硬脂组成对其热性质、微观结构及形态的影响

旨在为全氢化硬脂在塑性脂肪、油凝胶等的应用提供一定的开发依据和理论基础,全面分析硬脂组成对其晶体性质的影响。测定了全氢化棕榈仁油(HPKO)、全氢化棕榈油(HPO)、全氢化棉籽油(HCSO)、全氢化大豆油(HSO)、全氢化低芥酸菜籽油(HCO)、全氢化高芥酸菜籽油(HRO)、精炼漆蜡(LW)、可可脂(CCB)的脂肪酸与甘三酯组成、热性质、微观结构及形态,研究硬脂的组成对其热性质、微观结构及形态的影响。结果表明：HPO、HCSO、HSO、HCO均以棕榈酸和硬脂酸为主,HPKO以月桂酸和豆蔻酸为主,HRO以硬脂酸和山嵛酸为主,LW以棕榈酸和油酸为主,CCB以硬脂酸、油酸、棕榈酸为主;硬脂的甘三酯组成对其熔点有很大影响,CCB、HPKO的熔化温度较低,HSO、HCO、HRO的熔化温度较高;HRO虽然含有大量的山嵛酸,但其熔化温度低于HSO和HCO,这可能与甘三酯间的相互作用有关;油脂中高熔点甘三酯含量影响油脂的固体脂肪含量曲线,相同温度下高熔点甘三酯含量高的油脂具有更高的固体脂肪含量,甘三酯间的相互作用也会影响油脂的固体脂肪含量曲线;CCB晶型为β型,HPKO、HPO、HCSO为β′型,HC...     

棉籽油干法分提工艺的研究

以棉籽油为原料,利用干法分提对其进行改性。考察了结晶温度、冷却速率、养晶时间及搅拌速率对棉籽固脂碘值、0℃固体脂肪含量(SFC)及固脂得率的影响。确定的最佳分提工艺条件为:结晶温度5℃,冷却速率2℃/h,养晶时间10 h,搅拌速率15 r/min。所得固脂的碘值(I)为91 g/100 g,0℃SFC为31.6%,固脂得率为12.89%。     

全氢化棉籽油的理化性质、脂肪酸组成及微观结构分析北大核心CSCD

为开发不含反式脂肪酸的固态基料油,对全氢化棉籽油的理化性质、脂肪酸组成和微观结构进行研究。参照相应的国标方法对全氢化棉籽油的基本理化指标进行测定,利用气相色谱分析其脂肪酸组成,通过脉冲核磁共振仪测定其固体脂肪含量,最后采用偏光显微镜观察、差示扫描量热法以及X射线衍射对其晶体结构进行表征。结果表明:全氢化棉籽油的基本理化指标均符合国标对食用氢化油的要求;全氢化棉籽油脂肪酸组成主要为棕榈酸和硬脂酸,几乎不含反式脂肪酸;固体脂肪含量结果显示全氢化棉籽油在40℃时依然保持固态,适合与液态油复配使用;另外,全氢化棉籽油的微观形态呈细小、密集的针状,符合β′晶型,也存在一定量的β晶型。研究表明以全氢化棉籽油为酯交换共混物基料油、医药原料、化妆品原料具有一定的应用和开发前景。     

油脂氢化反应速率常数与碘值的定量关系

本文自理论上导出油脂氢化反应的速率常数与碘值间的函数关系。指出其速率常数只是单烯酸(酯)反应的常数。且受选择指数的限制。用不同催化剂对豆油氢化的结果证明理论与实验相一致。 基于油脂的化学组成与结构特点,油脂化学家断定,油脂氢化反应速率不会与油脂的不饱和程度间没有关系。Allen注意到:大多数氢化反应的性质近乎是单分子反应,氢化速率常数与油脂的不饱和程度大致成比例。但反应的性质总受到各氢化条件的影响。棉籽油的氢化曲线——碘值的对数对氢化时间t作图,有的呈直线,有的呈曲线。Albright曾假设过棉籽油的氢化速率等于碘值随时间的变化率,与碘值成正比1982年Szukaiska总结出菜籽油氢化速率常数与碘值的关系式。1986年SunChol及其同事在豆油氢化中也用了这一关系,该式与Albright的假设一致。这都是些经验公式,且总速率常数与油脂中各不同双键基团氢化的速率常数间的关系,含混不清。 本文从理论上导出氢化速率常数与碘值的函数关系,并明确该关系的适用条件。对有关问题也做了验证。     

