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10
Rice Bran Oil
Frank T. Orthoefer
1. INTRODUCTION
Rice oil, also called rice bran oil, has been used extensively in Asian countries such
as Japan, Korea, China, Taiwan, Thailand, and Pakistan (1, 2). It is the preferred oil
in Japan for its subtle flavor and odor. Interest in rice oil in the United States was
initiated after WWII, primarily to provide an additional revenue stream to the rice
miller. More recently, interest in rice oil escalated with its identification as a
‘‘healthy oil’’ that reduces serum cholesterol (3, 4).
Three facilities were constructed in the United States to produce rice oil (5). The
first facility began operation in the late 1950s, and a second facility was started in
the 1960s. Both were shut down in the early 1980s because of economics. A third
production facility began operation in the early 1990s and continues producing both
bulk and packaged oils for the domestic and export markets. Attempts at further
development of rice oil production have not been successful because of high capital
requirement to construct an oil extraction plant and refining facility and limited
availability of stabilized rice bran (6).
Rice oil is a minor constituent of rough rice when compared with the carbohy-
drate and protein content. Two major classes of lipids are present: those internal
within the endosperm and those associated with the bran. The internal lipids con-
tribute to the nutritional, functional, and sensory qualities of rice (7).
Rice bran is the main source of rice oil. The majority of available bran continues
to be used for animal feeds without being extracted for the oil. The food industry
Bailey’s Industrial Oil and Fat Products, Sixth Edition, Six Volume Set.
Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.
465
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466
RICE BRAN OIL
uses minor quantities of stabilized rice bran as a source of dietary fiber, protein, and
desirable oil.
This chapter reviews the source and composition of rice bran oil, its nutritional
characteristics, production, and refining of the oil and its applications.
2. COMPOSITION OF RICE AND RICE BRAN LIPIDS
The structure of the rice kernel is given in Figure 1. Lipids are present as sphero-
somes or lipid droplets less than 1.5 mm in diameter in the aleurone layer, less than
1.0 mm in the subaleurone layer, and less than 0.7 mm in the embryo of the rice
grain (7, 9). Most of the lipids in the endosperm are associated with protein bodies
and the starch granules as bound lipids (10). The lipids are broadly classified as
nonstarch and starch lipids (Table 1). The majority of the lipids are the nonstarch
lipids. Starch lipids consist primarily of lysophospholipids, triacylglycerols, and
free fatty acids (13). Major phospholipid species are lysophophatidylethanolamine
and lysophosphatidylcholine. The major fatty acids are palmitic and linoleic acids
along with oleic acid. Minor amounts of monoacylglycerols, diacylglycerols, and
sterols are also found. Glycolipids found are diglycosyl monoacylglycerols and
monoglycosyl monoacylglycerols. The component sugars are galactose and glu-
cose.
The nonstarch lipids in the aleurone, subaleurone, and germ layers were 86–91%
neutral lipids, 2–5% glycolipids, and 7–9% phospholipids, although these are vari-
able because of different milling degrees (11). The fatty acid composition of
Figure 1. Relative proportion of major rice caryopsis components (8).
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467
COMPOSITION OF RICE AND RICE BRAN LIPIDS
TABLE 1. Lipid Composition of Rice and its Fractions (7, 9, 11, 12). a
Nonwaxy
Nonstarch Lipids in Rice Fractions Starch Lipid in
—————————————————— ———————
Brown
Milled
Property
Hull
Brown Milled
Bran
Germ Polish
Rice
Rice
Lipid content
0.4
2.7
0.8
18.3
30.2
10.8
0.6
.05
Saponification no.
145
181
190
184
189
Iodine no.
69
94
100
99
101
Unsaponifiable matter
26
6
6
6
34
Fatty acid composition Wt % of total
Palmitic
18
23
33
23
24
23
46
45
Oleic
42
35
21
37
36
35
12
11
Linoleic
28
38
40
36
37
38
38
40
Others
12
4
6
4
3
4
4
4
Neutral lipids, % of total lipids
64
86
82
89
91
87
28
26
Triglyceride
—
71
58
76
79
72
4
2
Free fatty acids
—
7
15
4
4
5
20
21
Glycolipids, % of total lipids
25
5
8
4
2
5
19
16
Phospholipids, % total lipids
11
9
10
7
7
8
53
58
Phosphotidylcholine
—
4
9
3
3
3
4
4
Phosphatidylethanolamine
—
4
4
3
3
3
5
5
Lysophosphatidylcholine
—
< 1
2
< 1
< 1
< 1
21
23
Lysophosphatidylethanolamine
—
—
1
—
—
—
22
25
a Based on 6% bran-germ, 4% polish, and 90% milled rice from brown rice.
nonstarch lipids showed 22–25% palmitic, 37–41% oleic acid, and 37–41% linoleic
acid (Table 2). The brown rice non-starch lipids was 14–18% in germ, 39–41% in
bran, 15–21% in polish, and 25–33% in milled rice. The composition was 83–87%
triacylglycerol together with 7–9% free fatty acids, diacylglycerols, sterols together
with sterol esters, hydrocarbons, and wax. Oil extracted from rice bran contained
20.1% total lipid, 89.2% neutral lipids, 6.8% glycolipid, and 4.0% phospholipid
(14). A component of rice bran oil that has promise as a nutraceutical compound
is g-oryzanol (15). g-Oryzanol was first isolated from soapstock from rice oil
TABLE 2. Major Lipid Classes of Crude Bran Oil Extracted from Raw Rice Bran
and Their Fatty Acid Composition (14).
