摘要:

Molecular-level structures of lipids and related organic long-chain compounds were investigated by means of vibrational spectroscopic and X-ray diffraction methods. Various spectroscopic techniques applicable to structural studies of lipid systems were developed. Various types of solid-state phase transformations were found in even- and odd-numbered saturated fatty acids and their molecular mechanisms were considered. Crystal structures of some modifications of a series ofcis-mono-unsaturated fatty acids were determined by the three-dimensional X-ray analysis and new types of molecular conformation as well as of subcell arrangement of thecis-mono-unsaturated acyl chains were found. An order-disorder type phase transformation accompanied with a partial melting at the interface of the molecular layers was found in some modifications ofcis-mono-unsaturated fatty acids. Molecular conformations and crystal structures of the polymorphs of methyl oleate and triglycerides containing an oleoyl chain at the 2-position were investigated on the basis of the spectroscopic data.

ISSN:0193-2691    

DOI:10.1080/01932698908943179

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Polar lipids from aqueous liquid-crystalline phases which are the basis for the understanding of their functionality in technical applications. The structural characteristics of these phases and the relation between chemical structure of lipid molecules and their phase properties are reviewed. Special attention is given to new results on cubic phases, the most complex of lipid-water phases. The lipid bilayer is curved in space so that there are no selfintersections. There are two water-channel systems separated by the bilayer. The characteristic feature of the cubic phases is that the lipid bilayer has zero average curvature in all points.

ISSN:0193-2691    

DOI:10.1080/01932698908943180

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

This article reviews recent studies of crystallization behavior of polymorphic modifications of principal saturated and mono-cis-un-saturated fatty acids, and of mixed-acid triacylglycerols; stearic acid, oleic acid, erucic acid and SOS (symmetric l,3-di-stearoyl-2-oleoyl glycerol). Thermodynamic and kinetic aspects of the polymorphic crystallization are discussed in relation to molecular structures and thermal properties, which have newly been elucidated with X-ray diffractometry and vibrational spectroscopy.

ISSN:0193-2691    

DOI:10.1080/01932698908943181

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The molecular packing in triacylglycerols having different acyl chains has been examined by differential scanning calorimetry, powder X-ray diffraction and vibrational spectroscopy (infrared and Raman) techniques. In the triacylglycerols examined, the acyl chain length, unsaturation or the position of substitution on the glycerol were changed systematically to observe their influence on the molecular packing in different polymorphic forms. Variation in the 3-acyl chain length of 1,2-dipalmitoyl-3-acyl-sn-glycerols (PPX) influenced the molecular packing along the long axis in the stable polymorphic forms. Three different modes of packing were observed. If X ≤ 4, the compounds packed in a bilayer structure similar to diacylglycerols, or if X ≥ 10 and ≤ 16 the compounds packed in a bilayer structure but similar to mono acid triacylglycerols. However for intermediate 3-acyl chain lengths, as in PP6 and PP8 the stable packing can occured only through chain segregation resulting in a trilayer structure. In the triacylglycerols containing unsaturated acyl chains, 1,2-dioleoyl-3-acyl-sn-glycerols (00X) and 1,3-dioleoyl-Z-acyl-sn-glycerols (0X0) the stable polymorphic forms packed in a trilayer structure where the odd acyl chains segregated and formed a middle layer. In a metastable hexagonal packing (α-phase) the long range ordering is minimal. Because of this lack of specific chain-chain interaction the 3-short acyl chain compounds of PPX packed in a unimolecular length structure (except PP2) whereas the 3-long acyl chain compounds packed in a bilayer structure. In orthorhombic perpendicular and triclinic parallel packing where the specific chain-chain interaction is increased, the end plane methyl packing and the glycerol conformation played important roles in the formation of bi-, tri- and hexalayer structures. The driving force in the formation of these different structures is to minimize the crystal defects created by the odd acyl chains and to enhance the specific chain-chain interactions. The presence of an odd acyl chain influenced the lateral chain packing as well, e.g., the stability of the orthorhombic perpendicular packing is enhanced by the presence of an odd acyl chain and even in some cases it is favored over the triclinic parallel packing. The odd acyl chain at the 1- or 3position of -sn-glycerol stabilized the orthorhombic perpendicular packing. This indicates the glycerol conformation is probably perpendicular to the layer plane and thus is different from the monoacid triacylglycerols.

