Other properties

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Parboiled rice or rice powder gruel (Molla, Ahmed and Greenough, 1985), rice water (Wong, 1981; Rivera et al., 1983) and extrusion-cooked rice (Tribelhorn et al., 1986) have all been effectively used for the treatment of non-infectious diarrhoea since starch has a lower osmolality than glucose. Even the high concentration of 80 g rice per litre in an oral rehydration solution is drinkable by patients and is highly effective, providing four times more energy than does standard glucose oral rehydration solution (20 percent), (Molla, Ahmed and Greenough, 1985).

Consumption of cereal foods including rice has been correlated with dental caries (Bibby, 1985). Dentists agree that dental decay is the result of tooth demineralization by acids produced on the tooth surface when bacteria from carbohydrates ferment. Boiling, pressure cooking and extrusion cooking increase acid formation by starch in dental plaque. Phytate is an enamel-protective factor, together with amino acids, phosphates and lipids, etc. Refining removes cariespreventing factors from the rice foods and increases these foods' cariogenicity. The inclusion of rice bran or of a hot water extract of rice bran in human diets has a preventive action against caries (Ventura, 1977).

There is a popular belief that some rice varieties have medicinal properties, such as the Myanmar variety Na ma the lay. In China black rice is believed to have a body-strengthening fraction and pharmaceutical value. Thus it is known as "blood strengthening rice", "drug rice" or "(con)tributed rice" (Li and Lai, 1989). Blackrice, which has a pigment level of 1 ma per 100 g rice, has 3 mg vitamin C and 0.2 mg riboflavin per 100 g and has more iron, calcium and phosphorus than non-pigmented rice. In Kerala, India, the variety Navara is believed to have medicinal properties and is used to rejuvenate the nerves in paralytic conditions: oridine, an alkaloid present in rice, has some antineurotic properties when impure (Chopra, 1933).

The anthocyanin pigments of red rice, "tapol", extracted with 95 percent ethanol containing 0.1 percent hydrochloric acid, are 70 percent cyanidin-3-glucoside (chrysanthemin),12 percent peonidin-3-glucoside (oxycoccicy-anin) and two other anthocyanin pigments (Takahashi et al., 1989). Pigmented brown rices were shown to have higher riboflavin but similar thiamine contents to non-pigmented IR rices (Villareal and Juliano, 1989a). The total carbohydrates and starch contents of milled red rices were reported to be lower than those of unpigmented milled rice in India (Srinivasa Rao, 1976), probably because of the higher protein content and residual phenolics with 7 percent milling in India. As brown rice, purple Perurutong had a lower NPU in growing rats (59.1 percent) than red rice (66.6 percent) and non-pigmented brown rice (66.7 to 70.6 percent) because of the extremely reduced true digestibility of its protein (72.4 percent) due to its high levels of phenolics (anthocyanin), (0.62 percent versus 0.01 to 0.25 percent), (Eggum, Alabata and Juliano, 1981). These differences are removed upon milling, which removes most of the pigments.

Varietal differences were found in cadmium (Cd) levels of brown rice grown in Tsukuba, Japan (seedlings transplanted in June 1983 and June 1985); five semidwarf indica rices had 24 to 74 ppb Cd, as compared to 2 to 27 ppb Cd for japonica varieties and 4 to 56 ppb Cd for non-dwarf indica varieties (Morishita et al.,1987). The mean Cd content in rice from various countries ranged from 5 to 99 ppb on a wet basis, with the highest Cd content occurring in Hokuriku, Japan; daily Cd intake from rice ranged from I to 36 µg and was also highest in Hokuriku, but the same value (36µ) was also observed in Celibes, Indonesia, where the Cd content in rice was lower but rice intake was higher (Rival, Koyama and Suzuki, l 990). A high cadmium content in rice was one of the major causes of an epidemic of "itai-itai" disease in Japan (Kitagishi and Yamane, 1981).

