Rice Protein

Rice protein is suggested as one of the most important plant-based proteins, which can be applied or used as an ingredient in many products such as infant food and gluten-free products.

From: Rice Bran and Rice Bran Oil , 2019

Rice Protein and Rice Protein Products

H. Hoogenkamp , ... J.P.D. Wanasundara , in Sustainable Protein Sources, 2017

3.6.1 Reduction of Cholesterol and Triacylglycerol Levels

Rice protein extracted by alkaline with different composition of 23  kDa glutelin and 13   kDa prolamin both reduces the cholesterol level in plasma and liver and the triacylglycerol level in liver, one of the reasons for this effect being attributed to the enhancement of fecal steroid excretion (Yang et al., 2007).

Rice protein extracted by alkaline or α-amylase reduces both cholesterol and triacylglycerol levels in the liver, suppressing activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and malate dehydrogenase in liver and enhancing those of lipoprotein lipase and hepatic lipase (Yang et al., 2012). However, rice protein extracted by α-amylase is more effective to reduce the cholesterol level in liver than that extracted under alkaline conditions, probably because the former is more indigestible than the latter and promotes fecal excretion of bile acids (Yang et al., 2011). Rice protein extracted by alkaline or α-amylase suppresses activities of fatty acid synthase, glucose 6-phosphate dehydrogenase, and malate dehydrogenase in liver, and enhances those of lipoprotein lipase and hepatic lipase (Yang et al., 2012).

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Rice: Role in Diet

B.O. Juliano , in Encyclopedia of Food and Health, 2016

Chemical and Nutritional Composition

Protein: Rice has one of the lowest protein contents (7%) among the cereals. The bran layers and embryo are richer in nonstarch constituents than the milled (white) rice ( Table 1 ). The major nutritional advantage of brown rice, over milled rice, is its higher content of B vitamins and dietary fiber. Although higher in minerals, bran phytic acid forms complexes with minerals and proteins, reducing their bioavailability. Thus, the available iron (milligram per meal) is similar in brown and milled rice meals, but brown rice is probably higher in zinc (milligram per meal) than milled rice. The energy content of brown rice and bran is higher than milled rice, owing to the higher fat content. Rice contains no vitamin A, C, or D.

Table 1. Comparison of nutrient composition of brown rice, milled rice, and rice bran

Property Amounts (per 100   g)
Brown rice Milled rice Rice bran
Moisture (g) 14.0 14.0 14.0
Energy content (kJ) 1480–1610 1460–1560 1670–1990
Energy content (kcal) 355–385 349–373 399–476
Crude protein (g) 7.1–8.3 6.3–7.1 11.3–14.9
Crude fat (g) 1.6–2.8 0.3–0.6 15.0–19.7
Crude fiber (g) 0.6–1.0 0.2–0.5 7.0–11.4
Crude ash (g) 1.0–1.5 0.3–0.8 6.6–9.9
Available carbohydrates (g) 73–87 77–89 34–62
Total dietary fiber (g) 2.9–4.4 0.7–2.7 24–29
  Water-insoluble fiber (g) 2.0 0.5 15–27
Sugars (g) 0.8–1.9 0.1–0.5 5.5–6.9
Thiamin (mg) 0.4–0.6 0.07–0.17 1.2–2.5
Riboflavin (mg) 0.04–0.14 0.02–0.06 0.18–0.43
Niacin (mg) 3.5–6.2 1.3–2.5 27–50
Pantothenic acid (mg) 1.4–1.6 0.8–1.3 20–60
Vitamin B6 (mg) 0.5–0.7 0.1–0.4 3.7
Folate (μg) 16–20 4–9 40–140
Vitamin E, α-tocopherol (mg) 0.8–2.5 0.1–0.3 3–15
Calcium (mg) 10–50 10–30 30–120
Phosphorus (mg) 0.17–0.43 0.08–0.15 1.1–2.5
  Phytic acid P (mg) 0.13–0.27 0.02–0.07 0.9–2.2
Iron (mg) 1.4–5.2 0.3–0.8 8.6–43
Zinc (mg) 1.9–2.8 0.8–2.3 4.3–26

Source: Juliano, B. O. (2007). Rice chemistry and quality. Muñoz, Nueva Ecija: Philippine Rice Research Institute; Champagne, E. T., Wood, D. F., Juliano, B. O. and Bechtel, D. B. (2004). The rice grain and its gross composition. In: Champagne, E. T. (ed). Rice chemistry and technology (3rd ed.), pp. 77–108. St. Paul, MN: American Association of Cereal Chemists; United States Department of Agriculture (2014). National nutrient database for standard reference, Release 27. http://www.ars.usda.gov/ba/bhnrc/ndl.

