Castor Oil: Properties, Uses, and Optimization of
Processing Parameters in Commercial Production
1Department of Oils, Fats & Wa xes, Sardar Patel University, Gujarat, India. 2SDI Farms, Inc., Miami, FL, USA . 3Jayant Oils and Derivatives
Ltd., Vadodara, India. 4Department of Mathematics and Physical Sciences, Louisiana State University—Alexandria, L A, USA. 5Department
of Chemistr y, Oklahoma Baptist University, Shawnee, OK, USA. 6Process Analytical Technology, GlaxoSmithK line, King of Pr ussia, PA,
USA. 7Department of Chemistry, East Central University, Ada, OK, USA. 8The Marine Science Institute, College of Science, University
ofthePhilippines—Diliman, Quezon City, Philippines.
ABSTRAC T: Castor oil, produced from castor beans, has long been considered to be of important commercial value primarily for the manufacturing of
soaps, lubricants, and coatings, among others. Global castor oil production is concentrated primarily in a small geographic region of Gujarat in Western
India. is region is favorable due to its labor-intensive cultivation method and subtropical climate conditions. Entrepreneurs and castor processors in the
United States and South America also cultivate castor beans but are faced with the challenge of achieving high castor oil production eciency, as well as
obtaining the desired oil quality. In this manuscript, we provide a detailed analysis of novel processing methods involved in castor oil production. We discuss
novel processing methods by explaining specic processing pa rameters involved in castor oil production.
KEYWORDS: castor oil, castor beans, ricinoleic acid, nonedible oil, crude castor oil rening
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Castor oil has long been used commercially as a highly renewable
resource for the chemical industry.1,2 It is a vegetable oil obtained
by pressing the seeds of the castor oil plant (Ricinus communis L.)
that is mainly cultivated in Africa, South America, and India.3,4
Major castor oil-producing countries include Brazil, China, and
India. is oil is known to have been domesticated in Eastern
Africa and was introduced to China from India approximately
1,400 years ago.4 India is a net exporter of castor oil, account-
ing for over 90% of castor oil exports, while the United States,
European Union, and China are the major importers, account-
ing for 84% of imported castor oil.5,6
India is known as the world leader in castor seed and oil
production and leads the international castor oil trade. Castor
oil production in this country usually uctuates between
250,000 and 350,000 tons per year. Approximately 86% of
castor seed production in India is concentrated in Gujarat,
followed by Andhra Pradesh and Rajasthan. Specically, the
regions of Mehsana, Banaskantha, and Saurashtra/Kutch in
Gujarat and the districts of Nalgonda and Mahboobnagar of
Andhra Pradesh are the major areas of castor oil production
in India.7 e economic success of castor crops in Gujarat
in the 1980s and thereafter can be attributed to a combina-
tion of a good breeding program, a good extension model,
coupled with access to well-developed national and interna-
Castor is one of the oldest cultivated crops; however, it
contributes to only 0.15% of the vegetable oil produced in
the world. e oil produced from this crop is considered to
be of importance to the global specialty chemical industry
because it is the only commercial source of a hydroxylated
fatty acid.9 Even though castor oil accounts for only 0.15% of
the world production of vegetable oils, worldwide consump-
tion of this commodity has increased more than 50% during
the past 25 years, rising from approximately 400,000 tons
in 1985 to 610,000 tons in 2010.9,10 On average, worldwide
consumption of castor oil increased at a rate of 7.32 thousand
tons per year. In general, the current rate of castor oil pro-
duction is not considered sucient to meet the anticipated
increase in demand.
ere are various challenges that make castor crop cul-
tivation dicult to pursue. Climate adaptability is one of
the challenges restricting castor plantation in the U.S. e
plant also contains a toxic protein known as ricin, providing
a challenge from being produced in the U.S. It also requires
a labor-intensive harvesting process, which makes it almost
impossible for the U.S. and other developed countries to pur-
sue castor plantation.
Journal name: Lipid Insights
Journal ty pe: Review
Runni ng head verso: Patel et a l
Runni ng head recto: Castor oil: properties, uses, and optimizat ion of processing pa rameters
Patel et al
Castor plant grows optimally in tropical summer rainfall
areas. It grows well from the wet tropics to the subtropical dry
regions with an optimum temperature of 20°C–25°C. e
high content of the oil in the seeds can be attributed to the
warm climate conditions, but temperatures over 38°C can lead
to poor seed setting. Additionally, temperatures low enough
to induce the formation of frost is known to kill the plant.11
As of 2008, three countries (India, China, and Brazil)
produced 93% of the world’s supply of castor oil. Because pro-
duction is concentrated mainly in these three countries, total
castor production varies widely from year to year due to uctu-
ations in rainfall and the size of the areas utilized for planting.
