THE EFFECT OF CONTINOUS FRYING ON DIFFERENT EDIBLE VEGETABLE OIL A COMPARATIVE STUDY

ABSTRACT Cooking was a breakthrough for mankind that improved the flavor, digestibility and quality of food. This breakthrough is seen in a lot of cooking methods such as boiling, poaching, stewing, baking, roasting, microwaving and deep frying. Heat treatment is an operation widely used in food processing. People especially in developing countries believe in the need to manage resources, while giving less attention to the risk associated with what is consumed. As heat- processed foods are much appreciated, deep-fat frying produces desirable or undesirable flavor compounds and changes the flavor, stability and quality of the oil by hydrolysis, polymerization and oxidation. Oxidation involves the formation and propagation of lipid radicals, the uptake of oxygen, the rearrangement of the double bonds in unsaturated lipids and the eventual destruction of membrane lipids, producing variety of breakdown products, such as alcohols, ketones, alkanes and  aldehydes.  Reuse  of  heated  oil  accelerates  oxidative  degradation  of  lipids,  forming hazardous reactive oxygen species and depleting the natural antioxidant contents of the cooking oil. Samples of the oils were separately heated for thirty minutes. Sample of each oil was collected and analyzed before and after heating. Comparative study of the four edible oil before and after frying showed that the heating had a very distinct impact on the iodine value (IV), peroxide value (PV), acid value (AV), free fatty acid (FFA), p-anisidine value (p-AV), thiobarbituric acid (TBA), saponification value (SV), unsaponifiable matter (UM) and fat soluble antioxidant vitamins (A. D. E. K.). The samples were heated at 180 °C for different periods of time (10, 20 and 30 minutes). Saponification value, acid value, free fatty acid contents, iodine value and peroxide value were determined by titrimetric method. The chemical analysis showed that there was a significant (p < 0.05) difference in terms of the peroxide value, acid value, free fatty acid contents, TBA value and p-AV for each frying oil during the heating process. Heating process led to considerable increase. Results of IV, SV, UM and antioxidant vitamins further showed a progressive decrease for the frying oil during heating process. The results further indicates that there was a significant decrease in oil stability during heating process for the antioxidant  fat  soluble  vitamins.  Results  showed  that  palm  oil  had  the  highest  β-carotene contents, which was reduced progressively as the experimental time increased. The fatty acid profiles of the oil samples were not exactly the same. The difference may be either due to the method  of  processing  or  the  manufacturer’s  inconsistency.  Finally,  this  study  is  to  further increase awareness of the risk posed on consumer’s health, regarding the use of these oils repeatedly.

CHAPTER ONE

INTRODUCTION

There is an ever-increasing demand for oil/fat from plants (Borawski et al., 2016). The oils are used  mainly  for  nutritional  purposes.  For  instance,  palm  oil  and  groundnut  oil  are  highly nutritious and good sources of vitamin A (Falade et al., 2017). It has been suggested in recent years that the world is undergoing a nutrition transition, characterized by Western diet, high in saturated fats, sugar, and processed foods (Lieberman, 2003). On an evolutionary scale, the consumption of lipids from refined vegetable oils is a relatively recent phenomenon, dating back to 6000 years for the cultivation of olive oil (Cordain et al., 2005). Several other edible oil crops have enjoyed a similar history of cultivation  as olive oil. For example, archaeological and documentary evidence suggests that sesame oil competed with the olive in the Mediterranean basin and India from at least 1137 BC; the Aztecs produced groundnut oil in South America long before the arrival of European settlers in the fifteenth century; and palm oil originated in West Africa. But only in the last century did the biggest changes occur in global lipid consumption. These changes can be attributed to the Industrial Revolution, in which a combination of technological development and the beginnings of large-scale food production resulted in a truly global market (O’Rourke and Williamson, 2002; Cordain et al., 2005).

