Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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hydrated by water, offers a greater versatility in use

and poses no risk of acid residues in the processed oil.

Table 5 shows the processes used for degumming oils

and their effectiveness in reducing the phospholipid

content of oils. Ultrafiltration of the oil (in solvent) to

remove the phospholipids is also effective but more

costly than other processes.

0028 Removal of the phospholipids present in the oil

facilitates the subsequent stages of refining, as it re-

duces the tendency to form emulsions during neutral-

ization of the FFA and also permits operation at high

temperatures (> 200



C) without any risk of discolor-

ation. When the oil is to be refined physically, i.e.,

using stripping steam to remove the FFA from the

crude oil, the degumming process must also remove

traces of metals such as copper and iron, which would

discolor the oil at the temperatures used for steam-

stripping.

Chemical Refining

0029Neutralization All crude vegetable oils contain FFA

that should be removed in the interests of refined

oil quality. The seed oils for the most part contain

0.8–1.5% FFA, but palm oil may contain up to 5.0%

FFA as the result of enzymic action in the interval

between fruit harvesting and sterilization. Oils such

as ricebran oil and several of the more exotic fats,

e.g., sheanut butter and illipe fat, may contain more

than 5% FFA.

0030Although, in principle, any alkali may be used to

neutralize the FFA present in the crude or degummed

oil, sodium hydroxide solution (strength 8–24%,

depending on the oil to be refined – a dark oil will

normally be neutralized with a stronger alkali than an

oil that is light in color) is used almost universally

in industrial chemical refining of fatty oils. The

neutralization reaction is carried out at 80–90



(see Figure 3). In the conditions of intense mixing,

as practiced in modern centrifugal refining, it requires

contact times between crude oil and alkali of less than

60 s. The soaps formed by neutralization, known as

soapstock, are insoluble in the oil and are separated

centrifugally, the disk centrifuge being the preferred

type nowadays. As the soaps have a low but finite

solubility in the oil at the processing temperature

(soap content of oil ¼150–200 p.p.m.), it is necessary

to follow separation of the soapstock by a washing

Crude oil *

*Phosphatide-rich oils

normally water-degummed

prior to refining

Chemical refining Physical refining

Gums

Degumming

agent

Degumming agent

Alkali

Degumming

Neutralization

Bleaching

earth

Bleaching earth

Bleaching

Soapstock

Spent earth

Steam

Deodorization

To vacuum

system

To vacuum system

Steam-stripping/

deodorization

Phospholipid/

metal removal

(degumming)

Refined, Bleached, Deodorized (RBD) oil

fig0002 Figure 2 Refining options for edible oil.

tbl0004 Table 4 Phospholipid contents of major oils

Oil Phospholipids (%) Phosphorus (p.p.m.)

Rapeseed 0.5–3.5 200–1400

Soyabean 1.0–3.0 400–1200

Sunflower 0.5–1.3 200–500

Corn 0.7–2.0 250–800

Cottonseed 1.0–2.5 400–1000

Palm 0.03–0.1 15–30

5908 VEGETABLE OILS/Oil Production and Processing

stage, in which soft water is used to reduce the soap

content of the oil to below 30 p.p.m. The FFA content

of the neutralized oil should be below 0.1%.

0031 The soapstock contains a certain amount of neutral

oil owing to spontaneous emulsification taking place

at the oil–alkali interface in the course of the neutral-

ization reaction. This is reflected in the refining loss

experienced by refiners, defined as the ratio of oil loss

at the neutralization stage to the FFA present in the

crude oil and known as the refining factor. For most

oils, the refining loss in chemical refining can be

expected to be in the range of 1.5–2.0, although

lower refining factors have been obtained when

using nonturbulent alkali–oil contactors. The down-

grading of sound oil to the lower-valued soapstock or

acid oil produced by acidulation of soapstock results

in a significant cost charge against the process.

