universiti putra malaysia development of infrared spectroscopic
TRANSCRIPT
UNIVERSITI PUTRA MALAYSIA
DEVELOPMENT OF INFRARED SPECTROSCOPIC TECHNIQUES FOR THE DETERMINATION OF SOME
QUALITY PARAMETERS OF PALM OIL
FELIX MOH MEE HO
FSMB 1998 5
DEVELOPMENT OF INFRARED SPECTROSCOPIC TECHNIQUES FOR THE DETERMINATION OF SOME
QUALITY PARAMETERS OF PALM OIL
BY
FELIX MOD MEE DO
Thesis Submitted in Fulfillment of the Requirements for the Degree of Master of Science in
Faculty of Food Science and Biotechnology Universiti Putra Malaysia
March, 1998
Especially dedicated to my beloved fiancee .....
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to Professor Dr. Yaakob
Bin Che Man, the Chainnan of my Supervisor Committee, for his kind assistance
and guidance throughout the course of study till the preparation of this thesis. I
am also very grateful to the other members of the Supervisory Committee,
Associate Professor Dr. Jinap Selamat and Mr. Badlishah Sham Bin Baharin for
their support and. encouragements. I would like to acknowledge the Universiti
Putra Malaysia for providing IRP A and P ASCA siswazah funding for this
research.
Gratitude is also expressed to Prof. F.R. van de Voort of McGill
University, Quebec, Canada for his invaluable comments and advice, and Mr.
T.S. Tang of PORIM for this technical assistance as well as Chemophann Sdn.
Bhd. for the Bran+Luebbe NIR instrument. I would like to thank Dr. Mohd Said
Bin Saad of the Department of Agronomy and Horticulture for his NIRSystem
NIR spectroscopy and technical assistance.
My sincere appreciation is extended to the laboratory assistants of the
Faculty of Food Science and Biotechnology: Mr. Chan Tin Wan, Mr. Azman Abu
Yamin, Mr. Abd. Halim Rahman, and Mr. Rosli Aslim. To my colleagues and
friends namely Siah, Irwandi, Amin, Tri Haryati, Lai, Madihah and Rosfarizan
for their generous assistance. Also to my best friend, Mr. Lawrence Sii Tung Ung
11l
of Ministry of Science, Technology and Environment Malaysia for his moral
support and advice.
Not the least but the most important, I wish to express my deepest
appreciation to my parents, brothers and sisters for their moral support and
understanding throughout my studies. I shall forever recognize for their
encouragement, too. I would always remember their words, "we would be there
for you". Finally, but first in my thoughts, I also owe my special thanks to my
beloved fiancee, (Tina) Yang Yang, for her encouragement, understanding and
patient. Most of all, her care and love.
iv
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . . .. . . . . . . . . . . 111
LIST OF TABLES. . . . . . . . . ..... ......... .... ........ ........ ....... ... ...... V1I1
LIST OF FIGURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . . x
LIST OF PLATES... . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . X1I1
ABSTRACT. . . . . . ....... . . . . . . ..... . . . .... . . . . ..... . . . . . .. . . .... .. . . .. . . . .... XIV
ABSTRAK . . . . . . . . . . .. . . . . . . . . . . . . . . .. .. . . . . . . .. . . . . . . . . . .. ... . . . .. . . . . . . . . . . XVII
CHAPTER
1
2
GENERAL INTRODUCTION ...................... . .
REVIEW O F LITERATURE . . . . . . ... . . . . . . . . . . . . . . . . . Production and Characteristics of Palm Oil. . . . . . . . . . . . .
