Effects of soy-to-milk protein ratio and sucrose fatty acid ester addition on the stability of ice cream emulsions

• The stability of ice cream emulsions with different protein composition was studied.
• Destabilization depended on protein surface activity and protein-emulsifier interactions.
• Soy protein isolate increased the flocculation of fat droplets during pasteurization.
• Partial coalescence degree correlated with protein load for emulsions with sucrose ester.
• The crystallization of emulsified fat was influenced by the soy-to-milk protein ratio.

The protein composition and emulsifier adsorbed at the oil/water interface are very important in controlling the stability of fat droplets. In this study, the effect of soy-to-milk protein ratio in the presence or absence of sucrose fatty acid ester on the stability of ice cream emulsions was investigated. Parameters such as particle size distribution, dynamic surface pressure, surface protein adsorption, rheological properties and crystallization behavior of fat in the bulk and emulsified state were determined. The results indicated that destabilization of fat droplets depended on the protein surface adsorption activity, protein–protein and protein-sucrose fatty acid ester interactions at the interfacial layers. The addition of soy protein isolate significantly increased the flocculation of fat droplets during pasteurization. Emulsions containing sucrose fatty acid ester were distinguished by a higher partial coalescence degree (19.8–252.7%) of fat droplets compared to emulsions without sucrose fatty acid ester (5.5–37.3%) with the same protein composition. The particle size and adsorbed protein results showed a direct negative relationship between protein surface coverage and partial coalescence degree for emulsions with sucrose ester. The increased protein coverage when the soy-to-milk protein ratio was above 5:5 probably resulted from the enhanced protein–protein interactions. The supercooling needed for detection of crystalline fat was found to increase with the increase in soy-to-milk protein ratio up to 7:3. However, no significant correlation was found between the proportion of crystallized fat content and partial coalescence degree. These findings provided a theoretical basis for controlling the stability of aerated food emulsions with soy/milk protein mixture.

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