Chapter 10
Degumming and Lecithin Processing and Utilization
David R. Erickson
Consultant
American Soybean Association
St. Louis, MO
Introduction
Degumming is the process for removal of phosphatides from crude soybean and
other vegetable oils. The phosphatides are also called gums and lecithin. The latter
term is also the common name for phosphatidyl choline, but common usage refers
to the array of phosphatides present in all crude vegetable oils. Although all crude
vegetable oils contain gums, soybean oil is currently the major source of commercial lecithin, because it contains the largest amount of gums and is also the world's
leading vegetable oil (see Chapter 1).
The relative composition of commercial soybean lecithin from conventionally
solvent-extracted crude soybean oil is shown in Table 10.1. Changes from this composition, as affected by different extraction practices will be discussed in the following section, followed by a discussion of lecithin production and utilization.
Degumming Processes
Simply stated, degumming is the process used to remove phosphatides, or gums,
from crude soybean oil. As shown in Table 10.1, the gums obtained from degumming consist of a mixture of soybean oil and phosphatidyl compounds (1). The
chemical structures of the three major phosphatides are shown in Fig. 10.1.
In conventional solvent extraction, only half of the phosphatides present in soybeans are extracted with the composition shown in Table 10.1. Use of preparation
processes such as the Alcon process or expanders will change the array of phosphaTABLE 10.1 Approximate Composition of Natural
Commercial Soybean Lecithin (1)
%
Soybean oil
Phosphatidylcholine
Phosphatidyl ethanolamine
Phosphatidyl inositol
Phytoglycolipids, minor phosphatides
Carbohydrates
Moisture
174
35
16
14
10
17
7
1
D.R. Erickson
175
tides in the crude oil by increasing the phosphatidyl choline content by about 30 to
40% and will increase the total extracted phosphatides (2). In the Alcon process double the normal amount of gums is extracted, and use of the expander may approach
that level depending on the expander conditions of temperature, time, and moisture
addition (for details of these processes, see Chapter 6).
Degumming of soybean oil is done for one of the following reasons:
1. To produce lecithin
2. To prepare degummed oil for long-term storage or transport
3. To prepare a degummed oil for caustic or physical refining
The first reason is obvious and the second is necessary to prevent development of
troublesome sludges in storage or transport. Such sludges form because the phosphatides are hygroscopic and become hydrated by moisture from the air. Phosphatides are soluble in dry crude oil, but when hydrated, they become more dense than
the triglycerides and precipitate, or settle out, from the crude oil, causing the troublesome sludges. Although this phenomenon is unwanted in storage or transport of
crude oils, it is the basis for the process of degumming. Water is added to the crude
oil to hydrate the phosphatides and thus prepare them for removal by gravitational
forces or centrifugation. The latter is the modern process.
The process of degumming is simple, but the quality of the crude soybean oil
has an influence on the efficacy of degumming. The phosphatides in crude soybean
oil exist in either the hydratable or nonhydratable forms. The hydratable phosphatides (HP) are readily removed by the addition of water, whereas the nonhydrat-
9
I9
I 9
9
I 9
I9
CHJJOCR!
CH2OCR1
CHOCR
CHOCR
2
2
CH2OP-OCH2CH2N(CH3)3
CH20-P-0-CH2CH2NH3
Phosphatidyl choline
Phosphatidyl ethanolamine
Phosphatidyl inositol
Fig. 10.1. Structures of the three major phosphatides in soybean lecithin.
176
Degumming and Lecithin Processing
able phosphatides (NHP) are relatively unaffected by water and tend to be more oilsoluble (i.e., remain in the oil phase). The NHPs are generally considered to be the
calcium and magnesium salts of phosphatidic acids that arise from the enzymatic
action of phospholipases released by damage to the cellular structure of the soybean (3). Such damage may occur with handling, processing practices, or both. The
formation of NHPs is shown in Fig. 11.3.
Poor-quality soybean oils are defined by a higher FFA content (>1.0%) indicating a higher than normal NHP content. Other indicators of poor-quality crude soybean oils are a lower phosphatide content (<1.0%) in the extracted oil and a high
content (>0.79%) of phosphatides in degummed oils (4). Normal-quality soybean oil
from conventional solvent extraction will have about 90% HP and 10% NHP, and
their total phosphatide content will range from 1.1 to 3.2% (5). The FFA of goodquality crude soybean oil will be in the range of 0.5 to 1.0%, which will be reduced
by 20 to 40% in the degummed oil (6,7).
