The Research On Content And Variation Of Desmethylsterols In Rice Bran Oil Processing

Desmethyl-sterol, which has many functional properties, such as regulating blood lipidsand reducing serum cholesterol content, has interests many researchers enormously, and it hasbeen widely used in many fields, like food, medicine, chemical, etc. The material of this studywas rice bran oil, which has an ideally balanced fatty acid profile. A detection method of thedesmethyl-sterol in rice bran oil was established. The separation and quantification of the freeand esterified sterol were explored. The influence of the refining to the desmethyl-sterolcontent was studied. In addition, the refining conditions were optimized on the basis ofexperimental results, and the changes of the desmethyl-sterol composition under theoptimized conditions were analyzed and discussed.Comparing three widely uesd detection methods for sterol, the repeatability andscientificity of the desmethyl-sterol quantification results were included, and the resultsindicated that derivatization gas chromatography method not only had a high repeatability(RSD%was1.30%)，high recovery (97.4%) and a lower limit of detection which was satisfiedfor quantification the low content of sample, but also can determine the constitute ofdesmethyl-sterol and quantify each kind of desmethyl-sterol.Hydration degumming, alkali refining, bleaching, deodorization and dewaxing ofconventional refining method were adopted to refine the rice bran oil with high acid value(content of the desmethyl-sterol was approximately1412.83mg/100g) in the level oflaboratory, and converted the crude oil to be a second level. At this point, the content ofdesmethyl-sterol was742.71mg/100g. Concerning the whole refining process, the fatty acidcomposition and the desmethyl-sterol component of rica bran oil were approximately constant.Beta-sitosterol as the dominant sector accounted for above50%, followed by campesterol,and stigmasterol got the minimum proportion. The desmethyl-sterol loss in the refiningprocess was serious: the loss ratio was approximately17.6%after the alkali refining,24.0%after bleaching, and47.7%after deodorization. During this process, the evident decline ofcampesterol and increase of beta-sitosterol were discovered.Combining single factor experiment and orthogonal experiment, the maximum retentionof desmethyl-sterol in rice bran oil during the alkali refining were obtained and the reactionconditions optimized were as follows: reaction temperature55℃, alkali concentration26°Bé,excess alkali0.2%, the desmethyl-sterol absolute weight of retention44.02%, content ofretention86.56%, the rate of refining51.01%, acid value0.69mgKOH/g. The desmethyl-sterol loss rate during alkali refining changed from17.5%to13.3%compared withthe duguming oil.Using nitrogen as the inert stripping gas during the deodorization of rice bran oil, aftersingle factor experiment and orthogonal experiment, the reaction conditions optimized whichcan got the maximum retention of desmethyl-sterol were as follows: reaction temperature280℃, reaction time120min, nitrogen flow rate0.12m3/h. At this point, the desmethyl-sterolcontent of retention (compared with bleached oil)83.38%, the rate of refining93.01%, acidvalue0.25mgKOH/g. Compared with the previous refining, the desmethyl-sterol content ofoptimized refining had been enhanced. Compared with the bleached oil, the loss rate reducedfrom31.2%to optimized16.6%during the deodorization.Esterified and free sterols in rice bran oil of each refining stage were separated by silicagel column chromatography, and both fractions were quantitative analysis by GC. During therefining, a significant reduction in the content of free sterols and a clear increase in thecontent of esterified sterols were observed. The type of the desmethyl sterols in the esterifiedand the free sterols was same, but the ratio of three desmethyl sterols was different which wasnearly no change in both fractions during the refining.