| Rice bran oil is a kind of healthy and nutritious vegetable oil.The composition of fatty acid is reasonable and rich,rich in a variety of bioactive substances.However,the crude rice bran oil is rich in impurities,dark in color and difficult to refine.The quality of rice bran oil by traditional refining method is poor,and It needs to be refined repeatedly to reach the edible oil standard.Therefore,improving the refining process of rice bran oil for improving the quality of rice bran oil,enriching the domestic edible oil market and easing the import pressure of edible oil.Ultrasound is a new food processing technology.At present,the application of ultrasonic technology in various fields of oil processing has been rapidly developed,and has been widely used in the extraction of oil,but the research in the oil refining process is still in the preliminary stage.Therefore,in this paper,ultrasonic wave and oil refining technology were combined to study.The specific research content and results are as follows:(1)Ultrasound combined with acid degumming technology.The effects of various factors,such as the type of acid,the amount of acid added,the ultrasonic time,the ultrasonic power,water addition and the degumming temperature,on the degumming rate and the retention rate of oryzanol of rice bran oil were studied.The degumming process condition was optimized by using orthogonal experiment with degumming rate as index.The physical and chemical indexes and fatty acid composition of rice bran oil(crude oil,traditional degumming oil and ultrasound-assisted degumming oil)were determined and analyzed.The results showed that each factor had a significant effect on the degumming rate(P<0.05),but the effect on oryzanol was relatively small,and the retention rate of oryzanol in rice bran oil after degumming was more than 90%.Optimum process conditions of ultrasonic-assisted acid degumming method of rice bran oil is: the ultrasonic power is 300 W,the ultrasonic time of 2 min,degumming temperature of 60?,the amount of water is 3%,citric acid content of 0.20%,under the condition of the rice bran oil degumming rate of 93.91%.Compared with traditional degumming rice bran oil,ultrasonic-assisted degumming has better effect,faster speed,less loss of nutrients in rice bran oil and no significant change in fatty acid composition.Indicating that ultrasonic assisted degumming is an effective method for removing phospholipids.(2)Ultrasonic technology was applied in the process of ethanol extraction and deacidification.The effects of deacidification conditions(ethanol concentration,deacidification temperature,ultrasonic time,ultrasonic power,oil-solubility ratio and extraction times)on the deacidification rate,vitamin E and retention rate of oryzanol of rice bran oil were studied.The results showed that ethanol concentration,ultrasonic power,ultrasonic time,deacidification temperature,oil-solubility ratio and extraction times had significant effects on the deacidification rate of rice bran oil and the retention rate of oryzanol and vitamin E(P<0.05).The rate of deacidification rate,the retention of oryzanol and vitamin E as indicators,through the orthogonal experiment to optimize process conditions.And the best solution as follows: 95% ethanol concentration,ultrasonic time is 3 min,ultrasonic power is 300 W,oil-soluble ratio of 1:3,extracting 2 times,deacidification temperature 30 ?.Under these conditions,the acid removal rate of rice bran oil was 94.6%,the retention rate of oryzanol was 75.79% and the retention rate of vitamin E was 53.10%.Compared with traditional alkali refining,the indexes of acid value,peroxide value and fatty acid composition of rice bran oil obtained by ultrasound-assisted ethanol extraction and deacidification had little change,and the high retention rate of bioactive substances.Besides,this method has the advantages of short deacidification time,low temperature,safe operation and no pollution.(3)Ultrasonic technology was applied to the decolorization process of rice bran oil,and the effects of decolorization conditions(type of adsorbent,amount of active clay,ultrasonic time,ultrasonic power and decolorization temperature)on the decolorization effect of ultrasound-assisted rice bran oil were studied.Meanwhile,the adsorption mechanism(adsorption kinetics,adsorption thermodynamics and adsorption isotherms)of carotenoids and chlorophyll in rice bran oil by activated clay assisted by ultrasonic wave was studied.It was found that each factor had a significant effect on the decolorization rate(P<0.05),and the effect on the retention rate of oryzanol was relatively small.In the process of ultrasound-assisted adsorption of activated clay clay on carotenoids and chlorophyll,the pseudo-first-order kinetic model and Freundlich adsorption isotherm equation were more consistent,indicating that the ultrasound-assisted adsorption decolorization process was complex but beneficial to decolorization.Thermodynamic analysis shows that the decolorization process is spontaneous,endothermic and mainly affected by chemical adsorption.(4)The effects of ultrasound-assisted adsorption decolorizationand traditional adsorption decolorization on the color of rice bran oil were studied.The pigment in rice bran oil was separated by column chromatography with silica gel as stationary phase and solvent of different polarity as eluent.At the same time,ultraviolet visible spectrum(UV-vis),Fourier infrared spectrum scanning and thermogravimetry were used to analyze the pigment.The results showed that both decolorization methods could lighten the color of rice bran oil to a certain extent.After traditional decolorization,the color of rice bran oil tended to be red,while after ultrasound-assisted decolorization,the color of rice bran oil tended to be yellow.Three pigment bands were collected from rice bran oil before and after ultrasonic assisted decolorization by column chromatography.The three pigment bands in the same oil sample all have long carbon chain structure and all contain carbonyl group.However,the difference in the structure between pigment band 2 and 3 and pigment band 1 results in the difference in polarity.Compared with before decolorization,Some functional groups of pigment in rice bran oil changed after ultrasonic assisted decolorization,and the temperature of the fastest decomposition rate of pigment increased. |
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