Rice bran tocotrienols

Rice bran tocotrienols have not been as well studied as Palm Vitee, but recent work with hereditary hypercholesterolemic swine has shown promising results (Qureshi et al, 2001). Administration of rice bran tocotrienols for 6 weeks markedly lowered serum levels of total cholesterol (by 32-38%), LDL cholesterol (by 35 3%), and apolipoprotein B (by 20-28%) in the treated swine. Watkins et al (1999) showed that adults (aged 49-83) taking rice bran oil supplements for one year had 14% lower plasma total cholesterol levels, 20% lower LDL cholesterol levels, and higher high-density lipoprotein (HDL) C levels than individuals taking a placebo. No data are currently available for adolescents and young adults. 

Tocotrienols are another group of phytochemicals of rice bran which have a chemopreventive effect and have been demonstrated to inhibit breast cancer (Nesaremam et al., 1998). The polysaccharides of rice bran contain a-glucan, the anti-tumor effect of which has been demonstrated by its inhibition of gastrointestinal carcinogenesis (Akeshita et al., 1992). Rice bran agglutinin has been shown to induce apoptosis of cancer cells by the mechanism of cell cycle dysregulation (Miyoshi et al., 2001). 

Tocotrienols present in rice bran inhibit the liver microsomal enzyme HMGCoA reductase (Qureshi and Qureshi, 1992), the key enzyme involved in the endogenous synthesis of cholesterol, and this helps to lower the circulating cholesterol. Inhibition of another enzyme, ACAT (Acyl coenzyme A acyl transferase), by y-oryzanol results in lowered LDL-C synthesis and enrichment... 

Natural products have been noted for their potential health benefits from time immemorial and are the basis of Ayurveda, an ancient Indian medical practice (Bushkin and Bushkin, 2002). However, the potential benefits of several natural products reside in one or two active ingredients. For example green tea stands for polyphenols, soy for soy estrogens, broccoli for isothiocyanates and grape seed for polyphenols. The beauty of rice bran is that there are more than 100 antioxidants, several categories of bioactive phytonutrients, such as IP6, polyphenols, phytosterols, tocotrienols, y-oryzanol, B vitamins, minerals and trace minerals in addition to fat, protein, fiber, polysaccharides and other nutrients. These phytonutrients and antioxidants of rice bran are believed to act at the cellular level, and their synergestic function is responsible for the positive health benefits. 

QURESHI A A, SAMI s A, SALSER w A, KHAN F A (2001) Syuergistic effect of tocotrienol rich fraction (TRF 25) of rice bran and lovostatin on lipid parameters in hypercholesterolemic hamnns. J Nutri Biochem, 12 318-29. 

XU z, HUA N, GODBER s (2001) Antioxidant activity of tocopherols, tocotrienols, and y-oryzanol components from rice bran against cholesterol oxidation accelerated by 2, 2 -azobis(2-methylpropionamidine) dihydrochloride. J Agri Food Chem, 49 2077-81. 

Determination of vitamin E isomers in seeds and nuts Determination of tocopherol and tocotrienol in rice bran Investigation of vitamin E content in olives Determination of tocopherol and tocotrienol in olive oils... 

Determination of tocopherols in vegetable oils Determination of tocopherols and tocotrienols in rice bran Determination of tocopherols in tomato... 

Figure D1.5.3 Chromatogram of tocopherols and tocotrienols of rice bran oil in normal-phase HPLC (see Basic Protocol). p-Tocopherol was below the level of detection.

In normal-phase HPLC on a silica column, the order of elution of tocopherols and tocotrienols is a-tocopherol, a-tocotrienol, [3-tocopherol, (3-tocotrienol, y-tocopherol, y-tocotrienol, 8-tocopherol, and 5-tocotrienol. Figure Dl.5.3 is an example of a normal-phase chromatograph of tocopherols and tocotrienols in rice bran oil. 

Bran, tocopherols/tocotrienols in rice bran oil, 488 (figs.)... 

Reversed-phase high-performance liquid chromatography (RP-HPLC), cholesterol measurement, 456-458 Rhamnogalacturonanas, 735 Rice bran oil, tocopherols/tocotrienols in, 488 (figs.)... 

Fig. 13 HPLC of vitamin E. (A) Standards of vitamin E vitamers. Column, 5-p.m Supelcosil LC-Si (250 X 4.6-mm ID) mobile phase, isooctane/ethyl acetate (97.5 2.5), 1.6 ml/min fluorescence detection, excitation 290 nm, emission 330 nm. Peaks (1) a-tocopherol (2) a-tocotrienol (3) /3-tocopherol (4) y-tocopherol (5) /3-tocotrienol (6) y-tocotrienol (7) 5-tocopherol (8) 5-tocotrienol. (B) Saponified rice bran sample. Chromatographic conditions as in (A) except for mobile phase isooctane/ethyl acetate/2,2-dimethoxypropane (98.15 0.9 0.85 0.1). (From Ref. 228. AOCS Press.)...