1
4 4
Origin and Agronomy . . . . . . .. .. . . . . . . . . . . . . . . . '" 4 Production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 5 Physiochemical Characteristics. . . . . . . . . . . . . . . . . 5
Some Selected Quality Parameters of Palm Oil of Interest. . . . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Free fatty Acid. . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. 9 Peroxide Value. . . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Carotenoids. . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Limitations of Wet Chemical Methods. .. . . . . . . . . . . . . . . 14 Infrared Spectroscopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Principles of Infrared Spectroscopy. . .. . ... . . . . 1 5 Monochromator. . . . . . . . . . . . .. . . . . . . . . . . . . . . . ... . .. 17 Fourier Transform Interferometry. . . . . . . . . . . . . . 22
General Calibration Methods for Infrared Analysis. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 25
Multiple Linear Regression (MLR) Calibration . . . . . .. . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. 25 Partial Least Squares (PLS) Calibration... . .... 26
Mid Infrared Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ... 27 Basic Description of Mid Infrared (MIR).. . . . . 27 Fourier Transform Infrared (FTIR) Techniques in Food and Oil Analysis. . . . . . . . . . 28
Near Infrared Analysis. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Basic Description of Near Infrared (NIR).. . . . . 32 Near Infrared (NIR) Techniques for Food Analysis.. . . . . . . . . ..... . . . . . . . . .. . . . . . . . . . . . . 32 Near Infrared (NIR) Techniques in Fats and Oils Analysis . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. 34 Suggested Near Infrared (NIR) Applications in Palm Oil Analysis.. . . . . . . . . . . . . . . . ... . .. . . . . . . . 35
V
3
4
5
DETERMINATION OF FREE FATTY ACIDS IN PALM OIL USING NEAR INFRARED TRANSFLECTANCE SPECTROSCOPY ......... .
Introduction . . . . . . . . . . . . " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Materials and Methods . . . .. .. ... . . . .. . . . . . . . .. . . . . . . . .... ..
Reagents . . . . . . ' " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . .
Sample Preparation . . . . .. .. . . . . . . . ...... . . . . . . . .. . .
Chemical Analysis . .. . . . . .. . . .. . . . ... .. . . ... . . . . . . Instrumentation ...... ......... . . . . .............. . .. Calibration and Validation Procedures . . . . . . . . .
Results and Discussion . . . . . . . . . . . ..... .. .. .. . . . . . . . . . . . . . .
General Concept. . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . .
Near Infrared (NIR) Spectroscopy . . . . . . . . . ... . .
Multiple Linear Regression (MLR) Calibration .. . . . . .. . . .. . . . . . . . . . . .. . . . . ... ......... . .
Validation of Calibration Equations . . . . . . .... . . Summary .. . . . . . .. . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . .. .. . . . . . . . .
DETERMINATION OF FREE FATTY ACID IN CRUDE PALM OIL AND REFINEDBLEACHED-DEODORIZED PALM OLEIN USING FOURIER TRANSFORM INFRARED SPECTROSCOPy ..................................... .. Introduction . . . . .. . . . . . . . . . . .. .. . . . . . . . . .. . . . . .. . . . . .. . . . . . .
Materials and Methods . . . . . . . .. . .. . . . . . . . . . . . . .. . . . .. . . . . .
Reagents . .. ... . . . . . .... . . . . . . . . . . ..... . . . . . . . . . . .. .
Sample Preparation ... .. . . . . . . .. . . . . . . . . . . . . . . . . .
Chemical Analysis . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . .
Instrumental Analysis ..... . . . . ....... .. . . . .. . ... .
Calibration and Validation Procedures . .. . . . . . .
Results and Discussion . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. .
Preliminary Study ...... . . . ... . . . .... . . .. . .. ... . . .
General FTIR Statistical Spectroscopy . . . . . .. .
Partial Least Squares (PLS) Calibration ... . . . .
Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DETERMINATION OF PEROXIDE VALUE IN THERMALLY OXIDIZED CRUDE PALM OIL BY NEAR INFRARED TRANS MITT ANCE SPECTROSCOPy ...................................... .
Introduction . . . . .. . . . . ... . . . . . . ... . . . .. .. . . ..... .. . . . . .. . . . .
Materials and Methods .. .. ..... ... . . . . . . .. . .. . . . .. . .... . .. Sample Preparation . .. . . . .. . . . . . .. . . . . .. . . . . .... . .
Instrumentation/Sample Handling . . . . . . .. . . . . . .
CalibrationIV ali dation Procedures .. .. . . . . . . .. .
Results and Discussion . . . . . . .. . . . .. . . . . . . . . . . . . .. . . . . . . . .
Calibration Matrix ............................... .
General NIR Statistical Spectra . . . . .. . . . . . . . . . .
