【作者】 孙月娥；

【导师】 夏文水；

【作者基本信息】 江南大学 ， 食品科学， 2009， 博士

【摘要】 脂肪酸糖酯是一类具有重要生理活性的、绿色、安全、可生物降解的非离子表面活性剂,因其具有良好的乳化能力和杀菌性能以及对皮肤刺激性低等诸多优点而广泛应用于食品、医药、化妆品和农业。目前商业上使用的脂肪酸糖酯大多来自饱和脂肪酸和糖的合成,不饱和脂肪酸糖酯的文献及商品相对较少,然而不饱和脂肪酸具有许多特殊的保健功能以及较低的凝固点等优点,因此,不饱和脂肪酸糖酯已经成为近年来糖酯类表面活性剂研究的新焦点。不饱和脂肪酸及其酯很容易氧化,关于其在油相和水溶液中氧化行为的报道不尽相同。因此,本文对不饱和脂肪酸海藻糖单酯的合成、性质以及其在水溶液中的氧化行为进行了研究,并对胶束模型中不饱和脂肪酸海藻糖单酯的氧化行为与其自身结构的关系进行了探讨。在间歇式反应器中对固定化脂肪酶Novozym435催化合成不饱和脂肪酸海藻糖酯的工艺进行了研究。利用分子筛作为脱水剂,分别以油酸、亚油酸、亚麻酸和海藻糖为原料,采用直接酯化法合成了油酸海藻糖酯、亚油酸海藻糖酯和亚麻酸海藻糖酯。分别以EPA乙酯、DHA乙酯和海藻糖为原料,采用酯交换法合成了EPA海藻糖酯和DHA海藻糖酯。考察了反应时间、分子筛、溶剂、温度、脂肪酶、底物浓度等因素在酶催化反应中的作用和对不饱和脂肪酸海藻糖单酯转化率的影响,确定了有机相脂肪酶催化合成海藻糖酯的反应介质为叔丁醇,脱水剂选用4?分子筛。在此基础上,通过Box-Behnken二次回归正交设计对影响合成的主要工艺参数进行优化,确定了合成亚油酸海藻糖单酯的最佳工艺条件:海藻糖13.2 mmol/L,亚油酸41.7 mmol/L,分子筛添加量3.1 g,脂肪酶添加量0.3 g,在20 mL叔丁醇中,50 oC、150 rpm恒温水浴振荡器反应50.4 h,亚油酸海藻糖单酯的转化率达到74.5 %。对非水相酶法合成的不饱和脂肪酸海藻糖酯反应液采用硅胶柱层析分离,流动相为正己烷/异丙醇/甲醇（5/4/1,v/v/v）和正己烷/异丙醇/甲醇（4/4/2,v/v/v）,梯度洗脱,流速为1.3 mL/min。采用薄层层析（TLC）技术对不饱和脂肪酸海藻糖酯的组成进行定性分析,TLC的展开剂为乙酸乙酯/甲醇/水（8.5/1/0.5,v/v/v）,用饱和碘蒸气显色。采用制备HPLC对硅胶柱提纯的产物进行精制,提纯EPA海藻糖单酯的流动相为甲醇/水（80/20,v/v）,提纯其余四种糖酯的流动相为甲醇/水（85/15,v/v）,流速为8 mL/min。利用高效液相-质谱联用（HPLC-MS）技术对不饱和脂肪酸海藻糖单酯产品进行分析,并采用1H NMR和13C NMR对目标产物进行确认和结构鉴定,确定它们分别为6-O-油酸海藻糖单酯、6-O-亚油酸海藻糖单酯、6-O-亚麻酸海藻糖单酯、6-O-EPA海藻糖单酯和6-O-DHA海藻糖单酯。其中6-O-亚麻酸海藻糖单酯、6-O-EPA海藻糖单酯和6-O-DHA海藻糖单酯是新化合物。采用表面张力法研究了油酸海藻糖单酯、亚油酸海藻糖单酯、亚麻酸海藻糖单酯、EPA海藻糖单酯和DHA海藻糖单酯的吸附性质,得到了表征各个不饱和脂肪酸海藻糖单酯表面活性的参数CMC、γ_CMC、Г、A,并与对应的饱和脂肪酸糖酯表面活性剂进行比较,研究了酰基链上碳原子数量、双键数量和温度等因素对不饱和脂肪酸海藻糖单酯表面张力、CMC等界面性质的影响。结果表明,酰基链上碳原子数增加使CMC值减小,酰基链上双键数增加使CMC值增大,温度对不饱和脂肪酸海藻糖单酯CMC的影响很小,随着温度升高,CMC值略有下降。研究了油酸海藻糖单酯、亚油酸海藻糖单酯、亚麻酸海藻糖单酯、EPA海藻糖单酯和DHA海藻糖单酯在水溶液中的氧化行为。考察了酰基链上双键数量、脂肪酸链长以及不同浓度对不饱和脂肪酸海藻糖单酯在水溶液中氧化行为的影响、并分析了氧化与不饱和脂肪酸海藻糖单酯结构的关系。结果表明,当不饱和脂肪酸海藻糖单酯在水溶液中以单体状态存在时,其稳定性递减顺序为:油酸海藻糖单酯、亚油酸海藻糖单酯、亚麻酸海藻糖单酯、EPA海藻糖单酯和DHA海藻糖单酯;当不饱和脂肪酸海藻糖单酯在水溶液中以胶束状态存在时,其稳定性递增顺序为:亚麻酸海藻糖单酯、亚油酸海藻糖单酯、油酸海藻糖单酯、EPA海藻糖单酯和DHA海藻糖单酯。更多还原

