production site of dried bamboo shoots in China, as shown in Figure 4. Bamboo shoots are produced traditionally there. Prior to drying, the bamboo shoots are peeled and then smoked using firewood for 3 nights. After smoking, they are packed in sacks (25 kg of whole dried bamboo shoots per sack). The drying process was less hygienic, as shown in Figure 5.
Fresh bamboo shoots harvested in the forest
peeling
boiling cooling
slicing sorting
packing
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10
(a) (b)
(c) (d)
Figure 4. One of production site for drying whole bamboo shoots in China
Figure 5. (a) peeled bamboo shoots; (b) drying process; (c) dried bamboo shoots; (d) packed dried bamboo shoots, produced in China
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III.
MATERIALS AND METHODS
3.1
TIME AND PLACE
This study was conducted from June 12 to October 10, 2012. Drying process was done at Food Engineering Laboratory and Food Processing Laboratory in Scientific Laboratory 4; texture analysis was done at Post Harvest Laboratory, Scientific Laboratory 3; chemical analysis was done at Food Chemistry Laboratory and sensory analysis was done at Sensory Room in Scientific Laboratory 4, Mae Fah Luang University, Chiang Rai, Thailand.
3.2
MATERIALS AND INSTRUMENTS
Sample was fresh edible shoots of Dendracalamus membranaceus Munro harvested in Doi Tung, Chiang Rai, Thailand and commercial dried bamboo shoots purchased in Mae Sai market. Material used for blanching the bamboo shoots was sodium metabisulfite (Na2S2O5) food grade
purchased from Union Science Co., LTD, Chiang Mai, Thailand.
Instruments used in this research were laboratory scale-tray drier (Klue Nam Thai, Nicy Co. Ltd); hot wire anemometer (Digicon DA-44); thermo hygrometer (Digicon DM-760); analytical digital balance single pan (Mettler Toledo model AB204-S with accuracy or readability range of 0.0001 g); oven hot air (Contherm Model 2200, Lab Focus Co.) and aluminium crucible; activity water meter (Novasina AWC500); chromameter (Hunter Lab ColorQuest XE); texture analyzer (TA.XTPlus, Stable Micro System); steel caliper; laboratory glass for total residual sulfite analysis, i.e. 100 and 250 mL beaker, 250 and 500 mL erlenmeyer, 1 L volumetric flask, 50 mL burrette, 10 and 50 mL pipette, tip up pipette; watch glasses, glass stirrer; stirrer bar; magnetic stirrer; aluminium foil.
3.3
METHODS
3.3.1
Preliminary Research
The research was carried out in two stages. The first stage was a preliminary included preparation of raw bamboo shoots and adjustment of drying condition. The second stage was maain research included drying process of bamboo shoots, physical and chemical analysis of dried and rehydrated bamboo shoots, and sensory analysis of the best dried bamboo shoots. The stages of the research can be viewed in Figure 6.
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12
3.3.1.1
Sample Preparation
There were two ways to prepare the sample: 1) for bamboo shoots that would be dried in the same day they are harvested, and 2) for bamboo shoots that would be stored in refrigerator. Fresh bamboo shoots that just harvested from Doi Tung, removed from the bag, and then cooled using tap water (T= 25
⁰C) as quickly as possible to remove latent heat during transportation.The outer sheaths were peeled and then the peeled shoots were trimmed to remove some undesirable parts, washed to remove dirts, drained for an hour, and then packed in a plastic bag for storing in the refrigerator at 0-2 ⁰C. Three to five shoots were packed in one plastic bag (31 cm x 46 cm).
Bamboo shoots that would be dried in the same day they are harvested were peeled and then trimmed, washed, drained for an hour. After draining, the shoots were cut into the same shape and size and then blanched in sodium metabisulfite solution at 90-100 ⁰C for 10 minutes. After blanching, the shoots were drained for 15 minutes and then dried until reached 10% of moisture content using hot air drier. The above process can be viewed in Figure 7.