Analyses from 1979 to 1982 showed selenium (Se) deficiencies in feedstuffs in 70 percent of Chinese counties, where 80 percent of the feeds and forages analysed had less than 0.50 ppm Se (Liu, Lu and Su, 1985). The Se content of brown rice and of milled rice grown in Japan was reported to be 30 to 40 mg/g (Node, Hirai and Dambara, 1987). Distribution of Se is 13 percent in the hull, 15 percent in bran and 72 percent in milled rice (Ferretti and Levander, 1974).

The silicon (Si) content of six milled American rices was reported to be 0.046 ± 0.030 percent (Kennedy and Schelstraete, 1975); the silicon was located mainly in the outer layer of milled rice. Energy-dispersive X-ray fluorescence spectrometry of seven IR rices indicated a mean Si content (wet basis) of 0.041 ± 0.016 percent for brown rice and 0.015 ± 0.009 percent for milled rice (Villareal, Maranville and Juliano, 1991). Colorimetric Si assay using phosphomolybdate showed that in a 7 percent protein IR32 milled rice, the Si content was 0.035 percent in the subaleurone layer (outer 9 percent), 0.014 percent in the middle endosperm (next 11 percent) and 0.009 percent in the inner endosperm (80 percent), (Juliano, 1985b), equivalent to 0.010 percent Si in the entire grain.

Hypocholesterolaemic effect of rice bran

In hamsters, addition to the diet of 10 percent dietary fibre from stabilized rice bran, defatted, stabilized rice bran end oat bran significantly reduced the animals' plasma cholesterol compared to the control (Kahlon et al., 1990). In repeat experiments, only undefatted bran and oat bran lowered the cholesterol level (Haumann, 1989). Heat-stabilized rice bran providing 7 percent dietary fibre lowered the level of liver free cholesterol and surpassed wheat bran, when combined with 5 percent fish oil, in lowering plasma and hepatic triglycerides and hepatic lipogenesis (Topping et al., 1990). Recent confirmatory human studies demonstrated the hypocholesterolaemic effect of fullfat rice bran (Gerhardt and Gallo, 1989; Nicolosi, 1990; Saunders, 1990), but limited feeding trials did not confirm the hypocholesterolaemic activity of rice bran in Japanese (brown versus milled rice), (Miyoshi et al., 1987a, 1987b) or Filipino adults (Dens et al., 1987).

The hypocholesterolaemic effect of oat bran is due to its high content of soluble hemicelluloses. By contrast, the hypocholesterolaemic activity of ricebran oil in humans and rats (Raghuram, Brahmaji Rao and Rukmini, 1989) is due to the unsaponifiable matter fraction (Suzuki et al., 1962; Sharma and Rukmini, 1986, 1987). Rice-bran oil lowered human blood cholesterol more effectively than did sunflower, corn and safflower oils (Suzuki et al., 1962). A polysaccharide fraction in bran has also been reported to have a hypocholesterolaemic effect in rats (Vijayagopal and Kurup, 1972). The hypocholesterolaemic effect of rice-bran hemicellulose (defatted rice bran), (Ayano et al., 1980) was due to the reduction of dietary cholesterol absorption from the small intestine of rats (Age, Ohta and Ayano, 1989).

Antinutrition factors

Antinutrition factors in the rice grain are concentrated in the bran fraction (embryo and aleurone layer). They include phytin (phytate), trypsin inhibitor, oryzacystatin and haemagglutinin-lectin. All except oryzacystatin have been previously reviewed (Juliano, 1985b).

All the antinutrition factors are proteins and all except phytin (phytate) are subject to heat denaturation. Phytin is located in 1 - to 3-µm globoids in the aleurone and embryo protein bodies as the potassium magnesium salt. Its phosphate groups can readily complex with cations such as calcium, zinc and iron and with protein. It is heat stable and is responsible for the observed poorer mineral balance of subjects fed brown rice diets in comparison to that of subjects fed milled rice diets (Miyoshi et al., 1987a, 1987b).

Trypsin inhibitor has also been isolated from rice bran and characterized (Juliano, 1985b). The partially purified inhibitor is stable at acidic and neutral pH and retained more than 50 percent of its activity after 30 minutes of incubation at 90°C at pH 2 and 7. Steaming rice bran for 6 minutes at 100°C inactivates the trypsin inhibitor, but dry heating at 100°C for up to 30 minutes is not as effective. The inhibitor distribution is 85 to 95 percent in the embryo, 5 to 10 percent in germ-free bran and none in milled rice.

