30A-9 |
Freeze-thaw stability of oil-in-water emulsions |
J. N. COUPLAND and S. Vanapalli. Department of Food Science, The Pennsylvania State University, 103, Borland Lab, University Park, PA 16802 Partial coalescence is an essential process in the manufacture of dairy foods such as ice cream and whipped toppings. In real food emulsions, this process occurs under fluctuating temperatures, and can have a considerable influence on the stability of the emulsion and hence the bulk properties of foods. The objective of the present work was to study the effect of oil composition, dispersed phase volume fraction, cooling rate and flocculation on the freeze-thaw stability of emulsions as a model for partial coalescence in dairy emulsions. The freeze-thaw stability of emulsions was determined by cooling samples (and/or temperature cycling) in a differential scanning calorimeter (DSC) from 40°C to -10°C at either 1.5°C/min or 5°C/min. The following factors were considered in the present study; oil type (n-hexadecane and confectionery coating fat, CCF), oil volume fraction (10-40 wt%) and different levels of flocculation (induced by adding 0-0.3 wt% xanthan gum). Creaming studies and thermal-scanning microscopy were also used to investigate similar samples. All hexadecane emulsions studied were stable to freeze-thaw cycling in the DSC, i.e. they showed a single peak (at -1°C) due to crystallization of the emulsified fat. In contrast the CCF emulsions showed two peaks at 3°C and 13°C corresponding to emulsified and bulk fat crystallization respectively. The high temperature peak was attributed to fat destabilization and was observed only after cooling at 1.5°C/min. The amount of fat destabilization (ratio of high-temperature peak enthalpy to total crystallization enthalpy) increased with the number of freeze-thaw cycles, the dispersed phase volume fraction and reached a maximum at levels of xanthan required to induce creaming. The micrographs obtained using a cold stage supported these observations. These studies provide insights into the mechanism of partial coalescence in emulsions and therefore allow better control of their bulk properties.
Session 30A, Food Chemistry: Lipids
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