Preparation of raw bamboo shoots
Physical and chemical analyses of dried and rehydrated bamboo shoots
Adjustment of drying process
Drying process
Preliminary Research
Primary Research
The best sample
Sensory analysis for rehydrated best sample
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13
3.3.1.2
Adjustment of Drying Procedure
Prior to main research, it was needed some adjustments throughout the process, started from peeling until drying process. Besides, determination of drying time of unpretreated bamboo shoots was also done in this stage.
3.3.2
Main Research
3.3.2.1
Drying Procedure
Drying experiment was performed using laboratory scale-tray drier (Klue Nam Thai, Nicy Co. Ltd). The drier is capable of providing any desired drying temperature and constant air velocity. Airflow was adjusted by the fan speed control and the air velocity was recorded by hot wire anemometer. Air velocity used in this study was 1.0 m/s by applying fan speed about 625 rpm (25 out of 60;
60 is equivalent to 1400 rpm). Relative humidity at various locations around the system was also measured by a thermo hygrometer (Digicon DM-760).
Figure 7. Sample preparation Storing, 0-2 ⁰C
Pre-cooling, 25 ⁰C Fresh bamboo shoots
D. membranaceus Munro
Peeling
Washing
Cutting Draining, 15’
Blanching in Na2S2O5 (aq);
90-100 ⁰C; 10’
Drying
Dried bamboo shoots MC 10%
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14 Experiment was carried out approximately an hour after the drier turned on to reach its steady state condition. All samples were loaded onto a tray. Each concentration of sodium metabisulfite was presented by five samples. They were set into four groups, i.e. 0, 0.5%, 1.0%, and 1.5%. Position of each sample and each group was also rotated every 12 hours. Prior to drying, each group was weighed to same total weight and a sample of each group was taken for initial moisture content determination. Drying was applied until total weight of samples reduced to a level corresponding to moisture content of about 10% dry basis. The final total weight was obtained by calculation from initial moisture content and initial total weight of sample. The weight loss was monitored by digital balance with accuracy of 1 g. The drying experiment was conducted at three drying temperatures of 50 ⁰C, 60 ⁰C, and 70 ⁰C in triplicates for statistical purpose.
After drying was complete, the samples were allowed to condition at ambient temperature for 30 minutes. The conditioning process was applied to evenly distribute minimal residual moisture throughout all samples. It may reduce mold spoilage. After conditioning, one of samples were taken to determine its moisture content. It was done to obtain and confirm actual final moisture content of the dried shoots. Remaining samples were packed in plastics, labeled with name of product, date, concentration of sodium metabisulfite used, and drying temperature applied. The plastics were sealed tightly and stored in a dry and dark place.
3.3.2.2
Physical, Chemical, and Sensory Analyses
3.3.2.2.1
Determination of Moisture Content (AOAC 1995)
Moisture content of the sample was determined by drying milled sample (~2 g) for 24 hours at 105 ± 0.5 ⁰C to a constant mass. Analysis was done in triplicates (duplo for each replication) for sample before drying (initial moisture content) and sample after drying (final moisture content). Average moisture content in dry basis, expressed in percents, was calculated using the following equation:
w ( %) = ( m − m )
m × 100
where: m1 = mass of sample before drying (g)
m2 = mass of sample after drying (g)
3.3.2.2.2
Water Activity Measurement
Water activity of dried bamboo shoots was measured using water activity meter (Novasina AWC500). Approximately 3 ± 0.01 g of milled dried sample was placed in a container of aw meter and
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15 then the aw meter was tightly closed. The sample was left in aw
meter until obtained a constant value of aw. The determination was
done in triplicates and duplo per each replication.
3.3.2.2.3
Color Measurement (Hunter Lab)
Color of dried and rehydrated samples were measured using Chromameter (Hunter Lab ColorQuest XE). The instrument (Illuminant D65, 10⁰ Observer, ASTM E308) was calibrated with black and white reference tiles through L*, a*, and b* values, taking as standard values of the white background tile (L* 93.47, a* -0.95, b* 0.53). Analysis of color values was done six times (duplo for each part: bottom, middle, and top). Three parameters, i.e. L* (lightness), a* (redness), b* (yellowness), were used to study the color changes. L* refers to lightness of the sample and ranges from black (0) to white (100). Negative value of a* indicates green, while the positive one indicates red-purple color. Negative value of b* indicates blue, while the positive one indicates yellow color.
