Lactose spray-dried systems

Different localized levels of molecular order can coexist in some pharmaceutical materials, giving rise to the occurrence of partially crystalline (and partially amorphous ) systems. In most cases, the properties of such materials (e.g., density) are intermediate to those of the 100% amorphous and 100% crystalline samples. By deliberately varying the level of crystallinity in such systems, their properties can be customized for a particular purpose. An example of this is with the tableting excipients microcrystalline cellulose and spray-dried lactose, which have had their compression characteristics optimized by manipulating their amorphous content. The properties of partially crystalline materials may be approximated in many instances by making physical mixtures of the totally amorphous and crystalline samples. This is known as the two-state model for partially crystalline systems.However, such experiments should be undertaken with caution as the mixed two-state material can sometimes have significantly different properties from the partially crystalline material that is manufactured directly (the real one-state system). ... 

Gustafsson et al. used SSNMR and isothermal microcalorimetry to investigate the amorphous component of lactose. In general, the detection limits for crystalline forms are much better than for amorphous forms due to the much broader resonances characteristic of disordered systems. The two techniques were found to be in agreement with each other in the characterization of the degree of disorder in the system. Completely amorphous lactose (prepared by spray drying) was mixed with completely crystalline lactose monohydrate... 

The recrystallization of amorphous low molecular weight systems can be convoluted by the impact of structural changes on the material. For example, spray drying a-lactose monohydrate typically produces a material that is completely amorphous as determined... 

DuVall RN, Koshy KT, Dashiell RE. Comparative evaluation of dextrose and spray-dried lactose in direct compression systems. J Pharm Sci 1965 54 1196-1200. 

Figure 2 The dynamic vapor sorption chart for lactose. A humidity-induced recrystallization event of spray-dried lactose is marked. Steps refer to relative humidity changes. Source Courtesy of Surface Measurement Systems (1).

A hybrid membrane system used for processing milk may entail MF, UF, NF/RO and ED. Cheese whey, a by-product during cheese production, was traditionally concentrated by evaporation and spray drying. Membrane filtration was successfijl because it not only reduced energy and processing costs, it also improved product properties minimal protein denaturation as a consequence of lower process temperatures. Further, since UF both concentrated proteins and removed lactose and salt simultaneously. 

The retention or loss of aroma compounds is also influenced by the structure (amorphous or crystallized) of the dried product Structural changes can be used for spray drying encapsulation processes (Bhandari et al., 1992 Re, 1998). Crystallization tends to increase the loss of aroma, because it rejects impurities, including volatiles. Senoussi et al. (1995) measured the loss of diacetyl as a function of the rate of crystallization of lactose during storage. They found that when the lactose was stored at 20 °C above the glass transition temperature Tg, the amorphous product immediately crystallized and practically all diacetyl was lost after 6 days. Levi and Karel (1995) also found increased rates of loss of volatile (1-n-propanol) as a result of crystallization in an initially amorphous sucrose system. 

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