Experimentally, anti-oxidants such as gallic acid, ethyl gallate, oat flour (Findlay and Smith, 1945), sorbitan monostearate, glycerol monostearate, polyoxyethylene sorbitan monostearate (Hibbs and Ashworth, 1951), ascorbyl palmitate, dodecyl gallate (Abbot, 1971), high-oryzanol rice bran oil - containing tocopherols and tocotrienols (Nanua et al, 2000), nordihy-droguaiaretic acid, butylated hydroxyanisol, butylated hydroxy toluene and citric acid (Helal et al., 1976) have been used to enhance the oxidative stability of milk powders. 

Qureshi, A. A. Salser, W.A. Parmar, R. Emeson, E.E. 2001. Novel tocotrienols of rice bran inhibit atherosclerotic lesions in C57BL/6 ApoE-deficient mice. J. Nutr. 131 2606-2618. 

Tocopherols and tocotrienols, collectively known as tocols, are monophenolic and lipophilic compounds that are widely distributed in plant tissues (7). The main commercial source of natural tocopherols is the soybean oil. Tocotrienols, less common than tocopherols, are present in palm oil, rice bran oil, as well as cereals and legumes (11). Tocopherols and tocotrienols are classified into a-, (3-, y-, and 5-, depending on their chemical structures (Figure 7). In general, tocotrienols have a stronger antioxidant effect on lipid oxidation than tocopherols. The antioxidant activity of tocopherols is dependent on temperature and is in the order of 5- > y->P-> oc-tocopherol (7). Tocopherols (mixed natural concentrate) are a golden... 

The dominance of tocopherols, namely, alpha-, beta-, gamma-, and delta- and the corresponding tocotrienols, depends on the type of oil under investigation. Thus, tocotrienols occur primarily in palm and rice bran oils. Meanwhile, tocopherols are more widely present in different oils. However, their proportions in different oils is dependent on the source material. As an example, sunflower oil contains mainly alpha-tocopherol and very small amounts of other tocopherols, whereas soybean oil contains mainly gamma-tocopherol with decreasing amounts of delta-, alpha-, and beta-tocopherols as determined by high-performance liquid chromatography. 

TABLE 3. Tocopherol and Tocotrienol Concentrations (mg/100g) in Raw Rice Bran and Commercially Available Refined Oil (14). 

Rice bran oil and palm oil are the only readily available oils that contain significant levels (about 1000 ppm) tocotrienols (99). Tocotrienols belong to the Vitamin E family and have similar chemical stmcmres. According to Tomeo et al. (100), tocotrienols are powerful antioxidants. Commercially available RBO may contain 980 ppm y-tocotrienol (101). 

The tocopherol and tocotrienol contents of selected vegetable oils are shown in Table (7). Seed oils are mostly dominated by y- or a-tocopherol, but high levels of 5-tocopherol especially characterize soybean oil, which is the richest and commercially the most used source of tocopherols (46). Rice bran and pahn oils, on the other hand, represent the important sources of tocotrienols (45, 47). Rapeseed... 

Together with y-oryzanol, tocotrienols are responsible for the cholesterol-lowering effect of rice bran oil (250). Tocotrienol concentrates have been shown to have a hypocholesterolemic effect in animals and humans (251-257) possibly because of inhibition of hepatic 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase) (251, 258, 259). The presence of a-tocopherol at concentrations >20% in tocotrienol concentrates was, however, found to attenuate the inhibitory elfect of tocotrienols on HMG-COA reductase, thereby weakening their cholesterollowering activities (254). Tocotrienols were especially found to synergize the cholesterol-lowering effect of lovastatin (254). In addition, tocotrienols have been shown to influence certain hemostatic parameters and to reduce the occurrence of chemical-induced tumors in the rat (253). 

Oil extracted from rice bran and com fiber is especially rich in tocopherols, tocotrienols and sterols. Extraction of these valuable compounds is remarkably enhanced by heat pretreatment (Lane et al., 1999). For example, the level of extracted y-tocophcrol increased from 0.3% to 3.6% by subjecting com fiber to temperatures of 100-175°C (Moreau et al., 1999). Tocopherol- and tocotrienol-rich oils may be used as such as important sources of vitamin E, or the vitamers can be purified from them following the same protocols as above. 

For identification of tocopherols and tocotrienols after chromatographic separation, pure tocopherols and tocotrienol mixtures are commercially available. Their purity can be checked by both HPLC and GC and the concentration of stock solutions by UV spectroscopy (Table 1.6). It is common to use lipid extracts from cereals and rice bran and their mixtures with pure compounds and vegetable oils to tentatively identify the vitamers and to study the performance of the HPLC separation. 

Qureshi, A.A., Mo, H., Packer, L., and Peterson, D.M. 2000. Isolation and Identification of Novel Tocotrienols from Rice Bran with Hypocholesterolemic, Antioxidant and Antitumor Properties. J. Agric. Food Chem. 48 3130-3140. 

NuTriene [Eastman]. TMforaneutraceuti-cal supplement. A mixture of naturally occurring tocotrienols and tocopherols are extracted and concentrated from rice bran oil, a common cooking oil in Asia. 

The byproducts of rice-bran oil refining include waxes, lecithin, soap-stock (containing high-value oryzanol), and deodoriser distillate containing sterols, tocopherols, tocotrienols and squalene. The characteristics and physical properties of purified rice wax are similar to camauba wax (Sayre and Saunders... 

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