Although cereal proteins are deficient in lysine, rice protein has one of the staple foods having highest lysine contents, corresponding to an amino acid score of 65% in milled rice, based on the World Health Organization (2007) amino acid requirement pattern for 1–2-year-old children (5.2% lysine as 100%, Table 2 ).

Table 2. Essential amino acid profile and energy and nitrogen balance in five growing rats of raw brown rice, milled rice, and rice bran

Property Brown rice Milled rice Rice bran
Arginine (g per 16   g N) 7.2 7.9 7.5
Histidine (g per 16   g N) 2.4 2.2 2.5
Isoleucine (g per 16   g N) 4.0 4.1 4.0
Leucine (g per 16   g N) 7.9 7.8 7.3
Lysine (g per 16   g N) 3.6 3.4 4.6
Methionine (g per 16   g N) 2.1 2.2 2.2
Methionine   +   cystine (g per 16   g N) 3.3 4.2 4.4
Phenylalanine (g per 16   g N) 4.9 5.1 4.5
Phenylalanine   +   tyrosine (g per 16   g N) 8.5 8.3 7.5
Threonine (g per 16   g N) 3.5 3.4 4.0
Tryptophan (g per 16   g N) 1.2 1.1 0.8
Valine (g per 16   g N) 5.6 5.8 6.3
Digestible energy a (% of total) 94.3b 96.6a 67.4c
True digestibility a (TD, % of diet N) 96.9b 98.4a 78.8c
Biological value a (% of digested N) 68.9b 67.5b 86.6a
Net protein utilization a (% of diet N) 66.7b 66.4b 68.3a
Amino acid score b (%) 69lys 65lys 88lys
Amino acid score b   ×   TD (%) 67lys 64lys 69lys
a
Means in the same line followed by a common letter are not significantly different at the 5% by Duncan's multiple range test.
b
Lysine is the first limiting amino acid. Amino acid score is based on 5.2   g per 16   g N as 100%.

Source: United States Department of Agriculture. (2014). National nutrient database for standard reference, Release 27. http://www.ars.usda.gov/ba/bhnrc/ndl; Eggum, B. O., Juliano B. O. and Maniñgat, C. C. (1982). Protein and energy utilization of rice milling fractions by rats. Qualitas Plantarum Plant Foods for Human Nutrition 31, 371–376.

The solubility fractions of milled rice proteins are about 15% albumin–globulin (water- and salt-soluble), 20% prolamin (PB I, alcohol-soluble), and 65% glutelin (PB II, alkali-soluble). Bran proteins are 66–98% albumins. Prolamin is poor in lysine, but rich in sulfur-containing amino acids. The high lysine content of rice protein is due to the low prolamin content. From studies funded by the United Nations University/FAO/WHO, the mean safe-level protein requirements of rice-based diets are 1.02   g protein per kilogram body weight per day in adults and 1.38   g protein per kilogram body weight per day in preschool children, while safe-level protein requirements are 0.85   g protein per kilogram body weight per day for adults and about 1.00   g protein per kilogram body weight per day for preschool children. Organic rice contains less protein than conventionally grown rice because of reduced nutrients from organic fertilizer.

Energy digestibility is higher in milled rice than in brown rice because of the reduced dietary fiber and phytic acid, as verified by the poor energy digestibility of rice bran ( Table 2 ). The true digestibility (TD) of milled rice protein is also higher than brown rice, but the biological value (BV) is lower, resulting in similar net protein utilization (NPU). Bran protein has a lower TD, but a higher BV than brown and milled rice proteins. The amino acid score corrected for TD in rats, proposed by the Food and Agriculture Organization as a protein quality index, shows similar values to NPU for rice proteins. Black or purple rice has a lower NPU (72%) than brown rice and higher phenolics level (0.6%, anthocyanin) than red rice (NPU 83% and 0.2% phenolics, proanthocyanidins) and nonpigmented rice (NPU 97% and ≤0.02% phenolics), but these milled rice have identical NPUs. Japanese cooked milled rice protein has lower cysteine and slightly higher TD in rats than indica rice protein (tropical as compared with japonica, temperate, or Japanese rice). Rice complements legumes (deficient in sulfur-containing amino acids) in amino acid composition for human diets.