Vi
37 37 38 38 38 3 9 3 9 40 40 40 43
47 54 5 9
60 60 62 62 62 62 62 63 64 64 68 73 81 86
87 87 89 89 90 9 1 92 92 93
6
7
Partial Least Squares (PLS) Calibration....... 100 Validation .... ... .. .... .... . . .... ... .. ... . ....... '" 10 2
S ummary .. . . . ... . .... ... .. '" ...... ..... ....... ..... ....... liD
QUANTITATIVE ANALYSIS OF PALM CAROTENE USING FTIR AND NIR SPECTROSCOPy ...................................... .
Introduction ............................................... . Materials and Methods .................................. .
Sample and Chemicals ........................ '"
Column Chromatographic Extraction ........ . UV -visible Spectrophotometry ................ .
Fourier Transform Infrared (FTIR) Instrument ......................................... .
Near Infrared (NIR) Instrument... ............. . Data Treatments ................................ .
Results and Discussion .................................. . Sample Characteristics .......................... .
UV -visible Spectrophotometer. ............... . FTIR Spectroscopy ............................. . NIR Spectroscopy .............................. "
Validation ........................................ "
Summary .................................................. .
SUMMARY, CONCLUSION AND RECOMMENDATION ................................ .
Summary .................................................. .
Conclusion and Recommendation ..................... .
1 1 1 1 1 1 1 13 1 13 113 114
114 1 14 1 1 5 1 16 1 1 6
1 18 118 1 2 1
1 27 135
136 136
138
BIBLIOGRAPHy......... . .. ....... ..... ..... ................ ....... ....... 139 APENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '" 1 5 2 BIOGRAPHICAL SKETCH............................................... 1 63
vii
Table
I
2
3
4
5
6
7
8
9
1 0
1 1
1 2
13
14
15
LIST OF TABLES
Malaysia: Export of Palm Oil Products ('0 00 Tonnes) ..... " .
Malaysia: Planted Area Under Oil Palm (Hectares) ........... .
Physical and Chemical Properties of CPO ...................... .
Typical Fatty Acid Composition of Malaysia Palm Oil.. ",,"
Minor Components in Crude Palm Oil (ppm) ... " . . . . . . . . " . " .
PORAM Standard Specification for Refined Palm Oil and Fractions ....... "" . . . . . . . .. . .. . . . . . . . . .. . .. . . . .. . . . .
Infrared Spectral Regions ......................................... .
Characteristic Mid Infrared Absorption of Some Common Functional Groups ...................................... .
Basic Characterizing Wavelengths in Near Infrared Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Samples Used in Calibration and Validation Analyzed by Standard Chemical Method ................................... .
Basic Characteristic Wavelengths of C=O Functional Group and Their Relative Peak Positions of NIR Spectroscopy from 1 1 00 to 25 00 nm ............................ .
Effect of Different Wavelengths with 2040 nm as Measurement Wavelength in Constructing the Calibration in Palm Oil Samples ................................. .
Standard Deviation Values at Selected Wavelengths Obtained from Both Calibration and Validation Sets Using MLR Analysis .............................................. .
FF A (% as palmitic acid) of Additional Samples Determined by NIR Spectroscopy Calibration ................. .
Result of Mean Duplicate Analyses of CPO and RBD Palm Olein Obtained by AOCS (Reference) and the FTIR Method" ............................................. .
V111
Page
6
7
8
10
1 1
1 3
16
29
33
4 1
46
48
5 0
55
7 7
16
17
Statistical Comparison of FF A for CPO and RBD Palm Olein Obtained by AOCS (Reference) and FTIR Methods ....................................................... .
Some Common Band Characteristics of Crude Palm Oil in MIR Region .......................................... .
83
99
1 8 PLS Calibration Results Obtained from Different
1 9
20
2 1
22
Regions............................................. .. .. . . . .. . ... ... .. . 1 04
Mean PV of AOCS Chemical Method Against Near Infrared Spectroscopy (NIR) Method in Developing PLS Calibration Model.. ............................. .
Statistical Comparison of PV Obtained by AOCS Chemical Reference and NIR Methods .......................... .
Comparison of Mean Duplicate Sample" ....................... .
