I. Microencapsulation: Definition and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477 II. Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 III. Role of Emulsion Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479 B. Fat: Globule Size, Content, and Melting Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479 C. Emulsifier: Milk Protein Content, Type (Sodium Caseinate, Whey

Protein Powders, Skim Milk Powder) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480 D. Filler: Lactose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 E. Milk Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 F. Crystallization of Lactose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 G. Alternative Emulsifier-Fillers: Gum Acacia, Lipophilized Starches . . . . . . . . 481 H. Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

IV. Role of Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 A. Homogenization: Pressure, Number of Passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 B. Spray Drying Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

I. MICROENCAPSULATION: DEFINITION AND TERMINOLOGY

Emulsions, which have been stabilized by homogenization in the presence of an emulsifier, can be spray-dried to produce microencapsulated fat powders. Proteins, modified starches, or a hydrocolloid can be used as emulsifying agents. A non-emulsifying water-soluble material such as sugar or hydrolyzed starch is also used as filler. Combined emulsifying-filler agents such as modified starches or Acacia gum can also be used [1]. A comparison between

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a homogenized fat globule and a microencapsulated fat powder particle is shown in Figure 1. Fat globules, which have been homogenized in the presence of milk proteins, have a median particle size of 0.5 µm or less depending on the homogenization pressure and number of passes and an adsorbed protein layer that is 50 to 200 nm thick [2]. The prefix micro implies that all or at least 90% of the globules should be <1 µm. By contrast, spray-dried microencapsulated fat powder particles have a median particle size of 35 to 75 µm or greater. The oil globules in the powder particles retain the layer(s) of adsorbed emulsifier during drying, and in turn are embedded in a continuous phase of inert filler. In the U.S. literature, especially, fat is referred to as the core material and the emulsifier and inert filler as the wall materials. Any fat can be used as core, which implies that one of the wall materials must have emulsifying properties. Spray-dried powder particles also contain a large central vacuole up to 15 µm or more in diameter with small to medium-sized vacuoles in the wall [3]. One advantage of microencapsulation is that any fat or oil can be converted to powder form, using any emulsifying or filler materials of choice. Low levels of fat on the surface of the spray-dried particles should result in better powder flow properties or the production of higher fat powders using conventional dryers. Avoiding contact between the fat core and prooxidant materials present such as atmospheric oxygen should extend the shelf life of the powder product.