Influence of morphology and polymorphic transformation of fat crystals on the freeze-thaw stability of mayonnaise-type oil-in-water emulsions

•Destabilization mechanisms of O/W emulsion by freeze-thawing were proposed.•Partial coalescence was clearly observed in canola oil in water emulsion.•Soybean oil in water emulsion was destabilized by polymorphic transformation of fat crystals.

This study examined the destabilization of an oil-in-water (O/W) emulsion by freeze-thawing with a focus on the influence of the morphology and polymorph of fat crystals. For a model of food emulsion, this study used a mayonnaise-type O/W emulsion containing 70 wt% canola oil (canola emulsion) or soybean oil (soybean emulsion) stored at − 15, − 20, and − 30 °C. The freeze-thaw stabilities of the emulsions were evaluated by measuring the upper oil layer after freeze-thawing. The soybean emulsion kept at − 20 °C had the highest stability; the other emulsions were destabilized during 6 h of storage. Crystallization in the emulsions was determined using differential scanning calorimetry (DSC), time variation of temperature, X-ray diffraction measurement, and polarized light microscopy. DSC thermograms indicated that crystallization in emulsions occurred first in the high-melting fraction of oil, followed by water and, last, in the low-melting fraction of oil during cooling to − 40 °C. In the canola emulsion, the amount of fat crystals derived from the low-melting fraction of oil increased during storage at all temperatures, resulting in partial coalescence. The soybean emulsion was expected to be destabilized by polymorphic transformation (sub-α to β′ and β) of fat crystals derived from the high-melting fraction during storage at − 15 and − 20 °C. However, the soybean emulsion did not exhibit polymorphic transformation stored at − 30 °C, and the amount of fat crystals did not increase during freezing; thus, it was destabilized via a different mechanism.

Graphical abstractDownload high-res image (222KB)Download full-size image