Statistical Comparison of Carotene Data Obtained by Spectrophotometry (UV -visible) with FTIR and NIR Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IX
1 06
10 9
125
134
LIST OF FIGURES
Figure Page
2
3
4
5
6
7
8
9
10
II
1 2
13
14
1 5
16
Stretching and Bending Vibrational Modes. ............ ...... ... 18
Specular and Diffuse Reflectance ................................ . 20
Optical Diagram of a Double -Beam Grating Monochromator ..................................................... . 21
Optical Diagram of a Michelson Interferometer .............. . . 24
Original NIR Transflectance Spectra of Palm Oil Samples ......................................................... . 44
First Derivative Spectra of Palm Oil. ....................... , . . . . . 4 5
Plot Showing Calibration Data of F F A Content for CPO Obtained by MLR Analysis ........................... . . 5 1
Plot Showing Calibration Data of F F A Content for RBD Palm Olein Using MLR Analysis ..................... .. 52
Plot Showing Calibration Data of FF A Content for RBD Palm Oil Using MLR Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Plot Showing Validation Data of FF A Content for CPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Plot Showing Validation Data of FF A Content for RBD Palm Olein ............................................... . . 57
Plot Showing Validation Data of FF A Content for RBD Palm Oil. ................................................ . . 58
Overlaid ATR Spectra of CPO with Difference Concentration of FFA ........................................... . . 66
Plot of Percentage FFA vs. Absorbance @171 1 em'!
R2 = 0.986; SE = 0.06 ............................................ .. 67
Mean Spectrum Obtained from the CPO Calibration Standards ............................................................ . 69
Mean Spectrum Obtained from the RBD Palm Olein Calibration Standards ............................................. . . 70
x
17 Correlation Spectrum of CPO Calibration Standards Obtained Using FTIR Spectroscopy ...................... ' " . . . . . 7 1
18 Correlation Spectrum of RBD Palm Olein Calibration Set Using FTIR Spectroscopy ...................................... 7 2
1 9 Variance Spectrum Obtained from the CPO Calibration Standards ............................................... 74
20 Variance Spectrum Obtained from the RBD Palm Olein Calibration Standards Using F TIR Spectroscopy .............. 7 5
2 1 FF A Calibration Plot Constructed from CPO Calibration Standards ............................................... 7 8
22 FF A Calibration Plot Constructed from RBD Palm Olein Calibration Standards ........................................ 7 9
23 PRESS Plot from CPO Calibration Standards ................... 80
24 PRESS Plot from RBD Palm Olein Calibration Standards ......................................... ' " . . . . .. . . . . . . . .. . . 80
25 FF A Validation Plot for CPO Samples ........................... 82
26 FFA Validation Plot for RBD Palm Olein Samples ............ 85
27 Graph Showed the PV Generated in Oxidized CPO Through Time While Developing the Calibration Matrix ...... 94
28 Plot of First vs. Second PV Analyzed by Chemical Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
29 Mean Spectrum of 26 Samples Obtained from PV Calibration Set Using NIR Spectroscopy ........................ 96
30 A Typical Spectrum of CPO Using FTIR Spectroscopy ....... 98
30 Correlation Spectrum Obtained from PV Calibration Standards Using NIR Spectroscopy ............................... 101
32 PRESS Plot from PV Calibration Standards ..................... 103
33 Correlation Plot from Calibration Data of PV (meg/kg) in CPO by NIRS and Chemical Analyses ........................ 105
34 Correlation Plot from Validation Data of PV (meg/kg) in CPO by NIRS and Chemical Analyses ........................ 107
XI
35 The Effect of Different Solvents and Flow Rate on Adsorbents During the Extraction of Palm Carotene for the Development of Calibration Matrix ...................... Il7
36 Plot of First vs. Second Carotene Value Analyzed by UV -visible Spectrophotometry .................................... 119
37 Pure �-Carotene Spectrum Obtained Using FTIR Spectroscopy ................................................. 120
38 Overlaid Spectra of CPO Showing Different Concentration of �-Carotene Using FTIR ....................... 122