Lipids  are  considered  one  of  the  most  elemental  nutrients  for  humans.  Lipid  metabolism generates many bioactive lipid molecules, which are fundamental mediators of multiple signaling pathways and they are also indispensable compounds of cell membranes. Any kind of changes in lipid  metabolism  can  result  in  modification  of membrane  composition  and  subsequently  in changes in its permeability. It may also lead to disruption of signaling networks and could be associated with some pathological states, such as cancer, cardiovascular, neurodegenerative, and metabolic diseases, and similarly with inflammatory complications (Mišurcová  et al., 2011; Brenna et al., 2009). Lipids consist of fatty acids (FAs) classified mostly according to the presence or absence of double bonds as saturated (SFAs—without double bonds), monounsaturated (MUFAs—with one double bond) and polyunsaturated fatty acids (PUFAs with two or up to six double bonds); further, as cis or trans based on the configuration of the double bonds and as n-3 or n-6 PUFAs depending on the position of the first double bond from the fatty acid methyl-end. The human body cannot synthesize PUFAs with the first double bond on C-3 and C-6 from the methyl-end because of the absence of appropriate enzymes. Thus, these fatty acids are essential (EFAs) and they have to be obtained from a diet, particularly by the consumption of fish and fish oils (Brenna et al., 2002; Huang et al., 2015).

Fats and oils have always been an integral part of the human diet. Of prime importance is their role as a calorie-dense food component-they have nine kilocalories per gram versus four kilocalories per gram for starch or protein. The present-day concern with obesity and high fat content  is  actually  a  historical  and  geographical  anomaly.  For  the  greater  part  of  human existence, the search for adequate food energy sources occupied a large segment of time, and fat was a prized component of the diet (Cordain et al., 2005).

Oils  and  fats  are  important  parts  of  human  diet  and  more  than  90  per  cent  of  the  world production from vegetable, animal and marine sources is used as an ingredient in food products or as food. Oils and fats are a rich source of dietary energy and contain more than twice the caloric value of equivalent amount of sugar. Their functional and textural characteristics contribute to the flavour and palatability of natural and prepared foods (The State of Food and Agriculture 2012).

According to the importance of edible vegetable oils and their effects on the quality and texture of food, vegetable oils are liquid plant products mainly composed of the glycerides of the fatty acids. They are termed triglycerides and are esters of glycerol (Igwe, 2003). Disregarding the realm of food manufacture, vegetable oils are widely used in a diversity of industries. They are mainly used in manufacturing soap (which is by far the most important) and are actively utilized in the production of paints, varnishes, lubricants and plastics. Vegetable oils with negligible sulfur, nitrogen and metal contents are renewable, available and non-polluting energy resources. Due to these important characteristics, they are regarded as suitable materials for purposes other than food. For instance, alternative uses, like biodiesel production, are being investigated (Karaosmanoglu & Kurt, 1998; Kim et al., 2010). Currently, vegetable oils are mainly employed in nutrition.

Cooking was a breakthrough for mankind that improved the flavor, digestibility and quality of food. Heat treatment is an operation widely used in food processing. As heat-processed foods are much appreciated, analytical studies that can assess the changes caused by heating have been demanded from researchers (Lambelet et al., 2003). One of such changes is the production of peroxides.

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The peroxides turn into aldehydes, ketones, epoxides, dimers and polymers, undermining the quality of food. In order to minimize such effects, the food industry makes use of antioxidants (Litwinienko et al., 1999). A lot of cooking methods are used in catering, hotel industry and in household.  The  cooking  methods  or  cookery  processes  are  as  follows:  boiling,  poaching, stewing, braising, steaming, baking, roasting, pot roasting, grilling, shallow frying, deep frying, microwaving. Each is specific and has its advantages and disadvantages. Deep frying is cooking food in pre-heated deep oil or fat (Aladedunye et al., 2009).

1.1       Deep frying

Conventional deep-fried foods (except potatoes) are coated with milk and flour, egg and crumbs, batter or pastry to protect the surface of the food from the intense heat, to prevent the escape of moisture and nutrients and to modify the rapid penetration of the intense heat. The food is placed into deep pre-heated oil or fat, fried until cooked and golden brown, drained and served.

1.2       Lipids

Lipids are biological molecules characterized by their insolubility in water and solubility in nonpolar organic solvents. They are naturally occurring derivatives of fatty acids. Most lipids are amphipathic molecules,  which interact with other molecules and  with  aqueous solvents via hydrogen  bonds  and  electrostatic  interactions  (Brandt,  2011).  Plant  lipids  in  the  form  of vegetable oils have been extracted and processed for various non-food uses by people for well over 7000 years. The most abundant plant lipids are acyl (fatty acid containing) molecules such as phospholipids, glycolipids, and triacylglycerols. Other important lipids include sterols, carotenoids, tocopherols, phytols, and waxes (Murphy, 2012).

