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)).

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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).

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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 chemistryReigel 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.

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Fig 1:1-Generation flow sheet for refining and processing fats and

oils (according to G.S Breck and S.C Bhatia 2008).

CRUDE OIL

Margarine

votator

Shortening stock

Liquid Shortening

votator

Shortenings

Margining stock

Mixing Chiling

Steam salad and

cooking oils

Emulsifirs

Blended oils

Winterization

Rearrangement

Hydrogenation

Thermal Fractionation

Oil

Refined Bleached Deodourised

Red

Bleaching physical refining Deodourization

Spent Earth

Soap stock

Activated Earth Bleaching

Alkali

Water

Degumming

Crude Lecthin

Degummed oil

Alkali refining

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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)).

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The soap stock can be dried if refining is done adjacent to an

extraction plant or acidified again to remove fatty acids and sold

to the olechemical industry. The oil is then water washed and

centrifuge one or two times to remove residual soaps.

According to GS Breck and S.C Bhatia a total degumming

process for removing essentially all the phosphatide from

soyabean oil using first an acid and then an alkali and two

centrifuges has shown higher yields than conventional refining.

This process however does not remove prooxidant metals

efficiently and for this reason has not found commercial

acceptance in the united state.

G.S Breck and S.C Bhatia have stated that Dijkstra has described

a novel process where the washing water is recycled to the oil

feed and use to dilute concentrated alkali. This process does not

generate an aqueous effluent and can be used for both acid and

alkali refining thus allowing refiners to change gradually from

alkali refining to physical refining. Neutralization of soyabean oil

with alkali solution assures elimination of free fatty acids without

notable change in the phosphatide content. The phosphatidic

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concentration obtained from oil previously neutralized in the

miscella was of higher quality than the phosphatidic concentration

obtained from the oil of the starting miscella. Aqueous ammonia

has the advantage of being safe for the environment because the

deacidification agent can be repeated or reused. Oils especially

soyabean oil with low degree of oxidation can be fully deacidified

only with the help of the ammonia. The same effect can

frequently be achieved by a preliminary desliming with 5 percent

formic or citric acid. Deodourization at 210

0

c of oils that have

been deacidified with ammonia and washed with water yield

bland and pale edible oils having good storability (G.S Breck and

S.C Bhatia).

List and Erickson state that of all the unit processing operations

refining has the most significant effect on oil quality measured by

colour oxidative stability and storage properties.

If soyabean oil is not properly refined subsequent processing

operation such as bleaching hydrogenation and deodourization

will be impared so that finished products will not fail to meet

quality standards. Also poor refining will reduce the yield of

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natural oil thereby lowering manufacturing profits. (JAOCS Vol.

60).

According to G.S Breck and S.C Bhatia caustic refining

removes free fatty acid to 0.01-0.03percent level and remove

virtually all the phosphatides. Crude soyabean oil contains trace

amount (several part per million (ppm)) of prooxidant metals

such as iron and copper. Caustic refining usually removes 90-95

percent of these metals. However it should be emphasized that

even though caustic refining reduces metallic contamination to

low levels residual iron and copper still remain strong

prooxidants in refined oils and must be taken in to account during

storage and handling. At a constant percentage of water the

total amount of caustic used influences colour removal ie the

more caustic used the lower the colour of the refined oil.

List and Erickson reported that plots of residual iron versus

residual phosphorus content of deodourized oil showed that iron

increases at phosphorus content below about 1ppm reaches a

constant value of about 2-20ppm phosphorus then beings to

increase. Thus the decreased oxidative to stability at phosphorus

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content above 20ppm can be explained by the sufficiently high

iron content (ie greater than 0.2 ppm) which exerts a strong

prooxidant effect. Similarly decreased stability at phosphorus

content below 2ppm can also be explained because of the

increased iron content. At the same time it should also be

pointed out that the traditional method for calculating the amount

of refining lye is based on the free fatty acid content and

therefore gives no indication of conditions leading to optimum

phosphorus removal. Phosphatide content generally exceed that

free fatty acids in crude soyabean oil by a factor of about 6. In

refining process control crude oil is usually educated for refining

cost by the American oil chemist‟s society (AOCS)

chromatographic method. (JAOCS vol 60).

1.3 STATEMENT OF THE PROBLEM

In the market today most vegetable oils solidify at a low

temperature of less than 25

0

c. This work is to process and refine

edible and quality soyabean oil that will not undergo solidification

at a low temperature.

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1.4 OBJECTIVES OF THE STUDY

The objective of refining and processing fats and oils include:

 Removal of free fatty acids phospholipids (gums) colour and

off-flavour/odour compounds and toxic substances to

produce light- coloured and bland products with long shelf

lives.

 Obtaining a mixture of the triacyl-glycerols with the desired

solid content profiles over the range of product use.

 Preparation and storage of semi-solid products with desired

textures.

1.5 SCOPE OF THE STUDY

The crude oil extracted from soyabean needs further treatment to

convert it to a bland stable nutrition products that is used to

manufacture margarine shortening salad and cooking oil

mayoniaise food products Olechemicals.

This study entails the process of producing good quality oil

through caustic/alkali refining process which is going to be

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compared with other good quality products in the market like

grand product etc.

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