Effect of high hydrostatic pressure on lipid crystalline structure in palm stearin emulsions

Lipid crystal structures (polymorphs) are the determinant factors for sensorial,textural properties and the stability of the emulsions. Therefore, controlledcrystallization gains importance during the production of foods such as margarine,confectionery, chocolate, etc. In literature, studies on the effect of high hydrostaticpressure (HHP) on lipid crystallization have contradictory results. To inspect thecrystallization characteristics and response to the HHP treatment, palm stearinwateremulsions were prepared with two different emulsifiers (sodium caseinateand hydrogenated soy lecithin-xanthan gum mixture) and pressurized at 100 and500 MPa, at 10, 20 and 40°C for 15 minutes. Particle size analysis, differentialscanning calorimetry (DSC), transverse relaxation time (T2) and self-diffusioncoefficient (SDC) determinations and small angle x-ray scattering (SAXS) wereconducted to investigate the changes induced by HHP treatment. According to theresults, HHP did not affect droplet size of sodium caseinate (SC) emulsions so it was observed that mean particle size was affected only by the types of emulsifiersand storage time. In addition, sodium caseinate has the capability to produce smallerparticles than 80H_XG emulsion. HHP has no significant effect on the meltingtemperature of polymorphs; but pressure and storage time have significant effect oncrystal polymorphs' content in emulsions. HHP induced formation of more stableβ crystals in both sodium caseinate and soy lecithin-xanthan gum mixtureemulsions. In addition to this, HHP also induced solid wall formation in soylecithin-xanthan gum mixture emulsions. Changes in α and β contents with respectto pressure and storage time were detected by T2 and SDC measurements. Thesefindings suggested that the beginning of emulsions' destabilization can be detectedby NMR measurements. The pressure effect may easily be seen in the ab-initiostructural model with SAXS measurements. The pressure application caused astructural change from spherical form to cylindrical form in sodium caseinate (SC)solution and SC emulsion droplets reached more compact spherical likeaggregations.