High-shear blending optimizes dairy-based beverage.

The quality of a beverage is often directly correlated to the size of the particles of which it is composed. Larger particles will precipitate faster. Research indicates that mixing equipment, water temperature and shear rate all affect the size of the particles, and thus directly contribute to the quality of the beverage, and how well it is accepted by consumers.

Scientists at Kansas State University wanted to determine the best mixing conditions that would lead to the smallest casein size, the least sedimentation and the least foam production of reconstituted nonfat dry milk (NFDM). The researchers examined the impact of a range of variables, including high-shear blending and recirculation equipment, water temperatures of 4 C and 22 C, and high-and low-shear rates. They found that the mixing approach that would best improve the shelf life of dairy-based beverages appears to be high-shear blending at 22 C.

The investigators reconstituted NFDM with distilled deionized water to 11% w/v at 4 C for all treatments. A randomized block design was used with four replications. Particle size was measured on a commercial laser scattering particle size distribution analyzer on the day of mixing. The researchers monitored sedimentation for seven days after mixing. Foam volume and stability were measured for two hours after mixing as well.

High-shear blending at 22 C produced the smallest casein size-0.155 [micro]m-without any sedimentation, but a moderate amount of stable foam. Overall, higher shear rates resulted in smaller casein sizes (2%) than the lower shear rates did after mixing. NFDM reconstituted at 4 C had larger casein sizes (3.6%) than NFDM reconstituted at 22 C.

The investigators did not see any sedimentation for any treatment. Foam stability was the greatest when using high-shear blending at 22 C. Foams produced using the recirculation method were low in volume and unstable.

Further information. Karen Schmidt, Food Science Institute, Department of Animal Sciences and Industry, Kansas State University, 224 Call Hall, Manhattan, KS 66506; phone: [phone]; email: [e-mail].