1.2.1    Vegetable Oils

Vegetable oil can be narrowly defined as referring only to oily substances that are liquid at room temperature, or broadly defined without regard to a substance’s state of matter at a given temperature. For this reason, vegetable oils that are solid at room temperature are sometimes called vegetable fats (Zielinska and Nowak, 2014).

Vegetables oils can be obtained from plant sources like soya beans, groundnut, shea butter, oil palm, melon, corn, coconut, etc. Oils such as palm, olive and corn, are pressed out of its endosperm portion. Some of these vegetable oils are used for domestic (edible) and industrial purposes. On the other hand, most vegetable oils are extracted from seeds, fruits and nuts of plants  by  pressing  and/or  solvent  extraction  (Aluyor  and  Ori-jesu,  2008).  Unlike  butter  or coconut oil, these vegetable oils can’t be extracted just by pressing or separating naturally. They must be chemically removed, deodorized and altered (Jun et al., 2016).

1.2.1    Minor Components

The minor components of vegetable oils include:

1.   Free Fatty Acids: Free fatty acids are the unattached fatty acids present in a fat. Some unrefined oils may contain as much as several percent free fatty acids while others may not. The levels of free fatty acids are reduced in the refining process. Fully refined fats and oils usually have a free fatty acid content of less than 0.1% (Zielinska and Nowak, 2014).

2.   Mono- and Diglycerides: Mono- and diglycerides are mono- and diesters of fatty acids and glycerol. They occur naturally in very minor amounts in both animal fats and vegetable oils. Oil composed mainly of diglycerides has also been used as a replacement for oil composed of triglycerides (Zielinska and Nowak, 2014).

3.   Sterols: Sterols are found in both vegetable oils and animal fat, but there are obvious biological differences between them. Cholesterol is the primary animal fat sterol and is found in trace amounts in vegetable oils. Vegetable oil sterols are collectively called “phytosterols.” Stigmasterol and sitosterol are the best-known vegetable oil sterols. The type and amount of vegetable oil sterols vary with the source of the oil (Zielinska and Nowak, 2014).

4.   Phosphatides: This is also known as phospholipids, consisting of an alcohol (usually glycerol) combined with fatty acids, and a phosphate ester. The majority of the phosphatides are removed from oil during refining. Phosphatides are an important source of natural emulsifiers marketed as lecithin (Zielinska and Nowak, 2014).

5.   Pigment: Carotenoids are yellow to deep red color materials that occur naturally in fats and oils. They consist mainly of carotenes such as lycopene, and xanthophylls such as lutein. Palm oil contains the highest concentration of carotene. Chlorophyll is the green coloring matter of plants which plays an essential role in photosynthesis. Canola oil contains the highest levels of chlorophyll among common vegetable oils.  The levels of most of these color bodies are reduced during the normal processing of oils to give them acceptable color, flavor, and stability (Zielinska and Nowak, 2014).

6.   Tocopherols and Tocotrienols: Tocopherols and tocotrienols are important constituents of most vegetable fats. They serve as antioxidants to retard rancidity and as sources of the essential nutrient vitamin E. The common types of tocopherols and tocotrienols are alpha (α), beta (β), gamma (γ), and delta (δ). They vary in antioxidation and vitamin E activity. Among tocopherols, alpha-tocopherol has the highest vitamin E activity and the lowest antioxidant activity. Delta tocopherol has the highest antioxidant activity. Tocopherol

which occur naturally in most vegetable oils are partially removed during processing

(Zielinska and Nowak, 2014).

