Effects of fat crystallization on the behavior of proteins and lipids at oil droplet surfaces

The effects of fat crystallization induced by thermal treatment on the rheo logical properties of creams and physical phenomena at the oil droplet surf aces were investigated. Creams A or B were prepared from commercial proprie tary fats A or B (vegetable oils with different triacylglycerol composition ) and aqueous solution containing proteins. Thermal treatment of the creams at the "critical temperatures" (temperatures inducing a small percentage o f solid fats in the oil droplets) caused a rapid increase of solid fat cont ents in the following cooling process. The thermal treatment of cream B at the "critical temperature" caused an increase of viscosity of the cream and an increase of protein surface coverage during the subsequent cooling proc ess. These results suggest that the oil droplet aggregation induced by the thermal treatment at the "critical temperature" and the subsequent cooling occurred via further adsorption of proteins. Electron spin resonance measur ement demonstrated the dramatic reduction of fluidity of triacylglycerol mo lecules at the oil droplet surface in cream B during the cooling process af ter thermal treatment at temperatures below "critical." Based on these resu lts, we speculated on the mechanism for the destabilization of thermally tr eated creams during the cooling process.