39 PRESS Plot from Carotene Calibration Standards Using FTIR Spectroscopy .......................................... 123
40 Calibration Plot of FTIR Predicted vs. Actual Spectrophotometry Carotene ...................................... 124
41 Mean Spectrum of 30 Samples Obtained from �-Carotene Calibration Set Using NIR Spectroscopy .......... 126
42 Correlation Spectrum Obtained from�-Carotene Calibration Standards Using NIR Spectroscopy ................. 128
43 PRESS Plot from Carotene Calibration Standards Using NIR Spectroscopy ........................................... 129
44 Calibration Plot ofNIR Predicted vs. Actual Spectrophotometry Carotene ...................................... 130
45 Validation Plot of FTIR Predicted vs. Actual Spectrophotometry Carotene ...................................... 131
46 Validation Plot of NIR Predicted vs. Actual Spectrophotometry Carotene ....................................... 132
47 FTIR Spectrum of an Empty Background ........................ 154
48 Spectrum of an Empty BaF2 Flow Through Transmission Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
49 Spectrum of DL-a Tocopherol from Omnic Library Showing the Major Absorption Bands ............................ 156
50 Spectrum of Unknown Aromatic Compound from Omnic Library Showing the Major Aromatic Bands ........... 157
xii
LIST OF PLATES
Plate Page
1 Near Infrared Spectroscopy (Bran+Luebbe, InfraA1yser 5 00) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9
2 "Dutch cup" or Gold Cup ......................................... . 159
3 Fourier Transform Infrared Spectroscopy (Perkin Elmer 1725 X) ............................................ . 160
4 Attenuated Total Reflectance Accessory (ZnSe 45°) .......... . 160
5 Fourier Transform Infrared Spectroscopy (Perkin Elmer 1600) ............................................... . 161
6 Near Infrared Spectroscopy (NIRSystem 65 00) .............. . . 161
7 Water Jacketed Chromatographic Column ..................... . 162
8 Rotary Vacuum Evaporator ..................................... . . 162
xiii
Abstract of the Thesis Presented to the Senate of Universiti Putra Malaysia in Fulfillment of the Requirements for the Degree of Master of Science.
DEVELOPMENT OF INFRARED SPECTROSCOPIC TECHNIQUES FOR THE DETERMINATION OF SOME QUALITY PARAMETERS
OF PALM OIL
B Y
FELIX MOH MEE HO
March, 1998
Chairman: Professor Yaakob Bin Che Man, Ph. D.
Faculty : Food Science and Biotechnology
Several parameters for good quality crude palm oil (CPO) and its
fractions such as free fatty acid (FF A), oxidative value, moisture and impurities,
iodine value and antioxidant composition are very crucial in palm oil industry.
For trading purposes in Malaysia, the standard of these quality parameters h ave to
be accomplished by all the refiners in accordance to the Palm Oil Refiners
Association of Malaysia (PORAM) standard specifications.
Conventionally, the analytical techniques used to analyze the quality
parameters in palm oil are by wet chemical methods based on the American Oil
Chemists' Society (AOCS) procedures which involve titration. Normally this
chemical techniques require large amount of chemicals and reagents which may
xiv
be unfriendly to environment and hazardous to health. Moreover, most analyses
are time consuming and laborious especially for large number of samples. To
overcome the problem, numerous studies on instrumental techniques have been
carried out over the years. From this standpoint, near infrared (NIR) spectroscopy
and Fourier transform infrared (FTIR) spectroscopy are considered the
instrumental approaches of choice.
1bree parameters were selected in the study. For the determination of
FF A, NIR transflectance and FTIR transmittance techniques were investigated.
Range of FF A concentration were prepared by hydrolyzing oil with 0.15% (w/w)
lipase in an incubator at 60°C (200 rpm). In NIR approach, sample preparation
was performed in Dutch cup and optimized calibration models were constructed
with mUltiple linear regression (MLR) analysis based on C=O overtone regions.
The best wavelength combinations were found to be 1882,2010 and 2040 nm for
CPO and refined bleached deodorized (RBD) oils. For FTIR technique, partial
least squares (PLS) analysis was used to replace the previous simple linear
regression model developed for predicting FF A. Both IR techniques showed
excellent results in predicting the FF A values of the unknown samples.
