【作者】 曹昱；

【导师】 王小宁；

【作者基本信息】 华南理工大学 ， 微生物学， 2013， 博士

【摘要】 肥胖已成为影响人类健康的一种全球性问题。肥胖的发生和膳食结构密切相关，尤其与富含油脂的高热量食品的过量摄取有关。脂肪是食物的重要组成部分，对食物的口感、风味和饱腹感都具有重要的作用。然而，人们对脂肪的摄取已超过食物总热量比的30%。在此情况下，研究人员开发出了多种脂肪替代品和低热量油脂，包括蔗糖脂肪酸聚酯、中链脂肪酸甘油酯、短长链脂肪酸甘油酯和甘油二酯等。这些产品以低热量或改变油脂在体内的代谢方式来控制脂肪在体内的积聚。其中较为成功的产品有P&G公司的Caprenin产品和Nabiso公司开发的Salatrim系列产品，以及日本花王公司的甘油二酯产品。作为一种理想的油脂替代品，必须具有和传统油脂高度的通用性，即在使用方法、使用条件、感官特性上不得有大的改变，同时必须具有高的安全性和完好的营养特性。以上提及的油脂替代品或多或少有着各自的缺陷，目前还没有一种完全符合理想标准的产品。未来对低热量油脂替代品的市场需求将不断扩大。因此，开发与普通油脂性能相似的油脂替代品具有重要的学术价值和应用潜力。本研究所开发的新型结构脂，在其甘油骨架的sn-2位为短链脂肪酸。此结构脂可利用甘油三酯分子在体内的代谢差异减少餐后血脂水平，具有降低脂肪在体内积聚的功能。普通油脂中甘油三酯分子在体内代谢时，会被肠道中的胰脂肪酶水解为2-长链脂肪酸单甘酯和游离脂肪酸，进入小肠绒毛细胞后会被重新合成为甘油三酯，随后并通过淋巴系统穿过胸导管依靠血液系统转运至身体各处。而新型结构脂进入人体代谢系统后，会形成2-短链脂肪酸单甘酯，能够被迅速吸收进入门静脉并运送至肝脏快速代谢，减少了小肠绒毛细胞中甘油三酯的重合成，从而降低餐后血脂水平，达到防止脂肪堆积的效果。本研究对新型结构脂的酯交换反应合成条件进行了优化，选用Lipozyme RM IM脂肪酶催化三丁酸甘油酯和大豆油脂肪酸甲酯的酯交换反应体系，考察了反应时间、反应温度和加酶量等参数对酯交换反应合成结构脂过程的影响。以长链脂肪酸插入率、酰基转移率和长链脂肪酸甘油三酯(LLL-TAG)的含量为响应值，利用中心旋转组合设计对Lipozyme RM IM脂肪酶催化酯交换反应进行了优化，最佳反应条件为：反应温度为51.4℃，反应时间为6.77h,加酶量为8.11wt%，此时的长链脂肪酸插入率为43.2%，酰基转移率为5.33%，LLL-TAG含量为0.42%。本研究同时考察了双酶两步法合成新型结构脂的工艺条件，发现Novozyme脂肪酶在使用较高摩尔比(乙醇/三丁酸甘油酯)和较低的反应温度时可以得到高含量的2-丁酸单甘酯。获得2-丁酸单甘酯的最佳反应条件为：无水乙醇与三丁酸甘油酯的摩尔比为65:1，反应温度为25℃，加酶量为5wt%；反应2h后，2-丁酸单甘酯的含量和得率分别为21.6%和62.8%。最后使用Lipozyme RM IM脂肪酶催化2-丁酸单甘酯和脂肪酸甲酯反应合成的S2型结构脂，长链脂肪酸插入率达到52%以上，且酰基转移率只有1.1%。但双酶两步法工艺较为复杂，需消耗大量有机溶剂用于纯化2-丁酸单甘酯，无法用于新型结构脂的批量生产，故后期实验仍然选用一步酯交换法合成新型结构脂。研究了批量合成和纯化新型结构脂的方法，并考察了使用分子蒸馏方法对结构脂分离的影响。结果发现，在进料速度为2g/min，蒸馏系统压力为1Pa，冷却水温度为40℃，刮膜电机转速250r/min，蒸发面温度为200℃时，可以实现新型结构脂的良好分离。使用循环批次反应法合成新型结构脂，结构脂产品的总得率达到64%，经检测发现短链脂肪酸（丁酸）主要分布在甘油酯的sn-2位，所得目标结构脂的含量可以达到80.9%。通过理化性能评价发现，新型结构脂在外观、酸价、皂化价、折光指数等指标上与其长链脂肪酸的酰基供体油大豆油的相关指标十分接近，但烟点比大豆油低，新型结构脂分子量较小而具有更低的熔点。由此可见，新型结构脂可能对普通食用油脂进行全替代使用。随后通过餐后血脂实验和动物成长实验对新型结构脂进行了功能性评价。结果发现，新型结构脂可使小鼠的餐后血液甘油三酯水平降低。在动物成长实验中，对小鼠饲喂第6周时，发现高剂量新型结构脂组的小鼠平均体重低于猪油组，血脂分析结果显示新型结构脂组小鼠的血液总胆固醇浓度具有降低的趋势。肝脏病理学切片观察发现，中剂量和高剂量新型结构脂组小鼠的肝脏中脂肪滴的数量和大小都会相对减少，肾脏病理学切片观察未见异常。以上结果说明新型结构脂具有控制血脂升高，防止脂肪积累的功能，并具有完全替代普通油脂使用的潜力。更多还原

