| Diacylglycerol (DG) is a kind of structured lipid that hydroxyl replace acyl in the sn-1, 2, 3 position of triacylglycerol (TG). DG is a natural minor component of various edible oils and the endogenetic intermediate metabolite of lipid. Moreover, it is generally recognized as safe (GRAS) by FDA. Many researches have shown that dietary DG can reduce visceral fats and blood lipid and suppress the increase of body weight. The preparation, purification, oxidation stability and function of DG were studied in the present study.Firstly, we studied the preparation of DG by enzymatic glycerolysis of rapeseed oil in the solvent-free system. The optimum reaction conditions were got by single-factor experiment and they are as follows: ratio of rapeseed oil to glycerol is 2∶1, water content of glycerol is 1%, dosage of Lipozyme TL IM is 20IUN/g substrate, reaction temperature is 65℃ , reaction time is 10h. The DG and 1,3-DG content in the yield were 62% and 50% respectively under the above conditions.Secondly, the synthesis of DG by enzymatic esterification of fatty acid with glycerol in solvent-free system was studied. At first, we got the optimum conditions for the preparation of fatty acid by the hydrolysis of rapeseed oil. For Lipase CL, the conversion rate reached to 71% under the condition of enzyme dosage 300HU/g substrate, mole ratio of water to oil 20∶1, reaction temperature 35℃ and reaction time 7h. However, for Novozym 435, the conversion rate reached to 85% under the condition of enzyme dosage 300HU/g substrate, mole ratio of water to oil 30∶1, reaction temperature 67.5℃ and reaction time 7h.Then, the optimal process conditions for the enzymatic esterification of fatty acid with glycerol were obtained. They are vaccum water removal, Lipozyme RM IM dosage 45EU/g substrate, mole ratio of fatty acid to glycerol 2∶1, reaction 60℃ for 8 h. At the above conditions, the conversion rate of fatty acid is more than 90%, and the content of DG is about 70%. Besides, the half-life of the lipase is 20 times.By two-stage molecular distillation, the purity of DG product was increased from 60.5% to 90.2% and the yield and recovery of DG product were 52% and 77.5% respectively. Moreover, the physiochemical properties of DG product were determined and the results showed that the AV, POV and color of DG product were similar to the national standard of rapeseed salad oil, however, the smoking point of DG product was below to 220℃.The antioxidant effects of six antioxidants on the DG product were studied. The six antioxidants were butylated hydroxyanisol (BHA), butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), tocophenol (VE), tea polyphenol (TPP) and lycopene (LP). It was shown that the antioxidant effect on DG product was as follows: TBHQ>TPP>LP>BHT>VE>BHA. The effect of different dosage of three natural antioxidants on the induction time of DG product was investigated. The suggested dosage of the three natural antioxidants is 200 ppm.It was shown by animal experiment that DG may suppress the increase of body weight and the inhibitory effect showed a dose-dependent relativity. DG may reduce the Lee's index and the ratio of visceral fat to body weight of rats significantly, which means that DG may suppress the accumulation of visceral fat of rats and reduce the obesity degree of rats significantly. Besides, DG can lower the TG concentration of rats' serum significantly, but can't lower the total cholesterol (TC) concentration significantly. Moreover, no significant difference in the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was observed between the DG and TG diet, which suggested that DG would not damage the liver cell.DG added with stanol ester (SE) can not only suppress the increase the body weight of rats significantly, but also reduce the TC and low-density lipoprotein cholesterol (LDL-C) concentration of rats' serum significantly. As we know, DG mainly reduces the triacylglycerol concentration, while SE mainly decreases the TC and LDL-C concent...
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