Wettability of milk powders,

There is little or no information in the literature on the role of milk-fat on the bulk density, scortched particles, wettability, dispersibility and flowabil-ity of milk powder. Tuohy (1989) found considerable differences between the packed bulk density of regular SMP (0.85 g/cm3), WMP (0.68 g/cm3) and fat-filled milk powder (0.47 g/cm3). The packed bulk density of fat-filled... 

Milk powder particles <100 pm in size are often difficult to wet and tend to become lumpy when dispersed in water (Schubert, 1987). Hence, milk powder is agglomerated during manufacture to make the powder instantly wettable in warm (>45°C) water. Agglomeration is the process of forming porous clusters of powder particles to increase the volume of occluded air, thereby increasing its dispersibility and making the powder... 

Powder characteristics of a physico-chemical nature, such as solubility, wettability, dispersability, and measures of the instant properties of powders (sludge, slowly dispersible particles, hot water sediment and coffee test), are determined by a variety of empirical physical tests, some of which incorporate subjective elements. These and the other tests for whole milk powders identified above are described in detail by Westergaard (1994) and Pisecky (1997). 

Lecithin is used to improve the wettability and dispersibihty of various milk powders including whole milk powder (229, 230) and casemates (231). Oldfield et al. (232) demonstrated that lecithinated whole milk powder had increased coffee stability, with decreased coffee sediment levels over a water hardness range of 0-308 mg/L. 

The physicochemical state of fat in milk powder particles, which markedly influences the wettability and dispersibility of the powder on reconstitution, depends on the manufacturing process. The fat occurs either in a finely emulsified or in a partly coalesced, de-emulsified state. In the latter case, the membrane has been ruptured or completely removed, causing the globules to run together to form pools of free fat. The amount of de-emulsified free fat depends on the manufacturing method and storage conditions. Typical values for free fat (as a percentage of total fat) in milk powders are spray-dried powders, 3.3-20% roller-dried powders, 91.6-95.8% freeze-dried powders, 43-75% foam-dried powders, less than 10%. 

The replacement (partly) of maltodextrin by sucrose led to more regular particles and better powder wettability. Flowability and regular shape of skim milk powder were better than that of whole milk due to absence/presence of fat. 

Sizes are additives that decrease the wettability of the paper for certain applications (printing with aqueous inks, manufacturing of milk cartons and paper cups). - Rosin (gum rosin, wood rosin or tall oil rosin) in the form of its sodium or potassium salt or as free acid are used as powder, solution or dispersion. They are excellent sizes, which are used together with alum to develop lull sizing power. Reaction products of rosin with maleic anhydride or fu-maric acid (fortified sizes) are more effective. They are saponified and used as pastes or dispersions. Free rosin emulsions are the newest and most effective sizes. For ordinary rosin 15-20 kg are necessary per mt of paper, fortified rosin requires 5-8 kg/mt and free rosin emulsion only 2-4 kg/mt to get the same effect. 

The state of fat in powder has a major influence on wettability, i.e. the ease with which the powder particles make contact with water. Adequate wettability is a prerequisite for good dispersibility. Free fat has a water-repelling effect on the particles during dissolution, making the powder difficult to reconstitute. Clumps of fat and oily patches appear on the surface of the reconstituted powder, as well as greasy films on the walls of containers. The presence of free fat on the surface of the particles tends to increase the susceptibility of fat to oxidation. A scum of fat-protein complexes may appear on the surface of reconstituted milk the propensity to scum formation is increased by high storage temperatures. 

---