The Arabs introduced rice to Egypt in around 600 AD, probably from Spain. Rice, which is the preferred food by most Egyptians, contributes about 20% to the per capita cereal consumption. Its impact on the economy lies within the fact that rice occupies about 22% of the cultivated area in Egypt during the summer season, thus consuming about 18% of the total water resource. Rice farming also engages one million families, which correspond to about 10% of the Egyptian population. Rice is also one of the most effective and profitable means of reclaiming hundreds of thousands of feddans of saline lands 1. China contributes 32.7% of the world’s rice production on 24% of the world’s rice-growing area, and India contributes 26% of the production on 28% of the area 2.
Rice bran is the outer brown layer including the rice germ that is removed during the milling process of brown grain. This milling byproduct is reported to be high in natural vitamins and minerals, particularly vitamin E. Bran is particularly rich in dietary fiber and essential fatty acids and contains significant quantities of starch, protein, vitamins, and dietary minerals 3. It contains various antioxidants that impart beneficial effects on human health. A major rice bran fraction contains 12–13% oil and highly unsaponifiable components (4.3%). This fraction contains tocotrienols (a form of vitamin E), γ-oryzanol, and β-sitosterol; all these constituents may contribute to the lowering of the plasma levels of the various parameters of the lipid profile. Rice bran also contains a high level of dietary fibers (such as β-glucan, pectin, and gum). In addition, it also contains ferulic acid, which is also a component of the structure of nonlignified cell walls. The high oil content of bran makes it subject to rancidification, one of the reasons that it is often separated from the grain before storage or further processing. The bran itself can be heat-treated to increase its longevity 4.
The fatty acid profile of rice bran oil indicated that oleic and linoleic acids were about 77% 5. Vegetable oils are regarded as a rich natural source of dietary plant sterols. The majority of crude vegetable oils contain 1–5 g/kg of phytosterols, but rice bran oil can contain up to 30 g/kg of phytosterols. The level of tocotrienols in rice bran oil is also very high compared with other vegetable oils 6.
Rice bran is considered to be one of the most nutrient-dense naturally occurring foods available, but it is routinely thrown away as an unused food resource. This is because rice bran contains an enzyme that causes rancidity within hours of milling, making it unfit for human consumption. In fact, more than 60 million metric tons of rice bran each year ends up as animal feed 7. Therefore, the purpose of this study was to assess the quality and quantity of rice bran and rice bran oil of some Egyptian rice varieties commonly produced in Egypt by determining their chemical composition. Another objective was to assess the acceptance of the rice bran edible oil produced and the utilization of rice bran in bread production.
Materials and methods
Experimental study was carried out on 13 rice variety cultivated in Egypt.
Bran extraction and stabilization 8
The rice bran was extracted from 13 rice variety cultivated in Egypt, immediately after harvesting or after storage for 1 year (six samples from each variety). The bran was stabilized to inhibit the lipase enzyme activity by heating the bran in a microwave at 850 W for 3 min then after cooling it; the bran was stored in top zipper plastic bags.
Bread production using rice bran
Bread was prepared from one variety of extracted rice bran (Giza172). Rice bran was added to wheat flour at three different concentrations (5, 10, and 15%). The three concentrations depended on the texture of the dough during processing.
Rice bran oil manufacturing
The oil was extracted from bran using n-hexane. The n-hexane was removed from the oil by evaporation. The produced oil was refined through neutralization and degumming followed by bleaching, winterization, and then deodorization 9.
Chemical analysis of rice bran
Samples from 13 Egyptian rice varieties were milled and bran fractions were collected and tested to determine the amount of bran. Moisture content, crude protein, crude fat, carbohydrates, ash, and crude fiber were determined according to AOAC 10.
Total content of P, K, Na, Ca, Fe, Mn, Zn, Cu, and Mg was determined in samples as soleplate using the wet ashing method with acid mixture (nitric : perchloric : sulfuric acid in a ratio of 8 : 1 : 1). Phosphorus content in the digested material was determined using the microvandate–molybdate yellow method. Microelements such as Na, K, Ca, and Mg were determined in the digested solution using atomic absorption FMD3 (Shimadzu, Japan) 11.