Haemagglutinins (lectins) are globulins that agglutinate mammalian red blood cells and precipitate glycoconjugates or polysaccharides. The toxicity of lectins stems from their ability to bind specific carbohydrate receptor sites on the intestinal mucosal cells and to interfere with the absorption of nutrients across the intestinal wall. Rice-bran lectin binds specifically to 2-acetamido-2-deoxy-Dglucose (Poole, 1989). It is stable for 2 hours at 75°C but sharply loses activity after 30 minutes at 80°C or 2 minutes at 100°C (Ory, Bog-Hansen and Mod, 1981). Rice lectin agglutinates human A, B and O group erythrocytes. It is located in the embryo but has receptors in both rice embryo and endosperm (Miao and Tang, 1986).

Oryzacystatin is a proteinaceous (globulin) cysteine proteinase inhibitor (cystatin) from rice seed and is probably the first well-defined cystatin superfamily member of plant origin (Kondo, Abe and Arai, 1989). Incubation at pH 7 for 30 minutes at 100°C had no effect on its activity but inhibition decreased IS percent at 110°C and 45 percent at 120°C. Oryzacystatin effectively inhibited cysteine proteinases such as papain, ficin, chymopapain and cathepsin C and had no effect on serine proteinases (trypsin, chymotrypsin and subtilisin) or carboxyl proteinase (pepsin).

An allergenic protein in rice grain, causing rice-associated atopic dermatitis in Japan, is an a-globulin and shows stable immunoreactivity (60 percent) even on heating for 60 minutes at 100°C (Matsuda et al., 1988). It is present mainly in milled rice rather than in the bran. Hypoallergenic rice grains may be prepared by incubating milled rice in actinase to hydrolyse globulins in the presence of a surfactant at an alkaline pH (Watanabe et al., 1990a) and washing. The color of the processed grain is improved by treatment with 0.5-N hydrochloric acid and washing with water (Watanabe et al., 1990b).

Protein requirements of preschool children and adults on rice diets

The daily safe-level-of-protein requirements of preschool Filipino children consuming rice-based diets (as measured by the multilevel N balance or slope ratio method, two-thirds of nitrogen from rice) is lower for rice/milk (1.11 g/kg body wt) and rice/fish (1.18 g/kg) diets than for rice/mung bean (1.34 to 1.56 g/kg) and rice ( 1.44 g/kg) diets (Intengan et al., 1984; Cabrera-Santiago et al., 1986). True digestibilities were 70 to 78 percent. Amino acid scores of these Filipino weaning diets based on 5.8 percent lysine as 100 percent were 100 percent for rice/fish, 93 percent for rice/milk, 90 percent for rice/whole mung bean, 81 percent for rice/dehulled toasted mung bean and 60 percent for IR58 rice. The protein quality of the IR58 high-protein rice, as determined by the very short-term N balance index for three children, was 79 to 80 percent that of milk (CabreraSantiago et al., 1986). On the basis of the safe-level-of-protein requirements for milk of 0.89 g/kg body weight (Huang, Lin and Hsu, 1980), IR58 rice had 62 percent the protein quality of milk. Toasting and dehulling of mung bean prior to boiling did not significantly improve the rice/mung bean diet because of amino acid decomposition during toasting (Eggum et al., 1984). The true digestibility of rice/mung bean (2:1 by weight) diets in Thai children was 72.7 + 6.1 percent for whole mung bean and 74.6 + 5.9 percent for dehulled mung bean (Hussein, Tontisirin and Chaowanakarnkit, 1983).

Long-term studies in preschool children, testing protein intakes derived from short-term studies, were undertaken on two rice/fish weaning diets at 1.7 g/kg/day (Tontisirin, Ajmanwra and Valyasevi, 1984; Cabrera et al., 1987). The results tend to indicate that at the protein level of 1.7 g/kg/day, the currently recommended energy intake of 100 kcal/kg/day is inadequate for growth, but further investigations using more subjects are necessary. The calculated safe level of protein intake for a 6- to 9-month-old child is 1.75 g/kg/day in developing countries, where children are exposed to infections and perhaps periodic shortages of food (WHO, 1985).