The determination of peroxide value (PV) was based on NIR
transmittance spectroscopy. Calibration standards (2 to 11 PV) were prepared by
oxidized CPO at 90°C. The best NIR region for predicting unknown was from
1350 to 1480 nm with referenced to single-point baseline at 1514 nm. The
standard error of performance (SEP) was similar to the calibration to within 0. 1 %
PV.
xv
The final aspect studied was the determination of p-carotene in CPO
using different techniques. Both FTIR and NIR spectroscopy were compared with
the UV -visible spectrophotometric reference method. PLS calibration model for
predicting p-carotene was developed for the FTIR spectral region from 976 to
926 em'] due to trans -CH=CH- conjugated deformation modes. The study
showed that NIR spectra did not correlate well with the component of interest.
However, highest correlation was found in the visible spectral region from 546 to
8 19 nm. Statistical results showed that both FTIR and NIR spectroscopy can
accurately predict {3-carotene to 5% error; this value was 4% higher as compared
to the reference method.
Results from this study indicated that both NIR and FTIR spectroscopy
were useful techniques for measuring palm oil quality parameters. Compared to
the conventional wet chemical method, NIR and FTIR spectroscopy are capable
of measuring hundreds of samples in a day and yet meet the trading specification.
In addition, by applying these techniques, the amount of hazardous solvents can
be reduced dramatically as well as the cost of labor.
XVI
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Sarjana Sains.
PENGEMBANGAN TEKNIK SPEKTROSKOPI INFRAMERAH UNTUK PENENTUAN BEBERAP A PARAMETER KUALITI BAGI
MINY AK SA WIT
OLEH
FELIX MOH MEE HO
Mac, 1998
Pengerusi : Profesor Yaakob Bin Che Man, Ph.D.
Fakulti : Sains Makanan dan Biotechnologi
Beberapa paraIlleter kualiti yang baik untuk minyak sawit mentah (CPO)
dan pecahan-pecaharmya seperti asid lemak bebas (FF A), nilai pengoksidaan,
lembapan dan bendasing, nilai iodin dan kandungan antioksida adalah penting
dalaIll industry minyak kelapa sawit. Bagi tujuan perdagangan di Malaysia,
piawaian untuk kualiti paraIlleter-paraIlleter tersebut mesti dicapai oleh semua
pengilang-pengilang sejajar dengan spesifikasi piawaian Persatuan Pengilang-
pengilang Kelapa Sawit Malaysia (PORAM).
Secara lazimnya, teknik-teknik analisis yang digunakan untuk
menganalisis paraIlleter-paraIlleter bagi sawit adalah secara kimia basah
berdasarkan prosedur AOCS yang melibatkan titrasi. Kebiasaarmya teknik kimia
XIV
tersebut memerlukan sejumlah besar bahan-bahan kimia yang diantaranya
mungkin tidak mesra dengan alam sekitar dan merbahaya kepada kesihatan.
Bahkan kebanyakan analisis kimia tersebut memeriukan masa yang lama serta
rumit terutamanya bagi jumlah sampel yang banyak. Untuk mengatasi masalah
ini, beberapa kajian teknik instrumentasi telah dijalankan sejak beberapa tahun
dahulu. Dari segi ini, spektroskopi inframerah dekat (NlR) dan transformasi
Fourier spektroskopi inframerah (FTIR) menjadi pilihan untuk pendekatan
instrumentasi.
Dalam kajian ini, tiga parameter telah dipilih. Bagi penentuan FF A, teknik
transflektan NIR dan FTIR telah dikaji. Julat kepekatan FF A disediakan dengan
menghidrolisis minyak dengan 0.15% (w/w) lipase di dalam inkubator pada suhu
60°C (200 rpm). Bagi pendekatan NIR, penyediaan sampel dilakukan di dalam
cawan Dutch dan model kalibrasi pengoptimuman dibentuk dengan analisis
multipel linear regresi (MLR) berdasarkan pada daerah overtone C=O.
Kombinasi panjang gelombang yang terbaik diperolehi pada 1882, 2010 dan
2040 nm untuk CPO dan minyak tulin, terluntur dan temyahbau (RBD). Untuk
teknik FTIR, analysis 'partial least squares' (PLS) telah digunakan untuk
menggantikan model regresi linear yang sebelum ini dibangunkan bagi
menganggar FF A. Kedua-dua teknik IR tersebut menunjukkan keputusan terbaik
dalam menganggar nilai FF A bagi sampel yang tidak diketahui.