Cooking and parboiling reduce the TD in growing rats by 5–15%, with a corresponding increase in BV, but little change in NPU. However, lysine digestibility remains close to 100%, while cystine digestibility drops to about 82%. The fraction that remains in the feces, as fecal protein particles, represents the lipid-rich core of large PB I, with less than 1% lysine in the protein, but is rich in cystine. PB II is readily digested.

Rice is hypoallergenic, but some individuals are allergic to the 14–16   kD alpha-amylase/trypsin inhibitor and 33   kD Oryza glyoxalase 1. Both allergens are still active in cooked milled rice.

Starch: Starch varies in apparent amylose content (true amylose plus long-chain amylopectin as determined by iodine colorimetry in acetate buffer pH   4.5): waxy 0–2%, very low 2–10%, low 10–20%, intermediate 20–25%, and high >25%, all on a milled rice dry-weight basis since the 1950s. Actual amylose content values, measured using differential scanning calorimetry (by melting or crystallization enthalpy of amylose–lysolecithin complex), are slightly lower and closer to values determined using iodine colorimetry (ammonium buffer pH   9) (low 10–17%, intermediate 17–22%, and high >22%).

Rice starches also differ in gelatinization temperature, the point when granules start to swell irreversibly in hot water: low 55–70   °C, intermediate 70–74   °C, and high >74   °C. Gelatinization temperature correlates positively with cooking time.

The glycemic index of cooked brown rice tends to be lower than cooked milled rice owing to the greater amounts of phytic acid and fiber in brown rice, but only in waxy and low-amylose content rice. Brown and milled rice have similar glycemic index in intermediate- and high-amylose content rice. Among cooked milled and brown rice, glycemic index decreases with increasing amylose content regardless of the cooking method. With high amylose content, glycemic indexes are lower in those cooked in excess water; when cooked in a rice cooker with the same water–rice ratio and cooking time, low-gelatinization temperature rice has a higher glycemic index than intermediate-gelatinization temperature rice. Processing, including parboiling, tends to reduce the glycemic index. Resistant starch in vivo, as determined in ileostomy patients, is ≤5% and may not be as discriminating as glycemic index for humans. Short-term satiety has been found to be similar in milled and brown rice cooked to the same hardness by adjusting water content, regardless of amylose content.

Rice bran: The use of rice bran and brown rice in cereal products has increased in recent years owing to its recognition as a whole grain and hypocholesterolemic effect of the unsaponifiable fraction (up to 4.4%) of bran oil, which contains gamma-oryzanol (cycloartenol, 24-methylene-cycloartanol, and campesterol esters of ferulic acid), tocopherols, and tocotrienols, an analog of tocopherol (vitamin E). Defatted bran has no hypocholesterolemic activity, unlike in oats where the active component is soluble β-glucan. Inactivation of antinutrition factors – trypsin inhibitor, oryzacystatin, and hemagglutinin–lectin – and lipase and lipoxygenase, which are concentrated in rice bran by heat treatment (including cooking) and extrusion, improves the shelf life of bran and its nutritional value to poultry. In contrast, phytic acid is heat-stable and, in rice bran and brown rice, has been reported to have some activity in preventing/reducing the risk of colon cancer. Phytic acid content of rice bran is the highest among cereal brans (3–8% phytic acid).

The major fatty acids of rice oil are palmitic, oleic, and linoleic. Essential fatty acid content of rice oil is 33.4% linoleic acid and 1.6% linolenic acid. Levels of oryzanol, tocopherols, tocotrienols, and unsaponifiable matter differ among crude rice bran oils, and oryzanol, tocopherols, and tocotrienols may be reduced by up to 90% by conventional refining and deodorizing. These antioxidants seem to be lower in Philippine rice than rice grown in the United States.

Breeding for improved nutritive value: Breeding efforts to improve the nutritional value of rice grain include a higher micronutrient density (higher iron, zinc, and vitamin A), low phytic acid (high inorganic phosphate) content, low prolamin content, elimination of lipoxygenase-3 activity and allergenic globulin, and transgenic rice endosperm with provitamin A (β-carotene) (golden rice 2), soybean glycinin, or ferritin genes. Efforts to increase protein content from 7% to 9% at IRRI in 1966–79 were not successful.