Phosphatides also form complexes with metals (iron and copper), and their content in degummed and refined oils is reduced as discussed in Chapter 11.
Recognition of the role of calcium and magnesium has led to the use of demineralized (soft) water for degumming and the use of phosphoric or citric acids as aids in
degumming. These latter two acids are food-grade and combine with the calcium
and magnesium salts, allowing transfer of the phosphatidic acids from the oil to the
aqueous phase, thus removing them from the crude oil. The use of acids in degumming is not recommended for gums intended for use as lecithins, because their presence will cause darkening of the lecithin. The effect of the NHPs on caustic refining
is discussed in Chapter 11.
Some plants use steam condensates for degumming rather than deionized water;
however, the absence of iron in the condensate should be ensured. Some plants also use
excess stripping steam in the last stages of miscella desolventizing as a means for hydration of phosphatides, but this is more difficult to control than simple water addition.
Water Degumming
In degumming of soybean oil for lecithin production, it is standard practice to filter
the crude oil first to remove meal fines, which affect the clarity of lecithin and contribute to the hexane-insoluble content (8). If the degumming centrifuge is self-clean¬
ing and the gums are destined for return to the meal stream, it may not be necessary
to filter the crude oil; however, some plants filter the crude oil routinely to prevent the
possible increase of free fatty acids during storage and to reduce refining losses (7).
In the batch water degumming process, soft water at a level of 1 to 2%, depending on the phosphatide content, is added to warm (70°C, 158°F) oil and mixed thoroughly for 30 to 60 minutes, followed by settling or centrifugation. The amount of
water to add is about 75% of the phosphatide content (9), but some plants routinely
add a fixed percentage based on experience.
A diagram of the process of continuous water degumming is shown in
Fig. 10.2 (10). In this case, the oil is heated to about 70 to 80°C (158 to 176°F), soft
D.R. Erickson
177
water is added by an in-line proportioning system, the oil and water are mixed inline, and then the mixture flows to a retention vessel, where it is held for 15 to 30
minutes and then sent to a centrifuge.
For best results in both batch and continuous degumming, it is absolutely essential to provide sufficient time for the water and the phosphatides to react. Hydration
of phosphatides is not an instantaneous reaction and requires initial intensive mixing, followed by sufficient time to allow hydration and coalescence of the hydrated
micelles. An excellent general discussion of the chemistry of degumming has been
published by Dijkstra (11).
Experience with degumming and caustic refining systems for soybean oils with
little or no retention times ("short-mix") has shown that such systems are not adequate for production of optimum-quality soybean oils (12,13,14).
With good-quality crude soybean oil, simple water degumming will reduce the
phosphorus content to less than 50 ppm (0.005%), which is well below the 200 ppm
(0.02%) level specified in the National Oilseed Processors Association (NOPA) trading rules for crude degummed soybean oil (15). The relation between phosphorus
and phosphatide content is
% Phosphatides = 30.0 x % Phosphorus content
Filtered, warm, crude oil
Water
_J
Flow meter
L_
Flow meter
T
Pipeline dwell
agitator
Centrifuge
Gums
Oil
Heat
Vacuum dryer
Bleaching agent
Fluidity agent
Cooler
Mixing tank
Agitated-film
evaporator
Vacuum
Condenser
Cooler
Condensate
receiver
Dry lecithin
Degummed
dry
soybean oil
To storage
Condensate
+> To packaging
Fig. 10.2. Flowsheet for degumming soybean oil and crude lecithin production.
Source: Brian, R., /. Amer. Oil Chem. Soc. 53: 27, (1976).
178
Degumming and Lecithin Processing
Degumming of Nonconventional Solvent-Extracted Oils
As just mentioned, only about 50% of the phosphatides present in soybeans are
extracted by conventional extraction processes. However, it has long been recognized that there is an increase in hexane-extractables of soybean meal after the heat
and moisture treatment in the desolventizer-toaster. Subsequently, it was discovered
and patented by Koch (16) that a heat and moisture treatment of flaked soybeans
before extraction essentially doubled the amount of phosphatides in the extracted
crude soybean oil. It was also found that there was a different array of phosphatides
and that the hydratability was increased, resulting in degummed oils of 0.03 to
0.09% phosphatides (10-30 ppm P). These findings have been commercialized and
called the Alcon process (Lurgi Ol. Gas. Chemie Gmbh, Frankfurt, Germany). A
description of this process, and plant results, have been published by Penk (17). The
lecithin produced by this is of a different composition than lecithin from conventional extraction processes, being enriched 30 to 40% in phosphatidyl choline.