The daily safe-level-of-protein requirements for rice-based Chinese (Chen et al., 1984; Huang and Lin, 1982) and Filipino (Intengan et al., 1976) adult diets ranged from 1.14 to 1.18 g/kg body weight. By contrast, the safe-level-of-protein requirements for egg protein in adults were 0.89 g/kg/day (Huang and Lin, 1982) and 0.99 g/kg/day (Tontisirin, Sirichakawal and Valyasevi, 1981). The aggregated value for highly digestible, good-quality protein in healthy young men is 0.63 g/kg/day (WHO, 1985). On this basis, the rice diets provided 68 to 98 percent of the protein quality of the reference proteins. The relative NPU of rice protein in Japanese adults has been estimated by the slope ratio method as 65 percent that of egg protein (Inoue et al., 1981), while NPUs of 56 percent for an egg diet and 43 percent for a Chinese rice diet have been reported (Huang and Lin, 1982).

Long-term studies (50 to 90 days) in adults, testing protein intakes derived from short-term studies, showed that protein intakes of 0.94 to 1.23 g/kg/ day, at energy intakes of 37 to 63 kcal/kg/day, were adequate for Chilean, Chinese, Filipino, Korean and Thai subjects (Intengan et al., 1982; Rand, Uauy and Scrimshaw, 1984). The amino acid score for the Filipino rice diet was 100 percent (Intengan et al., 1982) based on the WHO/FAO/UNU (WHO, 1985) amino acid scoring pattern for preschool children. Rice diets were calculated to be sufficient in lysine (Autret et al., 1968). The calculated true digestibility of protein ranged from 80 to 87 percent for the rice diets. Based on 0.75 g of good-quality protein as the safe-level-of-protein requirement (WHO, 1985), the rice diets tested had 61 to 80 percent of the quality of the reference animal proteins. Digestibility appears to be the most important factor determining the capacity of the protein sources in a usual mixed diet to meet the protein needs of adults (WHO, 1985). Thus, because of the relatively high level of sulphur amino acids and 3.5 to 4.0 percent lysine in rice protein, milled rice complements lysine-rich sulphur amino acid deficient legume proteins in human diets, the combination having a higher amino acid score than either rice or legume alone.

Protein, energy and mineral utilization of brown and milled rices and rice diets

FAD/WHO and the United Nations University have reviewed the research findings on energy and protein requirements using typical diets in developing countries (Town, Young and Rand, 1981; Rand, Uauy and Scrimshaw, 1984).

Compared with milled rice, brown rice has a higher content of protein, minerals and vitamins and a higher lysine content in its protein (Resurrección, Juliano and Tanaka, 1979; Eggum, Juliano and Maningat, 1982), (Table 35); however, it also has a higher level of phytin, neutral detergent fibre and antinutrition factors (trypsin inhibitor, oryzacystatin, haemagglutinin) in the bran fraction. Nitrogen balance studies in rats showed a slightly lower true digestibility for the protein in brown rice, but similar biological value and NPU for both brown and milled rices (Eggum, Juliano and Maniñgat, 1982), (Table 36). IR480-5-9 brown rice (10.9 percent protein) had a true digestibility of 90.8 percent, biological value of 70.8 percent and NPU of 64.2 percent (Eggum and Juliano, 1973). Digestible energy is lower in brown rice than in milled rice. Fat digestibility was 95.8 ± 0.5 percent for milled rice and 95.0 ± 0.4 percent for brown rice (Miyoshi, Okuda and Koishi, 1988). Protein digestibility was 95.3 ± 0.7 percent for milled rice and 94.1 ± 0.5 percent for brown rice.

TABLE 35 - Composition and nutritional value of milling fractions of IR32 brown rice at 14% moisture

Source: Eggum, Juliano and Maniñgat, 1982.

