A Comparative Study On The Physio-Chemical Properties Of Vegetable Oils
Physiochemical properties of some brands of edible oils (namely:- Turkey, Grand, Gino, tropical, Power, Mammador, local vegetable oil and kuli-kuli (raw/locally extracted groundnut oil) sold in mile 1 market, Everyday supermarket and Next-time supermarket in Port Harcourt, Rivers state were studied to determine their quality and compare the results with some standards. All the oils were characterized for flash point, cloud point, iodine value, saponification value, unsaponifiable matter, acid value and peroxide value using standard methods of analysis.
The results obtained show that the free fatty acid contents of the local and kuli-kuli oils were higher (0.709 and 1.96 respectively) than the maximum recommended value of 0.3 by SON and NIS while other brands were within the range. The measured moisture content values for Turkey, Grand, Gino and Mammador were higher than the standard range of 0.05 in the samples from Mile 1 market and in some supermarkets. Specific gravity, melting point, and cloud point were satisfactory except for Grand that showed a different cloud point of less than 2. Iodine value for the local oil is 20.25 (Wij’s) indicating the predominance of lauric acid while that of kuli-kuli (94.6 Wij’s) suggests the predominance of Oleic acid.
The other brands showed iodine value of 46-50 Wij’s which indicates predominance of palmitic acid except the Grand oil that had the highest value of 125-128 (Wij’s). Saponification values and unsaponifiable matter were within the standard range of saponification value (245- 255) and unsaponifiable matter (0.1-0.15) for all the brands. Acid and Peroxide values of all the brands showed results within the standard. These results of the measured parameters show that the oils sold in the supermarkets are better protected from light induced oxidation (photoxidation) than those sold in open markets.
Vegetable oils constitute a significant part of the human diet as a source of energy, fat-soluble vitamins and essential fatty acids (FAO, 2009).They are extracted from seeds and nuts of various plants and are composed mainly of triacylglycerols.
Despite their importance, one major drawback in their handling and utilization is their ease of oxidative deterioration, which renders them less acceptable to consumers or for industrial use especially as food ingredients.
The quality of any oil is indicated by some physico-chemical properties. The specific value of some of
these properties provides an indication of both the nutritive and physical quality of the oil. These properties include iodine value, peroxide value, saponification value, unsaponifiable value, free fatty acid, color appearance etc. For example, oils with low melting point may readily go rancid due to the high level of unsaturation. Recently, palm oil has become the second most consumed oil all over the world as a result of its being rich in natural antioxidants, vitamins and exhibiting high oxidative stability with attendant long shelf life. However, its high melting point lowers the level of acceptance among some consumers (Edem, 2002).
The exposure of oils to either a source of heat, light or moisture can alter some of the quality indicators.
The extent of alteration (spoilage) depends on the duration of exposure, temperature and condition of storage (Aidos, et al., 2002; Fekarurhobo, et al., 2009). The stability of oils to oxidation is an important indicator in determining oil quality and shelf-life (Choe and Min, 2006).
Two common practices that render vegetable oils in most commercial centres prone to oxidative
deterioration are packaging in transparent containers (plastic bottles and sachets) and displaying oils either under direct sunlight or artificial lights.
Studies have shown that some vegetable oils available in the market do meet therecommended standards for edible oils (Reyes Hernandez, et al., 2007).
Considerable amount of attention has been given in recent years to test for the extent and nature of oil oxidation. Primary oxidation products are measured by peroxide value which is a value of the quantity of hydroperoxides present in the oil (Maduelosi, et al., 2012). It is usually expressed in milli-equivalent of oxygen per kg of oil. The secondary oxidation products are assessed by measuring the Para or p-anisidine value. The panisidine value measures mainly the amount of alpha-beta unsaturated aldehydes (2-alkanals) and ketones present in the oil. The primary oxidation products (peroxide and hydro peroxides) are unstable and gives very little off-flavour, but the secondary oxidation products (aldehyde and ketones) gives undesirable off-flavour to the oil and cannot be completely removed on refining (Denenu and Eze, 1983).Some of the oxygenated decomposition products are implicated in degenerative diseases such as aging, membrane damage, heart disease and cancer; as a result the study of lipid oxidation has received great attention recently (Angaye, et al., 2013).
The sources and characteristics of a good number of edible oils are not known. It is therefore, very important that the quality and oxidative stabilities of commercially available vegetable oils be examined to ascertain their suitability for consumption.
The aim of this study is to compare the quality of some brands of vegetables oils sold in Port Harcourt
with known standards and also compare the effect of storage conditions on the oxidative stability of the oils.
Vegetable oils among other options could be investigated in developing a new lubricating fluid where high performance in forming operations with good environmental capabilities could be achieved. The most important characteristics of vegetable oil are their safety and biodegradability. Compared to petroleum based oil (mineral oil), 3 Vegetable oil has been shown to replace mineral oil as lubricants in previous researches carried out (Syahrullail et al 2011),. Also it has higher flash point and natural viscosity than mineral oil, thus improving the surface finish and extending tool life. It also does not contribute to health hazard via toxic mist and skin cancer and does not pollute the environment.
Objective Of The Study
The aim of this research work is to evaluate the physic-chemical properties of vegetable oil.
The specific objective are:
- To know the content of the free fatty acid of the local and kuli-kuli oil.
- To know the measured moisture content value of vegetable oil
- To evaluate the specific gravity, melting point, cloud point of vegetable oil.
- To determine if the oil sold in the supermarkets are better protected from light induced oxidation than those sold in open market.
The exposure of vegetable oils to light and heat results in their degradation affecting their physicochemical properties. This is of interest to scientists because the products of such degradation reactions are linked to some cardiovascular diseases. The effect is more on the oils sold in the open markets than those sold in supermarkets. This may be attributed to the harsh storage/display conditions of the products in the open markets. The findings from this research show that some of the vegetable oils sold in the markets are substandard. It also reveals that oils with low free fatty acids tend to have high smoke point, high flash point and low peroxide value which are good quality attributes of ideal vegetable oils.
Vegetable oils should be stored in lacquered cans or sachets and not clear glass jars or plastic bottles often used which allows ultraviolet radiation to damage the oil.
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