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Rice

Ragab Khir , Zhongli Pan , in Integrated Processing Technologies for Food and Agricultural By-Products, 2019

6.1.1 Protein Source

Rice protein contains lysine that is considered hypoallergenic and is therefore favorable for human consumption ( Helm and Burks, 1996). Different extraction methods have been studied to extract proteins from rice by-products. Alkali hydrolysis under different conditions has been explored to improve the yield of extracted protein (Lew et al., 1975; Bera and Mukherjee, 1989; Gnanasambandam and Hettiarachchy, 1995). Alkali hydrolysis followed by acid precipitation has been studied by Ansharullah and Chesterman (1997). In this method, deoiled rice bran was suspended in distilled water (1   g in 5   mL of water). Then the suspension was adjusted to pH 11 by sodium hydroxide (NaOH) solution. The reaction was carried out at 30°C and alkali hydrolysis for 45   min. After the reaction, the pH of the suspension was adjusted to pH 7 with hydrochloric acid (HCl) solution to stop the reaction. The residue bran was separated from the soluble product with a vacuum filter using a filter paper, then the soluble portion was assayed for extracted protein. This is a simple method, but the high pH conditions could reduce the protein yield because of degradation phenomenon (Jiamyangyuen et al., 2005). Moreover, high pH conditions could also lead to undesirable effects like molecular cross-linking and rearrangements, resulting in decrease in nutritive value and formation of toxic compounds, such as lysinoalanine (Cheftel et al., 1985; Otterburn, 1989).

A subcritical water hydrolysis method was studied by Sereewatthanawut et al. (2008) as an alternative method for rice protein extraction. In this method, a deoiled rice bran suspended in distilled water (1   g in 5   mL of water) was charged into a batch reactor and heated to 100–220°C by an electric furnace heater for up to 30   min. The pressure in the reactor was estimated to be between 101.35   kPa and 3.97   MPa. Then the reactor was cooled to room temperature by immersion in a cool water bath. The soluble portion was separated from the residue bran with a vacuum filter and assayed for extracted protein. It was reported that the amount of produced protein increased with an increase in temperature. The highest yield of protein was 219   ±   26   mg/g of dry bran at extraction conditions of 200°C for 30   min.

Enzymatic methods have also been used to improve protein extractability at neutral pH. Ansharullah and Chesterman (1997) studied the enzymatic pretreatment using different concentrations of carbohydrases (Viscozyme, 0–120 FBG unit) and (Celluclast 1.5   L, 0–360 NC unit), time of incubation (1–5   h), pH (3.8–5.4), and temperatures of 40°C and 50°C. They found that the maximum protein extraction was obtained when the Viscozyme-Celluclast mixture used at pH 3.8 with incubation time of 5   h and temperature of 40°C. While, at the process temperature of 50°C, the use of Viscozyme alone, under similar conditions, had a significant effect in increasing the efficiency of the protein extraction.

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Rice in brewing

Masaki Okuda , ... Dong Wang , in Rice (Fourth Edition), 2019

1.3.3.2 Proteins

It is known that about 90% of rice proteins exist as seed storage proteins in the protein granules called protein bodies (PBs). Prolamin accumulates in PB-І and glutelin accumulates in PB-ІІ ( Tanaka et al., 1980; Ogawa et al., 1987). In the production of sake, glutelin is digested to amino acids and oligopeptides whereas prolamin is hardly digested by the enzyme of koji (Furukawa et al., 2000; Iwano et al., 2001, 2002; Hashizume et al., 2006a, 2007a, Okuda et al., 2016). The nitrogen balance in small-scale brewing of sake (Iemura et al., 1996; Hashizume et al., 2006b) were reported. Fifty-five percent of the nitrogen in the material rice was liquefied in the sake mash and 30%–33% was transferred to the sake (Hashizume et al., 2006b). Approximately 44%–47% of the nitrogen in the sake was in the form of free amino acids, and almost all the residue of the nitrogen was believed to be oligopeptides (Hashizume et al., 2006b).

