Deacidification of high-acid rice bran oil by reesterification with monoglyceride

Autocatalytic esterification of free fatty acids (FFA) in rice bran oil (RBO) containing high FFA (9.5 to 35.0% w/w) was examined at a high temperature (210°C) and under low pressure (10 mm Hg). The study was conducted to determine the effectiveness of monoglyceride in esterifying the FFA of RBO. The study showed that monoglycerides can reduce the FFA level of degummed, dewaxed, and bleached RBO to an acceptable level (0.5±0.10 to 3.5±0.19% w/w) depending on the FFA content of the crude oil. This allows RBO to be alkali refined, bleached, and deodorized or simply deodorized after monoglyceride treatment to obtain a good quality oil. The color of the refined oil is dependent upon the color of the crude oil used.     

Evaluation of the stability of blends of sunflower and rice bran oil

Blends of sunflower oil (SFO) and rice bran oil (RBO) were evaluated for their stability. Additionally, known amounts of natural antioxidants extracted from RBO were added to SFO, and their protective effect was compared to that of the blends. The results found indicate that by raising the amount of RBO, from 10 to 50%, an increase of OLO, OLP, PPL, OOO, PPO, OPO, 18:1 and 16:0 occurred, followed by a decrease of LLL, LLO, and 18:2. These changes in fatty acid and triacylglycerol (TAG) composition led to an increase of the oil stability index at 120 °C and a reduction of polymer TAG formation in the heated blends at 180 °C during 8 h. A comparable protective effect of natural antioxidants to that of blending was observed in a 50 : 50 blend, by remarkably increasing the induction period.     

Deacidifying rice bran oil by solvent extraction and membrane technology

Crude rice bran oil containing 16.5% free fatty acids (FFA) was deacidified by extracting with methanol. At the optimal ratio of 1.8:1 methanol/oil by weight, the concentration of FFA in the crude rice bran oil was reduced to 3.7%. A second extraction at 1:1 ratio reduced FFA in the oil to 0.33%. The FFA in the methanol extract was recovered by nanofiltration using commercial membranes. The DS-5 membrane from Osmonics/Desal and the BW-30 membrane from Dow/Film Tec gave average FFA rejection of 93–96% and an average flux of 41 L/m²·h (LMH) to concentrate the FFA from 4.69% to 20%. The permeate, containing 0.4–0.7% FFA, can be nanofiltered again to recover more FFA with flux of 67–75 LMH. Design estimates indicate a two-stage membrane system can recover 97.8% of the FFA and can result in a final retentate stream with 20% FFA or more and a permeate stream with negligible FFA (0.13%) that can be recycled for FFA extraction. The capital cost of the membrane plant would be about $48/kg oil processed/h and annual operating cost would be about $15/ton FFA recovered. The process has several advantages in that it does not require alkali for neutralization, no soapstock nor wastewater is produced, and effluent discharges are minimized.     

Rice bran FFA determination by diffuse reflectance IR spectroscopy

Rice bran with FFA levels above 0.1% cannot be used as a food ingredient due to oxidative off-flavor formation. However, extracting high FFA oil from bran by in situ methanolic esterification of rice bran oil to produce methyl ester biodiesel produces greater yields relative to low-FFA rice bran oil. Therefore, high-FFA bran could be exploited for biodiesel production. This study describes an FTIR spectroscopic method to measure rice bran FFA rapidly. Commercial rice bran was incubated at 37°C and 70% humidity for a 13-d incubation period. Diffuse reflectance IR Fourier transform spectra of the bran were obtained and the percentage of FFA was determined by extraction and acid/base titration throughout this period. Partial least squares (PLS) regression and a calibration/validation analysis were done using the IR spectral regions 4000-400 cm⁻¹ and 1731-1631 cm⁻¹. The diffuse reflectance IR Fourier transform spectra indicated an increasing FFA carbonyl response at the expense of the ester peak during incubation, and the regression coefficients obtained by PLS analysis also demonstrated that these functional groups and the carboxyl ion were important in predicting FFA levels. FFA rice bran changes also could be observed qualitatively by visual examination of the spectra. Calibration models obtained using the spectral regions 4000-400 cm⁻¹ and 1731-1631 cm⁻¹ produced correlation coefficients R and root mean square error (RMSE) of cross-validation of R=0.99, RMSE=1.78, and R=0.92, RMSE=4.67, respectively. Validation model statistics using the 4000-400 cm⁻¹ and 1731-1631 cm⁻¹ ranges were R=0.96, RMSE=3.64, and R=0.88, RMSE=5.80, respectively.     