【Abstract】 Obesity has become a global problem, threatening to human health. The incidence ofobesity is closely related to the dietary pattern, particularly to the excessive intake ofhigh-calorie fatty foods. Fat is an essential part of diet foods, and it contributes to the taste,flavor and satiety of the food. Nowadays, the fat intake by people is more than30%of thetotal calories from food. Under such circumstance, varieties of low-calorie fats and fatsubstitutes, such as sucrose fatty acid polyesters, medium-chain triglycerides, short-andlong-chain triglycerides and diglycerides, have been designed and developed. The relativelysuccessful products are Caprenin product (P&G), Salatrim product (Nabiso) and diglycerides(Kao, Japan). They can control the accumulation of fat in the body either by providing lowercalorie or altering the metabolism of fats. As an ideal fat substitute, it should have a highdegree of universality with traditional oils and fats, that means it should not change a lot inthe usage method, usage conditions and sensory characteristic. Moreover, the fat substitutesshould have good in nutritional properties and high safety. However, most of the fat substituteproducts have their inherent shortcomings which make them only partially meet the abovecriteria. From the point of view to better improve human health, the market requirement fornew low-calorie fat substitutes will continue growing. Therefore, it has important researchmerit and potential market application to develop low-calorie fat substitutes with highsimilarity to the ordinary oils and fats.We designed a novel structured lipid, which contained a short chain fatty acid at sn-2position. The novel structured lipid can reduce postprandial lipid levels by the differentmetabolism of triglyceride molecules and thus reduce the accumulation of fat in the body.When an edible oil is took into digestive tract, the majority of ingested triacylglycerols (TAGs)are partially hydrolyzed by pancreatic lipase to2-monoacylglycerols (2-MAGs) containinglong-chain fatty acids and fatty acids (FAs), the2-MAGs are immediately resynthesized intoTAGs molecules after absorbed by the small intestinal epithelial cells. The resynthesizedTAGs will be transferred throughout the body by the lymphatic system and thoracic duct. Inthe case of the novel structured lipids, they are partially hydrolyzed by pancreatic lipase to2-MAGs containing short-chain fatty acids (SFAs) and FAs. The SFAs are rapidly absorbedand metabolized to carbon dioxide in liver. Thereby, the resynthesized TAGs by lipases insmall intestinal epithelial cells could be reduced, resulting in reducing postprandial lipidlevels and preventing fat accumulation in body.Firstly, the novel structured lipids were synthesized by transesterification of tributyrin and soybean oil fatty acid methyl esters using Lipozyme RM IM lipase. Central compositerotatable design (CCRD) was used to optimize the reaction variables, i.e, reaction time,reaction temperature and lipase dosage. The incorporation of long chain fatty acids, acylmigration level and content of long-chain triglycerides (LLL-TAG) were set as evaluationcriteria. The optimal reaction conditions were as follows: reaction temperature is51.4℃,reaction time is6.77h and lipase dosage is8.11wt%, and the resulting long chain fatty acidsincorporation rate is43.2%, acyl migration level is5.33%and LLL-TAG content is0.42%under optimized conditions.Secondly, the novel structured lipids were synthesized by two-step method using twoenzymes systems. It was found that a higher content of2-monobutyrin was obtained by usinglower temperature and higher molar ratio of ethanol to tributyrin. The optimal reactionconditions were as follows:65:1of of ethanol to tributyrin,25℃of reaction temperature,5wt%of enzyme amount and2h of reaction time. Under these conditions, the content of2-monobutyrin was21.6%and the yield was62.8%. The incorporated long chain fatty acidscontent reached to52%in the final product, and the acyl migration level was only1.1%.However, the method is complex and large amount of organic solvents is required to purify2-MAGs. Moreover, it’s difficult for scale-up production. Thus, one-step interesterificationmethod was selected to synthesize the novel structured lipids for the following work in thisthesis.Thirdly, a scale-up synthesis of novel structured lipids by transesterification of tributyrinand soybean oil fatty acid methyl esters using Lipozyme RM IM lipase was carried out.Molecular distillation was employed to purify the structured lipids and the effect ofevaporation temperature on the purification was examined. Results showed that betterseparation of transesterification product was achieved under the following conditions:2g/minof the feed rate,1Pa of the distillation system pressure,40℃of the cooling watertemperature at light phase,250r/min of the scraping membrane motor speed and200℃ofthe evaporation temperature. Furthermore, circulating method of scale-up synthesis of novelstructured lipid was studied. The results showed that the total yield was about64%, thecontent of LSL-TAG was80.9%, and most of the butyric acids were distributed in Sn-2position of the TAGs. The physicochemical properties of the novel structured lipids wereevaluated, and the results indicated that the appearance, acid value, saponification value,refractive index and other indicators were very similar to soybean oil which was the acyldonor of long-chain fatty acids. However, the structured lipid had a lower smoking point due to a smaller molecular presented in the product. The results of physicochemical propertiessuggested that the ordinary diet oil could be completely replaced by the structured lipid.TBHQ can effectively improve oxidation stability of the structured lipid.Finally, the lipid lowering property of novel structured lipids were evaluated by rapidfasting experiment and animal growth experiment. It was found that the novel structured lipidcould reduce the postprandial plasma triglyceride levels of mice. After feeding for six weeks,the group received high fat diet containing high dosage of structured lipids had lowerbodyweight, comparing with control group of high fat diet containing high dosage of lard.The plasma cholesterol (TC) content in the group received high fat diet containing mediumand high dosage of structured lipid showed a decreasing trend comparing with the controlgroup. For the tested group, the histological slices of liver and kidney were observed undermicroscope, the number and size of fat droplets in liver were found to be reduced, and theresults of kidney histological slices showed no abnormal symptom. In summary, our resultsshowed that the novel low-calorie structured lipid could control the plasma lipid and preventthe accumulation of body fat.更多还原