TABLE OF CONTENTs
Title page ii
Certification iii
Dedication iv
Acknowledgements v
Title of contents vi
List of table xi
List of figures xii
Abbreviations xiv
Abstract xv
1.0 CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction 1
1.1.1 Background of Problem 2
1.1.2 Statement of Problems 4
1.1.3 Justification of the Research Work 6
1.1.4 Scope of Work 6
1.1.5 Aim and Objectives 7
1.2 Literature Review 8
1.2.1 Vegetable Oil 8
1.2.1.1 Sources of Vegetable Oil 8
1.2.1.2 Characterization of Fats and Oils 9
1.2.2 Nonglyceride Components of Fats and Oils 12
1.2.2.1 Phospholipids 12
1.2.2.2 Tocopherols and Tocotrienols 14
1.2.2.3 Sterols 17
1.2.2.4 Pigments 17
1.2.2.5 Pesticides 19
1.2.2.6 Trace Metals 20
1.2.3.1 Applications of vegetable oil in Food Preparations 20
1.2.3.2 Industrial Applications 21
1.2.4 Palm Oil 22
1.2.4.1 Palm Oil Composition and Physical Properties 22
1.2.5 Peanut Oil 23
1.2.5.1 Peanut Oil Composition and Physical Properties 24
1.2.6 Vegetable Oil Extraction 25
1.2.6.1 Mechanical Pressing 26
1.2.6.2 Chemical Methods 26
1.2.6.5 Supercritical Fluid Extraction (SFE) 28
1.2.6.6 Steam Distillation 30
1.2.7 Vegetable Oil Refining 30
1.2.7.1 Degumming 31
1.2.7.2 Neutralizing 31
1.2.7.3 Bleaching 31
1.2.7.4 Winterizing 32
1.2.7.5 Dewaxing 32
1.2.7.6 Deodorizing 32
1.2.8 Oxidation of Vegetable Oil 33
1.2.8.1 Mechanisms of Autoxidation in Edible Oil 35
1.2.8.2 Mechanisms of Hydroperoxide Decomposition to form 37
Secondary Oxidation Products
1.2.8.3 Protection against Oxidative Deterioration 39
1.2.8.14 Synergistic Antioxidant Mixtures 48
1.2.9 Fats and Oils Analysis 49
1.2.9.1 N on-Fatty Impurities 50
1.2.9.2 Moisture Analysis 50
1.2.9.3 Trace Metals Analysis 51
1.2.9.4 Soap Analysis 51
2.1.9.5 Composition Analysis 52
1.2.9.6 Saponification Value 53
1.2.9.7 Iodine Value 53
1.2.9.8 Rancidity Analysis 56
1.2.9.9 Peroxide Value 56
1.2.9.10 Anisidine Value 58
1.2.9.11 Smoke Point 58
1.2.9.12 Colour and Appearance 59
1.2.9.13 Lovibond (British Standard) 60
1.2.10 UV Spectroscopy 61
1.2.10.1 Applications of UV spectroscopy for Vegetable Oil analysis 61
1.2.10.2 The Basic Principle of UV Spectroscopy 62
1.2.10.3 Instrumentation and Working of UV Spectroscopy 63
1.2.11 Electrical Conductivity 64
2.0 CHAPTER TWO: MATERIALS AND METHODS
2.1 Materials 67
2.2 Method 68
2.2.1 Determination of Peroxide Value 68
2.2.2 Determination of Iodine Value 69
2.2.3 Determination of electrical conductivity of the vegetable 71
oils
2.2.4 Determination of the absorbance at 233 nm of the UV 71
spectrum
2.2.5 Statistical Analysis 71
3.0 CHAPTER THREE: RESILTS AND DISCUSSION
3.1 Changes in properties of groundnut oil and palm oil over 74
storage
3.2 Correlation studies 78
3.3 Conclusion 88
3.4 Recommendation 89
REFERENCES 90
LIST OF TABLES
Table 3.1 Changes in the Peroxide Value (PV), Iodine Value (IV), Absorbance at
233nm (A233nm) and Electrical Conductivity (EC) of Groundnut Oil
and Palm Oil.