As a consequence, this concentration has led to cyclic castor
production. us, diversication of castor production regions
and production under irrigation would hopefully reduce the
climatic impact on castor supplies.9
In the United States, the hazardous chemical products
found in the castor plant, especially ricin has been a major
concern.9,12–15 e body of scientic literature related to
castor plants, especially on the detailed processing parameters
involved in commercial production, has been relatively small
over the past century.9 Over the years, there has been consid-
erable interest and research done on the uses and properties of
castor but not on a commercial scale. Castor oil studies have
shown increasing growth with the number of manuscripts
increasing sixfold since the 1980s (Fig. 1). While alterna-
tive breeding programs and marketing can lead to economic
growth of castor oil production, at the commercial level,
various projects fail due to the lack of knowledge about novel
processing methods and parameters used in castor oil produc-
tion. is manuscript discusses those processing parameters in
detail. Although the castor bean processing method can typi-
cally be considered a simple process, it can also be complicated
if the operators are unaware of its exact processing parameters
and operating procedures. Specically, process parameters for
castor oil production should be optimized to achieve high oil
extraction eciency through a solvent extraction method.16,17
No scientic literature currently exists discussing in detail the
commercial castor processing parameters. is contribution
discusses in detail the commercial castor processing parameters
and the important key points needed on how to manufacture
the desired quality of castor oil, both of which are important
to castor oil producers.
Castor Oil and its Properties
Castor beans are cultivated for their seeds (Fig. 2), yield-
ing a viscous, pale yellow nonvolatile and nondrying castor
oil.18 e physical properties of castor oil have been studied
(Table 1). Comparative analysis showed that the values of
viscosity, density, thermal conductivity, and pour point for
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PHYSICAL PRO PERTIES
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Castor oil: properties, uses, and optimization of processing parameters
castor oil were higher than the values of a standard lubricant
(SAE 40 engine oil).19
e unique structure of castor oil oers interesting prop-
erties, making it appropriate for various industrial applica-
tions. Castor oil is known to consist of up to 90% ricinoleic,
4% linoleic, 3% oleic, 1% stearic, and less than 1% linolenic
fatty acids. Castor oil is valuable due to the high content of
ricinoleic acid (R A), which is used in a variety of applications
in the chemical industry (Fig. 3).20
e hydroxyl functionality of RA makes the castor oil a
natural polyol providing oxidative stability to the oil, and a rela-
tively high shelf life compared to other oils by preventing perox-
ide formation. e presence of the hydroxyl group in RA and RA
derivatives provides a functional group location for performing
a variety of chemical reactions including halogenation, dehydra-
tion, alkoxylation, esterication, and sulfation. As a result, this
unique functionality allows the castor oil to be used in industrial
applications such as paints, coatings, inks, and lubricants.20
Castor beans, the source of castor oil, contain some aller-
genic (2S albumin) proteins as well as ricin; however, pro-
cessed or rened castor oil is free from any of these substances
and can be safely used in pharmaceutical applications. is can
be attributed to its wide range of biological eects on higher
organisms.13,21 Ricin is found exclusively in the endosperm of
castor seeds and is classied as a type 2 ribosome-inactivating
protein.22,23 Type 2 ribosome-inactivating proteins such as
ricin from castor oil are lectins, which irreversibly inactivate
ribosomes, thus stopping protein synthesis and eventually
leading to cell death. is makes ricin a potent plant toxin.24
Applications of castor oil and its derivatives.
Fuel and biodiesel. Castor is considered to be one of the
most promising nonedible oil crops, due to its high annual
seed production and yield, and since it can be grown on mar-
ginal land and in semiarid climate. Few studies have been
done regarding castor fuel-related properties in pure form or
as a blend with diesel fuel, primarily due to the extremely high
content of RA. In a study by Berman et al,25 it was found
that methyl esters of castor oil can be used as a biodiesel
alternative feedstock when blended with diesel fuel. How-
ever, the maximum blending level is limited to 10% due to
the high levels of RA present in the oil, which directly aects
biodiesel’s kinematic viscosity and distillation temperature.
Another study by Shojaeefard et al26 examined the eects of
castor oil biodiesel blends on diesel engine performance and
emissions. ey found that a 15% blend of castor oil–biodiesel
was an optimized blend of biodiesel–diesel proportions. e
results indicated that lower blends of biodiesel provide accept-
able engine performance and even improve it. Similar to the
study by Shojaeefard et al,26 Panwar et al27 prepared the castor
methyl ester by transesterication using potassium hydroxide
(KOH) as catalyst. ey then tested this methyl ester by using
it in a four-stroke, single cylinder variable compression ratio
type diesel engine. It was concluded that the lower blends of
biodiesel increased the break thermal eciency and reduced
the fuel consumption. Further, the exhaust gas temperature
increased with increasing biodiesel concentration. Results of
their study proved that the use of biodiesel from castor seed
oil in a compression ignition engine is a viable alternative
to diesel. e transesterication reactions of castor oil with
ethanol and methanol as transesterication agents were also
studied in the presence of several classical catalytic systems.
