Study On The Causative Factors And Removal Effect Of The Color Of Rice Bran Oil

The annual production of rice bran in China was nearly 1400 million tons, and more than 200 million tons rice bran oils could be produced if all the rice bran were used. What’s more, because of balanced fatty acid composition, rich in oryzanol and vitamin E, rice bran oil was known as a kind of nourishing edible oil. Under the pressure of increasing of import amount of edible oil year by year in our country, researching and developing rice bran oil production technology had an important significance for improving self-sufficiency rate of domestic edible oil, enriching the edible oil market and using of rice resource efficiently.At present, the utilization of rice bran oil was only about 20% due to large refining loss, high production cost which caused by easily rancidity of rice bran, high acid value of crude rice bran oil, deep color and difficult to removal of crude rice bran oil. In recent years, the stabilization of rice bran and oil refining technology had a great development because of the researchers and rice bran oil production companies’ continuous research on rice bran oil production technology. However, the problem of crude rice bran oil’s ultra-deep color and difficult to decolorization were still unsolved. In this thesis the forming reason of crude rice bran oil’s ultra-deep color, components of the pigment, and their influence on the bleaching of crude rice bran oil were analyzed and studied, aimed at seeking for an index which could characterized the color of crude rice bran oil, eliminating these negative factors at the source, and looking for targeted process technology to remove the pigment efficiently, according to the type of figments.Rice bran would become rancidity during storage and caused increasing of crude oil. However, whether the rancidity of rice bran would cause the deepen of color and pigment fixed, How about the influence degree of the rancidity on color deepened, whether the heating and molding would cause the deepen of color and pigment fixed and caused adversely effect on the decolorization of crude rice bran, all the above problems need to solve in this thesis. In this paper, rice bran were stored at two different conditions: a good storage condition of ventilated environment with room temperature(18℃±2℃)and undesirable storage condition of high temperature and high humidity(50 ℃, 70% relative humidity). The contents of crude fat and crude protein of rice bran in different storage time, and acid value, peroxide value, color of the corresponding crude rice bran oil were detected, to analysis and study the impact of storage condition on the quality of rice bran and the corresponding crude oil. Undeserved storage caused heating and molding of rice bran, it’s influence on the forming of crude rice bran’s color, pigment type, difficult degree of decoloration were studied by comparing the effect of adsorption bleaching(decolourization ratio)of crude oils extracted from rice bran stored at two different storage conditions. The result showed that, both storage conditions caused rise of acid value of crude rice bran oil. The influence of good storage condition on the crude oil’s color and adsorption effect was not significant. While to the rice bran stored at undesirable condition, the extracted crude oil was dark brown and with unpleasant moldy smell and acid value increased to121.24 mgKOH/g because of the heating and molding of rice bran. The crude oil’s color was difficult to remove even bleached with 13% active clay, and the Lovibond R value was 6.7 after the adsorption bleaching, also the decolourization ratio was only 71.4%, far lower than the lowest national standard requirement on the color of rice bran oil. Therefore, the main reason of crude rice bran oil’s extra-deep color, pigment fixed and difficult to removing was the heating and molding and severe rancidity of rice bran during its storage.The influence of extrusion on the stabilization of rice bran and controlling acid value of crude oil was significant, however, new pigments may form and fixed during extrusion of rice bran. In this issue, crude oils were extracted from extruded rice bran and un-extruded rice bran by solvent extraction, and the quality and decolorization effect of two kind crude oils were compared. The result showed that, compared the crude oil extracted from extruded rice bran with that of un-extruded rice bran, the former’s acid value and content of Vitamin E decreased obviously, while the oryzanol content increased and color deepened significantly. The adsorption bleaching test showed that, with the dosage of 2%, 4%, 6% clay, the decolourization ratio of un-extruded rice bran oil were all higher than that of extruded rice bran oil by an average of 9.47%. Accordingly, the color of crude rice bran oil deepened and new pigment that difficult to remove formed during extrusion processing. Stored the extruded rice bran on the condition of high temperature and high humidity(50℃, relative humidity of 75%) for 60 days, the acid value(mgKOH/g)of crude oil extracted from the rice bran raised from 7.5 to 32.64, the color deepened and the content of Vitamin E decreased obviously. And the adsorption bleaching test showed that, with same dosage of clay, the decolourization ratio of the crude oil reduced by 28%~34% than that of fresh extruded rice bran. Therefore, even the stability of rice bran was improved during the extrusion, it was not suitable to storage for a long time under the