Effects of varying casein and pectin concentrations on the rheology of high-protein cultured milk beverages stored at ambient temperature

摘要

Shelf-stable cultured milk beverages that have high protein levels can be difficult to successfully manufac-ture. With increasing protein level, rapid phase sepa-ration and gel formation occur in cultured beverages, which may not be prevented even with the inclusion of stabilizers such as high methoxy (HM) pectin. To limit protein aggregation in cultured milk beverages we in-vestigated micellar casein as an interesting alternative to milk, due to the absence of whey proteins, which can contribute to increased gel strength in cultured prod-ucts. In this study, micellar casein dispersed in ultrafil -tered milk permeate was fermented to pH 4.1, blended with HM pectin, homogenized, thermally processed, and bottled for storage at ambient temperature for 6 mo. Utilizing response surface methodology with a cen-tral composite rotatable design, the protein and pectin contents were varied between 5 and 9 and 0.0 and 1.0, respectively. The elastic modulus, loss tangent, and yield stress of these beverages were measured dur -ing storage to observe the extent of bond restructuring, whereas particle size and visual phase separation were measured to determine stability. Response variables were measured initially after thermally processing the beverages, and after 1 and 6 mo of storage at ambient temperature. All samples quickly formed gels after ho-mogenizing, regardless of the pectin level. The stiffness (elastic modulus) of all samples increased throughout storage and was determined mainly by the protein con -tent; however, the growth of elastic bonds over time was slowed with high levels of pectin. At 6 mo of stor-age, yield stress values were significantly lower for bev-erages with 0.85 pectin. Prediction models for visual phase separation in beverages stored for 6 mo were signifi-cantly affected by the protein content, with increasing instability at lower protein levels. Models were used to identify optimal protein (0.85) concentrations to minimize the stiffness of gels during ambient storage. Samples in this optimized region were predicted to have low yield stress values and were easily fluidized of the bottle at 6 mo.