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The objective of refining vegetable oils is to remove unacceptable materials with the least possible effect on desirable components and the least possible loss of oil. Generally the process of refining affects mainly the non triglyceride part of the oil i.e. the minor components of the oil. The literature survey shows that Jung et al., (1989) studied the effect of processing steps on the content of minor compounds and oxidation of soya bean oil, and found out that the process of refining removes 99.8% of phospholipids, 90.7% of iron, 100% chlorophyll, 97.3% of free fat acid and 31.8% of tocopherols. With their refining process the order of oxidation stability was crude> deodorized> degummed> alkali refined> bleached. Table 1 summaries Jung et al., results. Based on their results, it is therefore very important to monitor the loss of tocopherols in the process of refining to improve the stability of the oil. Since tocopherols, acts as antioxidant in the oil, therefore hinders the oxidation of the oil, and improve the shelf life. However, Jung et al., did not study the effect of refining on the composition of sterol in oils.
Karabulut et al., (2005) studied the effects the industrial refining process on some properties of hazelnut oil. The fatty acid composition, mainly oleic acid (81%), did not change significantly during the process. The amounts of total tocopherols and phytosterols decreased from 51.89 to 46.67mg/100g and from 168.04 to 141.48mg/100g, respectively. They also found that the biggest losses of both tocopherols and sterols were observed after neutralization. Deodorization resulted into a slight decrease in the amount of sterols. Î±-Tocopherol (36.19mg/100g), Î²-tocopherol (9.3mg/100g), and Î³-sitosterol (120.28mg/100g) were the predominant unsaponifiables in refined hazelnut oil. The minor component contents progressively decreased during refining, especially during neutralization (Karabulut et al., 2005).
Verleyen et al., (2002), studied the influence of the refining process on the distribution of free and esterified phytosterols in corn, palm, and soybean oil, It was found that water degumming did not affect the phytosterol content or its composition. A slight increase in the content of free sterols was observed during acid degumming and bleaching due to acid-catalyzed hydrolysis of steryl esters. A significant reduction in the content of total sterols during neutralization was observed, which was attributed to a reduction in the free sterol fraction. They also find out that during deodorization, free sterols are distilled from the oil, resulting in a gradual reduction in the total sterol content as a function of the deodorization temperature (220-260Â°C). A considerable increase in the steryl ester fraction was found during physical refining
According to Smouse the typical degumming efficiencies reduces the phospholipids from about 3% in crude oil to less than 0.09% in degummed oil, a 97% reduction. Any remaining phospholipids in the degummed oil are removed during caustic refining. In the case of physical refining, an acid-pretreatment step is necessary to reduce phosphorus from phospholipids to less than 3 ppm. Beal et al., showed that phosphorus in a water-degummed oil should be in the range of 2-20 ppm for optimal oxidative stability.
Naz et al.,(2010) investigated the changes of total and individual tocopherols during different sunflower oil refining stages and their results revealed that the levels of total and individual tocopherol content were decreased during the neutralization, bleaching, and deodorization processes. The overall loss of total tocopherols during these stages was found to be 43.6%, out of which 16.3%, 7.14% and 20.16% were from neutralization, bleaching and deodorization respectively
Molik et al., (2008) studies the effect of deodorization temperature (between 220 and 270 7C) on tocopherol retention in physically refined rapeseed oil. The retention of total tocopherols decreased considerably from 91.5% at 220 7C to 54.7% at 270 7C, approaching a value of about 80% in the main area of concern between 230 and 240 7C (molík et al., 2008).
The effect of processing on the quality and stability was studied by (Mariod et al., 2006) it is clear that the contents of phosphatides, peroxides, tocopherols, sterols as well as oxidative stability were reduced during processing, while FFA were nearly totally removed. The content of phosphorus was reduced in crude oils from Sclerocarya birrea (SCO), sorghum bugs (SBO), water-extracted melon bugs (MBO H2O) and solvent- extracted melon bugs (MBO SOL) by 26, 19, 12, and 78%, respectively, while complete oil processing removed 95, 99, 96 and 99% of the FFA in crude oils, respectively. Total sterols decreased by 42-92% in the processed oils, com- pared with crude oils. The level of total tocopherols decreased during processing by 38.7, 83.8, 100, and 33.3%, respectively. Their results also confirm no change in the fatty acid composition during refining.