0032The effluent resulting from chemical neutralization

has been recognized as an environmental problem,

and this has resulted in a change to physical refining,

particularly in Europe. When chemical refining is

used to remove only low levels (< 0.15%) of FFA, as

in the case of an oil already refined in the country of

origin and then transported intercontinentally, it is

possible to use a hydrogel silica or a modified magne-

sium aluminum silicate to adsorb the soaps formed,

tbl0005 Table 5 Degumming processes

Process Suitable for Residual phospholipids (p.p.m. phosphorus)

Water degumming Crude oil 100–250

Acid degumming Crude oil 20–50

Acid refining Crude oil <20

Superdegumming (Unilever) Crude or wdg oil 5–15

TOP degumming (Vandenmoortele) Crude or wdg oil 5–10

Enzymatic degumming wdg oil 5–10

SOFT degumming (Tirtiaux) Crude oil <5

IMPAC degumming Crude oil 3–10

wdg, water-degummed.

Condensate

TC TC

Oil feed

Strainer

Crude oil

pump

(To ratio

controller)

Heater

Steam

Steam Steam

Steam

Condensate

By pass

Static

mixers

Static

mixers

Retention

mixers

Refining

heater

Refined oil

heater

Soapstock

separator

Soapstock

tank

Soapstock

pump

Soft

water

Retention

mixer

To flow ratio

controller

Caustic

pump

Strainer

Steam

Waterwash

separator

Wash water

outlet

Vacuum

dryer

Dry oil

pump

To bleaching

Vacuum system

To soapstock

splitting plant

atmosphere

fig0003 Figure 3 Vegetable oil neutralization plant arrangement. Based on a flowsheet produced by Europa Crown Ltd., Hessle, North

Humberside, UK.

VEGETABLE OILS/Oil Production and Processing 5909

instead of washing them out of the oil. Similarly, these

materials can be used to replace the wash centrifuge

in normal refining in order to remove the soap

content remaining in the refined oil after soapstock

separation, thus again avoiding the formation of add-

itional liquid effluent.

0033 Bleaching The neutralized oil to be bleached is

deaerated and dried at a pressure of approximately

50 mbar to a moisture content of not more than

0.1%. Use of acid-activated bleaching earth (bleach-

ing clay in the USA) will remove traces of metals such

as copper and iron from the oil in addition to pig-

ments and residual soap, which is important from the

point of view of oil keepability. Cocurrent or counter-

current bleaching may be used to reduce the bleaching

earth requirements, with savings of 10–15% relative

to batch bleaching being reported for the cocurrent

option and up to 40% for countercurrent processing.

Oil leaving the bleacher is filtered to separate spent

bleaching earth, but this retains high levels of oil

unless it is processed further, e.g., by blowing steam

or nitrogen through the press. Spent earth destined

for disposal to a landfill site will generally still contain

approximately 30% oil. This therefore becomes a

charge against the process, additional to the refining

loss explained above. The spent bleaching earth is

also a fire hazard.

0034 In recent years, a number of alternatives to acid-

activated bleaching earth have been developed for use

in edible oil refining. The use of silica as an adsorbent

and filter aid, generally in admixture with bleaching

earth, has been shown to be feasible, though the cost

is higher than that of the more traditional bleaching

earths. A number of multistage bleaching processes

are available, their purpose being to reduce the

bleaching earth requirement per tonne of oil pro-

cessed.

0035 An oil contaminated with polycyclic aromatic

hydrocarbons (PAH) requires the addition of a small

quantity of activated carbon to ensure that the PAH

content of the fully processed oil is reduced to accept-

able levels.

0036 Deodorization The final stage of oil processing,

deodorization, has the function of removing volatile

components remaining in the oil after the previous

stages of refining as well as those volatile compounds

formed during deodorization itself. In addition, some

heat-bleaching is likely to occur at this stage, owing to

the high temperatures used. The removal of volatile

components is achieved by the passage of open steam

through the oil at temperatures of 200–220



Cata

pressure of 4–10 mbar. Stripping steam consumption

in the process can be expected to be in the range of

0.5–3.0%. In order to ensure stability of the pro-

cessed oil, its peroxide value should be below 1.0,

preferably below 0.5 meq of O

per kilogram of oil,

which requires rapid cooling of the oil after the

completion of deodorization.

0037Deodorization can be carried out batchwise, semi-

continuously or fully continuously, and in the case of

a fully continuous operation, either a crosscurrent or

countercurrent mode of steam–oil contact may be

used. The extent of removal of volatile components

is directly proportional to the volatility of the com-

ponent and is therefore a function of the operating

temperature. At the same time, it is also inversely

proportional to the operating pressure. Since deodor-

ization is a dynamic process, the interfacial area

between the stripping medium and the oil to be

deodorized is a vital parameter in determining strip-

ping efficiency.