3.3.2.2.4
Determination of Rehydration Ratio (Doymaz 2008,
modified)
A dried sample was weighed using digital balance with accuracy of 0.1 and soaked into distilled water (25-26 ⁰C) with a 1:100 ratio at room temperature (± 26 ⁰C) for 12 hours. After rehydration, the sample was taken out and drained for 5 minutes, and then adhering water was absorbed carefully using tissue paper. After that, the rehydrated sample was weighed. Analysis was done in triplicates and duplo for each replication. The rehydration ratio (RR) was calculated as following:
RR = m m
where: mR = mass of rehydrated sample (g)
md = mass of dried sample used for rehydration (g)
3.3.2.2.5
Determination of Dimensional Changes (Shrinkage)
(Dehkordi 2010, modified)
Sample height and diameter before and after drying were measured. Both height and diameter were measured using a steel caliper with accuracy of 0.02 mm. The measurement were carried out at three different areas on each sample. Shrinkage was expressed as a percentage change in volume of sample. Both dried and
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16 rehydrated bamboo shoots were assumed as cones. Dimensional changes (shrinkage) was calculated as following:
( %) = − × 100
where: V0 = volume of sample before drying (cm3)
Vt = volume of sample after time (t) of drying (cm3)
3.3.2.2.6
Texture Analysis
Texture analyzer (TA.XTPlus, Stable Micro System, UK) fitted with a knife blade probe was used. Dried and rehydrated bamboo shoots were cut into pieces of uniform size and shape (30 mm x 5 mm x 5 mm). Each sample was aligned vertically on the central of heavy duty platform (HDP/90). Three measurements were carried out on each sample. TA.XTPlus settings can be seen in the Table 2.
Table 2. TA.XTPlus settings
Mode Measure Force in compression
Option Return to start
Pre-Test Speed 2.0 mm/s
Test Speed 2.0 mm/s
Post-Test Speed 10.0 mm/s
Distance 5 mm
Trigger Type Auto – 5g
Data Acquisition Rate 200 pps
The analysis was performed in triplicates. Firmness of dried and rehydrated bamboo shoots were automatically computed from curves using texture analyzer software macro (Texture Exponent 32 Stable Micro System).
3.3.2.2.7
Determination of Total Residual Sulfites (AOAC
1970; FAO JECFA 2006)
Approximately 0.2 g of the milled dried bamboo shoots to the nearest mg, added to 50.0 ml of 0.1 N iodine in a glass-stoppered flask, and the flask was stoppered. It was allowed to stand for five minutes in the dark, and then 1 ml of hydrochloric acid added. After that, the excess iodine was titrated with freshly standardized 0.1 N sodium thiosulfate (Na2S2O3). Approximately 2-3 ml 0.5% starch
indicator solution was added as the end point was approached (light-straw color), and then the titration was continued until the blue color disappeared. Each ml of 0.1 N iodine is equivalent to 3.203 mg of
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17 sulfur dioxide. Total residual sulfites, expressed in SO2, was
calculated as follows:
SO ( ppm) = ( V − V )
m × N Na S O × 3.203 mg × 1000
where: V1 = volume of 0.1 N Na2S2O3 to titrate blank (ml)
V2 = volume of 0.1 N Na2S2O3 to titrate sample (ml)
m = mass of milled dried bamboo shoots used (g)
3.3.2.2.8
Determination of The Best Sample (Zaboj 2002;
DFPNI 2010, modified)
In this study, sample catagorized as the best one was the sample with good color of dried and rehydrated forms (high L* value, low a* value, and high b* value), high rehydration ability, good texture (high firmness on dried form and similar firmness on rehydrated form when compared with the fresh form), and low total residual sulfites.
The best sample was chosen based on arbitrary weighting method. The process of deriving weights and scores was depicted on Figure 8.
Figure 8. Weighting method to determine the best sample
There were four attributes chosen, i.e. color including L*, a*, and b* values of dried and rehydrated bamboo shoots, rehydration ratio, dimensional changes (shrinkage), and firmness (dried and rehydration bamboo shoots). Each attribute had a weighted factor, as shown in Table 3. The weighted factors were determined with regard to the desired quality of product, as mentioned above.