Penentuan nilai peroksida (PV) adalah berdasarkan kepada spektroskopi
transflektan NIR. Piawaian kalibrasi (2 hingga I I PV) dibuatkan dengan
menyediakan CPO beroksida pada 90°C. Daerah NIR tebaik bagi menganggarkan
sampel yang belum diketahui adalah pada 1350 hingga 1480 nm dengan merujuk
xviii
kepada 'single-point baseline' pada 1514 run. 'Standard error of performance'
(SEP) yang diperolehi adalah bersamaan dengan kalibrasi dalam lingkungan
O.l%PV.
Aspek terakhir yang telah dikaji adalah penentuan j3-karotin sawit. Kedua
dua spektroskopi FTIR dan NIR dibandingkan dengan kaedah 'UV-visible'
spektrophotometri dalam penentuan j3-karotin di dalam CPO menggunakan
model pendekatan transmisi. Model kalibrasi PLS untuk menganggar j3-karotin
telah dibangunkan pada daerah spektra FTIR pada 970-926 cm·1 yang disebabkan
oleh trans-CH=CH- mod konjugat pembentukan semula. Dalam kajian ini, ia
menunjukkan bahawa spektra N1R tidak berkorelasi dengan komponen
komponen yang dikaji. Bagaimanapun, korelasi didapati paling tinggi pada
daerah spektral tampak dari 546-819 run. Keputusan analisis statistik
menunjukkan bahawa FTIR dan NIR telah dapat menganggar j3-karotin dengan
tepat ke tahap 5% kesilapan iaitu 4% lebih tinggi berbanding dengan kaedah
rujukan.
Keputusan daripada kajian ini menunjukkan bahawa kedua-dua cara
spektroskopi NIR dan FTIR merupakan teknik yang lebih berkesan digunakan
untuk mengukur parameter kualiti minyak kelapa sawit berbanding dengan
kaedah kimia basah yang lazim. Spektroskopi NIR dan FTIR berkeupayaan
mengukur beratus sampel sehari dan masih mampu memenuhi spesifikasi
perdagangan. Disamping itu, melalui pengunaan teknik ini jumlah penggunaan
pelarut yang merbahaya dapat dikurangkan secara dramatik dan juga kos tenaga
kerja.
XIX
CHAPTER 1
INTRODUCTION
The crude palm oil (CPO) is extracted from the fleshy portion
(mesocarp) of the fruits of the oil palm. In Malaysia, commercial oil palm
cultivated today, Elaeis guineensis Jacq., is the high yielding hybrid of Dura x
Pisifera known as Tenera (Pantzaris, 1987). Palm oil is a very versatile oil with a
range of distinct properties which enable it to meet most of the technological
requirements for formulation of fat based products. About 90% of the palm oil
currently goes into food application and the remaining 1 0% into non-food
products. Apart from its direct use in cooking and frying, palm oil is also used in
margarines, vanaspati, confectioneries, filled milk and many more products after
fractionation, hydrogenation or interesterification processes.
In order to produce quality finished products of palm oil, the control
of raw material, extraction processes and refining processes are essential. The
quality is indicated by means of several quality parameters namely iodine value
(IV), peroxide value (PV), free fatty acid (FF A) content, moisture, impurities and
etc. For trading purposes in Malaysia, the standard of these quality parameters
have to be accomplished by all the refiners in accordance to the Palm Oil Refiners
Association of Malaysia (PORAM) standard specifications.
1
2
Conventionally, the analytical techniques used to analyse the quality
parameters are by the wet chemical titration methods based on the American Oil
Chemists' Society (AOCS) procedures (AOCS, 1 989). The estimation of FFA,
for instance, is done by titration of the palm oil with an alcoholic solution of
potassium or sodium hydroxide. The end point is determined when permanent
pink colour is obtained using phenolphthalein as indicator. The determination of
IV in palm oil is time consuming which takes more than an hour per sample.
Other procedures use substantial amounts of chemicals and reagents during
analyses. Besides, solvents used in prediction of IV like carbon tetrachloride are
normally not environmental friendly as well as being a health hazard.
