Rheological properties of creme fraiche affected by conditions of the cream.

Creme fraiche--a heavy cream slightly soured with bacterial culture, but not as sour or as thick as sour cream--is produced by the fermentation of pasteurized and homogenized cream. Some believe that the cream obtained from different suppliers may influence the properties of creme fraiche.

Scientists at California Polytechnic State University believe that differences observed in the rheology of creme fraiche can be related to the thermal history and homogenization conditions of the cream. The researchers wanted to determine if there is a relationship between cream homogenization and pasteurization conditions and the viscoelastic properties--the elastic modulus and viscous modulus--of creme fraiche. They found that the homogenization and pasteurization conditions of the cream indeed impact the viscous and elastic properties of creme fraiche. This information can improve our ability to select cream processing conditions that help control the texture of this product.

In their experiments, the scientists used a randomized 2x2 factorial experimental design that involved a two-stage cream homogenization at 10.3/3.5 MPa or 13.8/3.5 MPa, and high-temperature short-time cream pasteurization at 74.4 C or 80 C for 15 seconds. Each treatment was run in triplicate.

After the treatments, the investigators inoculated each batch with a lactic culture. Each was transferred to 120 mL cups and fermented at 20 C until a pH of 4.5 was reached, which took approximately 18 hours. The researchers then cooled the samples at 4 C for 48 hours before rheological analysis.

The scientists lightly stirred the samples before they tested them. Oscillatory frequency sweep measurements from 1Hz to 100 Hz were performed using a controlled-stress rheometer equipped with cone-and-plate geometry at a 0.5% strain. The temperature was maintained at 10 C. An orthogonal polynomial model was used to fit the frequency sweep curves for analyzing the elastic viscous moduli of creme fraiche.

There were significant differences in the elastic modulus of creme fraiche caused by the different pasteurization treatments and homogenization treatments. There also was a significant difference in the viscous modulus caused by the different homogenization treatments.

Further information. Phillip Tong, Department of Dairy Science, California Polytechnic State University, Building 18, Room 100, San Luis Obispo, CA 93407; phone: [phone]; email: [e-mail].