Fatty Acid Composition (%)
——————————————————————————————————————————
Lipid class a
wt%
14:0
16:0
18:0
18:1
18:2
18:3
20:0
saturated unsaturated
TL
20.1
.40
22.21
2.21
38.85
34.58
1.14
0.61
25.43
74.57
NL
89.2
0.43
23.41
1.88
37.24
35.29
1.07
0.68
26.40
73.60
GL
6.8
0.09
27.34
0.28
36.45
35.76
0.18
27.61
72.39
PL
4.0
0.11
22.13
0.16
38.11
39.32
0.17
22.40
77.60
a TL ¼ total lipids; NL ¼ neutral lipids (nonpolar lipid and free fatty acids); GL ¼ glycolipids; PL ¼ phospholipids.
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RICE BRAN OIL
CH 3 O
32
1
7
8
4
H
CH
CH
COOR
(ROH see below)
56
ROH
= campesterol
= O sitosterol
= cycloartenol
= 24 methylene-cycloartenol
= cyclobranol
Figure 2. Major ferulates in oryzanol (9).
refining (16). Although originally thought to be a single compound, it is now known
to be a mixture of steryl and other triterpenyl esters of ferulic acids (cycloartenyl
ferulate, 24 methylenecycloartenyl ferulate, and b sitosterol ferulate and campesteryl
ferulate) (Figure 2). It is present at 1.5–2.9% of rice bran oil with a m.p. of 138.5 C.
The oryzanol content is dependent on rice grain variety with long grain rice at
6.42 mg/g and medium grain rice at 5.17 mg/g (17).
Tocopherols and tocotrienols (tocols) are present in rice oil (Figure 3). Crude
rice bran oil was found to contain, per 100 g of oil, 19–46 mg of a-tocopherol,
1–3mgofb-tocopherol, 1–10 mg of g-tocopherol, and 0.4–0.9 mg of d-tocopherol,
14–33 mg of a-tocotrienol, and 9-69 mg of g-tocotrienol (18, 19) (Table 3). The
mean tocol content was 93 mg/100 g for crude oil and 50 mg/100 g for refined
oil (19). Close to 370 mg/100 g has been reported (20). Rice bran stabilization
and storage (21) and method of extraction (22) affects the concentration of tocols
in the oil. g-Tocotrienol is more stable and persists to a greater extent during storage
than other tocols (21). Other factors influencing toco content are milling and variety
(17, 23). Long-grain varieties have higher levels of tocotrienols than medium grain
rice (17).
R 3
R 2
O
HO
R 1
R 2
R 3
R 1
α-T(3)
β
CH 3
H 3
H
H
CH 3
H
CH 3
H
CH 3
CH 3
CH 3
CH 3
-T(3)
γ-T(3)
δ-T(3)
Tocopherols (T)
R 3
R 2
O
HO
R 1
Tocotrienols (T3)
Figure 3. Structure of tocopherol and tocotrienol (9).
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469
COMPOSITION OF RICE AND RICE BRAN LIPIDS
TABLE 3. Tocopherol and Tocotrienol Concentrations (mg/100g) in Raw Rice Bran
and Commercially Available Refined Oil (14).
Source
a -T
b -T
g -T
d -T
a -T3
g -T3
d -T3
Rice bran
6.3
0.9
3.20
0.20
3.8
12.0
0.7
Brown rice a
0.63
0.09
0.32
0.02
0.38
1.2
0.07
Crude oil a
31.50
4.50
16.00
1.00
19.0
60.0
3.5
Refined oil
8.2
12.80
1.3
2.1
42.9
3.5
a Calculated values.
Waxes are present as long-chain fatty acid esters with fatty alcohols, methanol,
and ethanol. Fatty acid analysis showed that behenic (C:22), lignoceric (C:24), and
palmitic acids (C:16) are the major fatty acid for longer alkyl esters and oleic and
palmitic for the shorter alkyl esters (Table 4) (24). The major alcohols found are for
longer alkyl esters. These are as follows:
TABLE 4. Fatty Acids of Sterol and Alkyl Esters, Alcohols of Longer Alkyl Esters,
and Alkanes and Alkenes of Rice Bran Waxy Lipids (24).
Fatty Acids Composition of:
——————————————————————————————————————————
Carbon and
Alcohols of
Double Bond
Longer Alkyl
Shorter Alkyl
Longer Alkyl
No.
Sterol Esters
Esters
Esters
Alkane
Alkenes
14.0
0.6
1.8
2.2
—
—
—
16.0
11.1
23.8
35.5
—
—
—
18:0
1.0
3.8
0.8
—
—
—
18:1
33.1
2.9
60.2
—
—
—
18:2
51.1
0.3
1.5
—
—
—
18:3
2.0
—
—
—
—
—
20:0
0.7
3.6
—
0.1
——
22:0
—
32.6
—
2.0
——
23:0
—
31.2
—
—
1.3
—
24:0
—
—
—
11.2
0.2
—
25:0
—
—
—
—
2.0
—
26:0
—
—
—
6.3
0.8
—
27:0
—
—
—
—
9.5
7.9
28:0
—
—
—
12.5
3.6
1.3
29:0
—
—
—
—
46.5
38.8
30:0
—
—
—
19.1
3.0
0.9
31:0
—
—
—
—
23.7
20.8
32:0
—
—
—
10.5 (5.1)
1.4
0.5
33:0
—
—
—
—
6.5
18.8
34:0
—
—
—
6.6 (18.3)
0.7
1.4
35:0
—
—
—
—
0.8
8.4
36:0
—
—
—
3.0 (5.4)
—
0.1
37:0
—
—
—
—
—
1.6
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