0038Modern deodorizers, almost all of which operate

semicontinuously or fully continuously, are fitted

with heat-recovery systems that can recover up to

80% of the energy needed to heat the incoming oil

to the operating temperature. The vacuum system,

normally consisting of a series of steam jet ejectors,

also uses substantial quantities of steam in the form of

motive steam, a ratio of 5–7 kg of motive steam per

kilogram of stripping steam evacuated being required

in temperate regions when operating at a head pres-

sure of 4–6 mbar. The motive steam requirement can

be reduced by chilling the water used to condense the

mixed vapors from the deodorizer or by using a ‘dry’

vacuum system that makes use of mechanical vacuum

pumps instead of steam jet ejectors.

0039Apart from high-energy consumption, the environ-

mental impact of deodorization manifests itself in the

liquid and gaseous emissions created by the process.

Entrainment of oil in the stripping vapors leaving

the deodorizer constitutes a process loss, generally

0.2–0.3% of the oil processed, but if not trapped in

a scrubber or condenser, this entrainment will appear

in the effluent stream leaving the plant. In recent

years, steps have also been taken to reduce the

odoriferous gaseous effluent from the deodorizer.

0040In addition to removing the undesirable minor

components of the oil reaching the deodorizer, the

stripping steam will also remove, at least partially,

valuable components such as tocopherols and sterols.

The tocopherols constitute a valuable byproduct that

can be converted to natural vitamin E concentrates.

However, the a-tocopherol content of most vegetable

oils accounts for only a small proportion of the total

tocopherol content (Table 6), and the deodorizer dis-

tillate requires removal of the nontocopherol com-

ponents but also conversion of the other tocopherol

isomers to the a -form if the product is intended as

5910 VEGETABLE OILS/Oil Production and Processing

a diet supplement. It is also possible to recover

sterols, which can be converted to pharmaceutical

products, from the deodorizer distillate when refining

soyabean oil.

Physical Refining

0041 Physical refining of a vegetable oil requires operation

at a temperature significantly higher than the tem-

perature used in the deodorization stage of chemical

refining, as the process depends principally on the

volatility of the FFA present in the oil, which are

removed by reaction in chemical refining. Processing

temperatures in the stripper are therefore generally in

the range of 220–250



C, which means that the oil

being processed is subjected to greater thermal stress

than the oil deodorized following chemical refining.

0042 Degumming As already indicated, degumming of

an oil that is to be physically refined must be designed

to achieve higher standards of removal of undesirable

components than when degumming as part of a

chemical refining process. Acid refining, in which

phosphoric acid is used to hydrate the phospholipids

not hydrated by water and alkali is then added to

neutralize the excess acid, can be used to reduce

phospholipids to below 10 p.p.m. Bleaching earth is

then added to adsorb the precipitated material, and

the mixture of oil and earth is filtered conventionally.

With the simultaneous removal of metals, the acid-

refined oil is suitable for physical refining.

0043 The bleaching earth requirement for the physical

refining process is higher than that for chemical refin-

ing, and this fact counterbalances to some extent the

lower refining losses in physical refining. Table 7

compares the bleaching earth requirements for

various oils in chemical and physical refining.

0044 Stripping/deodorizing The requirement for removal

of FFA by steam-stripping in physical refining distin-

guishes this operation from the apparently closely

related operation of deodorization in a number of

important respects – a significantly higher operating

temperature is needed in order to reach fatty acid

vapor pressures at which stripping becomes practical;

the molar fraction of fatty acids in the vapor stream

leaving the stripper contributes significantly to the

total vapor flow and therefore to the design of the

condenser used to recover material from the vapour

stream; and the higher operating temperature leads to

a greater loss of other volatile components, e.g., toco-

pherols, from the oil. A further consequence of the

higher process temperature is the greater possibility

of trans-fatty acid (TFA) formation.

0045Stripper design is generally similar to the design of

deodorizer discussed earlier, but batch operation is

not appropriate. In practice, steam-stripping of fatty

acids uses slightly higher quantities of stripping steam

per unit of oil processed than deodorization. The

condensed stripper vapors, being richer in FFA than

deodorizer distillate, have a proportionately lower

content of the valuable tocopherols than the distillate

and therefore constitute a lower-value byproduct.