The largest part of dried products is rehydration. Almost dried products including dried bamboo shoots must be rehydrated before
Identification of attributes
Weighting
Scoring
Interpreting Calculating
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18 final using (Jayaraman and Das Gupta 1995; Lewicki 1998; Taiwo
et al. 2002; Krokida and Philippopoulos 2005; Singh et al. 2006; Ramallo and Mascheroni 2012). Due to its major role, rehydration ratio was given 40% of total weighted factors. Besides rehydration ability, texture (firmness) also plays major role on quality of dried products (Bourne 2008; Vega-Gàlvez et al. 2008; Marzec et al.
2010; Bonazzi and Dumoulin 2011). Firmness was also given 40% of total weighted factors.
Color is also important quality parameter that influences consumer acceptance (Krokida and Marinos-Kouris 2003; Kulshreshtha et al. 2009). Color had 30% of total weighted factors, 20% for dried form and 10% for rehydrated form. It was considered that rehydrated bamboo shoots may be futher processed and the shoots may also be mixed with other materials during cooking. Thus, color of rehydrated product was given 0.1. In the other side, the color of dried form was given 0.2. The color of dried bamboo shoots produced at the lab was expected better than existing commercial dried bamboo shoots, thus the color of dried form was considered more important than the color of rehydrated form and given 0.2. On the contrary, shrinkage is an undesired attribute. It has a negative impact on quality of dried products (Aguilera 2003; Mayor and Sereno 2004). Thus, shrinkage or dimensional change was given -0.1.
Table 3. Weighted factors
Attribute Weighted factor
L*_dried 0.2
a*_dried -0.2
b*_dried 0.2
L*_rehydrated 0.1
a*_rehydrated -0.1
b*_rehydrated 0.1
Rehydration ratio 0.4
Shrinkage -0.1
Firmness_dried 0.2
Firmness_rehydrated 0.2
Total 1.0
Mean value of each attribute was determined as a score. Thus, weighted score was obtained by multiplying the determined weighted factor by mean value of the attribute. The best sample was sample which had the highest total weighted score. Yet, it should be considered that the sample chosen as the the best sample had to have total residual sulfites less than 2500 ppm SO2.
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19
3.3.2.2.9
Sensory Analysis
Sensory analysis was carried out on the best sample. The best sample produced at the lab and commercial dried bamboo shoots purchased in Mae Sai were tested using hedonic rating. Before testing, both samples were soaked into distilled water (25-26 ⁰C) at room temperature (± 26 ⁰C) for 12 hours and then boiled for an hour. After that, the samples were cut into same shape and size (50 mm x 5mm x 5 mm). Both samples were presented in pairs according to the predetermined order. They were also coded by 3 random numbers.
Thirty five untrained panelists (Lawless and Heymann 1998) were asked to give preference score of the attributes on a scale from 1 to 5. Criteria for each attribute tested, including color, aroma, taste, texture, and overall, was shown in Table 4.
Table 4. Category scales for rating hedonic test
Scale Criteria
1 Dislike extremely
2 Dislike moderately
3 Neither like or dislike
4 Like moderately
5 Like extremely
3.3.3
Experimental Design
Experimental design used in this research was completely randomized factorial design with two factors, i.e. drying temperature (code: T) and concentration of sodium metabisulfite used in blanching solution (code: N). There were three levels of the drying temperature, i.e. 50 ⁰C (T1), 60 ⁰C (T2), and 70 ⁰C (T3), while four levels of the
concentration of sodium metabisulfite, i.e. 0 (N0), 0.5% (N1), 1.0% (N2), and 1.5% (N3),
thus there were 12 treatment combinations tested in this research. The treatment combinations were shown in Table 5. Each combination had three replicates, thus the plot of experiments used a total of 36 experimental units.