Determination of physical and chemical properties of the rice bran oil
Refractive index, acid value, iodine value, peroxide value, and saponification number were determined according to AOCS 12.
Vitamin E and γ-oryzanol analysis
Normal-phase and reverse-phase high-pressure liquid chromatography (HPLC) were used to determine the concentration of vitamin E and γ-oryzanol, respectively. Standards were obtained from Sigma-Aldrich (Germany). For vitamin E, the mobile phase was hexane, ethyl acetate, and acetic acid (99, 0.5, and 0.5%, respectively) and the flow rate was 1.8 ml/min. Excitation and emission wavelengths of fluorescence detector were 290 and 330 nm, respectively. Vitamin E concentration was reported as the sum of concentrations of α-tocopherol, α-tocotrienol, γ-tocopherol, and γ-tocotrienol. The reverse-phase HPLC system used to measure γ-oryzanol concentration consisted of a C18 column (Rainin Instrument Company, Woburn, Massachusetts, USA), auto sampler, absorbance detector, and ultraviolet detector. The mobile phase was methanol, acetonitrile, dichloromethane, and acetic acid (50 : 44 : 3 : 3) and the flow rate was 2 ml/min. The wavelength of ultraviolet detector was 330 nm (Waters, Milford, Massachusetts, USA). HPLC analysis of each variety, milling time, and component combination was conducted in triplicate 13.
A panel test was conducted on different breads produced from three different addition levels of rice bran as well as the blank, which was made by whole wheat flour bread. The samples were coded and panelist scored the four types of bread from 1 to 5 with respect to taste, smell, texture, and appearance.
A panel test was conducted on rice bran oil produced, corn oil, and sunflower oil, which were added to different portions of Karish cheese. An organoleptic evaluation based on taste, smell, texture, and appearance was assessed by 10 panelists using a numerical rating 1–5. The samples were coded and panelists were asked to compare the three samples.
Statistical package for social sciences (version 19.0; SPSS Inc., Chicago, Illinois, USA) was used. The χ2-test was used to test for the association and/or differences between categorical variables at 5% significance.
The mean percentage of rice bran of newly harvested rice ranged from 8.83 to 19.17% and in stored rice ranged from 8.13 to 18.77%, with significant differences in the percentage of bran between the different varieties. The decrease in bran due to storage ranged from 0.91% for Giza171 to 12.84% for Sakha102. The mean percentage of oil in rice bran ranged from 11.6 to 14.83 for newly harvested rice and increased for stored rice to range from 12.07 to 15.2% (Table 1).
The mean values of the percentage of moisture in bran of newly harvested rice ranged from 5.84 to 6.13% that decreased by 6.16% in bran produced from stored rice. The mean value of crude protein in bran of newly harvested rice was 14.62% that decreased to 14.37% upon storage of rice. The analysis of variance indicated significant differences in the percentage of moisture, protein, oil, carbohydrates, fiber, and ash of the 13 rice varieties. Carbohydrate constitutes the highest percentage in the bran (45.62%). Oil, carbohydrates, and crude fiber concentrations increased by 4.68, 0.48, and 3.77%, respectively, after storage, whereas crude protein and ash concentrations decreased by 1.71 and 2.86%, respectively (Table 2).
The caloric content of 100 g bread containing 5% rice bran was 260 kcals, which slightly decreased to 258 kcals for bread containing 10% rice bran then decreased to 243 kcals for bread containing 15% rice bran. The protein and carbohydrate also decreased with the increase in the percentage of rice bran in bread. However, the fat content increased from 4.2 to 4.5% then to 4.9% for bread containing 5, 10, and 15% rice bran, respectively (Table 3).