pH处理对米糠蛋白理化特性及结构的影响

目的分析pH处理对米糠蛋白理化特性及结构的影响。方法制备米糠蛋白,经不同pH值的缓冲液处理后,分别采用福林酚法、ANS荧光探针法、DNTB法、荧光光谱法、SDS-PAGE法检测米糠蛋白的溶解性、表面疏水性、游离巯基含量、蛋白质三级结构和亚基组成。结果 pH为4、6时,米糠蛋白的溶解性最低;而pH4和pH6时,米糠蛋白的溶解性均有不同程度的升高,且在碱性条件下,米糠蛋白的溶解性比在酸性环境中更好。米糠蛋白的溶解性与表面疏水性、游离巯基含量呈正相关。pH处理对米糠蛋白的荧光光谱有一定影响,使其微环境发生了变化。在酸性环境中,米糠蛋白的亚基组成有明显变化,高相对分子质量的亚基解聚为低相对分子质量的亚基;而中性及碱性环境对米糠蛋白的亚基组成无影响。结论本实验分析了pH处理对米糠蛋白溶解性、表面疏水性、游离巯基、荧光光谱和亚基组成的影响,为米糠蛋白在食品工业中的应用提供了参考。     

Refining of rice bran oil by neutralization with calcium hydroxide

The applicability of calcium hydroxide (lime) in the neutralization of rice bran oil (RBO) was investigated. Crude RBO samples of three different free fatty acids (FFAs) (3.5–8.4 wt%) were degummed, dewaxed, bleached, and neutralized with lime and deodorized. The oils obtained thus were characterized by determining the color, peroxide value (PV), content of unsaponifiable matter (UM), and FFA. Conventionally practiced caustic soda neutralization (at 80–90°C) of FFA has in the present investigation been replaced by a high temperature (150–210°C) low pressure (2–4 mm Hg) reaction with lime. It was observed that neutralization with Ca(OH)₂ at high temperature (210°C) and under low pressure (2–4 mm Hg pressure) may substantially reduce the FFA content (0.8 wt%, after 2 h). The deodorized oil was found to be of acceptable color, PV, and content of UM and FFA. Neutralization of oil was also carried out by using NaHCO₃ and Na₂CO₃, nonconventional alkalies for neutralization, and the results were compared with NaOH and Ca(OH)₂. Overall recovery of oil in Ca(OH)₂ refining process (88.5 ± 0.6 wt%, for Sample 1 containing 8.4%‐wt FFA) was found to be more than other competitive processes studied.     

Supercritical CO2 extraction of rice bran

Extraction of rice bran lipids with supercritical carbon dioxide (SC-CO₂) was performed. To investigate the pressure effect on extraction yield, two isobaric conditions, 7000 and 9000 psi, were selected. A Soxhlet extraction with hexane (modified AOCS method Aa 4–38; 4 h at 69°C) was also conducted and used as the comparison basis. Rice bran with a moisture content of 6%, 90% passable through a sieve with 0.297 mm opening, was used for extraction. A maximum rice bran oil (RBO) yield of 20.5%, which represents 99+% lipid recovery, was obtained with hexane. RBO yield with SC-CO₂ ranged between 19.2 and 20.4%. RBO yield increased with temperature at isobaric conditions. At the 80°C isotherm, an increase in RBO yield was obtained with an increase in pressure. The pressure effect may be attributed to the increase in SC-CO₂ density, which is closely related to the value of the Hildebrand solubility parameter. RBO extracted with SC-CO₂ had a far superior color quality when compared with hexane-extracted RBO. The level of sterols in SC-CO₂-extracted RBO increased with pressure and temperature.     