Results of their study show that biodiesel can be obtained by
transesterication of castor oil using either ethanol or metha-
nol as the transesterication agents.28 Although these studies
have shown promising results for the use of castor oil as a tech-
nically feasible biodiesel fuel, a major obstacle still exists in its
use as a biodiesel in some countries such as Brazil. In Brazil,
government policies promoted castor as a biodiesel feedstock
in an attempt to bring social benets to small farmers in the
semiarid region of the country.29,30 However, seven years after
Figure 3. GF9A2B4:%C8>@B8@>9%PW%>2B23P:92B%4B2?=%8F9%L>2A4>5%BPALP3938%PW%B4C8P>%P2:7
Patel et al
the Brazilian biodiesel program was launched, negligible
amounts of castor oil have been used for biodiesel produc-
tion. It was found that the castor oil produced in this program
was not primarily used for biodiesel but sold for higher prices
to the chemical industry.30 Another major constraint in the
use of castor oil as a feedstock for biodiesel has been the high
price paid for the oil as industrial oil rather than its physi-
cal and chemical properties. Castor oil is in high demand by
the chemical industry for the manufacture of very high value
products. For this reason, it is not economical to use this oil
as a replacement for diesel.9 Finally, although castor oil can be
used directly to replace normal diesel fuel, the high viscosity
of this oil limits its application.31
Polymer materials. Castor oil and its derivatives can be used
in the synthesis of renewable monomers and polymers.2 In one
study, castor oil was polymerized and cross-linked with sulfur
or diisocyanates to form the vulcanized and urethane deriva-
tives, respectively.32 In another study, full-interpenetrating
polymer networks (IPNs) were prepared from epoxy and cas-
tor oil-based polyurethane (PU), by the sequential mode of
synthesis.33 Similar to the aforementioned study, a series of
two-component IPN of modied castor oil-based PU and
polystyrene (PS) were prepared by the sequential method.34
IPN can be elaborated as a special class of polymers in which
there is a combination of two polymers in which one is synthe-
sized or polymerized in the presence of another.35, 36 us, IPN
formulation can be considered a useful method to develop a
product with excellent physicomechanical properties than the
normal polyblends. IPN is also known as polymer alloys and
is considered to be one of the fastest growing research areas in
the eld of polymer blends in the last two decades.34
Castor oil polymer (COP) has also been shown to have
a sealing ability as a root-end lling material. A root-end
lling material simply refers to root-end preparations lled
with experimental materials. e main objective of this type
of material is to provide an apical seal preventing the move-
ments of bacteria and the diusion of bacterial products from
the root canal system into the periapical tissues.37 In a study
conducted by de Martins et al,38 the sealing ability of COP,
mineral trioxide aggregate (MTA), and glass ionomer cement
(GIC) as root-end lling materials were evaluated. MTA is
primarily composed of tricalcic silicate, tricalcic alluminate,
and bismuth oxide and is a particular endodontic cement.39
GICs, on the other hand, are mainstream restorative materials
that are bioactive and have a wide range of uses such as lining,
bonding, sealing, luting, or restoring a tooth.40 Results of their
study show that the COP had a greater sealing ability when
used as a root-end lling material than MTA and GIC.
Biodegradable polyesters are one of the most common
applications using castor oil.41 Polyesters are the rst syn-
thetic condensation polymers prepared by Carothers during
the 1930s.42,43 ey are known to be biodegradable and envi-
ronmental friendly, with a wide array of applications in the
biomedical eld, as well in the preparation of elastomers and
packaging materials.44,45 Fatty acid scaolds are desirable
biodegradable polymers, though they are restricted by their
monofunctional property. at is, most fatty acids have a
single carboxylic acid group. RA, however, is known to be one
of the few naturally available bifunctional fatty acids with an
additional 12-hydroxy group along with the terminal carbox-
ylic acid (Fig. 3). e presence of this hydroxyl group provides
additional functionality for the preparation of polyesters or
polyester-anhydrides. e dangling chains of the RA impart
hydrophobicity to the resulting polyesters, thereby inuenc-
ing the mechanical and physical property of the polymers.
ese chains act as plasticizers by reducing the glass transition
temperatures of the polyesters.41,4 6 Castor oil can be combined
with other monomers to produce an array of copolymers.
Fine-tuning these copolymers can provide materials with
dierent properties that nd use in products ranging from
solid implants to in situ injectable hydrophobic gel.41
Soaps, waxes, and greases. Castor oil has been used to
produce soaps in some studies.47–49 Some studies also utilize
castor oil in waxes.50–53 One study by Dwivedi and Sapre54
utilized castor oil in total vegetable oil greases. Total vegetable
oil greases are those in which both the lubricant and gellant
are formed from vegetable oil. eir study utilized a simul-
taneous reaction scheme to form sodium and lithium greases
using castor oil.
Lubricants, hydraulic, and brake uids. Castor oil has also
been used for developing low pour point lubricant base stocks
through the synthesis of acyloxy castor polyol esters.55 e low
pour point property helps to provide full lubrication when the
equipment is started and is easier to handle in cold weather.56
An interesting study by Singh showed the excellent poten-
tial of castor oil-based lubricant as a smoke pollution reducer.