1.3       Some types of vegetable oil

1.3.1    Palm oil

Palm oil is extracted from the ripened mesocarp of the fruits of oil palm tree (Elaeis guineensis). The oil palm fruit is a drupe formed in spiky tight bunches. The five leading producing countries are Indonesia, Malaysia, Thailand, Colombia and Nigeria. The oil palm tree gives the highest yield of oil per unit area of cultivated land, an estimated 58.431 million metric tons (MT) per year. One hectare of oil palm plantation is able to produce up to 10 times more oil than other leading oilseed crops. Palm fruit produces two distinct types of oils: crude palm oil (CPO) from the mesocarp and palm kernel oil (PKO) from the inside kernel. Palm oil has a unique fatty acid (FA) and triacylglycerol (TAG) profile which makes it suitable for numerous food applications. It is the only vegetable oil with almost 50 –50 composition of saturated and unsaturated fatty acids. Palm oil is a mixture of different fatty acids; saturated, unsaturated and polyunsaturated fatty acids, depending on the presence and number of double bond(s) or indeed the absence of it. However it contains by higher proportion more of the saturated fatty acids. Palm oil is top prime among frying oils. The hot oil serves as a medium of heat and mass transfer. During frying, some of the oil is absorbed by the product, while moisture in the form of vapor is given off. Thus, frying combines cooking and drying. Important chemical and physical changes occur during frying. Examples are starch gelatinization, protein denaturation, water vaporization and crust formation (Mattson et al., 1985). Fried food quality is a function of oil quality. The degradation of cooking oils affects the texture, taste, and overall flavor perception of the food (Tan, 2003).

1.3.2    Olive oil

People in the Mediterranean region generally consumed high fat diet rich in olive oil, yet they have low incidence of cardiovascular disease as compared to other Western countries (Keys,1970). Olive oil is highly enrich in oleic acid and epidemiologists assumed that oleic acid was

the reason for the low cardiovascular disease incidence in the Mediterranean countries. Mattson and Grundy (1985) using a liquid formula diet showed that high-oleic-acid safflower oil was as hypocholesterolemic as high-linoleic-acid safflower oil in male patients in a metabolic ward. Gustafsson et al. (1994) showed a diet rich in high-oleic-acid rapeseed oil effectively reduced serum lipoprotein cholesterol concentrations in hyperlipidemic subjects.

Olive oil is considered to be resistant to oxidation in comparison with other vegetable oils because of its low content of polyunsaturated fatty acids and the presence of natural antioxidants. Olive oil’s characteristic aroma, taste, color and nutritive properties, stability distinguish it from other edible vegetable oils. Olive oil consumption reduces coronary heart diseases, diabetes, certain cancer risks such as breast, prostate and colon cancers, certain malignant tumors (endometrium, digestive tract, skin tumors) and some other chronic diseases (Huang et al., 2015). Olive oil is produced by mechanical means without using solvents or re-esterification processes.

I.      Virgin olive oil: The oil obtained from the fruit of the olive tree only by mechanical or other physical conditions, peculiarly thermal conditions, that do not cause alterations in the oil, and which has not undergone any treatment other than washing, decantation, centrifugation, and filtration.

II.      Refined olive oil: The olive oil obtained from virgin olive oils by refining methods which do not alter in the initial glyceride structure.

III.      Olive oil: The oil consisting of a blend of refined olive oil and virgin olive oils fit for consumption.  It  is  marketed according  to  the  following  designations  and  definitions (IOC, 1996):

1.3.3    Groundnut oil

It has been reported that South America was the place from where cultivation of groundnut originated and spread to Brazil, Southern Bolivia and North-western Argentina. Groundnut was introduced by the Portuguese from Brazil to West Africa and then to south-western India in the

16th century. Almost every part of groundnut is of commercial value.

The production of groundnut is concentrated in Asia and Africa with 56% and 40% of the global area and 68% and 25% of the global production, respectively. Cultivated groundnut has two subspecies, hypogaea and fastigiata, which in turn have two botanical varieties (var hypogaea and var aequatoriana). Each of these botanical varieties have different plants, pod and seed characteristics.

