CHAPTER ONE
1.1 INTRODUCTION
Refining of vegetable oils is essential to ensure removal of germs, phosphatides and free fatty acids (F.F.A) from the oil, to impact uniform colour by removal of colouring pigments and to get rid of unpleasant smell from the oil by removal of odiferous matter.
Refining is carried out either on batch operation or as continuous operation. With certain oils even physical refining can be carried out instead of chemical.
For processing less than thirty tones of oil per 24 hours, and when oil has F.F.A content of 1 percent or less normally batch process is recommended. Batch process involves low capital investments, simplicity of operation and low maintenance, making refining economically a viable proposition even at capacity as low as 10 tonnes per 24 hours. (According to Dietary fats and oils in Human Nutrition. (Rome 1977)).
Soyabean oil is produced from the seed of the legume called soja max or calyclue max. The seed has an oil content of about 20%, it is the highest volume vegetable oil produced in the world. The crude oil is obtained by pressing or solvent extraction method. The main uses of the oil after refining, bleaching and deodorization and partial hydrogenation are in the manufacture of Magrine and shortening. The unhydrogenated oil is also used in blends with other oil but its tending to revert when exposed to air or higher temperatures limits its use. (Hand book of industrial chemistry, Reigel et al, (2003)).
Soyabean oil is also used extensively in the manufacture of drying oil products.
Crude soyabean oil of good quality has a lighter amber colour which upon alkali refining is reduced to the light yellow colour of most vegetable seed oils. Soyabean oil produced from green or immature beans may contain sufficient chlorophyll to have a greenish cast but this is not usually very evident until after the yellow red pigment of the oil have been bleached in hydrogenation (G.S Breck and S.C Bhatia, 2008).
The crude oil particularly that obtained by solvent extraction contains relatively large amount of non-glyceride materials consisting chiefly of phosphatide. They are removed by water washing during refining processes. The phosphatides removed by water washing are converted to soya lecithin. The free fatty acid content of good crude soyabean oil like that many other vegetable oil is slightly in excess of 0.5 percent. (Hand book of Industrial chemistry,Reigel et al (2003)).
1.3 BACKGROUND OF THE STUDY
Crude fats and oils are processed by general scheme shown below with modifications or exceptions for specific species.
The phospholipids (Lecithins) must be removed to avoid darkening of the oil during high temperature deodourization and in deep-fat- frying applications. This removal typically is accomplished during the alkali refining process or in a separate water/acidic water degumming step before alkali refining. Crude soyabean oil has an unusually high (2-3.5 percent) phospholipid content among oils and often is degummed in a separate operation to not more than a 300 ppm level (as phosphorus) to avoid precipitation during shipping and storage. Refine soyabean oil contains 10ppm or less phospholipid. Degumming is achieved by mixing crude soyabean oil with water to hydrate the phospholipids and enable their removal by centrifuge. Critrics and other acids sometimes are added in a step called supper degumming to help remove phospholipids that are not hydrated by water. Degummed soyabean oil or crude oils of other species are neutralized with sodium hydroxide solution to from sodium salts of the fatty acids which are removed as soap stock by a continuous centrifuge. The soapstock also includes remaining phospholipids, some colour and flavor compound. (Hand book of industrial chemistry, Reigel et al (2003)).