In his research, a biodegradable two-stroke (2T) oil, a popular
variety of lubricating oil used on two-stroke engines in scoot-
ers and motorcycles,57 was developed from castor oil, which
consisted of tolyl monoesters and performance additives, but
no miscibility solvent. eir performance evaluations showed
that it reduced smoke by 50%–70% at a 1% oil–fuel ratio,
and it was on par with standard product specication.58 In
addition to the possible use as a car engine lubricant, a modi-
ed version of castor oil lubricant comprising 100 parts of cas-
tor oil and 20–110 parts of a chemically and thermally stable,
low viscosity blending uid, soluble in castor oil showed its
potential as a lubricant for refrigerator systems.59 Although
castor oil has been used as a DOT 2 rating brake uid, it is
considered an outdated type of brake uid that should not be
used in any modern vehicles.60,61
Fertilizers. Production of castor oil generates two main by-
products: husks and meal. For each ton of castor oil, 1.31 tons
of husks and 1.1 tons of meal are generated. A study by Lima
et al62 showed that blends of castor meal and castor husks
used as fertilizer promoted substantial plant growth up to the
dose of 4.5% (in volume) of meal. However, doses exceeding
4.5% caused reduction in plant growth and even plant death.
Castor oil: properties, uses, and optimization of processing parameters
eir study showed that castor meal may be used as a good
organic fertilizer due to its high nitrogen and phosphorus con-
tent, but blending with castor husks is not necessary.
Coatings. Coatings and paints are also another appli-
cation of castor oil. Castor oil can be eectively dehydrated
by nonconjugated oil–maleic anhydride adducts to give use-
ful paint or furniture oil applications (Fig. 4).63 Trevino and
Trumb o 64 studied the utilization of castor oil as a coating
application by converting the hydroxyl functionalities of cas-
tor oil to β-ketoesters using t-butyl acetoacetate. e reaction
is known to be relatively rapid and proceeded to high yield
under mild conditions. Results showed that the 60° glosses of
the lms and lm exibilities were good. In a separate study
by akur and Karak,65 advanced surface coating materials
were synthesized from castor oil-based hyperbranched poly-
urethanes (HBPUs), a highly branched macromolecule. e
HBPs exhibited excellent performance as surface coating
materials with the monoglyceride-based HBPU, exhibiting
higher tensile strength than direct oil-based coatings. Both the
HBPUs have acceptable dielectric properties with greater than
250°C thermal stability for both the polymers. Ceramer coat-
ings are also another coating application of castor oil. de Luca
et al66 synthesized ceramer coatings from castor oil or epoxi-
dized castor oil and tetraethoxysilane. Most recently, high-
performance hybrid coatings were synthesized by Allauddin
et al67 using a methodology that included introducing hydro-
lyzable –Si-OCH3 groups onto castor oil that have been used
for the development of PU/urea–silica hybrid coatings.
Pharmacological and medicinal use. While castor oil is well
known as a powerful laxative, the medicinal use of the oil is
relatively minor (!1%). Beyond this infamous application of
castor oil, it is considered to be an important feedstock uti-
lized by the chemical industry, particularly in producing a
wide array of materials, many of which are superior to equiva-
lent products derived from petroleum. e high percent com-
position of RA in proximity to the double bond makes this oil
poised for various physical, chemical, and even physiological
activities, as described in the aforementioned paragraphs.5
Owing to the activity of RA in the intestine, castor oil
has been widely used in various bioassays involving antidiar-
rhea activity on laboratory animals. Castor oil is often admin-
istered orally to induce diarrhea in rats.68–70 is assay has led
to a fast and ecient method of preliminary screening of vari-
ous phytochemicals for potential drug-like candidates from
In modern-day medicine, castor oil is also used as a
drug delivery vehicle. An example is Kolliphor EL or for-
merly known as Cremophor EL, which is a registered prod-
uct of BASF Corp. e product is a polyexthoxylated castor
oil, a mixture (CAS No. 61791-12-6) that is prepared when
35 moles of ethylene oxide is made to react with one mole of
castor oil. is product is often used as an excipient or additive
in drugs and is also used to form stable emulsions of nonpolar
materials in various aqueous systems. It is also often used as
a drug delivery vehicle for very nonpolar drugs such as the
anticancer drugs paclitaxel and docetaxel.71–73
Castor Oil Extraction
Castor oil seed contains about 30%–50% oil (m/m).74,75 Castor
oil can be extracted from castor beans by either mechanical
Figure 4. $9F5?>482P3%>94B82P3%CBF9A9%PW%>2B23P:92B%4B2?7
Patel et al
pressing, solvent extraction, or a combination of pressing and
extraction.74 After harvesting, the seeds are allowed to dry so
that the seed hull will split open, releasing the seed inside. e
extraction process begins with the removal of the hull from
the seeds. is can be accomplished mechanically with the aid
of a castor bean dehuller or manually with the hands. When
economically feasible, the use of a machine to aid in the dehu-
lling process is more preferable.
