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B. W. BARNES¹, M. Corredig, and L. Wicker. (1) Department of Food Science & Technology, University of Georgia, 1020 Cedar and East Campus Road, Athens, GA 30602

In the absence of a stabilizer, acid milk systems are unstable. Pectin is used in these products to prevent physical separation.

Three commercial pectins were investigated to develop an understanding of the relationship between acid milk dispersion stability/behavior and pectin characterization.

Acid milk dispersions (pH 4.1, 3.2% protein, 8.0 MSNF) containing one of three pectins at four concentrations, based on uronic acid content (0.11%, 0.21%, 0.32%, and 0.45%), were produced. After homogenization (2500 psi), half of the dispersions were pasteurized (75° C, 60 seconds). Particle size analysis was conducted at 1, 30, and 60 days. To measure stability, sedimentation levels after centrifugation (3000xg, 20 minutes) and a serum separation time study (60 days) were performed. Protein and uronic acid retention and particle size analysis using integrated light scattering were conducted on the supernatants from centrifugation to further assess stability. Supernatant and pellet proteins from centrifugation were analyzed using gel electrophoresis and quantified by image densitometry. Rheological properties of the dispersions were analyzed at 1 and 60 days of storage to determine fluid behavior and time dependency.

Pasteurization of dispersions containing 0.11% uronic acid led to instability, increased particle size, protein loss, and shear thinning behavior for all pectins. Particle size increased upon pasteurization for all samples. However, only a slight increase in sedimentation and no change in supernatant particle size was observed in dispersions containing > 0.11% uronic acid. Increasing uronic acid levels reduced the occurrence of sedimentation. Rheological behavior of the dispersions varied between uronic acid concentrations and the different pectins used.

While uronic acid concentration directly affects the stability of acid milk dispersions, differences observed in rheological analysis seem to be a better indicator of the molecular differences that exist between the pectins studied.