Groundnut is one of the most popular commercial crops in Nigeria. Nigeria produces 41% of the total groundnut production in West Africa (Acharya, 1984). It is cultivated for its kernels, the oil and hay for livestock. Groundnut cake is often deep fired or dried to make a snack locally called kuli-kuli. Groundnut flour is used as an ingredient in soups, sweet, confectionaries and puddings. Groundnut especially those produced in developing countries has been used traditionally since the origin of humanity. It is rich in oil and protein and has a high energy value (Acharya, 1984). Asia accounts for about 70% of world production while the major producers, India and China together represent over two-thirds of global output. Other important producers of groundnut are: Nigeria, Senegal, Sudan and Argentina. Groundnut is called as the ‘king’ of oilseeds. It is one of the most important food and cash crops of our country. While being a valuable source of all the nutrients, it is a low priced commodity. Groundnut is also called as wonder nut and poor men’s cashew nut. The groundnut is particularly valued for its protein content (26%). On equal weight basis (Kg for Kg), groundnuts contain more protein than meat and about two and a half times more than eggs. In addition to protein, groundnuts are a good source of calcium, phosphorus, iron, zinc and boron. The groundnuts also contain vitamin ‘E’ and small amounts of vitamin ‘B’ complex. High in calories, 5.6 calories nut -1 (calorific value of 567). Being an oil seed crop, it contains 40 to 49% of oil (Acharya, 1984). The groundnut oil has several uses but it is mainly used as cooking oil. It is used in many preparations, like soap making, fuel, cosmetics, shaving cream, leather dressings, furniture cream, lubricants, etc. Groundnut oil is also used in making vanaspati ghee and in fatty acids manufacturing. It is also used as a medium of preservation for preparation of pickles, chutney, etc. The groundnut oil is used in making different types of medicated ointments, plasters, syrups and medicated emulsion. It is also used to make various food preparations like butter, milk, candy and chocolate, chutney, groundnut pack, laddu, barfi (chukii), etc. Groundnut cake is a good feed for animals and poultry due to its nutritive value and palatability. Groundnut shell has great potential for commercial use. It is used as a fuel, filler in cattle feed, hard particleboard, cork substitute, activated carbon, etc.

1.3.4    Soybean Oil

Vegetable soybean is also known as soya or soja bean, and formerly classified as Glycine soja. Soybean is most widely commercialized oil seed worldwide and said to be the world’s most

important leguminous crop (Bennett et al., 2003). It is an herbaceous plant from the Fabaceae family (legume) naturally known to have originated in south-eastern Asia that was domesticated about 3,000 years ago because of its young pods and edible seeds. Soybean is of two general genotyped categories namely: large and small-seeded soybean. The large-seeded type are mainly used for the fresh market in oriental populations and urban areas, whereas the small-seeded types are used to prepare soybean sprouts.

Soybean seeds borne on different nodes of the stem and are subjected to positional effects (Bennett et al., 2003). Oil content and fatty acid composition in soybean seeds vary between positions along the plant axis (Guleria et al., 2008). Seeds in the upper one fourth of the plant contain a higher concentration of protein and lower concentration of oil than that from lower one fourth  of  the  plant  (Escalante  and  Wilcox  1993).  These  differences  in  the  oil  and  protein availability is due to the variations occurring in specific nutrients and assimilates supply and other related factors, probably influencing the germination of the seed (Sharma et al., 2009). Soybean contains high amount of oil and protein, and they are used in different food products, including soy milk, soy paste, soy curd and fermented soy cakes. Such hydrolyzed protein is a meat substitute used for many people. Flour made from soybeans is utilized in processed foods, as  a  stabilizer  and  to  increase  protein  content.  The  soy  derivatives  that  remains  after  oil extraction is used to produce fiber, textiles, adhesives, and livestock feed. Soy oil is used in cooking, such as margarine, shortening, salad oil as well as in paints, printing inks, disinfectants, detergents and biofuel as industrial products. Trace metals are also found in soybean oil in ppm concentration but when the oil is refined, concentrations of all minor constituents are reduced (Naz et al., 2005).

Soybean oil is one of the readily available oils that contains high amounts of monounsaturated and polyunsaturated fatty acids (MUFA and PUFA respectively).Though it is highly susceptible to oxidative process, the fatty acid composition of soybean plays a key role in that it helps to reduce blood cholesterol, thus lowering the risk of heart disease (Naz et al., 2005). The susceptible characteristic is brought about by many factors which could be microbial, light, heat, and oxygen. In order to increase the oxidative stability of soybean oil, antioxidants, such as butylated hydroxyanisole (BHA), tertbutylhydroquinone (TBHQ), and butylated hydroxytoluene (BHT) have been widely used as food additives (Eshghi et al., 2014).

1.4       Rancidity

Oil and fat components are responsible for the main sensory alterations that occur in foods during their shelf lives due to lipid oxidation, also known as rancidity. Rancidity can be divided into hydrolytic rancidity and oxidative rancidity.

1.   Hydrolytic rancidity is the hydrolysis of an ester bond by lipase or moisture. It refers to fats and oil hydrolysis producing free fatty acids (FFA) by the action of enzymes present in the oilseed grains or of microbiological origin. Also, hydrolytic rancidity   may  occur   non-enzymatically   at   high   temperatures   producing   FFA (Mirzaee, and Marangoni, 2013).