Trans fatty acid content and positional distribution in refined and heated rice bran oil

The objective of this study was to evaluate the impact of the refining process and of heating at frying temperature (180 °C, 8 h) on the content of trans fatty acids and their positional distribution in sn-positions of triacylglycerols (TAG) of rice bran oil. Tr-18:2 was an artifact specific to the deodorization step, which additionally changed its distribution at the 2-MAG and 1,3-DAG positions. No correlation between the formation of polymer TAG and trans fatty acids could be observed.     

Structured lipids from rice bran oil and stearic acid using immobilized lipase from Rhizomucor miehei

The major objective of the present study was to prepare structured lipids rich in stearic acid from rice bran oil (RBO) using immobilized lipase (IM 60) from Rhizomucor miehei. The effects of incubation time and temperature, substrate molar ratio, and enzyme load on incorporation of stearic acid were studied. Acidolysis reactions were performed in hexane. Pancreatic lipase‐catalyzed sn‐2 positional analysis and tocopherol analyses were performed before and after enzymatic modification. The kinetics of the reaction was studied and maximum incorporation of stearic acid was observed at 6 h, at 37 °C, when the triacylglycerol and stearic acid molar ratio was maintained at 1 : 6 and the enzyme concentration was 10% of total substrates weight. Stearic acid in RBO after acidolysis was increased from 2.28 to 48.5%, with a simultaneous decrease in palmitic, oleic and linoleic acids. HPLC analysis of tocopherols and tocotrienols was carried out and their content in modified RBO was not significantly affected compared to that of native RBO. The oryzanol content of the modified RBO was reduced from 1.02 to 0.68%. Melting and crystallizing characteristics of the modified fat were studied using differential scanning calorimetry. The total solid fat content at 25 °C increased from 26.12 to 34.8% with an increase in stearic acid incorporation into RBO from 38 to 48%, but it was comparatively less than for cocoa butter and vanaspati. However, the modified RBO completely melted at 37 °C and was useful as plastic fat for various culinary purposes, bakery and confectionary applications. The results of the present study indicated that structured lipids prepared from RBO rich in stearic acid retained their beneficial nutraceuticals; in addition, they do not contain any trans fatty acids.     

Effect of stirring on the thermooxidative stability of refined rice bran oil

The aim of this study was to find out how the refining process affects the susceptibility of rice bran oil to oxygen of air at high temperature. Samples of crude and refined rice bran oil were heated at 180 °C for 8 h with and without stirring in laboratory‐scale experiments. After every 30 min, samples were taken for analysis. The influence of stirring on rice bran oil heat stability was related to the loss of tocopherols and sterols, and to the thermooxidative state of the samples, which was evaluated according to polymer formation and changes occurring in fatty acid composition and triacylglycerol (TAG) structure. The results demonstrated a significant loss of natural antioxidants during the heating process with stirring, accompanied by a decrease in the levels of linoleic acid (18:2) and TAG (LLO, LLP and OLO) which resulted in a substantial increase of polymer TAG. The unsaturated fatty acids in the sn‐2 and sn‐1,3 positions were differently affected during the heating process.     

In situ esterification of rice bran oil with methanol and ethanol

In situ esterifications of high-acidity rice bran oil with methanol and ethanol and with sulfuric acid as catalyst were investigated. In the esterification with methanol, all free fatty acids (FFA) dissolved in methanol were interesterified within 15 min, and it was possible to obtain nearly pure methyl esters. The amount of methyl esters obtained from a given rice bran was dependent on the FFA content of the rice bran oil. In the esterification with ethanol, it was not possible to obtain pure esters as in methanol esterification, because the solubilities of oil components in ethanol were much higher than those in methanol.     