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88
Panelist
Score
Color
Aroma
Taste
Texture
Overall
A
B
A
B
A
B
A
B
A
B
1
4
2
3
2
3
3
2
2
3
2
2
5
2
3
4
3
3
5
1
4
3
3
3
5
2
4
4
4
5
5
4
5
4
5
2
5
2
4
1
4
1
4
1
5
3
3
2
2
3
3
3
3
3
3
6
4
1
5
1
3
1
4
1
4
1
7
5
3
3
2
4
3
4
4
4
3
8
5
1
4
1
2
1
2
1
3
1
9
3
1
3
3
3
3
4
1
4
2
10
3
3
3
3
1
1
4
4
3
3
11
4
4
4
4
5
4
4
3
5
4
12
5
4
4
5
4
2
5
5
5
3
13
4
3
4
4
4
2
3
3
4
4
14
4
2
3
2
3
3
3
2
3
2
15
4
2
3
2
1
1
3
1
3
2
16
3
4
2
4
3
3
3
4
3
4
17
4
3
4
3
4
4
4
2
4
2
18
2
4
2
3
2
3
2
4
2
3
19
3
4
4
2
4
4
4
3
4
3
20
4
2
3
1
4
3
3
2
4
2
21
3
3
3
3
3
3
3
3
3
3
22
2
5
1
4
3
3
2
5
3
5
23
4
3
5
2
4
3
3
1
3
2
24
3
2
4
1
4
4
3
2
3
3
25
3
2
4
3
3
4
4
3
4
3
26
4
2
4
3
3
1
4
3
4
2
27
4
3
4
2
3
4
4
4
4
4
28
4
3
5
4
2
3
1
4
2
3
29
3
3
2
2
2
3
3
1
2
2
30
3
2
3
2
3
1
3
3
3
3
31
4
2
3
2
3
1
3
3
3
3
32
4
2
3
3
4
2
4
2
4
2
33
5
2
4
2
4
1
4
1
4
2
34
4
3
4
2
3
3
3
2
4
2
35
3
2
4
2
4
3
3
3
4
2
Description of rating scale can be seen in
Appendix 3.
A = rehydrated-dried bamboo shoot produced at the lab
B = rehydrated-commercial dried bamboo shoots
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89
Appendix 36.
Results of t-Test: two-sample assuming equal variances for rating hedonic
test of rehydrated bamboo shoots
Color:
RBS_lab
RBS_commercial
Mean
3.714285714
2.685714286
Variance
0.680672269
1.045378151
Observations
35
35
Pooled Variance
0.86302521
Hypothesized Mean Difference
0
df
68
t Stat
4.631714053
P(T<=t) one-tail
8.44035E-06*
t Critical one-tail
1.667572281
P(T<=t) two-tail
1.68807E-05
t Critical two-tail
1.995468907
Aroma:
RBS_lab
RBS_commercial
Mean
3.4
2.6
Variance
0.952941176
1.070588235
Observations
35
35
Pooled Variance
1.011764706
Hypothesized Mean Difference
0
df
68
t Stat
3.327126003
P(T<=t) one-tail
0.000709179*
t Critical one-tail
1.667572281
P(T<=t) two-tail
0.001418358
t Critical two-tail
1.995468907
(3)
90
test of rehydrated bamboo shoots [Cont’d]
Taste:
RBS_lab
RBS_commercial
Mean
3.2
2.6
Variance
0.811764706
1.188235294
Observations
35
35
Pooled Variance
1
Hypothesized Mean Difference
0
df
68
t Stat
2.50998008
P(T<=t) one-tail
0.007229538*
t Critical one-tail
1.667572281
P(T<=t) two-tail
0.014459077
t Critical two-tail
1.995468907
Texture:
RBS_lab
RBS_commercial
Mean
3.371428571
2.628571429
Variance
0.828571429
1.65210084
Observations
35
35
Pooled Variance
1.240336134
Hypothesized Mean Difference
0
df
68
t Stat
2.79032397
P(T<=t) one-tail
0.003413358*
t Critical one-tail
1.667572281
P(T<=t) two-tail
0.006826716
t Critical two-tail
1.995468907
(4)
91
Appendix 34.