The use of expanders in preparation for extraction gives results approaching
those found with the Alcon process, depending on the degree of moist heat treatment
occurring in the expander.
Degumming Agents
In addition to water, other additives have been studied and or used to facilitate
degumming. The use of phosphoric and citric acid for removal of NHPs has already
been mentioned. Other acids studied have been acetic, oxalic, nitric, boric, and tannic (18), but to our knowledge they have never been commercialized. The use of
acetic anhydride for degumming of soybean oil has been done on a commercial scale
in the United States (19) and is in use in some plants. The advantage is a higher yield
of lecithin (i.e., lower gum content of the degummed oil) and ready removal of the
volatile acetic acid in drying of the lecithin.
Degumming to Prepare an Oil for Caustic or Physical Refining
Caustic refining of soybean oil may be done on either crude or crude degummed oil.
Since the market for soybean lecithins is much less than the potential supply as will
be shown in this chapter, it is a practice in the United States simply to caustic refine
crude soybean oil, thereby disposing of lecithin into the soapstock, when not making lecithin. The conventional thinking has been that the loss of neutral oil in refining
crude oil is less than the combined losses of degumming followed by caustic refining
of the degummed oil.
When a refinery is adjacent to an extraction plant, it has the possibility of adding
the wet gums to the meal stream and getting at least a meal price for the gums. Such
practice will then reduce the refining loss by caustic-refining degummed oil. In addition, there would be less soapstock, and it would give fewer problems in acidulation.
Although it is not necessary to degum and refine soybean oil sequentially, the
decision as whether to do so or simply to refine crude oil may be more involved than
just considering refining losses, due to the effects just mentioned.
D.R. Erickson
179
Degumming of soybean oil, as a preparatory step for physical refining, has
received considerable attention in the last few years and has recently been well
reviewed by Dijkstra (11). The principal impetus for physical refining of soybean oil
is to avoid the environmental problems associated with soapstocks from caustic
refining. For a discussion of physical refining, see Chapter 14.
In the published results of degumming practices for physical refining, the
degummed oils have a P content of 5 to 10 ppm for "good" oils and >30 for "poor"
oils (20). To date, even with the use of special degumming techniques, physically
refined soybean oils do not meet the flavor and flavor stability requirements of the
U.S. market. They have met market requirements in other countries whose consumers are less demanding.
Production of Lecithin
The potential supply of lecithin from soybean oil is about 374,000 metric tons (802
million lbs) on a worldwide basis, but the market for lecithin is estimated at 100,000
to 150,000 metric tons. The other routes for use or disposal of the excess lecithin are
to return it to the meal stream at the extraction plant or to caustic-refine crude oil,
which disposes of the excess lecithin into the soapstock.
The process for lecithin production is shown in Fig. 10.2, and the important
aspects up to and including the centrifugation have been discussed in the foregoing
section on degumming. The wet gums coming from the centrifugation will contain
about 50% water, with the nonaqueous portion having the composition shown in
Table 10.1. Wet gums are susceptible to microbial fermentation and require immediate drying or treatment, for brief storage, with a preservative such as a dilute solution of hydrogen peroxide. Required dosage will depend on expected storage time,
ambient temperature, and sanitary conditions (microbial types and load). Any storage of wet gums is not recommended, and the brief storage just mentioned is for necessary accumulation for batch drying systems.
In the process flow shown in Fig. 10.2, the wet gums from the centrifuges are
transferred to a mixing tank, where bleaching agents, fluidity agents, or both can be
added. With or without additives, the wet gums, containing about 50% water, must
then be dried down to a maximum of 1% moisture.
The drying of lecithins is a critical step, because the gums tend to darken with
heat, and during drying there is a large viscosity increase as the moisture is reduced.
This phenomenon is shown in Fig. 10.3, where the increase in viscosity begins at
about 20% moisture, peaks at about 8% moisture, and then falls rapidly between 7
and 4% reduction (21).