Lipase‐catalyzed production of biodiesel from rice bran oil

Biodiesel has attracted considerable attention as an alternative fuel during the past decades. The main hurdle to the commercialization of biodiesel is the cost of the raw material. Use of an inexpensive raw material such as rice bran oil is an attractive option to lower the cost of biodiesel. Two commercially available immobilized lipases, Novozym 435 and IM 60, were employed as catalyst for the reaction of rice bran oil and methanol. Novozym 435 was found to be more effective in catalyzing the methanolysis of rice bran oil. Methanolysis of refined rice bran oil and fatty acids (derived from rice bran oil) catalyzed by Novozym 435 (5% based on oil weight) can reach a conversion of over 98% in 6 h and 1 h, respectively. Methanolysis of rice bran oil with a free fatty acid content higher than 18% resulted in lower conversions (<68%). A two‐step lipase‐catalyzed methanolysis of rice bran oil was developed for the efficient conversion of both free fatty acid and acylglycerides into fatty acid methyl ester. More than 98% conversion can be obtained in 4–6 h depending on the relative proportion of free fatty acid and acylglycerides in the rice bran oil. Inactivation of lipase by phospholipids and other minor components was observed during the methanolysis of crude rice bran oil. Simultaneous dewaxing/degumming proved to be efficient in removing phospholipids and other minor components that inhibit lipase activity from crude rice bran oil. Copyright © 2005 Society of Chemical Industry     

Effect of method of stabilization on aqueous extraction of rice bran oil

Rice bran oil is widely used in pharmaceutical, food and chemical industries due to its unique properties and high medicinal value. In this study aqueous extraction of rice bran oil from rice bran available in Sri Lanka, was studied. Key factors controlling the extraction and optimal operating conditions were identified. Several methods of bran stabilization were tested and the results were analyzed. The yield and quality of aqueous extracted oil was compared with hexane extracted oil.Aqueous extraction experiments were conducted in laboratory scale mixer–settler unit. Steaming, hot air drying, chemical stabilization and refrigeration better controls the lipase activity compared to solar drying. Steaming is the most effective stabilization technique. The extraction capacity was highest at solution pH range 10–12. Higher oil yield was observed at higher operating temperatures (60–80 °C). Kinetic studies revealed that extraction was fast with 95% or more of the extraction occurring within first 10–15 min of contact time. Parboiling of paddy increases the oil yield. Highest oil yield of 161 and 131 mg/g were observed for aqueous extraction of parboiled bran and raw rice bran respectively. The aqueous extracted oil was low in free fatty acid content and color compared to hexane extracted rice bran oil and other commonly used oils. Major lipid species in rice bran oil were oleic, linoleic and palmitic.     

Study on the composition of rice bran oil and its higher free fatty acids value

The compositions of rice bran oils (RBO) and three commercial vegetable oils were investigated. For refined groundnut oil, refined sunflower oil, and refined safflower oil, color values were 1.5–2.0 Lovibond units, unsaponifiable matter contents were 0.15–1.40%, tocopherol contents were 30–60 mg%, and FFA levels were 0.05–0.10%, whereas refined RBO samples showed higher values of 7.6–15.5 Lovibond units for color, 2.5–3.2% for unsaponifiable matter, 48–70 mg% for tocopherols content, and 0.14–0.55% for FFA levels. Of the four oils, only RBO contained oryzanol, ranging from 0.14 to 1.39%. Highoryzanol RBO also showed higher FFA values compared with the other vegetable oils studied. The analyses of FA and glyceride compositions showed higher palmitic, oleic, and linoleic acid contents than reported values in some cases and higher partial glycerides content in RBO than the commonly used vegetable oils. Consequently, the TG level was 79.9–92% in RBO whereas it was >95% in the other oils studied. Thus, refined RBO showed higher FFA values, variable oryzanol contents, and higher partial acylglycerol contents than commercial vegetable oils having lower FFA values and higher TG levels. The higher oryzanol levels in RBO may contribute to the higher FFA values in this oil.     

