BEST MIXING PRACTICES TO MINIMIZE THE PARTICLE SIZE IN RECONSTITUTED NONFAT DRY MILK

Abstract

ABSTRACT The objective was to determine processing parameters that would minimize the particle size of reconstituted nonfat dry milk (NDM). Four mixing parameters were evaluated: equipment (blender versus recirculation), shear rate (high versus low), mixing temperature (4 versus 22C) and holding temperatures (4 versus 22C). In a second experiment, lab-scale homogenization and pH adjustment were evaluated. NDM reconstituted in a blender at 22C had the smallest particle sizes (0.133 to 0.135 µm). Shear rate did not affect particle size. Homogenization induced multimodal particle size distributions within a single dispersion, and this effect was exacerbated if the reconstituted NDM was adjusted to pH 5, 6 or 7. Changes in casein micelle structure may explain the effect of homogenization on particle size. PRACTICAL APPLICATIONS Mixing practices vary in a manufacturing setting, and this work shows that the particle size in reconstituted nonfat dry milk (NDM) was minimized using blender-style equipment and ambient temperatures (22 versus 4C). Homogenization is a process step used to manufacture beverages as it aids ingredient mixing and component interactions, and potentially extends stability. But in this work, homogenization induced aggregate formation of smaller-sized particles in reconstituted NDM. At a beverage pH of 5, the aggregates destabilized the beverage, but this was not observed in beverages from pH 6 to 7. Thus, in the formulating and processing of dairy-based beverages, homogenization should be evaluated for impact on overall stability.