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 carbohydrate and protein content. Two major classes of lipids are present: those internal within the endosperm and those associated with the bran. The internal lipids contribute 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.

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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 spherosomes 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 glucose. 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 variable because of different milling degrees (11). The fatty acid composition of

Figure 1. Relative proportion of major rice caryopsis components (8).

COMPOSITION OF RICE AND RICE BRAN LIPIDS

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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 Hull Brown Milled Bran Germ Polish Rice Rice

Property

Lipid content 0.4 Saponification no. 145 Iodine no. 69 Unsaponifiable matter 26 Fatty acid composition Wt % of total Palmitic 18 Oleic 42 Linoleic 28 Others 12 Neutral lipids, % of total lipids 64 Triglyceride — Free fatty acids — Glycolipids, % of total lipids 25 Phospholipids, % total lipids 11 Phosphotidylcholine — Phosphatidylethanolamine — Lysophosphatidylcholine — Lysophosphatidylethanolamine — a

2.7 181 94 6

0.8 190 100 6

18.3 184 99 6

30.2 189 101 34

10.8

0.6

.05

23 35 38 4 86 71 7 5 9 4 4