Lecithin aqueous dispersion

Manufacturing techniques employed in producing instant products include spray-coating dry powders with fluid lecithin products, cospray drying powders with more hydrophihc lecithins such as the oil-free forms, or hydroxylated lecithin, and agglomeration of the powder with an aqueous dispersion of a hydrophihc lecithin. Some types of powders, for example, starches, gums, and chocolate drink mixes, require agglomeration with an aqueous dispersion of lecithin to achieve optimum wettabihty and dispersibility. 

Continuous, multipurpose ovens that are used to precook foods may use water-filled dip tanks for cleaning and rinsing the conveyor belt. An aqueous release system, containing a water-dispersible lecithin, is added to the dip tank to facilitate release of the food from the oven belt, as well as promote better rinsing and cleaning during cooking. A 10% aqueous dispersion of lecithin is commonly used for this application (224). 

Lecithin has some catalytic or cocatalytic effects in multiphase systems because of its surface-active properties. Lecithin is reported to be useful as an emulsifier in the curing of aqueous dispersions of unsaturated polyesters (337). The products are more easily removed from their molds and have improved mechanical properties when lecithin is used. In a fermentation application, 1.5% soybean lecithin acts as an inducer in the preparation of cholesterol esterase using a strain of Pseudomonas bacteria (338). Aside from its role as a catalyst, initiator, or modifier, lecithin may have ancillary uses in catalyst systems as part of a protective coating (339). 

Fluorometric and spectrophotometric studies of filipin-cholesterol interaction showed that the stoichiometry of the interaction was 1 1 [150] or 1 1.5 [146,147]. UV spectrophotometry changes have been used to monitor the stoichiometry of the interaction between filipin and free or liposome-bound cholesterol. Analysis of aqueous dispersions suggested that the stoichiometry was 1 1 [171]. Lecithin, dicetyl phosphate-cholesterol liposomes only produced maximal spectral changes of filipin when the sterol polyene ratio was 1 1 [172]. Filipin released trapped ion markers from sterol—phospholipid liposomes. The rate of release was dependent upon cholesterol content of the liposome membrane (maximum at sterol phospholipid ratio of 1 1) and upon the molar fllipin sterol ratio (maximum at fllipin sterol ratio of 1 1). 

Phospholipids contribute specific aroma to heated milk, meat and other cooked foods through lipid oxidation derived volatile compounds and interaction with Maillard reaction products. Most of the aroma significant volatiles from soybean lecithin are derived from lipid decomposition and Maillard reaction products including short-chain fatty acids, 2-heptanone, hexanal, and short-chain branched aldehydes formed by Strecker degradation (reactions of a-dicarbonyl compounds with amino acids). The most odor-active volatiles identified from aqueous dispersions of phosphatidylcholine and phos-phatidylethanolamine include fra 5 -4,5-epoxy-c/5-2-decenal, fran5,fran5-2,4-decadienal, hexanal, fra 5, d5, d5 -2,4,7-tridecatrienal (Table 11.9). Upon heating, these phospholipids produced cis- and franj-2-decenal and fra 5-2-undecenal. Besides fatty acid composition, other unknown factors apparently affect the formation of carbonyl compounds from heated phospholipids. 

Many substances as found in nature (lipids) exhibit unique properties in aqueous media. Some lipids (such as lecithins or alike), when dispersed in water, form very well-defined assemblies, in which the alkyl part of the molecule is in close proximity to each other. This leads to self-assembly formation with many important consequences. 

The lecithin serves as an emulsifying agent that allows the aqueous and lipid phases to be dispersed in each other and increases the time required for phase separation. 

Soybean lecithins can be chemically altered to modify their emulsifying properties and improve their dispersibihty in aqueous systems. Phospholipids may be hydrolyzed by acid, base, or enzyme to achieve better hydrophilic and emulsification properties. Hydroxylation of lecithin improves its oil-in-water emulsification property and water dispersibihty. Acetylation creates improved fluidity and emulsification, water dispersion properties, and heat stability (200). 