Tasan and Demirci (2005) also studied the contents of total and individual tocopherols of sunflower oils at different stages of industrial chemical and physical refining processes the total and individual tocopherol contents gradually decreased until the end of the refining processes. The average losses of total tocopherol content during the chemical and physical refining processes were found to be 30.2% and 35.5%, respectively. The steam distillation stage of the physical refining process caused greatest overall reduction (average 24.6%) in total tocopherol content. In contrast to the physical refining process, the degumming neutralizing stage in the chemical refining process caused greatest overall reduction (average 14.7%) in total tocopherol content. An additional average loss of 11.0% occurred during deodorizing in the chemical refining process. In both chemical and physical refining, the bleaching stage caused similar effects. The physical refining process caused higher loss in the total and individual tocopherol contents when compared with the chemical refining process. The conditions of the re- fining processes should be carefully evaluated to reduce the loss of tocopherols (Tasan and Demirci, 2005).
Ortega-Garcia et al., (2006) study the influence of the industrial process steps. Degumming, bleaching and deodorization steps removed 91.4% of free fatty acids, 96.31% of oxidation primary products (PV), and 54.57% of oxidation secondary products (PAV), from crude high oleic safflower oil. Like verleyen et al., (2002) degumming process neither affected the content of sterified sterols nor its proportion with respect to the crude oil. a slightly increase in the content of free sterols was observed during degumming and bleaching due to the acid-catalyzed hydrolysis of steryl ester. During deodorization, free sterols were distilled from oil, with a gradual reduction in the total sterol content as a function of the deodorization temperature. Î±- and Î³-tocopherols represented 93.3% of the total tocopherols in high oleic safflower crude oil. Their refining process removed 28.5% of the tocopherols. (Ortega-García et al., 2006)
REFINING VEGETABLE OILS FOR BIODIESEL
Currently most of the existing refining technologies have been towards obtaining edible grade oils. The refining process is therefore limited to parameters like color, taste and the like which are not related to the quality of biodiesel. The reviewed literature shows little have been documented on the modifications of refining process to meet the biodiesel qualities. Some authors have been able to produce biodiesel from crude oils and stated that the biodiesel produced have met the required quality withoutâ€¦â€¦..
Is it possible to go without refining?
What are the benefits of refining?
What are the effects on the quality of b100 different from quality of edible oil?
The importance of refining vegetable oils for alkali transesterication have beenâ€¦â€¦â€¦
Most of the literatures have been too general on the subject, like â€¦.
BEAL, R. E., LANCASTER, E. B. & BREKKE, O. L. (1956) The phosphorus content of refined soybean oil as a criterion of quality. Journal of the American Oil Chemists' Society, 33, 619-624.
JUNG, M., YOON, S. & MIN, D. (1989) Effects of processing steps on the contents of minor compounds and oxidation of soybean oil. Journal of the American Oil Chemists' Society, 66, 118-120.
KARABULUT, I., TOPCU, A., YORULMAZ, A., TEKIN, A. & OZAY, D. S. (2005) Effects of the industrial refining process on some properties of hazelnut oil. European Journal of Lipid Science and Technology, 107, 476-480.
MARIOD, A., MATTHÄUS, B., EICHNER, K. & HUSSEIN, I. H. (2006) Effects of processing on the quality and stability of three unconventional Sudanese oils. European Journal of Lipid Science and Technology, 108, 298-308.
MOLÍK, J. Í., POKORNYÂ´, J. & SVOBODA, Z. R. A. Z. K. (2008) Tocopherol retention in physically refined rapeseed oil as a function of deodorization temperature. European Journal of Lipid Science and Technology, 110, 754-759.
NAZ, S., SHERAZI, S. & TALPUR, F. (2010) Changes of Total Tocopherol and Tocopherol Species During Sunflower Oil Processing. Journal of the American Oil Chemists' Society, 88, 127-132.
ORTEGA-GARCÍA, J., GÁMEZ-MEZA, N., NORIEGA-RODRIGUEZ, J. A., DENNIS-QUIÑONEZ, O., GARCÍA-GALINDO, H. S., ANGULO-GUERRERO, J. O. & MEDINA-JUÁREZ, L. A. (2006) Refining of high oleic safflower oil: Effect on the sterols and tocopherols content. European Food Research and Technology, 223, 775-779.
SMOUSE, T. H. (1995) Factors affecting oil quality and stability. Methods to assess quality and stability of oils and fat-containing foods. The American Oil Chemists Society.
TASAN, M. & DEMIRCI, M. (2005) Total and individual tocopherol contents of sunflower oil at different steps of refining. European Food Research and Technology, 220, 251-254.
VERLEYEN, T., SOSINSKA, U., IOANNIDOU, S., VERHE, R., DEWETTINCK, K., HUYGHEBAERT, A. & DE GREYT, W. (2002) Influence of the vegetable oil refining process on free and esterified sterols. Journal of the American Oil Chemists' Society, 79, 947-953.