Results of t-Test: two-sample assuming equal variances for rating hedonic
test of rehydrated bamboo shoots [Cont’d]
Overall:
RBS_lab
RBS_commercial
Mean
3.514285714
2.685714286
Variance
0.551260504
0.986554622
Observations
35
35
Pooled Variance
0.768907563
Hypothesized Mean Difference
0
df
68
t Stat
3.952864355
P(T<=t) one-tail
9.3191E-05*
t Critical one-tail
1.667572281
P(T<=t) two-tail
0.000186382
t Critical two-tail
1.995468907
(5)
92
Attribute
Weighted
factor
50
⁰
C
0
0.5
1.0
1.5
L*_dried
0.2
39.31
7.86
43.98
8.80
52.92 10.58
55.02 11.00
a*_dried
-0.2
12.22
-2.44
8.83
-1.77
10.20
-2.04
5.80
-1.16
b*_dried
0.2
18.53
3.71
23.31
4.66
28.56
5.71
28.50
5.70
L*_rehydrated
0.1
69.05
6.91
71.44
7.14
74.81
7.48
79.81
7.98
a*_rehydrated
-0.1
4.39
-0.44
2.24
-0.22
1.92
-0.19
1.45
-0.15
b*_rehydrated
0.1
21.69
2.17
22.92
2.29
22.75
2.28
28.98
2.90
Rehydration ratio
0.4
3.35
1.34
3.83
1.53
4.31
1.72
4.24
1.70
Shrinkage
-0.1
71.94
-7.19
72.10
-7.21
65.55
-6.56
65.55
-6.56
Firmness_dried
0.2 107.65
21.53
125.23
25.05
112.04
22.41
129.03
25.81
Firmness_rehydrated
0.2
39.86
7.97
57.67
11.53
30.27
6.05
42.04
8.41
Total weighted score
1.0
41.41
51.80
47.45
55.63
Attribute
Weighted
factors
60
⁰
C
0
0.5
1.0
1.5
L*_dried
0.2
44.13
8.83
45.57
9.11
54.90 10.98
55.95 11.19
a*_dried
-0.2
11.42
-2.28
9.59
-1.92
6.49
-1.30
6.74
-1.35
b*_dried
0.2
16.30
3.26
22.26
4.45
24.87
4.97
26.73
5.35
L*_rehydrated
0.1
60.80
6.08
69.32
6.93
74.38
7.44
76.08
7.61
a*_rehydrated
-0.1
5.13
-0.51
5.15
-0.52
1.76
-0.18
1.78
-0.18
b*_rehydrated
0.1
24.68
2.47
27.04
2.70
27.54
2.75
26.55
2.66
Rehydration ratio
0.4
3.46
1.38
3.42
1.37
3.67
1.47
4.13
1.65
Shrinkage
-0.1
69.55
-6.96
68.69
-6.87
67.42
-6.74
68.28
-6.83
Firmness_dried
0.2 158.50
31.70
150.86
30.17 132.04 26.41
141.37
28.27
Firmness_rehydrated
0.2
55.93
11.19
46.78
9.36
94.14
18.83
77.85
15.57
Total weighted score
1.0
55.15
54.80
64.63
63.94
Attribute
Weighted
factor
70
⁰
C
0
0.5
1.0
1.5
L*_dried
0.2
36.40
7.28
35.64
7.13
48.86
9.77
53.08
10.62
a*_dried
-0.2
13.45
-2.69
12.73
-2.55
9.89
-1.98
9.42
-1.88
b*_dried
0.2
10.75
2.15
14.66
2.93
20.68
4.14
25.89
5.18
L*_rehydrated
0.1
49.45
4.95
53.00
5.30
73.11
7.31
78.21
7.82
a*_rehydrated
-0.1
11.91
-1.19
7.13
-0.71
7.10
-0.71
1.09
-0.11
b*_rehydrated
0.1
26.55
2.66
22.90
2.29
29.82
2.98
30.31
3.03
Rehydration ratio
0.4
2.63
1.05
2.88
1.15
3.29
1.32
3.40
1.36
Shrinkage
-0.1
66.00
-6.60
66.48
-6.65
68.85
-6.89
68.76
-6.88
Firmness_dried
0.2 179.73
35.95
183.76
36.75
186.72
37.34
191.34 38.27
Firmness_rehydrated
0.2
46.47
9.29
71.41
14.28
49.33
9.87
63.62 12.72
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