2.   Oxidative  rancidity  is  very  complex  and  involves  a  considerable  number  of reactions. The oxidation rate is affected by the fatty acid composition of the foods, degree of unsaturation of the fats, presence and activity of pro-oxidants and antioxidants, partial pressure of the oxygen and storage conditions of the foods, such as temperature, and exposure to light and humidity (Jaarin, 2011).

Rancidity has a great economic impact on the food industry because it leads to undesirable flavors and odors. Moreover, it can diminish the nutritional quality of foods and produce toxic products. Since the acceptance of foods containing lipids in their constitution depends on the extent of their oxidation, monitoring lipid oxidation is crucial to determine the quality of foods (Naz, et al., 2005). It is mediated by atmospheric oxygen and an unsaturated fat leading to the formation of initial products denominated hydroperoxides and final products such as aldehydes, polymers, glycerides, diglycerides and fatty acids. Analytical determinations, such as for free fatty acids (FFA), peroxide values (PV), p-anisidine values (AV), and TBA numbers are used to monitor lipid oxidation.

Vegetable oils are one of the main constituents of the diet used for cooking purposes. Several researchers studied the impact of temperature on the stability, density, peroxide value, and iodine value to assess the quality and functionality. Generally, processes where elevated temperatures are used mostly affect the amounts of phytosterols and formation of their oxidation products. Different physical and chemical parameters of vegetable oils were used to monitor the compositional quality of oils (Lee et al., 2013).

Sterols are the major components of vegetable oils after fatty acids, which forms majority of non-saponifiable matter. These components are similar in chemical structure to cholesterol the main animal origin sterol and the most researched sterol at all. It has been established that phytosterols are similarly prone to oxidative degradation as cholesterol. It means that during typical food processing and preparation their changes are expected and oxidation products can be found in food products. We have established that during frying operation oxidative degradation of sterols is happening faster in standard hydrogenated fats than in oils from which these fats were produced. In addition, oils with higher content of polyunsaturated fatty acids cause faster depletion of sterols. As effect of sterols, oxidative degradation variety of oxidation products are formed, indicating different kinetics of individual sterols oxidation. Processing of vegetable oils also affects phytosterols by changes in the amount and formation of oxidation products. We have established that each step of oil processing is affecting differently sterols and the amount of oxides formed, with deodorization affecting the most. During oil processing different oxidation products and amounts are formed indicating that kinetics of individual phytosterol oxidation during processing is different and often not related to chemical structure (Siger et al., 2008).

The scavenging action of plant constituents has been found to relate to polyphenolic compounds (Siger et al., 2008) which is also contained in the oil producing plants. According to Oomah & Sitter (2009), lignan occurs mainly in the hull of flaxseed. Although the constituents of flaxseed hull oil, which show free radical scavenging action is still unclear, it is possible that the antioxidative activity of flaxseed hull oil is caused, at least, by the presence of polyphenols (Hao and Beta, 2012). Based on the obtained results, we can conclude that flaxseed hull may play potential roles as health-promoting agents with antioxidant activity in human diets, as well as providing valuable natural antioxidants for the pharmaceutical industry.

High doses of synthetic antioxidative vitamins: A, E, C and β-carotene are often used on long- term basis in numerous preventive and therapeutic medical applications. Instead of expected health effects, the use of those vitamins may however lead to cases of hypervitaminosis and even to intoxication.

1.5       Vegetable Oil Production Process

Oil processing entails all the steps required to separate the oil from the oil-bearing material (seeds and fruits) with subsequent purification of the raw oil, in order to produce high quality vegetable oils. Triglycerides reside in specialized locations in seeds and fruits (mainly in cotyledons  and  endosperm  cells  in  seeds  and  in  mesocarp vacuoles  in  fruits) and  must  be extracted in the most selective and safest way. Oil processing however does not start only with the crude oil extracted from the raw material, but first from the raw material. This is because high quality oil is a product of high quality raw materials. Thus, the handling and storage of the raw material after harvest goes a long way to affect the quality of the oil produced (Yildirim, 2016). The steps involved in vegetable oil processing can be categorized into three major processes, namely: pre-treatment, extraction and refining processes. After the pre-treatment and extraction of oil to get the crude oil, then oil will be refined to get refined oil.

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