After the hull is removed from the seed, the seeds are
then cleaned to remove any foreign materials such as sticks,
stems, leaves, sand, or dirt.75 ese materials can usually be
removed using a series of revolving screens or reels. Magnets
used above the conveyer belts can remove iron. e seeds can
then be heated to harden the interior of the seeds for extrac-
tion. In this process, the seeds are warmed in a steam-jacketed
press to remove moisture, and this hardening process will
aid in extraction. e cooked seeds are then dried before the
extraction process begins. A continuous screw or hydraulic
press is used to crush the castor oil seeds to facilitate removal
of the oil (Fig. 5). e rst part of this extraction phase is
called prepressing. Prepressing usually involves using a screw
press called an oil expeller. e oil expeller is a high-pressure
continuous screw press to extract the oil.
Although this process can be done at a low temperature,
mechanical pressing leads to only about 45% recovery of oil
from the castor beans.16 Higher temperatures can increase the
eciency of the extraction. Yields of up to 80% of the avail-
able oil can be obtained by using high-temperature hydraulic
pressing in the extraction process.74 e extraction temper-
ature can be controlled by circulating cold water through a
pressing machine responsible for cold pressing of the seeds.
Cold-pressed castor oil has lower acid and iodine content and
is lighter in color than solvent-extracted castor oil.75
Following extraction, the oil is collected and ltered and
the ltered material is combined back with new, fresh seeds
for repeat extraction. In this way, the bulk ltered material
keeps getting collected and runs through several extraction
cycles combining with new bulk material as the process gets
repeated. is material is nally ejected from the press and is
known as castor cake. e castor cake from the press contains
up to approximately 10% castor oil content.75 After crushing
and extracting oil from the bulk of the castor oil seeds, fur-
ther extraction of oil from the leftover castor cake material
can be accomplished by crushing the castor cake and by using
solvent extraction methods. A Soxhlet or commercial solvent
extractor is used for extracting oil from the castor cake. Use of
organic solvents such as hexane, heptane, or a petroleum ether
as a solvent in the extraction process then results in removal
of most of the residual oil still inaccessible in the remaining
Castor oil ltration/purication. Following extrac-
tion of the oil through the use of a press, there still remain
impurities in the extracted oil. To aid in the removal of the
remaining impurities, ltration systems are usually employed.
e ltration systems are able to remove large and small size
particulates, any dissolved gases, acids, and even water from
the oil.75 e ltration system equipment normally used for
this task is the lter press. Crude castor seed oil is pale yellow
or straw colored but can be made colorless or near colorless fol-
lowing rening and bleaching. e crude oil also has a distinct
odor but can also be deodorized during the rening process.
Castor oil rening. After ltration, the crude or unre-
ned oil is sent to a renery for processing. During the ren-
ing process, impurities such as colloidal matter, phospholipids,
excess free fatty acids (FFAs), and coloring agents are removed
from the oil. Removal of these impurities facilitates the oil
not to deteriorate during extended storage. e rening pro-
cess steps include degumming, neutralization, bleaching, and
deodorization.16,74 e oil is degummed by adding hot water
to the oil, allowing the mixture to sit, and nally the aqueous
layer is removed. is process can be repeated. Following the
degumming step, a strong base such as sodium hydroxide is
added for neutralization. e base is then removed using hot
water and separation between the aqueous layer and oil allows
for removal of the water layer. Neutralization is followed by
bleaching to remove color, remaining phospholipids, and any
leftover oxidation products. e castor oil is then deodorized
to remove any odor from the oil. e rened castor oil typi-
cally has a long shelf life about 12 months as long as it is not
subjected to excessive heat. e steps involved in crude castor
oil rening are further discussed in the next section.
Crude Castor Oil Rening
While the previous section briey discussed the general over-
view involved in a castor oil rening step, this section thor-
oughly explains each of the processes involved in it. Unrened
castor oil leads to rapid degradation due to the presence of
impurities as mentioned in “Castor oil rening” section, mak-
ing it less suitable for most applications.1 Hence, a rening
process has to be conducted prior to the derivatization of
Figure 5. GPAA9>B24:%BP3823@P@C%CB>9I%L>9CC%4CC9AQ:57
Castor oil: properties, uses, and optimization of processing parameters
the oil. e order of the steps performed in the rening pro-
cess, which includes degumming, neutralization, bleaching,
deodorization, and sometimes winterization, should be taken
into consideration for ecient oil rening (Fig. 6) and are
described extensively and specically in a castor oil indus-
try setting in “Degumming”, “Neutralization”, “Bleaching”,
“Deodorization”, and “Winterization” sections.