Batch-type dryers operate under vacuum and are equipped with rotating coils
circulating water at about 60 to 70°C (140 to 158°F). More modern continuous dryers utilize agitated-film dryers for moisture removal. A comparison of the conditions
used in these two types of dryers is shown in Table 10.2 (21).
From the process flow shown in Fig. 10.2 a variety of lecithins may be produced, and the National Oilseed Processors Association (NOPA) publishes sped-
180
Degumming and Lecithin Processing
TABLE 10.2
Average Process Conditions for Drying Lecithin Sludge (Wet Gums) (21)a
Continuous
agitated-film
Process variable
Batch dryer
dryer
6
Temperature
°F
140-176
176-203
°C
60- 80
80- 95
Residence time, min
180-240
1- 2
Absolute pressure, mm Hg
20- 60
50-300
Starting product: Wet gums with 50% moisture. End product: Lecithin with less than 1 % moisture.
^Vacuum dryer with rotating, ball-shaped coils heated with warm water.
fications for six lecithin commercial grades, as shown in Table 2.14. Sullivan and
Szuhaj (23) created a useful classification of soybean lecithins as shown in Table 10.3.
In their classification, the NOPA products are considered "natural", followed by
"refined" lecithins, from custom blending and solvent treatments, and ending with
"Chemically modified" lecithins.
10,000 r
8,000
co
$
8
&
6,000
4,000
2,000 I
10
Moisture, %
15
20
Fig. 10.3. Viscosity of lecithin sludge at 158°F (70°C) in relation to moisture content. Source: Van Nieuwenhuyzen, W., J. Amer. Oil Chem. Soc. 53:425, (1976).
D.R. Erickson
181
TABLE 10.3 Classification of Soybean Lecithins (23)
I. Natural
A. Plastic
1. Unbleached
2. Single-bleached
3. Double-bleached
B. Fluid
1. Unbleached
2. Single-bleached
3. Double-bleached
II. Refined
A. Custom blended natural
B. Oil-free phosphatides
1. As is
2. Custom blended
C. Fractionated oil-free phophatides
1. Alcohol-soluble
a. As is
b. Custom blended
III. Chemically modified
Oil-free lecithins are produced by extracting the soybean oil from the natural
lecithins with acetone. This is done by both batch and continuous processes and
requires high-quality crude lecithin for best results. In turn, alcohol fractionation of
an oil-free lecithin can be employed to give an alcohol-soluble fraction high in
phosphatidyl choline, and an alcohol-insoluble fraction, enriched in phosphatidyl
inositol. The composition of oil-free lecithin and the alcohol fractionation products
is shown in Table 10.4. As shown in the table, the lecithin products vary in their
emulsifying properties.
Chemically modified lecithins include hydrogenated, hydroxylated, acetylated,
sulfonated, and halogenated products. All of the chemical modifications are
designed to modify the emulsifying properties of the lecithins and improve their dispersibility in aqueous systems (21).
TABLE 10.4 Approximate Composition of Commercially Refined Lecithin Fractions (23)
Fraction
Phosphatidyl choline
Cephalin
Inositol and other phosphatides,
including glycolipids
Soybean oil
Other constituents
Emulsion type favored
3
Oil-free
lecithin (%)
Alcohol-soluble
lecithin (%)
Alcohol-insoluble
lecithin (%)
29
29
60
30
4
29
32
3
7
Either oil-in-water
or water-in-oil
2
4
4
Oil-in-water
55
4
8
Water-in-oil
includes sucrose, raffinose, stachyose, and about 1 % moisture.
Degumming and Lecithin Processing
182
Soybean Lecithin Utilization
A comprehensive listing of the uses and functions of phospholipids has been published by Schneider (24) and is shown in Table 10.5.
Lecithin also has unique release properties and as such has been used in pan frying
formulations and in pan greases for baking (25). In addition, it is also used industrially
as a release agent for ready removal of both wooden and metal concrete casting forms.
A more detailed description of lecithin utilization, including those from other
oilseeds can be found in the recent AOCS monograph by Szuhaj (26).