【Abstract】 Carbohydrate fatty acid esters is a kind of nonion surfactant, which is made from renewable feedstock and does harmless to the environment. Due to their functional, nontoxic and nonskin-irritant properties, they have been widely used in food, pharmaceutical, cosmetic and detergent industries. Because the obviously defects of chemical synthesis, we adopt bio-catalytic process to synthesize the carbohydrate fatty acid esters. Most carbohydrate fatty acid esters saled on market are from saturated fatty acid and sugar. However, unsaturated fattty acid have many biological activities and physiological functions and other merits, so the research on carbohydrate unsaturated fatty acid esters attract the interest of many researchers. Lipids with high PUFAs content are susceptible to oxidation and it is reported that the oxidation of an unsaturated substrate in aqueous solution is different from that in bulk oil. We studied on the synthesis and properties of carbohydrate unsaturated fatty acid esters firstly, then investigated their oxidation in aqueous solution. The main results are as follows:Five carbohydrate fatty acid esters were synthesized from trehalose and unsaturated fatty acids or their ethyl esters in tert-butanol using microbial lipase as a biocatalyst in a batch stirred tank reactor. We systematically investigated the effect of many factors such as reaction time, molecular sieves, solvent, temperature, lipase, substrate concentration on the synthesis of carbohydrate fatty acid esters. The optimal condition for nonaqueous synthesis of monoacyl trehalose was as follows: trehalose concentration 13.2mmol/l, linoleic acid concentration 41.7 mmol/l, molecular sieves 3.1 g, lipase 0.3 g and tert-butanol 20 mL. The condensation was carryied at 50oC and 150 rpm for 50.4 h.The solvent was dehydrated by contact with molecular sieves （4 ?） for at least 24 h before use.The silica gel column chromatography with mobile phases of hexane-isopropanol- methanol 5:4:1（v/v/v） followed by 4:4:2 （v/v/v） for unsaturated trehalose esters at 1.3 mL/min was applied. The elution was collected and monitored by thin layer chromatography analysis （TLC）. The mobile phase for TLC was ethyl acetate/methanol/water （8.5/1/0.5, v/v/v） and iodine was used for development The fractions containing monoacyl trehalose was pooled. Further purification was performed using semi-preparative HPLC. The eluent was a mixture of methanol and water at 35 oC and 8 mL/min. The identities of the pure compounds were confirmed using MS, 1H NMR and 13C NMR as 6-O-oleoyl trehalose, 6-O-linoleoyl trehalose, 6-O-linolenoyl trehalose, 6-O-eicosapentaenoyl trehalose, 6-O-docosahexaenoyl trehalose. Among them, 6-O-linolenoyl trehalose, 6-O-eicosapentaenoyl trehalose, and 6-O-docosahexaenoyl trehalose are new compound.Surface properties of monoacyl trehaloses with different long unsaturated fatty acid chains were investigated at 30, 40, 50 and 60°C. Each monoacyl trehaloses was dispersed in double distilled water and surface tension of aqueous solution was measured using a Doüy ring method. The critical micelle concentrations （CMC）, surface tension at the CMC (γ_CMC), surface excess （Г） and residual area per molecule （A） of these amphiphilic compounds was studied and compared with other carbohydrate fatty acid esters. The effect of fatty acid chains length, double bond number and temperature on the surface properties of monoacyl trehaloses was also investigated. The value of CMC decreased as the chain length and temperature increased, while increased with more double bond when the chain length was the same.Oxidation of unsaturated monoacyl trehalose was studied in aqueous solution. Unsaturated monoacyl trehalose exist as monomers below the CMC, whereas they can aggregate spontaneously to form micelles above this concentration. Effect of double bond number, hydrophobic tail group size and concentration on the oxidative stability of unsaturated monoacyl trehalose in aqueous solution was studied. The results indicate that the oxidation of unsaturated monoacyl trehalose in micelles depended on both the degree of unsaturation and hydrophobic chain length. Oxidation increased as the number of double bonds increased in the unsaturated monoacyl trehaloses with identical hydrophobic chain length. However, when the hydrophobic chain length was different, the extent of oxidation decreased with chain length.更多还原