Degumming. e rst step in the castor oil rening
process, called degumming, is used to reduce the phospha-
tides and the metal content of the crude oil. e phosphatides
present in crude castor oil can be found in the form of leci-
thin, cephalin, and phosphatidic acids.76 ese phosphatides
can be classied into two dierent types: hydratable and
nonhydratable,77 and accordingly, a suitable degumming pro-
cedure (water degumming, acid degumming, and enzymatic
degumming) has to be performed for ecient removal of these
phosphatides. In general, crude vegetable oil contains about
10% of nonhydratable phosphatides.77 However, the amount
may vary signicantly depending on various factors such as
the type of seed, quality of seed, and conditions applied dur-
ing the milling operation. While hydratable phosphatides can
be removed in most part by water degumming, nonhydratable
phosphatides can only be removed by means of acid or enzy-
matic degumming procedures.77
Water degumming. Water degumming is a relatively
simple, inexpensive process to remove as much gums as
possible in the initial stages of oil rening. In this process,
the crude oil is heated to approximately 60°C–70°C. Water
is then added to the crude oil and the resulting mixture
is stirred well and allowed to stand for 30 minutes dur-
ing which time, the phosphatides present in the crude oil
become hydrated and thereby become oil-insoluble.78 e
hydrated phosphatides can be removed either by decan-
tation or centrifugation. Water degumming allows the
removal of even small amounts of nonhydratable phospha-
tides along with the hydratable phosphatides. e extracted
gums can be processed into lecithin for food, feed, or tech-
Acid degumming. In general, the acid degumming process
can be considered as the best alternative to the water degum-
ming process if the crude oil possesses a signicant amount of
nonhydratable phosphatides.79 In the acid degumming pro-
cess, the crude castor oil is treated with an acid (phosphoric
acid, malic acid, or citric acid) in the presence of water.77,80
Acid degumming is usually carried out at elevated tempera-
ture, typically around 90°C. e precipitated gums are then
separated by centrifugation followed by vacuum drying of the
Figure 6. Castor proc essing ow diagram.
Patel et al
Enzymatic degumming. e conversion of nonhydratable
phosphatides to hydratable phosphatides can also be attained
using enzymes.81 Here, the enzyme solution, which is a mix-
ture of an aqueous solution of citric acid, caustic soda, and
enzymes, is dispersed into the ltered oil at mild temperatures
normally between 45°C and 65°C. A high-speed rotating
mixer is used for eective mixing of oil and enzyme. e oil is
then separated from the hydrated gum by mechanical separa-
tion and is subjected to vacuum drying.82 A variety of these
so-called “microbial enzymes” exist. e rst of these were
the phospholipases A1 (Lecitase® Novo and Ultra) and, more
recently, a phospholipase C (Purine®). A lipid acyl transfer-
ase (LysoMax®) with PLA2 activity has also become avail-
able in commercial quantities. ese enzymes have specic
functions and specicities. For example, the Lecitases® and
the LysoMax® enzymes are capable of catalyzing the hydro-
lysis of all common phosphatides. e Purine® enzyme,
on the other hand, is specic for phosphatidylcholine and
Neutralization. Good quality castor seeds stored under
controlled conditions produce only low FFA content of approx-
imately 0.3%.82 Occasionally, oil seeds that are old or stored
for more than 12 months with high moisture content produce
a high FFA content of about 5% level.83 is excess FFA pres-
ent in the castor oil does not provide the same functionality
as the neutral oil and has the ability to alter its reactivity with
dierent substances. Hence, it is highly essential to remove
the high FFA content so as to produce a high-quality castor
oil. is process of removal of FFA from the degummed oil is
referred to as neutralization.82
In general, the rening process can be divided into two
methods: chemical and physical rening. Physical rening is
usually done by maintaining a high temperature above 200°C
with a low vacuum pressure. Under these processing condi-
tions, the low boiling point FFA is vacuum distilled from the
high boiling point triglycerides. However, physical rening is
not recommended in the case of castor oil, due to its sensitivity
to heat as it normally starts disintegrating above 150°C, which
can result in the hydrolysis of the hydroxyl groups. On the
other hand, chemical rening is based on the solubility princi-
ple of triglycerides and soaps of fatty acids.82 FFAs (acid) react
with alkali (strong base) to form soaps of fatty acids (Fig. 7).
e formed soap is generally insoluble in the oil and, hence,
can be easily separated from the oil based on the dierence in
specic gravity between the soap and triglycerides. e spe-
cic gravity of soap is higher than that of triglycerides and
therefore tends to settle at the bottom of the reactor. Most of
the modern reneries use high-speed centrifuges to separate
soap and oil mixture.
Alkali neutralization or chemical rening reduces the
content of the following components: FFAs, oxidation prod-
ucts of FFAs, residual proteins, phosphatides, carbohydrates,
traces of metals, and a part of the pigments. e degummed
castor oil is rst treated with an alkali solution (2% caustic
soda) between 85°C and 95°C with constant stirring for
approximately 45–60 minutes.84 At this stage, the alkali reacts
with FFAs and converts them into soap stock. e obtained
soap has a higher specic gravity than the neutral oil and
tends to settle at the bottom. e oil can be separated from
the soap either by gravity separation or by using commercial
centrifuges. Small-scale reners use gravity separation route,
whereas large capacity plants utilizes commercial vertical stack
bowl centrifuges. e separated oil is then washed with hot
water to remove soap, alkali solution, and other impurities.85
Figure 7. hP>A482P3%PW%CP4L%I28F%>2B23P:92B%4B2?7
Castor oil: properties, uses, and optimization of processing parameters
Typically, batch neutralization of castor oil requires about four
to six hot water washes so as to bring down the soap level to
below 100ppm.84 e oil, thus obtained, is vacuum dried and
is transferred to the next process, bleaching.