Modified lecithins. Lecithins may be modified chemically, e.g., hydrogenation, hydroxylation, acetylation, and by enzymatic hydrolysis, to produce products with improved heat resistance, emulsifying properties, and increased dispersibility in aqueous systems (7, 58, 59). One of the more important products is hydroxylated lecithin, which is easily and quickly dispersed in water and, in many instances, has fat-emulsifying properties superior to the natural product. Hydroxylated lecithin is approved for food applications under Title 21 of the Code of Federal Regulations 172.814 (1998) (60). 

Solubilization. Most lecithins can aid in the production of microemulsions, an example being oil-soluble flavors in aqueous systems. Although standard-grade lecithins do not disperse in water, many modified or fractionated lecithins are water-dispersible, and they can be used to produce microemulsions. Standard-grade lecithin can be blended with other surfactants (e.g., ethoxylated monoglycerides) to produce synergistic emulsifier blends that are also effective in producing microemulsions. 

Metal salts of lecithin have been patented as paint additives (435). These salts are reported to improve pigment dispersion, and act as drying promoters and inhibit yellowing of the product. The same patent also promotes the use of phosphorylated lecithin as a rust inhibitor in primer paints. Further, if metal oxides are chemically reacted with lecithin by heating, the dispersibility of metal oxides in both aqueous and organic solvents is improved (436). 

In the literature, the reported use of zeta potential measurement for non-aqueous suspensions is relatively infrequent because non-aqueous suspensions only represent a small percentage of all medicated suspensions. Su and others evaluated the flocculation-deflocculation behavior of cefazolin sodium in non-aqueous media and the effect of surfactants as measured by zeta potential along with sedimentation and porosity measurements. A significant difference in zeta potential was observed when the particles were dispersed in peanut oil and ethyl oleate. The addition of lecithin reduced the zeta potential of cefazolin sodium, resulting in a deflocculated state accompanied by a decrease in sedimentation volume. The effect of surfactant... 

All parenteral emulsions are oil-in-water formulations, with the oil as the internal phase dispersed as fine droplets in an aqueous continuous phase. An emulsifier, usually egg or soy lecithin, is needed to lower the interfacial tension and prevent flocculation and coalescence of the dispersed oil phase. Mechanical energy, usually in the form of homogenization, is required to disperse the oil phase into droplets of a suitable size. For IV administration, the droplet size should be below 1 p.m to avoid the potential for emboli formation. 

Emulsifiers to facilitate the formation/dispersion of oil drops (glycerides, proteins, lecithin, etc.). They are adsorbed on the periphery of oil drops (interface oil/aqueous phase), to decrease the surface tension of the drops and to form a barrier to prevent their coalescence. They are amphiphilic molecules including both hydrophilic and lipophilic groups. They may have a role of protection against oxidation. 

Fig. 14. Schematic depiction of selected physical and chemical events during fat digestion. The 1- and 3-ester linkages of triglyceride (upper left) are cleaved by lipase, forming 2-monoglyceride and fatty acid. These lipolytic products leave the oil-water interface and are dispersed in the aqueous phase as mixed bile acids-lipolytic product micelles. A proposed molecular arrangement of the bile acid-lipolytic product micelle is shown in cross-section this model is based on studies of the bile acid-lecithin micelle (65). In this model, the hydrophobic back of the bile acid molecule apposes the paraffinic chains of the lipolytic products, and the hydroxy groups of the bile acid molecule are toward the aqueous phase. The paraffin chains of the interior of the micelle are liquid, thus permitting other water-insoluble molecules such as cholesterol and fat-soluble vitamins to dissolve in the micelle. Indeed, the solvent capacity of the bile acid-lipolytic product micelle is contributed chiefly by the paraffin chains of the lipolytic products.

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