ISSN:0193-2691    

DOI:10.1080/01932698908943182

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Dynamic processes of morphological transformation of liposome were visualized by sensitive dark-field light microscopy, to study the formation mechanisms of vesicular organelles. We found that the liposomes transformed, depending on the external conditions, in a well-defined sequential manner through several specific transformation pathways, depending on the external conditions, A circular biconcave form, which is the initial shape of all pathways observed, transformed in to a flexible thin filament or small spheresviaa variety of transient forms which possessed geometrical symmetry. Osmotic pressure was the driving force of the morphological transformation of the liposome.

ISSN:0193-2691    

DOI:10.1080/01932698908943183

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Multiple emulsions, especially water-in-oil-in-water (W/O/W) type systems, have potential applications for the formulation and processing of foods, drugs, cosmetics, etc, as each dispersed globule in this type of emulsions consists of liquid compartments separated from the same liquid suspending medium by a thin layer of another immiscible liquid components. This article reviews a series of fundamental works on the formation and dispersion state of multiple emulsion systems and integrates advances made in the area of colloid science so as to obtain further insights into the formulation of W/O/W emulsions. The contents are divided into three sections: methods for preparing multiple emulsions in view of the phase diagram of mixed components, dynamic aspects of oil layer in W/O/W emulsions, and stability of this type of emulsions.

ISSN:0193-2691    

DOI:10.1080/01932698908943184

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The importance of proteins to provide steric stabilization of food emulsions is discussed. In aerated emulsions like ice cream and whipped cream, a partial destabilization of the fat globules is needed to obtain a satisfactory product. The destabilization process is controlled by surface active lipids (emulsifiers) which promote desorption of the interfacial protein film under specific temperature conditions. The formation of liquid crystalline films in o/w emulsions without proteins is also briefly discussed.

ISSN:0193-2691    

DOI:10.1080/01932698908943185

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Confectionery coatings employ hard butter fat systems made from both lauric and non-lauric source oils. These oils are routinely modified by a combination of treatments including hydrogenation, fractionation and interesterification to achieve desired physical properties. Such processing methods create heterogeneous triglyceride mixtures consisting of a variety of compositional and positional isomers. Published phase diagrams of “simple” binary triglyceride mixtures of closely related molecules are complex, and suggest that innumberable unique liquid and solid phases may co-exist at any given temperature ( and pressure ) in vastly more complex triglyceride mixtures such as confectionery hard butters. Thus we may view confectionery fat systems as multiphasic mixtures (liquid, solid and compositional) with a propensity to undergo liquid content fluctuations and crystal size/morphology changes in response to slight changes in temperature. A true equilibrium among all phases may indeed never be attained, and a potential for movement of certain components in response to temperature change is probably constant. Surface growth of long needle-like fat crystals, “fat bloom”, most likely results from this non-equilibrium condition and serves to reduce the system's free energy. The ever present, ever changing liquid phase(s) is viewed as the vehicle for free energy minimization via triglyceride migration and ongoing crystal growth.

ISSN:0193-2691    

DOI:10.1080/01932698908943186

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Enzymatic modification of fats and oils using lipases has recently come into limelight, giving rise to a breakthrough in modification technology. This paper describes the latest development and future trend of this new technology with respect to the enzyme lipases, lipase reactions, and bioreactor systems. Particular attention is paid to the utilization of this technology in industrial production of functional fats and oils. A new topic of the reasearch work of an enzymatic reaction of conversion from diglycerides to triglycerides in crude palm olein is presented in detail.

ISSN:0193-2691    

DOI:10.1080/01932698908943187

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Fungal mycelia were found to be new and rich sources of C2O−-polyunsaturated fatty acids through our screening for wide variety of microorganisms. A soil isolate,Mortierella alpine1S-4 produced 4.3 g/L (274 mg/g dry mycelia) of arachidonic on cultivation in a medium containing glucose. The value accounted for more than 65% of the total fatty acids in the extracted lipids from the mycelia. The mycelial dihomo-gamma-linolenic acid content of the same fungus was found to increase, (107 mg/g dry mycelia), with an accompanying marked decrease in its arachidonic acid content, on cultivation with sesame oil. This phenomenon was found to be due to a specific repression of the conversion of dihomo-gamma-linolenic acid to arachidonic acid. The fungus produced eicosapentaenoic acid (EPA) when grown at low temperature (12 C). The experimental results with cell-free extracts showed that this temperature-dependent formation of EPA is due to the activation of enzymes(s) in EPA production, probably from arachidonic acid at low temperature. The fungus efficietly converted an oil containing alpha-linolenic acid to an oil containing EPA (yield, 1.8 g/L). This conversion was found to be temperature-independent. Possible advantages of microorganisms as practical sources of the polyunsaturated fatty acids are also described.

ISSN:0193-2691    

DOI:10.1080/01932698908943188

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor