The physical characteristics of milk powders used in chocolate can have significant impact on the processing conditions needed to make that chocolate and the physical and organoleptic properties of the finished product. Four milk powders with different particle characteristics (size, shape, density) and "free" milk fat levels (easily extracted with organic solvent) were evaluated for their effect on the processing conditions and characteristics of chocolates in which they were used. Many aspects of chocolate manufacture and storage (tempering conditions, melt rheology, hardness, bloom stability) were dependent on the level of free milk fat in the milk powder. However, particle characteristics of the milk powder also influenced the physical and sensory properties of the final products.

Mixtures of model lipid systems containing highmelting and low-melting lipid classes were crystallized and microscope images obtained for analysis of crystal morphology and microstructure. Rheological properties of these semisolid systems were tested by use of a texture analyzer. The nature of the highmelting component in a mixture dominated the crystal morphology and, combined with interactions between crystalline and liquid materials, resulted in different microstructures that influenced the rheological properties. In addition to size, shape, and amount (solid fat content) of crystalline material, the crystal packing density, representing how densely the crystalline particles in every level (individual, aggregate, or floc) were arranged, and the nature (or strength) of the link (or bridge) connecting the crystalline particles were important microstructural factors to determine rheological properties. Depending on different crystal packing densities and linking bridges, two different systems were identified in terms of microstructure type-mobile and immobile-in which the relative mobility of microstructural components had different levels. These mobility levels led to different rheological responses.Paper no. J10975 in JAOCS 82, 399-408 (June 2005).The interactions between TAG solid and liquid phases significantly affect the properties and functionality of semisolid lipid systems. The quality, texture, and shelf stability of lipid-based products, such as butter, margarine, shortenings, chocolate, and compound coatings, are dependent on the lipid crystalline microstructure. Controlling formulation and processing variables in these products to obtain a desired structure will allow us to control their properties. Natural lipids are complex, containing sometimes up to hundreds of TAG. However, most fats can be described as a combination of a limited number of solid and liquid lipid classes that cover the major TAG components. Thus, studying welldesigned lipid classes will allow us to better understand the complex relationships among lipid composition, crystallization parameters, crystalline microstructures, and product textural properties (1-4). Products made with lipid materials of apparently the same physical properties [solid fat content (SFC), m.p., etc.) may result in very different textural properties. The reason for these differences must be in the nature of the crystalline structure formed during processing and storage, but the methods to quantify these different crystalline structures have been limited (5).Correlations have been developed among the structural attributes, rheological properties, and organoleptic characteristics of various foods (6-8). However, because of the complexity of TAG composition in natural lipids, it is often difficult to predict their physicochemical characteristics. The macroscopic rheological properties of the crystalline network structure are influenced by all levels of structure (the individual TAG, crystalline units, agglomerates, microstructural network, etc.) defined during ...

The crystallization of alpha-lactose monohydrate in a continuous cooling crystallizer was investigated at various temperatures and supersaturations. The population balance model was used to analyze the product crystal size distribution as determined by the Coulter MultiSizer for each condition studied. Nucleation and growth values were thereby determined for each temperature and supersaturation. Kinetic models were then developed for both nucleation and growth to demonstrate the effects of the operating parameters. The results showed that the nucleation process had a temperature dependence with an activation energy of 17.0 kcal/mole and that nucleation increased with the 1.9 power of supersaturation and the 1.0 power of the suspension density (mass of crystals). The growth process was found to have a temperature dependence with an activation cncrgy of 22.1 kcahmole and to be a second order function of the supersaturation.

No abstract

The continuous crystallization kinetics for lactose have been determined. Specifically, a model incorporating the effects of growth rate dispersion (GRD) on particle dynamics has been employed to determine continuous crystallization kinetics from experimentally determined size distributions. The existence of GRD was verified by the excessive number of fines (C 50 pm) observed. Crystal size distributions were successfully modeled using a two component rate distribution indicating the existence of two distinct types of nuclei. These could be classed as fast-growers (product crystals) and slow-growers (fines). Nucleation and growth kinetics of these populations were determined and compared to other methods of determining kinetics.