Study Of Cottonseed Oil Color Fixation And Preparation Of High Quality Cottonseed Oil

Annual cottonseed production is roughly13million tons in China, which provides richresources for cottonseed oil production. Due to current color fixation and processingtechnology cottonseed oil production faces the problems of low refining yield and poorquality. An explanation of color fixation and the technology of high-moisture cooking,miscella refining were investigated in this paper.Color fixation was conducted in refined-bleached-deodorized cottonseed oil. Freegossypol easily converted to fixed gossypol at high temperature causing a dark coloration ofcottonseed oil. Through full-band scanning and infrared spectrophotometer analysis, it wasfound that free gossypol underwent dehydration-condensation between an aldehyde and ahydroxyl group to form fixed gossypol. Fixed gossypol had deeper color than free gossypoland became neutral because of losing the active aldehyde. So it couldn’t be removed byconventional refining and bleaching procedures. Free gossypol may also react withphospholipids to form gossypol–phospholipid at high temperatures causing a darker color incottonseed oil than fixed gossypol.A solvent evaporating procedure of miscella crude oil was studied. It was drawn thatcolor fixation increased with longer evaporating time and higher temperature. Whenevaporating at90oC for50min, the red color of the crude oil reached11.3. The difference incrude oil quality between extraction by single and mixture solvent showed that free gossypoland phospholipids were the main factors for color fixation. By refining the color-fixed oil itwas found that over-high concentration and extra alkali made little effect on removing thecolor fixation, even if it would make more neutral oil loss.The results of high-moisture cooking of cottonseed showed that the free gossypol andphospholipid content of crude oil extracted from20%moisture cooked cottonseed were0.075%and0.87%, reducing by49.3%and46.6%compared to original moisture. The optimumconditions of high-moisture cooking were as follows:20%moisture, temperature95oC,reaction time65min, the free gossypol and phospholipids content of crude oil were0.073%and0.84%.When degumming the miscella crude oil, the results indicated that the degumming ratiomay reach above80%under the condition phosphoric acid amount of0.25-0.30%,temperature of55-65oC and reaction time of20-30min. The influences of oil content, alkaliconcentration, extra alkali amount, reaction temperature and reaction time on refining loss andthe color of refined oil were investigated. The results showed that miscella refining couldreduce the red color of the refined oil to below8. The condition optimization of the processwas conducted by using the response surface methodology. The optimal conditions for lowestrefining loss were determined to be an oil content60.5%, an alkali concentration17.1°Bé, anextra alkali amount0.34%at a reaction temperature55oC and reaction time40min. Underthese conditions, actually measured refining loss was2.41, in good agreement with thepredicted value.The bleaching procedure of miscella and conventional refined oil was studied. Theresults showed that the red color of miscella refined oil was reduced to3.3after bleachingwhen adsorbent amount was2.0%, reaching the highest level of national standard for cottonseed oil. When adsorbent amount was over2.0%, the red color of both oils were notsignificantly decreased and the conventional refined oil’s was always higher by about1.4-2.0,which indicated that there was more color fixation occurred during conventional refining.