LIST OF FIGURES
Fig. 1: Reaction between fatty acids and glycerol to form triglyceride
Fig. 1.2: general structure of phospholipids
Fig. 1.3: General structure for tocopherol
Fig. 1.4: General structure of tocotrienol
Fig. 1.5: Beta Carotene
Fig. 1.6: Gossypol Fig 3.1 Changes in properties of groundnut oil over storage
Fig 3.2: Changes in the properties of palm oil over storage
Fig 3.3 Plot of Iodine Value (IV) against Peroxide Value (PV) for Groundnut Oil
Fig 3.4: Plot of Iodine Value (IV) against Peroxide Value (PV) for Palm Oil
Fig 3.5: Plot of Iodine Value (IV) against Absorbance at 233nm for Groundnut Oil
Fig 3.6: Plot of Iodine Value (IV) against Peroxide Value (PV) for Palm Oil
Fig 3.7 Plot of Iodine Value (IV) against Electrical Conductivity (EC) for Groundnut Oil
Fig 3.8: Plot of Iodine Value (IV) against Electrical Conductivity (EC) for Palm Oil
Fig 3.9: Plot of Electrical Conductivity (EC) against Absorbance at 233nm for Groundnut Oil
Fig 3.10: Plot of Electrical Conductivity (EC) against Absorbance at 233nm for Palm Oil
Fig 3.11: Plot of Electrical Conductivity (EC) against Peroxide Value (PV) for Groundnut Oil
Fig 3.12: Plot of Electrical Conductivity (EC) against Peroxide Value (PV) for Palm Oil
Fig 3.13: Plot of Peroxide Value (PV) against Absorbance 233nm (A233) For Groundnut Oil
Fig 3.14: Plot of Peroxide Value (PV) against Absorbance 233nm (A233) For Palm Oil
abbreviations
A233nm Absorbance at 233nanometer
EC Electrical conductivity
FA Fatty acid
IV Iodine value
GO Groundnut oil
UV Ultraviolet
PO Palm oil
PV Peroxide value
ABSTRACT
Groundnut oil (GO) and palm oil (PO) were stored in opaque plastic containers at room temperature and the peroxide value (PV), iodine value (IV), UV absorbance at 233nm (A233nm) and the electrical conductivity (EC) were determined every two days over a one-month period. The peroxide value and iodine value were determined using standard AOAC method. The absorbance values were determined with a UV/Vis. spectrophotometer and the electrical conductivity with a conductivity / DO meter. The peroxide value, absorbance and electrical conductivity increased while the iodine values decreased during storage. The changes in properties before and after storage for groundnut oil were: PV( 6.5 -15.5), IV(89.0-86.7 ), A233nm (0.380-0.798 ) and EC(4.06 -6.62). That for palm oil were PV(4.1 – 8.80), IV(52.9 – 49.0), A233nm(0.610-1.350) and EC(6.42-10.00). With respect to the relationship between the parameters, the graphs of IV/PV, IV/A233nm and IV/EC showed strong negative correlations, while the graphs of EC/A233nm, EC/PV and PV/A233nm showed strong positive correlations. The strongest correlation was obtained for the graph of EC/PV for PO with r = 0.989 (p < 0.05). The strong r values obtained for all the plotted graphs means that the chemical parameters used in the study are highly associated. The corresponding regression equations can be used to predict the value of one parameter when the other is known. This might be useful in routine industrial quality control. ChApter one
1.0 INTRODUCTIONEdible oils from plant sources are of importance in some industries. They provide characteristic flavours and textures to foods as integral diet components (Odoemelam, 2005) and can also serve as sources of oleochemicals (Morrison et al., 1995). Oleochemicals are completely biodegradable and so could replace a number of petrochemicals. In Nigeria, the major sources of vegetable oils are groundnut also called peanut (Arachis hypogaea L.) and oil palm (Elaeis guineensis). These oils are used mainly as cooking oil and for the production of soap, margarine, and cosmetics (Ong et al., 1995). Peanut is an important source of edible oil for millions of people living in the tropics. In Nigeria, 1917 tons of peanuts are being produced annually (Ergül, 1988). Peanuts are among the oldest oil crops in Nigeria and are mostly consumed as snack, after roasting. Vegetable oils have made an important contribution to the diet in many countries, serving as good sources of protein, lipid and fatty acids for human nutrition including the repair of worn out tissues, new cell formation, as well as a useful source of energy (Gaydou et al., 1983). In recent years, vegetable oils are becoming increasingly important in industrial (non-food) applications. In particular, they are used as feedstocks for the production of fatty acid methylesters (FAME) through transesterification reaction, in applications as diverse as biofuels (biodiesel) (Knothe, 2005; Romano, 2006), insulating fluids in power systems ( Keshavamurthy, 1999) and the production of inks (Wang, 2002) . The widespread use of vegetable oils makes necessary a better characterization of their properties. Oil quality and its stability are therefore very important for the consumers and application industries. Thus, the study of the changes in quality properties such as peroxide value, iodine value, electrical conductivity and UV absorbance at 233nm of groundnut and palm oil during storage and investigation of the relationship between these properties are important. These aspects have been covered in the present studies
Background of Problem
Vegetable oil is an important and widely used lipid source in everyday diet. Its application is increasing day by day for food purposes and for the manufacturing of a number of toiletry products. However, some vegetable oils do not meet stipulated standards by way their physico-chemical properties or for the texture and stability of the food products (Reyes- Hernandez et al., 2007)
The dynamics of oil deterioration mostly due to oxidation depends upon the fatty acid content and presence or absence of antioxidants and pro-oxidants. Oxidative and hydrolytic degradations are main reactions occurring during and after oil processing that reduce shelf life and result in low quality products (Rajko et al., 2010).