双轴搅拌对晶粒降温结晶的影响

工业结晶过程中，一般希望结晶产物具有均匀的粒度和规则的晶形。考虑到带有外桨的双轴搅拌器能有效促进结晶过程的传质与传热，因此课题组以双轴搅拌器作为研究对象，通过实验考察了转速、桨型以及内外桨搅拌模式等参数对结晶产物粒度分布及晶型晶貌的影响；根据不同转速下测得的晶体成核生长动力学参数，建立氯化钾结晶成核速率与生长速率的预测公式。结果表明：双轴搅拌得到的晶体中值粒径明显高于单轴搅拌，但由于外桨的存在，使得粒度分布离散度变大；存在一个最佳转速使晶体中值粒径达到最大且粒度分布较为集中；内外桨同转、桨叶选用轴流桨或混流桨时更适用于结晶操作。氯化钾结晶成核速率与生长速率的预测公式为工业结晶提供一定的理论参考。     

单甘酯对棉籽油和棕榈硬脂酯交换体系结晶性质的影响

研究不同油酸单甘酯添加量对棉籽油和棕榈硬脂(质量比50:50)酶催化酯交换产物结晶性质的影响。结果表明:添加2%和5%的油酸甘油酯,酯交换产物的固体脂肪含量(SFC)与熔点基本不发生变化,添加量增大到10%,体系的SFC与熔点略有下降;添加不同量的油酸甘油酯,均使酯交换产物结晶温度发生变化,其中低熔点组分对应的峰温度随添加量增加而增大,高熔点组分对应的峰温度随添加量增大而下降;添加2%的油酸单甘酯对酯交换产物的成核速率和结晶速率不存在影响;添加不同量的油酸单甘酯后,酯交换产物中β′晶形比例下降,下降程度与添加量成负相关。     

氢化棕榈硬脂结晶特性及其对蜡烛外观的影响

为解决分提棕榈硬脂用作蜡材时渗油的问题,对其进行了不同程度的氢化。利用差示扫描量热仪、脉冲核磁共振仪、偏振光显微镜和X-射线衍射仪等手段对其结晶行为进行研究,并比较了氢化前后化学组成的变化。结果表明:棕榈硬脂氢化的第一个阶段,部分油酸和亚油酸迅速转变为反式油酸,它促进了α型晶体的形成及其向β'型的转变,虽然45℃以下时固体脂肪含量高于原料油,但其熔点却降低;氢化的第二个阶段,大量油酸和反式油酸转变为硬脂酸,高熔点组分增加,虽然晶型仍处于β'型,但此时熔点及各温度下的固体脂肪含量均高于原料油。氢化15 min后低熔点峰基本消失,蜡烛渗油现象也消失;继续氢化至20 min后样品结晶峰狭窄、尖锐,蜡烛容易断裂。因此,适度氢化样品(氢化15~20 min)较适合用作蜡材。     

巧克力涂层基料油理化性质和相容性的研究北大核心CSCD

选用棕榈油中间分提物(PMF)和氢化棕榈油(HPO)作为巧克力涂层的基料油,对两种油脂的理化性质进行了分析。同时,通过等温曲线和实测固体脂肪含量与理论固体脂肪含量的偏差曲线分析PMF和HPO的相容性。实验结果表明:PMF和HPO在脂肪酸和甘三酯的组成上相似,PMF和HPO具有良好的相容性,PMF和HPO按照比例3∶7(质量比)混合可以作为巧克力涂层基料油配方。     

巧克力涂层基料油理化性质和相容性的研究

选用棕榈油中间分提物(PMF)和氢化棕榈油(HPO)作为巧克力涂层的基料油,对两种油脂的理化性质进行了分析。同时,通过等温曲线和实测固体脂肪含量与理论固体脂肪含量的偏差曲线分析PMF和HPO的相容性。实验结果表明:PMF和HPO在脂肪酸和甘三酯的组成上相似,PMF和HPO具有良好的相容性,PMF和HPO按照比例3∶7(质量比)混合可以作为巧克力涂层基料油配方。     

制取高不饱和度亚麻籽油的方法研究

以亚麻籽油为原料,采用干法分提对其进行了分离改性,进一步分离出富含高不饱和脂肪酸的亚麻籽油。研究了搅拌速率、冷却速率、养晶时间、结晶温度对亚麻籽油液态油得率、碘值的影响。得到最佳的工艺条件为:搅拌速率15 r/min,冷却速率4℃/h,养晶时间12 h,结晶温度-8℃。在最佳工艺条件下所得液态油碘值(I)为198 g/100 g,液态油得率为89.2%。通过分析样品油与成品油的脂肪酸组成、含量和0℃固体脂肪含量发现,成品油的饱和脂肪酸和固体脂肪含量较样品油明显降低。     

