Propylenated fatty acids as emulsifiers

In general, for a surfactant to act as an emulsifier, it must show good surface activity and produce a low interfacial tension in the particular system in which it is to be used. This means that it must have a tendency to migrate to the interface, rather than to remain dissolved in either one of the bulk phases (1 ). The emulsifiers were used to improve bread volume and texture, to extend shelf-life, and to control cookers spread factor (2). Various food products, such as butter, low fat spreads, shortening, chocolate, and margarine are waterin oil (W/0) emulsions and require emulsifiers to prevent separation (3-5). The degree of solubility of surfactants in water often suggests approximate hydrophilic lipophilic balance (HLB) values are indicators of behavioral characteristics and do not indicate emulsifying efficiency. The selection of a suitable emulsifier for an 0/W or a W/0 emulsion must be determined by experimentation. However a low HLB value (3-6) will promote or stabilize W/0 emulsion, an intermediate HLB value (8-13) will stabilize 0/W emulsion, and a high HLB value (15-18) will act as a solubilizer (6).


INTRODUCTION
In general, for a surfactant to act as an emulsifier, it must show good surface activity and produce a low interfacial tension in the particular system in which it is to be used.This means that it must have a tendency to migrate to the interface, rather than to remain dissolved in either one of the bulk phases (1 ).The emulsifiers were used to improve bread volume and texture, to extend shelf-life, and to control cookers spread factor (2). Various food products, such as butter, low fat spreads, shortening, chocolate, and margarine are water-in -oil (W/0) emulsions and require emulsifiers to prevent separation (3)(4)(5).The degree of solubility of surfactants in water often suggests approximate hydrophilic lipophilic balance (HLB) values are indicators of behavioral characteristics and do not indicate emulsifying efficiency.The selection of a suitable emulsifier for an 0/W or a W/0 emulsion must be determined by experimentation.However a low HLB value (3)(4)(5)(6) will promote or stabilize W/0 emulsion, an intermediate HLB value (8)(9)(10)(11)(12)(13) will stabilize 0/W emulsion, and a high HLB value (15)(16)(17)(18) will act as a solubilizer (6).

MATERIAL AND METHOD
-Hydroxy propylenyl fatty acids were prepared by adding propylene oxide slowly to fatty acid at 160 °C while stirring for five hours.-pH was measured with a pH meter (Corlan model SA 520).-Surface tension was measured in distilled water at room temperature (15 °C) with a (Sc-Du Nouy Interfacial Tensiometer Model 70545) (7).-HLB was determined as described in (9).-Viscosity and shear stress were determined with Bohlin Visco 88 B v according to (10).-Solubility was determined in different solvents, as water, ether, petroleum ether (40/60), n-Hexane, oil and ethanol.-Emulsifying power was determined according to Titus (11).-Infrared (IR) spectra were determined with Backman according to (12).

RESULTS AND DISCUSSION
The solubility of the mentioned emulsifiers in different solvents are recorded in table I where it can be seen that all emulsifiers are soluble in both oil and ethanol at 75 °C.Generally, hydroxy propenyl stéarate and palmitate are insoluble with different degrees in all solvents at 25 °C while they are soluble in oil and ethanol only at 75 °C and insoluble in the rest of solvents at this temperature.
Water seems not to be the suitable solvent for solubility of these mentioned emulsifiers.The insolubility of these emulsifiers in water suggests a non polar nature, while the solubility of some emulsifiers in oil indicate that these emulsifiers can be blended with lipids during formation of food system without employing organic solvents (13).Figure 1 shows that pH values of the five emulsifiers are alkaline in character which agree with those of (c) Consejo Superior de Investigaciones Científicas Licencia Creative Commons 3.0 España (by-nc) http://grasasyaceites.revistas.csic.essorbitol fatty acids reported by (14).Melting point, as shown in Figure 2, indicates that the value concerning hydroxy propylenyl stéarate is more or less double of those of laurate and palmitate, while oléate and linoleate are liquid emulsifiers.Surface tension of the five emulsifiers are drawn in Figure 3.Those of stéarate, linoleate and laurate are more or less the same as the value of hydroxy propylenyl palmitate while hydroxy propylenyl oléate shows the lowest value.Those results are in close agreement with sorbitol fatty acids reported by (14).Viscosity of hydroxy propylenyl stéarate is more or less double the value of those of linoleate and oléate.Hydroxy propylenyl laurate has the lowest viscosity value and that of palmitate is much higher than that of laurate (Figure 4).Shear stress of hydroxy propylenyl stéarate is about three times of that of linoleate and oléate and about four times of that of laurate and palmitate as refere in Figure 5. Emulsifying power values are given in Figure 6, which shows that all emulsifiers tested have more or less the same value.On the other side the HLB range from 3.4 HLB to 6.2 HLB (Figure 7) so these emulsifiers promote or stabilize W/0 emulsions (15,16).The relation between both shear stress to viscosity and emulsifying power to HLB are more or less parallel to each other as shown in Figures 8 and  9. From Figures (10-14), concerning the infrared spectra, it can be stated that:

Table I Solubility of some synthetic emulsifiers
-Broad band appears for streching vibration of 0-H group absorbed near 3600-3400 cm^-1.-Forked band for streching vibration band for C-H group absorbed near 3000-2800 cm^-1 for methylene and methyl groups.The symmetrical bending vibration for (CH3) occures near 1373 cm^-1 and assymmetrical bending vibration near MSOcm'^-l. ''111

Figure 14
Figure 12Infra red spectrum of hydroxy propylenyl laureate