undesirable condition. Otherwise it would result in the crude rice bran oil’s acid value increasing and color deepening, and cause it difficult to remove the pigments from the crude oil.The crude rice bran oil was obtained through the process of desolventizing of the miscella, which extracted from the extruded rice bran. In this thesis, rice bran miscella was desloventized by atmospheric evaporation, vacuum evaporation, and molecular distillation to study the influence of desolventizing condition especially evaporation temperature on the decolorization effect and pigment forming of the crude rice bran oil. The result showed that, the color of crude oil varied obviously in different evaporation methods, for example, the Lovibond R value of the crude rice bran oil which obtained by atmospheric evaporation was 14.3, that of vacuum evaporation was 9.0, and that of molecular distillation was only 6.4. The adsorption bleaching experiment showed that, the decolorization ratio of crude oil obtained by atmospheric evaporation was the lowest, and the dosage of active clay increased from 4% to 12%, the decolorization ratio increased from 26.61% to 46.42%, while the decolorization ratio of the crude oil obtained by vacuum evaporation and molecular distillation were similarity, which increased from 31.54%, 32.93% to 65.71% and 66.85%, respectively. Therefore the desolventizing methods have a larger effect on the quality of crude oil and it will obviously cause the color deepened and decreased the decolorization effect by forming the fixed pigment during the desolventizing of the mixed oil.In this thesis, the UV-Vis spectroscopy of crude rice bran oils obtained from above chapters were analyzed to find indicators that could characterize the color deepness of crude rice bran oil and its decolorization ability. The result showed that the characterized adsorption peak was 670 nm when the color of rice bran oil deepened. Therefore, A670 nm could be used as the baisic indicators to characterize the color of crude rice bran oil and its index of decolorization ability. The correlation of color, A670 nm and decolourization ratio of crude oils extracted from rice bran with different mildew degree was studied. The result showed that, the color of crude oil was positive correlated with A670 nm, while the decolourization ratio was negative correlated with A670 nm. With the given absorbed condition, the color of crude rice bran oil that A670 nm <0.333 could reach the national standard requirement of finished product of rice bran oil, and the decolourization ratioes were over 50%. However, when the A670nm>0.333,the color of crude rice bran oils was difficult to remove and cannot reach the national standard requirement, and the decolourization ratioes were lower than 50%.In view of the above research, in order to understand the changes of process of color deepened. The pigments of crude oil extracted from not mildew and mildew rice bran were separated by chromatography column(CC) and thin layer chromatography(TLC) separation, and the obtained pigments were analyzed by UV-Vis and FTIR Spectrometer, in order to make a future research on the pigment of the crude rice bran oil. The result showed that, according to the polarity of the difference pigment, there were 3 kinds of pigments isolated from the crude oil extracted from not mildew rice bran, while there were 7 kinds of pigments isolated from the crude oil extracted from mildew rice bran, and two special chromatographic band, which present as dark green and green, after collection and enriched. With FTIR Spectrometer analysis, It could be speculated that, there were new functional groups formed, such as P=O bond, anhydride, P-O-Caromatics and R-S=O, and amount of functional groups such as benzene and carbonyl increased in the crude oil extracted from mildew rice bran. This was caused by the oxidative denaturation of components such as oryzanol, Vitamin E, phospholipid in oil, which contain benzene, double bond, carbonyl and other functional groups. There were also researches about the influence of material such as oryzanol, Vitamin E, phospholipid on the color of crude rice bran oil, the results of researches and the above speculation were supporting each other to some extent. The UV-Vis analysis on the pigments showed that, the two kinds of pigments isolated from crude oil extracted from mildew rice bran were similar to the crude oil. The mechanism of fineness and the peak position analyzing showed that, the color of the two pigments’ absorption peaks corresponded were yellow-green and blue-green, which were consistent with the appearance sensory color of isolated pigments. The result showed that, there were new pigments formed during the mildew of rice bran.In conclusion, the color would deepen and pigments fixed in crude rice bran oil because of the heating and molding of rice bran during the storage, extrusion process and high temperature of desolventizing. Heating and molding of rice bran was the source reason that caused extra-deep color of the crude rice bran oil, and was the key factor that influenced the bleaching effect and refining effect of rice bran oil. So, the adsorption intensity in 670 nm could be used as the indicator to evaluate the crude rice bran oil’s color deepness and decolorization ability, in order to find targeted methods to remove the pigments effectively. In addition, the pigments of crude rice bran oil were separated and analyzed, in order to make a future research on the pigment of the crude rice bran oil.