Castor oil neutralization is a high loss-rening step. is
loss is presumably due to the small dierence in specic grav-
ity of the generated soap and neutral viscous castor oil.83
Bleaching. Castor oil is used for many applications
where the nal product’s appearance is extremely important.
For instance, cosmetics formulations, lubricant additives, and
biomaterial manufacturing all demand the nal product’s
color to be within a certain limit. Although castor oil obtained
after degumming and neutralization processes yield a clear
liquid by appearance, it may still contain colored bodies, natu-
ral pigments, and antioxidants (tocopherols and tocotrienols),
which were extracted along with the crude oil from the castor
beans.86 e color pigments are extremely small ranging
from 10 to 50nm, which cannot be removed from the oil by
any unit operation.82 However, an adsorption process called
“bleaching” can be used to remove such colored pigments and
remaining phospholipids, using activated earths under mod-
erate vacuum conditions between 50 and 100mmHg. e
reduction in the oil color can be measured using an analytical
instrument, called a tintometer.
Activated earths are clay ores that contain minerals,
namely, bentonite and montmorillonite. ese types of clay
are generally found on every continent generated through
unique geographical movements millions of years ago.87 e
eciency of bleaching earth, also called the bleachability,
depends on the ability to adsorb color pigments and other
impurities on its surface. Normally, unprocessed clay has
lower bleachability than acid-activated or processed clays. e
unprocessed clays when activated by concentrated acid fol-
lowed by washing and drying acquire more adsorptive power
to adsorb color pigments from the oil.88
Bleaching of castor oil can be done under vacuum at
around 100°C while constantly stirring the oil with an appro-
priate amount of activated earths and carbon.78 e bleaching
process requires around 2% bleaching earth and carbon to pro-
duce a desirable light colored oil. Under these processing con-
ditions, colored bodies, soap, and phosphatides adsorb onto the
activated earth and carbon. e activated earth and carbon are
removed by using a commercial lter. e spent earth-carbon,
thus obtained, retains around 20%–25% oil content. Bleaching
castor oil containing higher phosphatide and soap content
often leads to high retention of oil due to the large amount of
activated earth used and thus causes ltration issues. Although
this retained oil on the spent earth can be recovered by boiling
the spent earth in water or by a solvent extraction method, the
recovered oil from the spent earth is highly colored with high
FFA and high peroxide content, normally greater than 10mg
KOH/g and 20meq/kg, respectively.88
Deodorization. Deodorization is simply a vacuum
steam distillation process that removes the relatively volatile
components that give rise to undesirable avors, colors, and
odors in fats and oils. Unlike other vegetable oils, castor oil
requires limited or no deodorization, as it is a nonedible oil
where slight pungent odor is not an issue for most of its appli-
cations, with the only exception being pharmaceutical grade
castor oil.89,90 Deodorization is usually done under high vac-
uum and at high temperature above 250°C to remove unde-
sirable odors caused by ketones, aldehydes, sterols, triterpene
alcohols, and short-chain fatty acids.85 Pharmaceutical grade
castor oil is deodorized at low temperatures, approximately
150°C–170°C under high vacuum for 8–10 hours to avoid
hydrolysis of hydroxy group of RA.86
Winterization. e majority of vegetable oils contain
high concentrations of waxes, fatty acids, and lipids. Hence, it
is subjected to the process of winterization before its nal use.
Winterization of oil is a process, whereby waxes are crystal-
lized and removed by a ltering process to avoid clouding of
the liquid fraction at cooler temperatures. Kieselguhr is the
generally used lter aid and the lter cake obtained at the end
can be recycled to a feed ingredient. In certain cases, a similar
process called “dewaxing” can also be utilized as a means to
clarify oil when the amount of cloudiness persists.91,92
Conclusions and Future Directions
Castor oil is a promising commodity that has a variety of
applications in the coming years, particularly as a renewable
Essential to the production and marketing of castor oil
is the scientic investigation of the processing parameters
needed to improve oil yield. In the recent years, machine
learning predictive modeling algorithms and calculations were
performed and implemented in the prediction and optimiza-
tion of any process parameters in castor oil production. Uti-
lization of an articial neural network (ANN) coupled with
genetic algorithm (GA) and central composite design (CCD)
experiments were able to develop a statistical model for opti-
mization of multiple variables predicting the best performance
conditions with minimum number of experiments and high
castor oil production.93 In a separate study by Mbah et al,17 a
multilevel factorial design using Minitab software was used
to determine the conditions, leading to the optimum yield of
castor oil extraction through a solvent extraction method. is
study found that optimum conditions that included leach-
ing time of two hours, leaching temperature of 50°C, and
solute:solvent ratio of 2g:40mL garnered optimum yield of
castor oil extraction. Such mathematical experimental design
and methodology can prove to be useful in the analysis of the
eects and interactions of many experimental factors involved
in castor oil production.