Rice protein constitutes 6%–10% of the weight of brown rice, and is affected by cultural conditions such as the amount of fertilizer used and changes in the temperature, as well as by the rice variety (Kizaki et al., 1993). The PB-II/PB-I ratios were determined not to change significantly during the polishing procedure (Kizaki et al., 1991). Crude protein content in the rice grains used for sake brewing showed a significant positive correlation with glutelin content (Okuda et al., 2018). Yamadanishiki cultivars showed lower crude protein and glutelin contents compared with Gohyakumangoku cultivars harvested from the same field (Okuda et al., 2018). The low glutelin level of Yamadanishiki may be an important reason for its empirically high evaluation in the Japanese sake brewing industry (Okuda et al., 2018).

In sake brewing, rice proteins are digested into amino acids or oligopeptides by enzymes of koji. The profile of nitrogen compounds from rice proteins has been previously reported (Iemura et al., 1995, 1996; Iwano et al., 2001; Maeda et al., 2011). The free amino acids or peptides in the sake mash serve as a nutrient source for yeast growth, and are also important factors involved in the formation of aroma and flavor of sake (Tajima and Fukimbara, 1969). But an excess of these compounds often gives sake a rough taste, deepens the color, and accelerates deterioration of its quality. Several bitter-tasting peptides and their ethyl esters have been found in sake (Hashizume et al., 2007b, 2012). Staling of stored sake was affected by levels of protein-associated sulfur-containing amino acids in the rice (Okuda et al., 2009c). Some amino acids such as leucine, valine, and isoleucine are assimilated by yeast to form higher alcohols such as isoamyl alcohol, isobutanol, and 2-methyl butanol, respectively. Among them, isoamyl alcohol is further reacted with acetyl coenzyme A to form isoamyl acetate, one of the main flavor components contributing to the aroma of sake.

As mentioned previously, white rice with high protein content is likely to form less sugar and more amino acid in mash fermentation. Because consumers prefer sake with a clear and light taste, various efforts have been made to decrease the protein content of steamed rice as well as to denature proteins, so that they are minimally decomposed by proteases in koji during such treatments as steaming for a long time or at a slightly higher pressure.

Recently, the development of new sake products with unique features to appeal to the diverse preferences of sake consumers has been the focus in the sake market in an effort to counteract the decrease in demand for sake. As shown in Fig. 18.9, the endosperm protein mutant lines with low contents of glutelin were developed (Iida et al., 1993, 1997, 1998) and the suitability of these mutant lines for sake was examined (Iwano et al., 2002, Uehara et al., 2002; Mizuma et al., 2002; Maruta et al., 2003, Furukawa et al., 2002, 2003, 2004, 2005, 2007). Because a digestible protein glutelin is poor in these mutant lines, the sake with a low amino acidity and a clear aroma can be brewed by using these cultivars for sake brewing. However, the utility rate of the raw material using these mutant lines was low and the brewed sake had a characteristic aroma (Iida et al., 2009; Mizuma et al., 2002; Furukawa et al., 2003, 2005). It was demonstrated that 4-Mercapto-4-methylpentan-2-one, one of the main characteristic aromatic volatile thiols in sauvignon blanc wine, contributes to the characteristic aroma perceived in brewed sake made from the endosperm protein mutant lines with low contents of glutelin (Iizuka-Furukawa et al., 2017).

Figure 18.9. SDS-PAGE of total protein in 70% polished rice. M, Molecular weight marker; Lane1, Mizuhonoka (endosperm protein mutant rice); Lane2; Gin'ohmi (ordinary rice).

 Data from Furukawa, S., Mizuma, T., Kiyokawa, Y., Iida, S., Matsushita, K., Maeda, H., Sunohara, Y., Wakai, Y., 2005. Use of amino-acid enrichment to suppress characteristic odor of sake brewed using low-glutelin rice. Seibutsukogaku 83, 108–116.