微波辐射法提取米糠中的肌醇研究

以盐酸、尿素为提取剂,脱脂米糠为原料,采用微波浸提、离子交换和微波水解从米糠中提取肌醇,并探讨其工艺条件。结果表明(1)微波浸提植酸较佳的工艺条件:功率为80 W,浸提时间5min,浸提温度55℃,中和方式二步法,离子交换流量(10~15)mL/min;(2)微波水解植酸制备肌醇的较佳工艺条件:V(甘油)∶V(水)=1∶1,植酸浓度0.5 mol/L,盐酸浓度0.05 mol/L,微波功率为120 W,辐射时间80 min。微波法从米糠中提取肌醇能显著缩短提取时间、降低成本,提高肌醇得率,并且具有操作简单,快速方便,环保友好等特点。     

Biological activities of the rice bran extract and physical characteristics of its entrapment in niosomes by supercritical carbon dioxide fluid

The objectives of this study were to compare the biological activities of the rice bran (Oryza sativa Linn.) extracts prepared by supercritical carbon dioxide fluid (scCO₂) and ethanolic maceration, and the physical properties of niosomes entrapped with the extracts prepared by scCO₂ and chloroform film method. The scCO₂ extract showed higher unsaturated fatty acid and phenolic contents than the maceration extract. All extracts showed no significant difference of biological activities. The characteristics of niosomes entrapped and not entrapped with the extract prepared by scCO₂ and chloroform film method were not different with a unilamellar nano-sized structure and the phase transition temperatures at 80 °C. The gradual decrease trend of the vesicular membrane microviscosity with less membrane rigidity at higher extract concentrations was observed. The scCO₂ technique is advantageous for the preparation of the rice bran extracts and niosomes because of no requirement of organic solvents and having less step.     

Continual conversion of free fatty acid in rice bran oil to triacylglycerol by immobilized lipase

Rice bran oil containing 30–50% free fatty acid was continually converted to an oil containing more than 75% of triacylglycerol (TG) by means of immobilized lipase. The reaction was carried out at 60°C for 24 h with dehydration and reactant mixing by dry nitrogen flow under a positive nitrogen atmosphere. Enzymatic TG synthesis with evaporation by heating was not suitable because of the increasing peroxide value of the oil. Part of this article was presented at the annual meeting of the Japan Oil Chemists' Society at Sendai, Japan, October, 16, 1990.     

The concentration of tocols from rice bran oil deodorizer distillate using solvent

Tocols (tocopherols + tocotrienols) have been concentrated efficiently from rice bran oil (RBO) deodorizer distillate using solvent at low temperature. The levels of total tocols, total tocopherols, and total tocotrienols in RBO deodorizer distillate (starting material) were 31.5, 14.9, and 16.6 mg/g, respectively. Nine different solvents were tested, and acetonitrile was selected as the optimal solvent for concentrating tocols from the RBO deodorizer distillate. There was a significant (p <0.05) increase in the tocol level of the liquid fractions with decreasing temperature, for incubation temperatures up to –20 °C. In addition, significant differences (p <0.05) were observed in the relative percentages of α‐tocopherol, γ‐tocopherol, α‐tocotrienol, and γ‐tocotrienol between the raw sample and liquid fractions obtained at different temperatures using acetonitrile as the solvent. The concentration of the tocols from the RBO deodorizer distillate was temperature dependent, and a maximum of 89.9 mg/g was attained in the liquid fraction at – 40 °C. The relative percentage of tocotrienol homologs in the liquid fraction obtained at – 40 °C was approximately 80%. With acetonitrile as the solvent, the optimal temperature for concentrating the tocols from RBO deodorizer distillate was –20 °C when yield was considered.