To overcome these problems, many laboratories are developing
modem instrumentation analytical procedures to replace the conventional
method, consequently, reduces the usage of hazardous chemicals and the labor
costs dramatically. The most common instrumental analyses in fats and oils
laboratories are high performance liquid chromatography (HPLC) and gas
chromatography (GC). They have been used in separating and quantifying
triglycerides (Plattner et aI., 1977), fatty acid methyl ester (Yoshida et aI., 1 992)
and also antioxidants such as tocols and carotenoids (Weber, 1 987).
In high-tech laboratories, sophisticated infrared (IR) spectroscopic
techniques have also been implemented in fats and oils analyses. Fourier
transform infrared (FTIR) spectroscopy operates in mid-IR region is an example.
It has been used extensively to determine the moisture content (Hartwig and
3
Hurburgh, 1 990) and to identify the trans fatty acid composition (Sleeter and
Matlock, 1 989). van de Voort and coworkers ( 1 993; 1 994a) developed several
calibration methods based on FTIR to measure some of the quality parameter in
edible oils such as IV, FFA and PV. Near infrared (NIR) on the other hand has
less been used. However, this technique also shows potential in fats and oils
analyses. Dong et al ( 1 997) has successfully measured the PV in variety of edible
oil using FT -NIR.
Based on a number of studies done on IR spectroscopy, it was
postulated that they can be ideal methods in palm oil analyses. The objectives of
this study were to develop IR spectroscopic methods to determine some of the
quality parameters in palm oil as follows:
1 . To determine the free fatty acid contents in palm oil using NIR and FTIR
spectroscopy
2. To measure peroxide value in thermally oxidized palm oil with NIR
spectroscopy
3. To compare NIR and FTIR spectroscopic methods with UV -visible
spectrophotometer in palm carotene analysis
CHAPTER 2
REVIEW OF LITERATURE
Production and Characteristics of Palm Oil
Origin and Agronomy
The commercial oil palm, Elaeis guineensis Jacq., cultivated in
Malaysia is known as tenera which is produced by crossing largely dura with
selected pisiferas varieties originated from Africa (Yap et al., 1991). It was first
introduced into Malaysia in 1870 as an ornamental plant. However, the first
commercial planting did not seriously take place until 19 17 (Pantzaris, 1987).
Oil palm grows well in tropical condition. It produces highest yield in
a climate with rainfall of 80 inches or more per year and with no marked dry and
wet seasons (PO RIM, 1985). The mean maximum temperature of about 29°C to
3 2°C and minimum temperature from 22°C to 24°C is suitable for the growth of
oil palm. Under the right plantation conditions, the rate of growth is about I to 2
feet per year and have a lifespan of more than 100 years. However, for
commercial palm, the palm is likely to be cut down and replanted after 25 years.
This is due to the decrease in yields and the increase of height which makes
harvesting difficult.
4
Production
Before 1 975, almost all of Malaysia's palm oil exports were in crude
form. After the introduction of physical refining plants, most of the attention has
shifted from plantations and mills to the refineries. In 1 993, export of processed
palm oil, amounted to 6.0 million tonnes (98%) compared to 1 02 tonnes for CPO.
The detail of the export of palm oil and its products is given in Table 1 .
Within a relatively short span of time, the planted areas under oil palm
increased tremendously (Table 2). In 1 960 the total planted area was 54,700
hectares but by 1 970 it had reached 290,000 hectares. In 1 993, a total of 2.3
million hectares had been planted. It is expected that in the year 2000 about 2.9
million hectares of land will be planted with oil palm (PORIM, 1 995a).
Physiochemical Characteristics
The physical and chemical properties of Malaysian CPO are given in
Table 3. Like all other vegetable oils and fats, palm oil composed predominantly
of triglycerides (or tri-ester) which are derived from one molecule of glycerol and
three molecules of fatty acids (Sonntag, 1 979). A mixed triglyceride is formed
when gylcerol reacts with different fatty acids. The profiles of triglyceride
molecular species are characteristic of the genetic background of the sources of
oils and fats (Litchfield, 1 972).
In contrast to other non-lauric oils, in commercial use, palm oil is