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Impact of climate change on rice grain quality

Lianxin Yang , Yunxia Wang , in Rice (Fourth Edition), 2019

5.3 Interaction of CO2 with temperature or ozone

The moderate warming of plant growth environment increased rice protein concentration, but high temperature led to opposite results ( Ziska et al., 1997; Liu et al., 2013). Temperature increase of 1°C had no effect on the concentration of protein and its fractions in grains of rice grown in ambient CO2, but increased the concentrations of most protein fractions when rice was grown in elevated CO2 (Jing et al., 2016c). High temperature leads to the increase of grain protein concentration, which is considered as a "concentration mechanism" that is, the effect of stress on starch accumulation is greater than that of protein synthesis (Yamakawa and Hakata, 2010; Wang and Frei, 2011). Unlike the findings by Jing et al. (2016c), Ziska et al. (1997) found that the temperature increase of 4°C during the whole growth period of rice could result in a significant decrease in grain protein concentration, and no interaction between CO2 and temperature. There is only one report on the interaction between CO2 and O3. Ozone stress increased the concentration of total nitrogen and protein-N in grains of rice plants grown under the ambient CO2 concentration, but no significant impact of ozone stress was found when plants were grown in elevated CO2 environment (Wang et al., 2014a).

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Gross structure and composition of the rice grain

Bienvenido O. Juliano , Arvin Paul P. Tuaño , in Rice (Fourth Edition), 2019

2 Gross composition of grain parts and milling fractions

Rice starch is discussed in Chapter 3 , rice proteins in Chapter 4, rice lipids in Chapter 5, rice minerals in Chapter 6, rice vitamins in Chapter 7, and rice phenolics and other natural products in Chapter 8. Utilization of rice hull is discussed in Chapter 19. Hence, these items they are not covered in this chapter.

Brown rice has the lowest protein content and total dietary fiber among cereal grains, and the highest content of starch and available carbohydrates (USDA, 2016) (Table 2.1).

Table 2.1. Comparison of gross composition of various cereal grains per 100   g edible portion at 14% moisture (USDA, 2016)

Nutrient per 100   g Brown rice Barley grain Corn white Oat grain Rye grain Sorghum grain Triticale grain Wheat flour
Water (g) 14.0 14.0 14.0 14.0 14.0 14.0 14.0 14.0
Energy (kJ) 1497 1412 1465 1542 1360 1352 1405 1372
Energy (kcal) 358 338 350 368 325 323 323 328
Crude protein (g) 7.4 10.3 9.0 16.0 10.0 10.4 13.0 12.7
Total lipids (g) 3.1 1.6 4.6 6.5 1.6 3.4 2.1 2.4
Ash (g) 1.2 1.2 1.2 1.6 1.5 1.4 2.2 1.5
Carbohydrates by difference (g) 73.5 72.9 71.2 62.8 73.0 70.8 72.1 69.3
Total dietary fiber (g) 3.5 9.9 7.0 10.0 14.5 16.6 14.6 10.3
Sugars (g) 0.6 0.8 2.0 0.9 0.9 2.5 2.0 0.4

It has the highest energy content next to oat. Removal of the inedible hull reduces the fiber content of brown rice. Its low dietary fiber content caused the delay in having the United States Food and Drug Administration consider brown rice as a whole grain, which usually requires 10% content of dietary fiber in the grain.

In brown rice, all nonstarch constituents are concentrated in the bran fraction, and the endosperm (milled rice) is richest in starch. Lipid bodies are concentrated in the embryo and the aleurone layer, and also in the subaleurone layer; hence, the energy level is highest in the bran, followed by brown rice, and then milled rice (Table 2.2) (Juliano and Bechtel, 1985; Champagne et al., 2004).

Table 2.2. Proximate analysis of parts of the rice grain per 100   g at 14% moisture

Nutrient per 100   g Rice hull Brown rice Milled rice Rice bran
Water (g) 14.0 14.0 14.0 14.0
Energy (kJ) 1110–1300 1480–1610 1460–1560 1670–1990
Energy (kcal) 266–311 358–388 349–373 399–476
Crude protein (g) 2.0–2.8 7.1–8.3 6.3–7.1 11.3–14.9
Total lipids (g) 0.3–0.8 1.6–3.1 0.3–0.7 15.0–19.7
Ash (g) 13–21 1.0–1.5 0.3–0.8 6.6–9.9
Carbohydrates by difference (g) 22–34 73–87 77–89 34–62
Total dietary fiber (g) 66–74 2.9–4.4 0.7–2.7 19–29
Sugars (g) 0.6 0.7–1.9 0.1–0.5 5.5–6.9

Adapted from Juliano, B.O., Bechtel, D.B., 1985. The rice grain and its gross composition. In: Juliano, B.O. (Ed.), Rice Chemistry and Technology, second ed. American Association of Cereal Chemists, Inc., St. Paul, MN, pp 17–57; Champagne, E.T., Wood, D., Juliano, B.O., Bechtel, D.B., 2004. The rice grain and its gross composition. In: Champagne, E.T. (Ed.), Rice Chemistry and Technology, third ed. American Association of Cereal Chemists, Inc., St. Paul, MN.

