The stability of whipped cream structure: The effect of heat treatment and the addition of stabilizer/emulsifier.

摘要

Whipping cream, with 35% butter fat, was high-temperature, short time pasteurized (75°C, 16s), and ultra-high temperature sterilized (140°C, 4s), with and without the addition of stabilizer/emulsifier, to study the effect of these processing conditions on the stability of foam structure. Processed creams were whipped to maximum overrun using a double beater system. Duplicate foams were refrigerated for 24 hours to compare with fresh foams. Low temperature scanning electron microscopy (LTSEM) was conducted to image foams and establish visual criteria for foam stability through quantitative stereology. Air bubble size, lamella length and volume fraction of air in the foam were calculated through computer assisted global measurement. Fresh foams were similar but significant differences in aged foam morphology were caused by heat treatment in both the stabilized and unstabilized foams. Results showed more large bubbles, thicker lamella and a higher volume fraction of air in aged HTST pasteurized foams compared to aged foam prepared from UHT sterilized cream. Rheological measurement of foam properties was then conducted by dynamic oscillatory testing to quantify visco-elasticity of foams structure to explain differences. Again, fresh foams were similar and differences were expressed in aged foams. Aging of stabilized foams caused a significant decrease in G′ (storage modulus) and G″ (loss modulus) values regardless of heat treatment. Differences due to heat treatment were expressed through tanδ (G″/G′ ) because of a proportionally higher value for G′ and greater dependence on frequency measured in the aged foam prepared from stabilized UHT sterilized cream. This result is indicative of lower visco-elasticity and less ability to withstand destabilization processes. Further work concentrated on study of the proteins in the foam to determine if the more severe heat treatment was affecting structure and therefore, the contribution of proteins to serum phase viscosity and integrity of bubble interface. It has been reported that β-lactoglobulin denatures above temperatures of 70°C and could account for loss of foam structure. However, electrophoresis (SDS-PAGE) did not show differences in the quantity of β-lactoglobulin or α-lactalbumin at the milk fat globule membrane (MFGM). Transmission electron microscopy did show differences in serum phase morphology with a loss in network structure caused by aging particularly in foam whipped from stabilized UHT sterilized cream.