Phospholipids colloidal properties

Surface-active lipids-colloidal properties of the phospholipids... 

Phospholipids. The phospholipids comprise approximately 1 % of the total lipid in bovine milk (ca.0.3 to 0.4 g/liter). While quantitatively minor, the ability of the phospholipids to form stable colloidal suspensions or emulsions in aqueous solution cause them to be important in the formation and secretion of milk fat. (Long and Patton 1978 Patton and Keenan 1975). Their physical properties as bipolar molecules and their relatively high concentration of unsaturated fatty acids also make them an important factor to consider during the storage and... 

The chapter has dealt with the stability and stabilisation of colloidal systems and covered topics such as their formation and aggregation. If the particle size of a colloidal particle determines its properties (such as viscosity or fate in the body), then maintenance of that particle size throughout the lifetime of the product is important. The emphasis in the section on stability is understandable. Various forms of emulsions, microemulsions and multiple emulsions have also been discussed, while other chapters deal with other important colloidal systems, such as protein and polymer micro- and nanospheres and phospholipid and surfactant vesicles. 

It was argued by some, early on in the story, that pol5water was simply impure water since boiling point elevation and freezing point depression are colligative properties characteristic of solutions. However, the flurry of papers emphasized the precautions that had been taken to avoid contamination, so for several years the existence of polywater was taken for granted as a real phenomenon. However, eventually the case for polywater began to crumble. Because it could only be formed in quartz capillaries of very small internal diameter, very little was available for analysis. When eventually small samples could be subjected to trace chemical analysis, polywater was shown to be contaminated with a variety of substances from silica to phospholipids. Moreover, electron microscopy revealed that polywater also contained finely divided colloidal particulates in suspension. 

Lipids exist in most foods as multiphased colloidal systems bound by surface-active phospholipids, proteins and emulsifiers. The oxidative stability of food lipids is greatly affected by the partitioning of the lipid substrates, metal initiators and antioxidants, which is complex and depends on the physical properties of the food. We may consider three types of food systems (see Chapter 10) ... 

Artificial lipid vesicles, termed liposomes, are colloid particles in which phospholipid bilayers or tetraether monolayers encapsulate an aqueous medium. Because of their physicochemical properties, liposomes are widely used as model systems for biological membranes and as delivery systems for biologically active molecules. In general, water-soluble molecules are encapsulated within the aqueous compartment whereas water insoluble substances may be intercalated into the liposomal membrane [147]. 

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