Nutrient composition and genetic diversity in rice were reviewed by Kennedy and Burlingame (2003). Protein content is slightly higher in brown rice than in milled rice because of the higher protein level in the bran (Table 2.2). Crude fat, crude ash, crude fiber, and total dietary fiber are also higher in brown than milled rice, being concentrated in the bran fraction. Sugars, phytic acid, and phenolics are also higher in brown rice. Pigments are located in the pericarp. Black or purple rice has more phenolics (0.6% anthocyanins) than red rice (0.2% proanthocyanidins) but nonpigmented brown rice has <0.02% phenolics (Shao et al., 2014). However, both anthocyanins and proanthocyanidins were reported present in a black rice (Finocchiaro et al., 2010). Antioxidant activity is higher in raw pigmented rice than in nonpigmented rice (Irakli et al., 2016) in free and bound forms.

The nonstarch polysaccharides of two brown rice samples were 2.5% pentosans, 0.6% water-soluble (1   →   3) (1   →   4) β-glucan, 0.5% arabinoxylan, 0.8% total soluble fructans, and 0.2% uronic acid (Henry, 1985). French milled rice (n  =   27) had 0.04%–1.4% β-glucans and 0.17%–0.24% arabinoxylans on dry basis (Vidal et al., 2007).

The nutrient distribution in milling fractions of brown rice was studied by Resurreccion et al. (1979) (Table 2.3). Starch has the opposite distribution in the various milling fractions than neutral detergent fiber, fat, and ash. Protein has the most even distribution. Composition of oil bodies isolated from rice bran was 83.7% lipid and 11.3% protein dry basis (Nantiyakul et al., 2013).

Table 2.3. Nutrient distribution in milling fractions of IR32 rice caryopsis

Nutrient Content in brown rice (% at 14% moisture) Distribution (% of nutrient in brown rice)
Bran Polish Endosperm (milled rice)
Subaleurone Middle Core
Weight (%) of brown rice 100 6 6 8 10 70
(0–6) (6–12) (12–20) (20–30) (30–100)
Starch (%) 66.4 1 4 7 11 77
Protein (N   ×   5.95) (%) 7.2 11 11 13 14 51
Neutral detergent fiber (%) 2.1 71 19 1 2 7
Crude fat (%) 2.9 51 32 10 1 6
Crude ash (%) 0.78 42 26 10 5 17

Adapted from Resurreccion, A.P., Juliano, B.O., Tanaka, Y., 1979. Nutrient content and distribution in milling fractions of rice grain. Journal of the Science of Food and Agriculture 30, 475–481.

Microscopy and energy dispersive X-ray microanalysis of globoids in rice embryo and endosperm tissues showed that phosphorus, magnesium, and potassium are commonly present in all globoids (Wada and Lott, 1997). Calcium was detected mainly in globoids of the aleurone layer. Iron was found mostly in radicle tissue globoids. Zinc was commonly found in globoids of the scutellar epithelium and in provascular tissues of the mesocotyl, coleoptile, and radicle. Manganese was distributed throughout most of the tissues examined, but the highest levels were detected in globoids from the coleoptile tip regions and the plumule.

Rice pollen has 18.8%–20.5% protein, 2.7%–3.1% lipids, 2.3%–2.5% ash, 5.3%–5.9% free sugars, 4.6%–6.2% reducing sugars, and 19.4%–23.7% starch (Blakeney and Matheson, 1984). Nonwaxy pollen starch has 21%–27% apparent amylose content (AC) based on iodine-binding capacity. Waxy pollen starch has only 1.0% AC. Pooled pollen protein has 7.3   g lysine/16   g   N (IRRI, unpubl. data).