A kinetic analysis of crystallization of a milk fat model system

Crystallization behavior of milk fat, pure triacylglycerol (TAG) fraction of milk fat and three blends of 30, 40 and 50% of high-melting fraction (MDP=47.5°C) in low-melting fraction (MDP=16.5°C) of milk fat were studied by turbidimetry and nuclear magnetic resonance (NMR). Nucleation behavior was similar for these systems. In all cases, curves of log of induction time vs. temperature were continuous, which means that when samples were crystallized from the melt, only one polymorphic form was obtained at all temperatures. X-ray patterns verified formation of the β′ form. The calculated activation free energies of nucleation were quite low, but close to the ones published for other fats systems, such as hydrogenated sunflower oil. Only a low supercooling was needed to start crystallization. When isothermal crystallization was studied by NMR, the same behavior was also found for all samples. For low supercooling (crystallization temperatures above 25°C), curves had sigmoidal shapes with a period of induction of crystallization at the beginning. For high supercooling (temperature below 25°C), no induction times were observed as crystallization occurred rapidly. An intermediate plateau in SFC was clearly visible in all curves. The step in this plateau decreased steadily both in rate and height as T_c was increased. The curves were interpreted with the Avrami kinetic model, and parameters K_n and n were calculated. In all cases, the best fit was obtained by setting n to 3. K_n was, on average, 10 times lower above 25°C.     

PARAMETERS THAT DETERMINE TRIPALMITIN CRYSTALLIZATION IN SESAME OIL

The crystallization of tripalmitin (TP) in sesame oil (0.98, 1.80 and 2.62% w/v) was investigated under isothermal conditions using a cooling rate similar to the one achieved by industrial crystallizers (1 K/min) and utilizing a modification of the Avrami equation. It was concluded that z, the crystallization rate constant, and the associated energy of activation (Ea) values determined through Avrami's original equation yield erroneous results. Additional results indicated that the increase in supercooling at constant oil phase viscosity (e.g., 5.25–5.5 dynes/cm²) during crystallization, produced a higher degree of nucleation without an appreciable effect on TP crystal size. In contrast, as viscosity of the oil phase decreased at equal supercooling conditions (e.g., 22.0 - 22.5C) the main crystallization process evaluated through z and Ea was crystal growth. It was also concluded that the characteristic crystallization stages of induction time for nucleation, crystal nucleation and growth, and end of crystallization were evident in the viscosity profile of the solid fraction developed during TP crystallization. The predominance of any of these processes (i.e., nucleation or crystal growth) as a function of supercooling and viscosity of the oil phase determines, to a great extent, the rheological profile during crystallization and the final viscosity value of the crystal suspension.     

High pressure crystallization of binary fat blend: A feasibility study

Crystallization mechanism of triglycerides plays an important role in structuring of the plastic fats, such as margarine and shortening. The effects of cooling under high pressure on crystallization and functional properties of a mixture of fully hydrogenated soybean oil and soybean oil (3:7 mass ratio) at 30 °C were investigated and compared against samples crystallized under atmospheric condition. Experiments were conducted using a face-centered central composite design. It is shown that pressure level, initial temperature, and maximum temperature under pressure affect sample's storage modulus, yield stress and percent oil loss. Holding time and pressure pulsing did not significantly influence the properties. Inverse relationships between the mechanical properties and percent oil loss were observed. Presence of crystal seeds in the sample prior to pressurization yielded lipid crystals with different polymorphic properties than those directly crystallized from the melt.Industrial relevanceThe study demonstrates that high pressure processing can improve plasticity and physical properties of fat blends with low saturated fat content. High pressure crystallization is proven to offer better crystallization properties with lower supercooling condition and prevent the need for long hour incubation.     

Avrami法研究微量司盘85对棕榈油结晶动力学的影响

采用差示扫描量热仪（differential scanning calorimetry,DSC）分析棕榈油及其与司盘85混合物的等温结晶及熔融行为,通过Hoffman-Weeks法计算出样品的平衡熔点。采用Avrami方程进一步研究样品的等温结晶动力学,从而得到与结晶动力学相关的参数。结果表明：DSC分析显示司盘85可明显降低棕榈油的结晶率和成核速率。通过Hoffman-Weeks法和Avrami方程求得的温度数据具有良好的线性关系,表明Avrami方程适用于棕榈油结晶过程的研究,但在结晶后期出现偏离。拟合得到的Avrami指数（n）在2.37～2.77之间,可知样品二维和三维晶体生长同时存在;结晶速率（k）和半结晶时间（t1/2）随着添加剂的添加均变小。     

Influence of chemical interesterification on thermal behavior,microstructure, polymorphism and crystallization properties of canola oil and fully hydrogenated cottonseed oil blends