Oil Modification

0046The three oil modification processes – hydrogenation,

fractionation, and interesterification – have made a

major contribution to the greater use of oils and

fats since their introduction in the twentieth century.

These processes principally serve to modify the rela-

tionship between liquid and solid content of an oil or

fat as a function of temperature, thus enhancing their

tbl0006 Table 6 Typical tocopherol contents of major vegetable oils

Oil Total tocopherol (p.p.m.) a-Tocopherol (p.p.m.) b-Tocopherol (p.p.m.) g-Tocopherol (p.p.m.) Reference

Soyabean 811 179 28 604 1

Rapeseed 553 216 10 326 2

Sunflower 570 564 2 4 1

Cottonseed 788 403 2 383 1

Corn 840 272 2 566 1

Palm

101 91 2 8 1

Also contains 180 p.p.m. of tocotrienols.

1, Journal of the American Oil Chemists Society 62(3): 531–538 (1985).

2, European Journal of Lipid Science and Technology 102: 618–623 (2000).

tbl0007Table 7 Bleaching earth consumption in physical and chemical

refining

Oil Percentage ofbleachingearth

Fully degummed oil

(for physical refining)

Neutralized

(chemicalrefining)

Sunflower 0.3 0.1–0.2

Rapeseed 0.7 0.5

Corn 0.8 0.5

From Kokken M (1996) World Conference on Oilseeds and Edible Oils,

Istanbul.

VEGETABLE OILS/Oil Production and Processing 5911

functionality. Hydrogenation is the most versatile of

these processes, primarily because at least three

process conditions can be used to modify process

performance.

0047 Although the modification processes are used indi-

vidually in many cases, their coupling, e.g., hydrogen-

ation followed by fractionation, or fractionation

coupled with interesterification, can lead to enhanced

versatility in the use of different oils and fats.

Hydrogenation

0048 Hydrogenation is used to reduce the unsaturation

present in oils and thereby to increase their solid fat

content. The conditions for hydrogenation must take

into account the different reaction rates for the range

of molecular species present in the oil. Nickel, in

various forms designed to maximize the active cata-

lyst surface area, is generally used as the reaction

catalyst, although other catalysts, e.g., platinum, pal-

ladium, and copper, are also effective. The catalyst is

precipitated on a carrier for the purpose of maximiz-

ing the catalyst surface area available for the reaction.

Sulfur addition to the nickel catalyst is used to pro-

mote steep melting curves in the hydrogenated fat,

but this is achieved by increasing the proportion of

TFA in the fat.

0049 When processing a well-refined oil, it is now pos-

sible to hydrogenate an oil with catalyst concentra-

tions as low as 40–50 p.p.m. (Table 8). The process

conditions employed, including hydrogen pressure,

temperature, and catalyst concentration, are chosen

to produce a hydrogenated product best suited to

the required functionality of the fat produced, bear-

ing in mind that the rate of conversion of linoleic

acid (C18:3) to linoleic (C18:2) acid is approxim-

ately 40 times greater than that of oleic (C18:1) acid

to stearic (C18:0) acid. The selectivity required in the

hydrogenation reaction, which expresses the above

relationships between the relative reaction rates

for the different triacylglycerols present, provides

guidance on the choice of catalyst. The process is

mostly carried out batchwise or, by linking a series

of batch reactors, in a semicontinuous manner. The

autoclave may be operated with or without hydrogen

recirculation. The loop reactor offers an alternative

form of the gas–liquid contactor.

0050The exothermic hydrogenation reaction leads to a

rise in temperature of the bulk oil of approximately

1.6



C per unit decrease in iodine value (the iodine

value of an oil is the standard measure of unsatur-

ation of oils and fats). Efficient cooling must therefore

be provided during the reaction in order to maintain

the oil at a stable temperature. After hydrogenation

the oil must be re-refined in order to remove traces of

catalyst from the oil.

0051Hydrogenation is particularly useful in situations

where it is important to maximize the use of one oil,

as the process conditions can be used to create a range

of hardened oils having different melting characteris-

tics and therefore suiting different applications. In the

case of soyabean oil, it is used to convert the relatively

unstable linolenic (C18:3) acid to more stable fatty

acids.