Rancidity parameters of rice bran oil extracted from newly harvested and stored rice varieties are presented in Table 4. Bran produced from newly harvested rice showed mean values of 3.63, 93.92, 186.85, and 15.91 for acid value, iodine value, saponification number, and peroxide number, respectively. These values increased by 53.99, 0.0, 0.74, and 2.26% for bran produced from stored rice.
Table 5 shows the antioxidants content in Giza172 rice bran oil. The storage of rice for 1 year does not affect the antioxidants content of rice bran oil. The total tocols was 3.2 g/100 g and the γ-oryzanol was 0.42 g/100 g.
The data in Table 6 indicated the sensory evaluation of bread prepared with different blends of wheat flour and rice bran and different types of oils. It is clear from the table that bread containing 15% rice bran showed the highest score percentage ranging from 83.0% for taste to 93.8 for texture. In the mean time, the control (100% wheat flour) showed the lowest score percentage ranging from 66.4% for taste to 77.0% for smell. The analysis of variance for panel test for bread containing different percentages of rice bran (data not shown) showed significant improvement in the texture and appearance of bread with increasing concentration of rice bran. The score percentage of texture increased by 34.84% compared with control. The sensory evaluation of different types of oils showed that rice bran oil recorded the highest score percentage for taste, smell, texture, and appearance ranging from 83.0% for taste to 91.6% for appearance, whereas sunflower oil showed the lowest percentage scores ranging from 75.0 to 85.0%. However, the analysis of variance (data not shown) indicated that the differences in these percentage scores were not significant.
Rice bran is the outer brown layer including the rice germ that is removed during the milling process of brown rice grain. This milling byproduct is reported to be high in natural vitamins and minerals, particularly vitamin E, amount 1/10 of the weight of rice grain 2.
The result of the present study indicated significant differences in the percentage of bran of the newly harvested 13 rice varieties, ranging from 8.83 to 19.17%. This result could be attributed to the differences in their genetic background and their grain shape, the first two cultivars; Giza172 is bold-shaped grain, whereas Giza178 is fine-shaped grain.
The chemical and nutritional quality of rice grain varies considerably, and this may be attributed to genetic factors, environmental influences, fertilizer treatments, degree of milling, and storage conditions. As a result, rice bran obtained from different rice varieties will exhibit different chemical composition and nutritional qualities; also, milling conditions and the degree of milling affect the quality of bran 2. Studies have revealed that the process of stabilizing rice bran through microwave heating did not result in any deleterious changes to major nutrients in the bran 14.
All rice bran of the different varieties grown in Egypt showed low moisture contents compared with previous studies with higher moisture contents range from 8.4 to 14.7% 2 and from 8.5 to 12% 15. Moisture in rice bran from Ghana was also reported to be very low, ranging from 3.0 to 7.1%. It has been suggested that the low moisture content could be because of low initial moisture content of the paddy before milling 16.
The percentage of crude protein in bran for newly harvested 13 rice varieties ranged from 14.40 to 14.87% and decreased in stored rice (from 14.60 to 14.10%). Other studies reported a range from 9.8 to 15.4% 2,17. The degree of milling greatly affects the level of protein. This is probably explained by the presence of ridges of kernel endosperm in deeper milling fractions, which are heavily loaded with starch granules and some protein bodies 18,19.
The mean values of the percentage of extracted oil of newly harvested rice ranged from 11.60 to 14.83%. The fat content of stabilized rice bran fractions in Malaysia ranged from 8.7 to 18.9%. However, various brands of rice bran available in Sri Lanka contain ∼20% oil. It was suggested that fat is more concentrated in the outer surface of bran layer, as most fat is found in the aleurone layer 3.
The mean ash percentage of newly harvested rice ranged from 8.40 to 9.10%. These values were in agreement with those indicated for some Malaysian rice varieties (7 and 8.1%) and were lower than other varieties (10 and 10.8%) 16,20. However, the values were lower compared with another result reporting that the ash content ranged from 10.53 to 11.08%. The higher ash content in all types of bran contributed to its high mineral content 3. Higher ash content in rice bran has been reported, up to 13%. Ash produced in rice husks depends on the variety, climate, and geographic location 21. The ash content of bran was an important component in determining the quality of milled rice, because the degree of milling of rice grain is determined on the basis of the content of ash and crude fat, degree of whiteness, and yield of the polished rice 2.