The quality of vegetable oils are evaluated by several physical and chemical parameters that are dependent on the source of oil, processing and storage conditions. Some physical parameters (moisture content, refractive index, viscosity, specific gravity, colour, etc) and chemical parameters (smoke point, saponification value, acid value, iodine value, ash content and peroxide value), can be used to evaluate the purity and quality of oils (Mohammed and Ali, 2015).
Studies have shown that there are changes in the properties of vegetable oils over time. Work on peroxide value and iodine value of palm oil and groundnut oil by Akin-osanaiye et al. (2015) showed that there was an increase in peroxide value and a decrease in iodine value over time.
Zhou et al. (2011) developed a method for measuring quality of oils by determining the electrical conductivity( EC) values of oils, and the results obtained using the EC method and those obtained using the other methods were highly consistent; moreover, the EC method showed good repeatability. However, the accuracy was not good, because the EC values were lower and the error in instrument reading was large. In addition, the results obtained using the EC method represented the total EC value. Yu et al. (2012) improved this method to determine the FFA content in edible oils based on the changes of EC values of a potassium hydroxide solution layer during the reaction of potassium hydroxide with the FFA. These results indicated that the EC method could be applied to detect the quality of oils. The method was simple and practicable. This work examines the changes in some physico-chemical quality parameters of groundnut and palm oil during short-term storage (one month)
Statement of Problems
There is no doubt that a lot has been put into the study of the properties of vegetable oils. Many different methods have been developed overtime but most of them have one problem or the other. Vegetable oils are widely employed in the food industry, but they get easily oxidized during processing, circulation, and preservation. The oxidation of fats and oils in food can result in food toxicity (Gotoh et al., 2011). From the perspectives of food quality and safety, the determination of the peroxide value (PV) is one of the most important quality control measurements for edible oils because it is an indicator of the primary oxidation status of the oils (Akinoso et al, 2010).
Over the past few years, a relatively large number of methods have been developed for determining peroxide value (PV) of edible oils. The conventional American Oil Chemist Society (AOCS) (2003) method used for determining the PV involves iodometric titration that measures the iodine liberated from potassium iodide (KI) after reacting with the peroxides present in oil samples (Cirlini et al., 2012), and other PV standard determination methods such as Association of Official Analytical Chemists (AOAC) (1990), Commission Regulation of European Economic Community (EEC) (1991), and International Union of Pure and Applied Chemistry (IUPAC) (1991) methods, are similar to AOCS method; these methods are labour-intensive, time consuming, requires a large amount of lipids, and more importantly, its accuracy depends strongly on the analytical conditions (Armenta et al., 2007).
A lot of work has been done on the electrical properties of vegetable oils as a possible substitute for mineral oil in transformers (Lakrai et al., 2013; Shah and Tahir, 2011)
The iodine value can be determined by the AOCS Method Cd 1-25 by adding an excess of Wij’s reagent to the sample, while the absorbance can be determined using a UV spectrophotometer. All these methods use one chemical or the other; some methods are very expensive while some take a lot of time.
1.1.3 Justification of Research Work
As earlier said a lot of research work has been done in the study of the properties of vegetable oils, but much has not been done to study the relationship between these properties.
This work intends to study the chemical properties (peroxide value and iodine values), electrical property ( electrical conductivity) and the UV absorbance at 233nm of groundnut and palm oils over a one-month storage period and examine the relationship between the properties via regression analysis. These analyses could be used to predict the value of one parameter, if the other is known. This could help to save cost and time in industrial quality control.
1.1.4 Scope of Work
This project involves purchasing vegetable oils (groundnut and palm oils) from a local market, analysing for initial values of the parameters and monitoring the quality parameters over a-month storage period. The properties of interest are peroxide value, iodine value, absorbance at 233nm and electrical conductivity of the oils. Regression equation will be provided and the correlation coefficient (r) between quality parameters will be obtained.