0052In recent years, the formation of TFA when hydro-

genating has given rise to much reconsideration of the

process, since these fatty acids are considered to be

health risk (see Figure 4). However, trans-isomeriza-

tion is favored where a fat with a high melting point

but without excessive reduction of its degree of un-

saturation is required. The formation of TFAs can be

controlled by limiting the reuse of catalyst, although

this obviously increases process costs. A solution to

this problem that is increasingly finding favor is to

hydrogenate the oil completely and thereafter inter-

esterify the fully hardened oil with a liquid oil.

Fractionation

0053In the harvesting year 1999/2000, palm oil accounted

for 25% of a total global vegetable oil production of

84 million tonnes, whereas in the year 1974/1975,

this oil accounted for only 8% of a total production

of approximately 30 million tonnes. The eight fold

increase in palm oil production reflected in these

figures largely accounts for the important role of

fractionation in modern edible oil processing, as

palm olein has become a major industrial frying oil.

0054Fractionation, the separation of liquid and solid

fractions of vegetable oils, is based on the reduction

in solubility of the more unsaturated in the more

saturated triacylglycerols as the bulk temperature is

reduced. Thus, cooling of the oil leads to progressive

crystallization of, in the first instance, trisaturated

triacylglycerols and thereafter disaturated triacylgly-

cerols. As crystallizing triacylglycerols exhibit differ-

ent polymorphic forms, it is essential to control

crystallization conditions in such a way as to minim-

ize occlusion of liquid (uncrystallized) material in the

crystallized phase. This normally requires slow

tbl0008 Table 8 Typical hydrogenation conditions

Temperature (



C) 100–250

Catalyst concentration (% Ni) 0.01–1.0

Hydrogen pressure (bar) 1–10

Hydrogen consumption (m

per tonne of oil

per unit iodine value drop)

0.93

Reaction rate (units of iodine value fall per

minute)

1–3

5912 VEGETABLE OILS/Oil Production and Processing

cooling of the oil to be fractionated. Separation of the

crystallized material from the liquid phase is generally

carried out by filtration. The occlusion of liquid oil in

the crystallized material means that the yield of fil-

trate is reduced, which is an important consideration

if the filtrate is the primary fraction. Where the filter

cake represents the primary fraction, this occlusion

reduces its ‘purity,’ which has an adverse effect on its

quality if this is required for specialized applications,

e.g., confectionery fats.

0055 The replacement of vacuum filters by the mem-

brane filter press in the 1980s reduced entrainment

of liquid oil in the filter cake, but membrane filter

press separation at 6 bar still leaves a cake containing

40–60% liquid oil.

0056 When fractionating expensive fats, it becomes

commercially feasible to fractionate oils in solvents

such as acetone or hexane, as this reduces oil entrain-

ment in the cake to less than 10% and at the same

time allows crystallization to be carried out far more

quickly.

0057 Fractionation is also used in combination with hy-

drogenation in the case of soyabean oil. In this case,

the conversion of linolenic (C18:3) to linoleic (C18:2)

acid is accompanied by the formation of some stearic

acid. In order to produce an oil clear at ambient tem-

perature, the hydrogenated oil is then fractionated.

0058 Fractionation has the advantage over other oil

modification processes of being a purely physical

process, carried out in conditions that do not affect

any of the components present beyond crystallizing

and melting them. The mild process operating condi-

tions also have the benefit of requiring only moderate

processing costs, but the process has the disadvantage

of depending on finding rewarding markets for its

secondary fractions.

0059Dewaxing of sunflower oil may be regarded as a

fractionation process, though in this case, the purpose

of the process is to remove minor quantities of wax

esters present in the oil, as these precipitate slowly at

low temperatures and give the oil a cloudy appear-

ance. The quantity of wax esters present in the oil

depends on whether whole seed or only the kernels

have been used for oil production, as more than 80%

of the wax present in the whole seed is found in the

hull. Oil from undehulled seed may contain more

than 1500 p.p.m. wax, whereas oil from dehulled

seed is likely to contain less than 500 p.p.m. Dewax-

ing is normally carried out by chilling the oil, which

should have had its phospholipid content reduced to

below 10 p.p.m., to approximately 0



C over a period

of 24 h in order to enable the wax to crystallize in

discrete form. The subsequent filtration can be accel-

erated by the addition of a filter aid to the wax–oil

slurry. The wax content of the processed oil should

not exceed 30 p.p.m. in this case. If a less stringent

specification applies, wax separation by centrifuga-

tion is feasible.