The mean values of the percentage crude fiber of newly harvested rice ranged from 6.28 to 7.11%. These results were lower than that of Malaysian rice bran reporting 18.3–30.5% total dietary fiber. Dietary fiber of stabilized rice bran varies with the degree of milling and the amounts of starch present 3,22.
Fiber adds bulk to the gastrointestinal system, causing more frequent stools, and absorbs more bile acids making it unavailable for absorption by the body in the lower gastrointestinal tract; this bile absorption causes the body to synthesize more from the available cholesterol, thus lowering cholesterol levels in the blood 23 and the tendency toward cardiovascular problems 21.
The mean values of the percentage carbohydrates of newly harvested rice ranged from 44.77 to 46.23%. Lower results were reported earlier for Malaysian rice bran reporting 22.2–44.8% total carbohydrates, others reported 26.61–46.34% 15 and 48.0–70.2% 3.
High level of carbohydrate may be possibly influenced by the presence of starchy endosperm ridges and broken pieces resulting from the final milling operation to remove the final traces of bran layers as well as the kernel endosperm, as indicated by a lower extracted lipid content 24. It is also important to note that microwave heat-stabilized rice bran showed significantly lower carbohydrate content compared with raw samples 14. Major carbohydrates in commercial rice bran are cellulose, hemicellulose (or pentosans), and starch 2.
A sample of stabilized rice bran Giza172 was subjected to micronutrients and macronutrients in rice bran. The levels of Na, K, P, Mg, and Ca were 440, 215, 178, 80.0, and 69.0 mg/100 g, respectively, whereas the levels of Fe, Mn, Zn, and Cu were 3.61, 1.585, 1.31, and 0.184mg/100 g, respectively. Se had a level of 28.7 μ/100 g. The content of minerals in rice bran reflects the rice variety, degree of milling, and growing environment 15.
Bread containing different percentages of rice bran
Fortification of rice flour and bran is evident across a number of markets, having found application in bread and fried dough. The chemical analysis of bread containing different percentages of rice bran indicated increased percentage of fat and ash with the increase in the level of added bran. The protein and the carbohydrate decreased with the increase in the percentage of rice bran in bread. The caloric content of 100 g bread containing 5% rice bran was 260 kcals, decreased to 243 kcals for bread containing 15% rice bran. It has been reported that protein, fat, ash, and fiber of the flakes were increased with increasing proportion of rice bran powder. It has been reported that intake of more fiber resulted in increasing fecal bulk and lowering of plasma cholesterol 25.
The present study demonstrated that bread containing 15% rice bran showed the highest score percent ranging from 83.0% for taste to 93.8% for texture (Table 6). In the mean time, the control (100% wheat flour) showed the lowest score percentage ranging from 66.4% for taste to 77.0% for smell. The analysis of variance for panel test for bread containing different percentages of rice bran (data not shown) showed significant improvement in the texture and appearance of bread with increase in the concentration of rice bran.
As reported by the rice campaign report, the annual production of rice is about seven million tons, and according to the present result the mean percentage of bran for the newly harvested rice varieties grown in Egypt was 11.68%, giving 0.82 million tons of bran. The substitution of wheat by this amount of bran will save millions of dollars annually 1.
Rice bran oil
Rice bran oil has been popular in India and Japan mainly as an edible oil source; however, worldwide consumption of rice bran oil is expected to increase because of its potential as a nutraceutical/functional food 5.
The mean values of the percentage acid value for bran oil of newly harvested rice ranged from 3.43 to 3.77%. The storage of rice for 1 year before milling resulted in significant increase in the percentage of acid value for bran oil of the 13 rice varieties (Table 4). Similar result has been reported (3.75%). However, it was reported that the free fatty acid (FFA) content of rice bran may be as high as 30–40% (w/w), if the bran is not processed properly before extraction of the oil 26. This is because of the lipolysis caused by the native lipase enzymes present in the bran 27.