TABLE 10.5
Uses and Functions of Phospholipids (24)
Product
Food
Instant food
Baked goods
Chocolate
Margarine
Dietetics
Feedstuffs
Calf milk replacers
Industry
Insecticides
Paints
Magnetic tapes
Leather
Textiles
Cosmetics
Hair care
Skin care
Pharmaceuticals
Parental nutrition
Suppositories
Cremes, lotions
References
Function
Wetting and dispersing agent; emulsifier
Modification of baking properties; emulsifier; antioxidant
Viscosity reduction; antioxidant
Emulsifier; antispattering agent; antioxidant
Nutritional supplement
Emulsifier; wetting and dispersing agent
Emulsifier; dispersing agent; active substance
Dispersing agent; stabilizer
Dispersing agent; emulsifier
Softening agent; oil penetrant
Softening; lubricant
Foam stabilizer; emollient
Emulsifier; emollient, refatting, wetting agent
Emulsifier
Softening agent; carrier
Emulsifier; penetration improver
1. Brekke, O.L., in Handbook of Soy Oil Processing and Utilization, edited by
D.R. Erickson et al., American Oil Chemists' Society, Champaign, IL, 1978, p. 77.
2. Kock, M., J. Amer. Oil Chem. Soc. 60: 210 (1983).
3. Hvolby, A., J. Amer. Oil Chem. Soc. 48: 503 (1971).
4. List, G.R., in Handbook of Soy Oil Processing and Utilization, edited by D.R. Erickson
et al., American Oil Chemists' Society, Champaign, IL, 1978, pp. 355-376.
5. Swem, D., in Bailey's Industrial Oil and Fat Products, edited by D. Swem, Vol. I,
4th edn., John Wiley and Sons, New York, 1979, p. 49.
6. Sleeter, R.T., J. Amer. Oil Chem. Soc. 58: 239 (1981).
7. Charpentier, R., INFORM 2: 208 (1991).
D.R. Erickson
183
8. Official Methods and Recommended Practices, 4th edn., American Oil Chemists'
Society, Champaign, IL, 1993. Method Ja 3-87 (1993)
9. Brekke, O.L., in Handbook of Soy Oil Processing and Utilization, edited by
D.R. Erickson et al., American Oil Chemists' Society, Champaign, IL, 1978, p. 73.
10. Brian, R., J. Amer. Oil Chem. Soc. 53: 27 (1976).
11. Dijkstra, A.J., in Proceedings of the World Conference on Oilseed Technology and
Utilization, edited by T.A. Applewhite, American Oil Chemists' Society, Champaign, IL,
1992, pp. 138-151.
12. Wiedermann, L.H., J. Amer. Oil Chem. Soc. 58: 159 (1981).
13. Erickson, D.R., J. Amer. Oil Chem. Soc. 60: 351 (1983).
14. Erickson, D.R., and L.H. Wiedermann, INFORM 2: 201 (1991).
15. Yearbook and Trading Rules, National Oilseed Processors Association, Washington, DC,
1993-1994, p. 86.
16. Kock, M., U.S. Patent 4,255,346 (1981).
17. Penk, G., in Proceedings: World Conference on Emerging Technologies in the Fats and
Oils Industry, edited by A. R. Baldwin, American Oil Chemists' Society, Champaign, IL,
1986, pp. 38^5.
18. Ohlson, R., and C. Svenson, J. Amer. Oil. Chem. Soc. 53: 8 (1976).
19. Meyers, N.W., J. Amer. Oil Chem. Soc. 34: 93 (1957).
20. Seger, J.C., and R. van de Sande, in World Conference Proceedings Edible Fats and Oils
Processing, edited by D.R. Erickson, American Oil Chemists' Society, Champaign, IL,
1990, pp. 88-93.
21. Van Nieuwenhuyzen, W, J. Amer. Oil. Chem. Soc. 53: 425 (1976).
22. Yearbook and Trading Rules, National Oilseed Processors Association, Washington, DC,
1993-1994, p. 98.
23. Sullivan, D.R., and B.F. Szuhaj, J. Amer. Oil Chem. Soc. 52: 152A (1975).
24. Schneider, M., in Proceedings World Conference on Emerging Technologies in the Fats
and Oils Industry, edited by A.R. Baldwin, American Oil Chemists' Society, Champaign,
EL, 1986, pp. 160-164.
25. Dashiell, G., in World Conference Proceedings Edible Fats and Oil Processing, edited
by D.R. Erickson, American Oil Chemists' Society, Champaign, IL, 1990, pp. 396-401.
26. Szuhaj, B.F., Lecithins: Sources, Manufacture, and Uses, American Oil Chemists'
Society, Champaign, IL, 1989.