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Sake: quality characteristics, flavour chemistry and sensory analysis

S. Furukawa , in Alcoholic Beverages, 2012

Amino acids

Most of the amino acids in sake are derived from rice proteins. The amino acids in sake are created from rice proteins by acid protease and acid carboxypeptidase from koji. In general, the sake main mash contains a large amount of arginine, alanine, threonine, glycine, proline, glutamic acid and leucine ( Kondo et al., 1983). The tastes of these are as follows:

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Arginine and threonine, gentle sweet,

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Alanine, very sweet,

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Glycine, fresh sweet,

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Proline, sweet and sour,

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Glutamic acid, strong umami and sour,

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Leucine, faintly sweet.

(Brewing Society of Japan, 1999).

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Low Protein Rice

Shaw Watanabe , ... Shigeru Beppu , in The Role of Functional Food Security in Global Health, 2019

13.4 Packed Low-Protein Rice

In 1992, researchers at the Niigata Prefectural Food Research Institute reported a method to reduce rice protein, phosphate, and potassium by digestion of boiled rice with lactic acid bacteria. We implemented the same method to produce low-protein rice but there were many problems, such as the length of metabolizing period by lactic acid bacteria, the production costs, and the effects of lactic acid bacterium on other products by cross-contamination in the factory. Therefore, we modified the original technique by using specific acid proteases, and we succeeded in releasing packed boiled rice in which the protein contents was reduced to 1/3 of nonprocessed rice [24]. Japanese people prefer cooked rice to be elastic and not sticky. Unfortunately, after ordinary boil cooking, the enzymatically treated low-protein rice became sticky like rice cakes. To circumvent the problem, rice was cooked for a short time at superhigh temperature, uniformly heating all layers down to the core, and keeping the starch inside. In addition, to be kept at room temperature, the final product had to be sterilized at 121°C for 4   minutes, in accordance with the Japanese Food Hygiene Law Fo3.1.

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Household Foods and Products

Rosalind Dalefield BVSc PhD DABVT DABT , in Veterinary Toxicology for Australia and New Zealand, 2017

Melamine

The adulteration with melamine and cynauric acid, by a Chinese company, of wheat gluten, corn gluten, and rice protein used in wet pet foods led to renal failure in hundreds of domestic cats and dogs in North America, Europe, and South Africa in 2007. Melamine by itself is considered to be of low toxicity, but current research indicates that the combination of melamine and cyanuric acid is hazardous. Postmortem histopathology of the kidney revealed the presence of characteristic crystals in the kidneys. Unfortunately these crystals are radiolucent in the live animal.

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Renal Toxicity

Manu Sebastian , in Handbook of Toxicology of Chemical Warfare Agents, 2009

6 Pet food-related toxicity by melamine and cyanuric acid

Since March 2007, several deaths were reported in dogs and cats associated with contamination of melamine and cyanuric acid in wheat gluten and rice protein (imported from China) used for manufacturing pet food in the USA. Melamine was identified in pet food and in the urine and kidneys of the cats that consumed the pet food. Analysis of the crystals revealed that they were composed of approximately 70% cyanuric acid and 30% melamine and were extremely insoluble. Significant clinical pathologic findings included azotemia and hyperphosphatemia, consistent with acute renal failure. In some cases, leukocytosis was observed. The majority of cases had oliguria or anuria and death was due to acute renal failure. No significant gross observations were noticed except in some cases which included gastric ulcer and green–yellow fluid with green crystals within the renal pelvis. Histopathological observations included degeneration and occasional necrosis of renal tubular epithelial cells with numerous crystals ( Figure 38.3) evenly distributed throughout the cortex and medulla, within renal tubules and collecting ducts. Under polarized light, these crystals showed birefringence. Many of them were round, pale brown, and appeared to have a rough surface as a result of smaller crystalline structures being arranged radially and more randomly within the entire birefringent crystal. In some areas, these crystal structures were arranged in concentric circles. The crystals were present within renal tubular epithelial cells and in the lumens of tubules, filling the lumen and at times distending the tubules. The melamine-containing crystals do not stain with Alizarin Red S or Von Kossa but do stain with Oil Red O. Calcium phosphate and calcium oxalate crystals do not stain with Oil Red O, which helps in the differential diagnosis of these crystals from crystals associated with EG toxicity (Thompson et al., 2008).

FIGURE 38.3. Melamine cyanuric acid poisoning, feline kidney; tubules are lined by degenerate, necrotic and flattened epithelium and contain crystalline material. Arrow shows crystalline material arranged in concentric pattern. H &amp; E stain ×40.

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