The edible rice bran oil in many regulations allows a maximal acid value of 0.2, equivalent to 0.1wt% FFA. The Indian regulation for the refined rice bran oil allows a maximal acid value of 0.5, which is equivalent to 0.25wt% FFA. Crude rice bran oil was reported to contain 16.5% FFAs 28. It was reported that the FFA content in untreated bran stored at 4°C for 8 weeks increased from 3.7 to 22.2%, whereas the FFA of microwave-heated bran samples (21% moisture content) stored identically as the untreated bran increased from 3.2 to 3.9%; however, another study reported an increase in FFA from 4.2 to 6.2% during a 6-week cold-storage period 9.
The mean values of the iodine number for bran oil of both newly harvested and stored rice ranged from 88.0 to 108.0. There was no change in the iodine number for bran oil of 11 rice varieties because of storage. The saponification number for bran oil of the newly harvested 13 rice varieties ranged from 180.0 to 190.0. Storage of paddy rice before milling resulted in significant increase in the saponification number for bran oil of the 13 rice varieties. The mean values of the peroxide number for bran oil of newly harvested rice ranged from 14.67 to 17.00 and increased significantly in stored rice.
Rice bran oil contains 95.6% saponifiable lipids, including glycolipid and phospholipids, and 4.2% unsaponifiable lipids, including tocopherols, tocotrienols, γ-oryzanol (-oryzanols), sterols, and carotenoids. Antioxidants contents in rice bran oil are most important components that increases its nutritive value. The result of the present study revealed that α-tocopherol and γ-tocopherol values were 600 and 500 mg/100 g, respectively. α-Tocotrienol and γ-tocotrienol estimates were 100 and 190 mg/100 g, respectively. In addition, the amount of total tocols was 3200 mg/100 g, and finally γ-oryzanol content was 4200 mg/100 g (Table 5). The results indicated that storage of paddy rice for 1 year before milling had no effect on the antioxidants contents. It has been reported that the oryzanol content in the extracted oil was 0.63% 29. Higher results were reported for oryzanol content in the extracted oil up to 1.8–3% 28. A study 30 on the fat-soluble neutraceuticals – oryzanol, tocopherols, and tocotrienols – and fatty acid composition of three varieties of Indian rice indicated that the range of oryzanol content was 500–720 ppm for brown rice, 10 700–14 300 ppm for brown rice lipids, 70–129 ppm for milled rice, and 4500–6300 ppm for milled rice lipids, which is higher than our results.
Oryzanols have certain biological and physiological abilities, such as antioxidation, antiblood cholesterol 31, and anticarcinogenic 32.
Rice bran oil showed the highest score percentage for taste, smell, texture, and appearance ranging from 83.0% for taste to 91.6% for appearance, whereas sunflower oil showed the lowest percentage scores ranging from 75.0 to 85.0%. Corn oil showed intermediate results ranging from 80% for texture to 90.0% for smell. However, the analysis of variance indicated that the differences in these percentage scores were not significant.
Conclusion and recommendations
Rice bran contains high nutritional components as well as phytochemicals such as vitamin E (i.e. tocopherols and tocotrienols) and the γ-oryzanol fraction that have positive effects on human health. Storage of paddy rice before milling resulted in significant effect on all studied rice bran characters and rice bran oil characters under the present investigation except crude protein and carbohydrates characters. Moreover, significant differences between cultivars were detected for all characters under study. Therefore, it is recommended to substitute wheat flour with rice bran by 15% in bread production to fortify the bread with vitamin E (tocopherol, tocotrienol, and oryzanol) with all its potentials and to reduce the amount of imported flour by replacing this amount (15%) with rice bran, which was used as an animal and poultry feed.
Conflicts of interest
There are no conflicts of interest.
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