This work evaluated chemical interesterification of canola oil (CaO) and fully hydrogenated cottonseed oil (FHCSO) blends, with 20%, 25%, 30%, 35% and 40% (w/w) FHCSO content. Interesterification produced reduction of trisaturated and increase in monounsaturated and diunsaturated triacylglycerols contents, which caused important changes in temperatures and enthalpies associated with the crystallization and melting thermograms. It was verified reduction in medium crystal diameter in all blends, in addition crystal morphology modification. Crystallization kinetics revealed that crystal formation induction period and maximum solid fat content were altered according to FHCSO content in original blends and as a result of random rearrangement. Changes in Avrami constant (k) and exponent (n) indicated, respectively, that interesterification decreased crystallization rates and altered crystalline morphology. However, X-ray diffraction analyses showed randomization did not change the original crystalline polymorphism. The original and interesterified blends had significant predominance of β′ polymorph, which is interesting for several food applications.     

司盘85对棕榈油结晶过程动力学的影响分析

采用核磁共振仪测定棕榈油及添加0.01%~0.1%司盘85棕榈油的等温结晶行为。采用Avrami方程进一步探究样品的等温结晶动力学,研究司盘85对棕榈油结晶行为的影响。结果表明:棕榈油及添加0.01%~0.1%司盘85棕榈油的Avrami指数在1.422~1.912之间,可知样品的晶体生长为二维;司盘85对棕榈油的结晶过程具有抑制作用,且随着司盘85添加量的增大,其抑制作用增强,表现为结晶速率常数减小,半结晶时间延长。     

Influence of shear on fat crystallization

Processing conditions greatly impact fat crystallization kinetics and growth mechanisms. Recently, there has been increased interest in elucidating the role of shear on fat crystallization. This review provides an overview of fat crystallization under static conditions followed by a summary of the current body of work pertaining to the effects of shear on fat crystallization, namely its effects on nucleation and growth, crystal network formation, polymorphic transitions, and microstructure modification at different length scales. The effects of shear are usually tied to critical shear rates but shear generally enhances nucleation and growth, accelerates crystallization and polymorphic transitions, and can cause orientation and structuring of fat crystal networks.     

Influence of emulsifier type on freeze-thaw stability of hydrogenated palm oil-in-water emulsions

The influence of emulsifier type (Tween 20, whey protein isolate, casein) on the physical properties of 20 wt% hydrogenated palm oil-in-water emulsions after crystallization of (i) the oil phase only or (ii) both the oil and water phases has been examined. Emulsion stability was assessed by differential scanning calorimetry measurements of fat destabilization after cool–heat cycles, and by measurements of mean particle size, oiling off, and gravitational separation after isothermal storage (−20 to 37 °C). Tween 20-stabilized emulsions showed appreciable fat destabilization at temperatures where the oil phase was partially crystalline, which was attributed to partial coalescence. Protein-stabilized emulsions were stable under these conditions, which was mainly attributed to the relatively thick interfacial membranes surrounding the droplets. When both oil and water phases crystallized, there was complete destabilization of Tween 20- and casein-stabilized emulsions, and extensive destabilization of whey protein-stabilized emulsions, which was attributed to ice crystallization. The results of this study could facilitate the development of frozen food products with improved properties.     

Isothermal batch crystallization of alpha-lactose: A kinetic model combining mutarotation,nucleation and growth steps

A kinetic model combining first-order differential equations of the three consecutive steps of lactose crystallization, i.e., mutarotation, nucleation and crystal growth rate, was developed. Numerical solutions successfully fitted the variations of crystal mass growth rate as a function of lactose concentration during unseeded isothermal batch crystallization, at different initial lactose concentrations and temperatures. The model allowed the induction phase and the influence of seeding to be simulated by taking into account the dependency of crystal growth rate on total crystal surface area and, consequently, on nucleation rate. The proposed model highlights the large influence of the mutarotation step, even in unseeded crystallization kinetics. The effects of high lactose supersaturations that prevail at industrial scale during whey powder manufacturing and the effects of alkaline pH (9.5) on lactose crystallization kinetic were successfully predicted.     

Influence of diglycerides on crystallisation of palm oil

Palm oil diglycerides and pure synthetic diglycerides of 1,2‐(2,3‐) and 1,3‐dipalmitoylglycerol, dioleoylglycerol and palmitoyloleoyl glycerol were added to purified triglycerides of palm oil. The crystallisation kinetics of the samples were studied by spectrophotometry, NMR analysis of the solid fat content and by X‐ray diffraction of the crystals obtained at 20°C. Palm oil diglycerides inhibited the nucleation process and retarded the crystal growth rate of palm triglycerides. The effect was less pronounced at a higher degree of supercooling. The extent of inhibition depended on the nature of the diglycerides and the concentration. © 1999 Society of Chemical Industry