Study On The Changes Of Free Sterols And Esterified Sterols In Corn Oil During Refining Processes

Phytosterols(phytostanols) and phytosteryl(phytostanyl) esters are a kind of health factor that can reduce human cardiovascular disease, and they have caused great interest in many fields, like food, medicine, chemical, etc. The material of this study was corn oil, and a detection method of esterified and free sterols in corn oil was established. The effects of crude corn oil during refining processes on the content of esterified and free sterols were studied.In addition, the refining conditions were optimized on the basis of experimental results, and the changes of the total content of two state sterols’ composition under the optimized conditions were analyzed and discussed.Esterified and free sterols were separated by silica gel column chromatography upon elution with n-hexane/ethyl acetate(90:10 v/v) followed by n-hexane/diethyl ether/ethanol(25:25:50 v/v/v). Both fractions were saponified, extracted, and derivatized and the phytosterol content was quantified by GC. The analytical method for the analysis of esterified and free sterols had a relative standard deviation of 1.32%,1.46% and joined self-made β-sitosterol linoleic acid ester as standard esterified sterol and β-sitosterol as standard free sterol with an accuracy of 90.71%,94.73%,respectively, and the analytical method had high precision and good stability,a lower limit of detection 0.1μg/mL which was satisfied for quantification the low content of sample.Thus, the method can be used for the separation and determine the content of two state phytosterols in the corn oil.Hydration degumming, alkali refining, bleaching, deodorization and solvent dewaxing refining were adopted to refine the corn oil(the total content of two state sterols was approximately 1167.31 mg/100g) in the level of laboratory, and converted the crude oil to be a second a level. At this point, the acid value was 0.24 mgKOH/g, the total content of two state sterols was 855.32mg/100 g, and the content of esterified and free sterols was 755.05mg/100 g, 100.26mg/100 g, respectively. Through the comparison of different refining stages, it was found that the loss rate of the total content of two state sterols in alkali refining(compared with degumming oil) and deodorization(compared with bleached oil) was 8.91% and 13.27% respectively. Thus, The optimization of these two stages was very important. Concerning the whole refining process, the fatty acid composition and the two state sterols component of corn oil were approximately constant. the content of esterified sterols are more great than free steols’,and in the refining, the proportion of esterified/free sterols was changed, and esterified fraction was gradually increased, the proportion of individual sterol in esterified state basically no change.Sitostanol was only in free state, sitosterol and sitostanol had a relative incease and decrease, respectively. But in each refining process can be considered a single ratio of the proportion of individual in esterified/free state was not much change.We explored the effects of different alkali refining conditions on the content of free and esterified sterols and the total content of two state sterols in the corn degumming oil. On the basis of single factor experiment, the optimal conditions of the total content of two state sterols’ absolute weight of retention in the corn degumming oil during the alkali refining were determined by orthogonal experiment. The results showed that primary and secondary factors affecting both of them were reaction temperature, followed by alkali concentration, excess alkali; the optimal conditions of the reaction conditions optimized were as follows: Initial reaction temperature 55°C, alkali concentration 10%, excess alkali 20%.Under the optimal conditions, the total content of two state sterols’ absolute weight of retention was 82.79%, the loss rate of free steols was 15.61%, the acid value of the oil loss ratio was 3.91, the acid value was 0.24mgKOH/g.The total content of two state sterols’ during alkali refining changed from 8.91% to 3.97% compared with the degumming oil.We explored the effects of different deodorization conditions on the content of free and esterified sterols and the total content of two state sterols in the corn bleached oil during deodorization with nitrogen. On the basis of single factor experiment, the optimal conditions of the total content of two state sterols in the corn bleached oil during the deodorization were determined by orthogonal experiment. The results showed that: primary and secondary factors affecting both of the percentage retention rate of the total content of two state sterols and the loss rate of free sterols were temperature, followed by time, nitrogen flow rate. The optimal conditions of the reaction conditions which can get the maximum retention of total content of two state sterols optimized were as follows: temperature 210°C, time 80 min, nitrogen flow rate 0.08m3/h. Under the optimal conditions, the percentage retention rate of the total content of two state sterols was 96.78%, the loss rate of free sterols was 13.16%, and the acid value was 0.21mgKOH/g. Compared with the bleached oil, the loss rate reduced from13.27% to optimized 3.22% during the deodorization. The refined oil of two state of total sterol content was 966.56mg/100 g, esterified sterols and free sterols was 757.18mg/100 g and 209.38mg/100 g, respectively. Vitamin E content was 769.81mg/kg, benzo(a) pyrene was 2.54 μg/kg.Three forms(illumination, airtight, refrigerator) of crude corn oil’s two state of total sterol content basically unchanged during the one year storage. Guessing that in light conditions free sterols and fatty acids could react to produce esterified sterols slightly, esterified sterols hydrolysis for free sterols in the refrigerator slightly.