With the advent of biotechnological innovations, genetic
engineering has the potential of improving both the quality
and quantity of castor oil. Genetic engineering can be catego-
rized into two parts: one approach is to increase certain fatty
acids, while the second approach is to engineer biosynthetic
Patel et al
pathways of industrially high-valued oils.94 For the latter,
biosynthetic gene clusters responsible for fatty acid produc-
tion can be mined for such purpose. In one particular study
by Lu et al,95 Arabidopsis thaliana expressing castor fatty acid
hydroxylase 12 (FAH12) was used to mine genes that can
improve the hydoxy fatty acid accumulation among devel-
oped transgenic seeds. e aforementioned study was able to
identify certain proteins that can improve the hydroxy fatty
acid content of castor seeds. ese proteins include oleosins
(a small protein involved in the formation of lipid bodies) and
phosphatidylethanolamine (a protein involved in fatty acid
modication and is channeled to triacylglycerol).96 rough
understanding the genetics behind oil production, better yield
can be achieved.
With the dawn of the –omics era, genomics, transcrip-
tomics, and proteomics can be key players in understand-
ing the genetics of improving the quality and quantity of oil
production. Advances in genomics have drafted the genome
sequence of the castor bean, which has led to insights about
its genetic diversity.97,98 A future direction would include a
tandem genomics and transcriptomics that can help reveal
dierences in gene expression levels across a spatiotemporal
parameter aecting oil quality and quantity. Further, pro-
teomics can be used to understand proteins and enzymes that
are expressed by the castor bean plant.99 Being a nonmodel
organism, homology-driven protein identication techniques
are possibly to be employed to understand the cellular and bio-
logical nature of oil production, leading to improved oil quali-
ties and quantities.
As a source of biodiesel, recent studies showed that the
biodiesel synthesis from castor oil is limited by a number of
factors that include having the proper reaction temperature,
oil-to-methanol molar ratio, and the quantity of catalyst.
A study using response surface methodology as a model has
been used to optimize the reaction factor for biodiesel syn-
thesis from castor oil.100 In another similar study, parameters
aecting castor oil transesterication reaction were investi-
gated. Using Taguchi method consisting of four parameters
(reaction temperature, mixing intensity, alcohol/oil ratio,
and catalyst concentration), the best experimental conditions
were determined. It was determined that the reaction tem-
perature and mixing intensity can be optimized. Using the
optimum results, the authors proposed a kinetic model that
resulted in establishing an equation for the beginning rate of
transesterication reaction.101 Besides the Taguchi method,
a full factorial design of experiment is also another approach
that was investigated to optimize biodiesel production from
castor oil. Second-order polynomial model was obtained to
predict biodiesel yield as a function of these variables. e
experimental results for the process garnered an average
yield of biodiesel of more than 90%.102 e use of models
and simulations can, indeed, greatly facilitate the eciency
of biodiesel production from castor oil. To add further, a
simple model using a ping-pong bi-bi mechanism has been
proposed, which summarizes an ecient method of noncata-
lytic transesterication of castor oil in supercritical metha-
nol and ethanol.103 It is an enzymatic reaction model that
involves two substrates and two products (referred to as bi-bi
system). An enzyme reacts rst with one substrate to form a
product and a modied enzyme. e modied enzyme would
then react with a second substrate to form a nal product
and would regenerate the original enzyme. In this model, an
enzyme is perceived as a ping-pong ball that bounces from
one state to another.
Biodiesel production from castor oil is, indeed, a promis-
ing enterprise. Advances in models and simulations have facil-
itated optimization of key processing parameters necessary to
obtain good yields of such biodiesel.
In this review, we present both an extensive and intensive
analysis of castor bean oil, ranging from its industrial to phar-
macological use. Moreover, this review discussed traditional
and modern castor bean oil processing and the future direc-
tions as we enter the –omics and computational analysis era.
ANN, articial neural network; AV, acid value; CCD,
central composite design; COP, castor oil polymer; DCO,
dehydrated castor oil; DOC, de-oiled cake; FAH12, fatty
acid hydroxylase 12; FFA, free fatty acid; GA, genetic algo-
rithm; GIC, glass ionomer cement; HBPUs, hyperbranched
polyurethanes; HV, hydroxyl value; IV, iodine value; IPNs,
interpenetrating polymer networks; KOH, potassium hydrox-
ide; MTA, mineral trioxide aggregate; SV, saponication
value; RA, ricinoleic acid; PU, polyurethane; PV, peroxide
value; Y + 5R; Yellow + 5(Red).
We would like to thank Jayant Oils and Derivatives and SDI
Farms, Inc for allowing us to use their facilities that led to the
conceptualization of this manuscript.
Conceived and designed the study: VRP, GGD, and LCKV.
Analyzed the data: VRP, GGD, and LCKV. Wrote the rst
draft of the manuscript: VRP. Contributed to the writing of
the manuscript: VRP, GGD, LCKV, RM, and BJJS. Agreed
with manuscript results and conclusions: VRP, GGD, LCKV,
RM, and BJJS. Jointly developed the structure and arguments
for the paper: VRP, GGD, LCKV, RM, and BJJS. Made
critical revisions and approved the nal version: VRP, GGD,
LCKV, RM, and BJJS. All the authors reviewed and approved
the nal manuscript.
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