Sulphided Ni catalyst

Trans-isomer

suppressing conditions

(Regular Ni catalyst)

Test results were obtained with a trans-isomer

promoting sulphided catalyst (Nysosel SP-10)

and a regular nickel catalyst (Nysosel-222).

Trans-isomer promoting conditions: 200 ⬚C, 0.5 bar H

Trans-isomer suppressing conditions: 140 ⬚C, 3 bar H

140 120 100 80 60 40 20 0

Iodine value

Trans fatty acid content (%)

Trans-isomer

promoting conditions

(Regular Ni catalyst)

fig0004 Figure 4 Hydrogenation of soyabean oil using sulfided and nonsulfided nickel catalysts.

VEGETABLE OILS/Oil Production and Processing 5913

Interesterification

0060 The fatty acid groups in triacylglycerols can be re-

arranged within a single oil (intraesterification) or by

exchange of fatty acid groups with those of other oils,

the latter being known as interesterification. As is the

case with the other oil modification processes, the

purpose of interesterification is to alter the melting

properties of the fat or fat blend in order to improve

the functional properties of the product. The reaction

requires the presence of a catalyst, and alkaline

catalysts are generally used. In particular, sodium

methylate, also referred to as sodium methoxide,

is extensively used, but metallic sodium has also

been used.

0061 In the early stages of the development of this pro-

cess, both directed interesterification and random

interesterification were proposed for use, the former

involving interesterification and simultaneous

cooling in order to crystallize the saturated triacylgly-

cerols being formed and thus move the equilibrium

towards the formation of more saturated triacylgly-

cerols. Random interesterification, however, simply

aims to randomize the distribution of the available

fatty acid groups on the glycerol molecule and

thereby to alter the melting properties of the fat or

oil blend.

0062The aggressive nature of the catalyst makes it es-

sential that the moisture content and the FFA content

of the oil to be processed are reduced to the lowest

practical values, as hydrolysis of the catalyst results in

significant oil losses. It is also of crucial importance

that the catalyst is handled with great care by the

process operators, as exposure to it is likely to inflict

serious injury.

0063Interesterification (Figure 5) has now become an

important tool in the use of fully hardened oils, as this

enables an oil processor to minimize the content of

TFA in an oil blend. The process finds application in

the production of fat blends for use in spreads and of

bakery fats, as it facilitates the tailoring of the melting

properties of fats to specific requirements (Table 9).

It is also used in the production of cocoa-butter

replacers.

0064Immobilized lipases have been used successfully

to achieve interesterification on an industrial

scale. Lipases have been developed that will retain

activity at temperatures up to 80



C, but increased

Steam

to refining

Interesterified oil

Polish filter

Bleach

filter

Spent bleach earth

Coating

Bleacher

Bleach earth

Vacuum unit

Citric

acid

Dryer-

reactor

Steam

NaOH

Oil

Catalyst

fig0005 Figure 5 Interesterification plant arrangement.

5914 VEGETABLE OILS/Oil Production and Processing

temperatures result in higher FFA and diacylglycerol

contents, which either require removal by refining

or can adversely affect the product properties.

Although reuse of the immobilized enzyme has

been shown to be feasible, the cost of the immobil-

ized enzyme remains too high for general applic-

ability of enzymic interesterification. Present use

of this process appears to be confined to high-

value fats.

Applications

0065 The principal use for oils and fats is in the form of

liquid oil, either as salad oils or as frying oils. A

salad oil must principally display oxidative stability

and clarity in appearance, and a wide range of

refined oils can meet this requirement. Olive oil is

the most obvious example of an oil satisfying these

criteria without having been refined, but other oils

are sometimes also used in the unrefined state.

Frying oils must be resistant to oxidation at high

temperature, a high smoke point, and a minimum

tendency to foam in use. In the case of oils used for

industrial frying, oil cost is an important consider-

ation, and refined, bleached, deodorized palm olein

is widely used for this purpose in Europe and

various Asian countries. Lightly hydrogenated soya-

bean oil is the first choice for industrial frying in

the USA.