Balance studies in rats showed digestible energy of 80.1 percent for ltalian rough rice and 67.4 percent for its bran; for rough rice, N digestibility was 87.8 percent, biological value 72.6 percent and NPU 63.7 percent (Pedersen and Eggum, 1983). For IR32 rice bran (5.8 percent lysine digestible energy was 67.4 percent, N digestibility 78.8 percent, biological value 86.6 percent and NPU 68.3 percent (Eggum, Juliano and Maniñgat, 1982). Corresponding values for rice polish (5.0 percent lysine) were 73.3 percent digestible energy, 82.5 percent apparent N digestibility, 86.3 percent biological value and 71.2 percent NPU. IR32 bran polish with 13.2 percent protein (4.4 g lysine per 16 g N) and 15.4 percent fat, fed to growing rats, had 79.1 percent digestible energy, 85.9 percent true N digestibility, 81.1 percent biological value and 69.7 percent NPU (Eggum, et al., 1984). Even with a mineral mixture in their diets, rats fed rough, brown and undermilled rices were unable to maintain their femur zinc concentration; deposition of calcium and phosphorus also appeared to be affected (Pedersen and Eggum, 1983).

TABLE 36 - Balance data for milling fractions of IR32 brown rice in five growing rats^a

^a Means in the same column followed by a common letter are not significantly different at the 5% level by Duncan's (1955) multiple range test.

Source: Eggum, Juliano and Maniñgat, 1982.

Similar N balance studies for brown and milled rices were made with preschool children fed rice/casein or rice/milk (2:1 N ratio) diets (Santiago et al., 1984), (Table 37). Energy absorption was better for milled rice than for brown and undermilled rice. Because of their similar N balance, the major nutritional advantage of brown rice over milled rice is its high level of B vitamins. Roxas, Loyola and Reyes (1978) reported that the true digestibility of a rice/milk diet (1:1 N source) in preschool children improved with milling: brown rice/milk, 78 ± 5 percent; undermilled rice/ milk, 85 ± 5 percent; regular milled rice/milk, 87 ± 4 percent; overmilled rice/milk, 88 ± 4 percent. The brown rice diet was significantly lower in protein digestibility than the other diets.

Digestibility and balance studies in Japanese adults on brown rice and milled rice diets at low (0.5 g/kg) and standard (1.2 g/kg) protein intakes showed a higher energy, protein and fat digestibility for milled rice (Miyoshi et al., 1986), (Table 38). Neutral detergent fibre intake was at least twice as high in the brown rice diet. These results are consistent with the data from studies on children and on rats. Studies on the same subjects showed lower apparent absorption rates for sodium, potassium and phosphorus and a lower phosphorus balance for the brown rice diet at the low protein intake (Miyoshi et al., 1987b) when mineral intake was adjusted to be similar for the two diets by adding a mineral mixture. At the standard protein intake, even with higher potassium, phosphorus, calcium and magnesium levels in the brown rice diet, absorption rates of potassium and phosphorus were still significantly lower for the brown rice diet (Miyoshi et al., 1987a). The contributing factor must be the high phytate level in the bran fraction (aleurone and germ) of brown rice. The results confirmed earlier balance studies comparing brown and milled rices (FAO, 1954).

TABLE 37 - Balance data for milling tractions of IR32 brown rice in five preschool children (% of intake) ^a,b

^a Means in the same column followed by a common letter are not significantly different at the 5% level by Duncan's (1955) multiple range test.
^b Intake of 200 g N/kg body weight daily. First rice-casein diet (2:1 N ratio) had 77%b mean N absorbed, 33%a N absorbed, 91%ab energy absorbed and 94%b fat absorbed

Source: Santiago et al., 1984.

TABLE 38 - Digestibility and nitrogen balance data for five men on brown rice and milled rice diets at low and standard protein intake (mean ± SE)

^a Low protein intake, 0.5 g/kg body wt; standard protein intake, 1.2 g/kg body wt.
^b Means in the same column followed by the same letter are not significantly different at the 5% level by Duncan's (1955) multiple range test.

Sources: Miyoshi et al., 1986, 1987a, 1987b.

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