The Freeze-Thaw Stability of Mayonnaise and the Effect of Octenyl Succinic Anhydride ModifiedStarch as Emulsifier

Abstract: Mayonnaise is a very popular food emulsion, traditionally made out of water, oil, hen egg yolk and vinegar, throughout the world. However, the quality is often reduced by separation when exposed to environmental stress, such as freeze-thawing which is an issue during transportation through regions of varying climates. The egg yolk proteins in the mayonnaise fail to keep the emulsion stable, thus limiting the freeze-thaw stability for longer time periods. Starches which are hydrophobically modified by octenyl succinic anhydride (OSA-starch) could generate a more freeze-thaw stable emulsion due to their higher molecular weight which generates a thicker layer on the oil droplets if adsorbed. The purpose of this master thesis was to investigate how freeze-thaw stability in mayonnaise could be increased and whether OSA-starch could provide a stabilizing effect in this context. The different parameters investigated included the size of the tubes in which the emulsions were frozen, pH at the time of emulsification, the amount and type of oil, preprocessing and amount of OSA-starch as well as the amount and type of egg yolk powder. Emulsions were prepared according to a standardized method, freeze-thawed and analyzed visually and in a microscope. The surface load of OSA-starch and egg yolk proteins at the interface of emulsions was determined according to the method of Aman (1994) and with BCA protein assay. Large variations were observed, thus limiting the possibility to draw conclusions from these results.Mayonnaise with rapeseed oil showed lower freeze-thaw stability than sunflower oil, most likely because of its tendency to form large ƒÀ-crystals in combination with having a higher degree of solid fat at -25‹C. Decreased oil content in mayonnaise generated higher freeze-thaw stability, probably because of lower collision frequency of the oil droplets. The size of the tubes used in this study did not appear to affect the freeze-thaw stability. An emulsion prepared at pH 3.5 showed a higher surface load of OSA-starch and egg yolk proteins but no increased freeze-thaw stability. This could potentially be explained with the surface layer being too thin or that OSA-starch just does not increase the freeze-thaw stability. An emulsion prepared with OSA-starch as the sole emulsifier demonstrated an increased surface load of OSA-starch at both pH 6.5 and 3.5 and maintained freeze-thaw stable after 7 days in the freezer. One possible explanation to these results is the lack of competitive adsorption from egg yolk proteins and the fact that the system is less complex with fewer components. In conclusion, a 56 % emulsion with OSA-starch as the sole emulsifier resulted in a very stable emulsion. It is without doubt that o/w emulsions stabilized with egg yolk is a very complex system. More research concerning egg yolk and its behavior during emulsifying and freeze-thawing of o/w emulsions is of great interest as it could generate new solutions and innovations in the production of food emulsions.