0066 Margarine and spreads have been a major source

of fat supply to the Western consumer. In the second

half of the twentieth century, the fat component

of margarine has increasingly been softened (by skill-

ful use of the various modification processes

discussed above) in order to make the product

spreadable at refrigerator temperatures. Spreads

have a lower fat content than margarine, and are

rapidly displacing them. The scraped surface heat

exchanger, which replaced the rotary cooler in the

production of margarines, has played an important

role in the growth of the margarine and spreads

industries.

0067Fats for baked products are widely used both

domestically and industrially, with the latter category

dominant. In some cases, these fats are blends of

individually partially hardened fats, blended to

achieve melting properties suitable for a specific ap-

plication. Emulsifiers may be added to the blend in

order to facilitate the incorporation of air in an appli-

cation.

0068Confectionery fats constitute a minor, but high-

value, part of the total applications field. Their

special characteristics of melting over a narrow tem-

perature range has meant that much work has gone

into identifying fats suitable for this application.

They are characterized by their high content of

symmetrical triacylglycerols, obtained by fraction-

ation in the case of cocoa-butter equivalents

(CBEs). Cocoa-butter substitutes, however, are

based on the oils rich in C14 fatty acids. As these

are incompatible with C18-rich fats in crystallized

form, care must be taken to exclude the lauric oils

from CBEs.

0069Nutritional aspects of oil and fat consumption

can be considered in terms of three characteristics –

the type of fatty acid present in the oils and fats

consumed, the modification of fatty acids by

processing, and the effect of processing on minor

components. Clearly, the ongoing debate about

healthy eating has favored the consumption of

more liquid oils (and thereby a reduction in the

consumption of hardened fats) in regions where

such choices exist. The choice between polyunsatur-

ated and monounsaturated fatty acids constitutes a

second level of consumer choice. The virtual elimin-

ation of erucic (C22:1) acid from rapeseed oil grown

tbl0009 Table 9 Solid fat content of fat blend (canola/soya stearin 70:30 w/w) before and after interesterification

Catalyst (sodium methoxide) concentration 0.3%

Temperature 110



Pressure 13 mbar

Solid fat content (%) Triacylglycerol composition (majorcomponents only)

Temperature (



C) Before

interesterification

After

interesterification

Before

interesterification

After

interesterification

10 42 47 LOO 11.6 5.3

21.1 38 25 OOO 45 17.8

26.7 38 22 OOS 1.6 33.3

33.3 37 15 SSS 24.1 2

40 35 9

L, linoleic acid; O, oleic acid; S, stearic acid.

From Journal of the American Oil Chemists’ Society 76: 783 (1999).

VEGETABLE OILS/Oil Production and Processing 5915

in Europe and North America has vastly increased

the quantity of this oil suitable for use in the food

world. Essential fatty acids are present in only a few

vegetable oils, and are often removed by hydrogen-

ation in the interests of oil stability.

0070 The most important modification of fatty acids

present in vegetable oils in the course of processing

is the formation of TFA. Hydrogenation is the main

source of TFA in edible oils, and earlier sections con-

sider some of the changes that have been made in

order to reduce the formation of TFA. Although it is

generally only a minor contributor to TFA content,

high-temperature deodorization (at temperatures of

> 250



C) does produce measurable quantities of

these fatty acids. High-temperature deodorization

may also result in an increase in polar lipids, includ-

ing polymers.

0071 Tocopherols present in crude oils are lost to

some extent in the bleaching stage as well as in

deodorization, but the latter stage is responsible

for the major share of the loss, particularly where

very high temperatures are used for this operation.

In Europe, deodorization temperatures have there-

fore been modified in order to reduce this loss.

When using chemical refining, the deodorizer distil-

late is easier to process for tocopherol recovery, and

in North America – where chemical refining is

preferred to physical refining – addition of toco-

pherol concentrate to oils is sometimes used to

compensate for the loss of tocopherols in the

deodorizer.

See also: Fats: Production of Animal Fats; Uses in the

Food Industry; Digestion, Absorption, and Transport;

Requirements; Fat Replacers; Classification; Occurrence;

Phospholipids: Determination; Physiology; Vegetable

Oils: Types and Properties; Composition and Analysis;

Dietary Importance