Crystallization freeze-dried lactose

Haque, K., and Roos, Y.H. (2005). Crystallization and x-ray diffraction of crystals formed in water-plasticized amorphous spray-dried and freeze-dried lactose-protein mixtures. Car-bohydr. Res. 340,293-301. 

Physical Structure, Water Plasticization, and Crystallization of Spray-Dried and Freeze-Dried Lactose... 

The Ter (onset) of spray-dried and freeze-dried materials obtained from dynamic DSC analysis are shovm in Figure 44.3 with respective water contents. The decreased with increasing water activities and water contents showing a similar behavior as Tg. T of freeze-dried lactose was higher than T r of spray-dried lactose in the anhydrous state and at all corresponding water contents (Figure 44.3). T for freeze-dried lactose was nearly the same as reported by Roos and Karel (1990) for freeze-dried anhydrous and humidified lactose over various RVP. Crystallization of lactose also occurred differently from differently dehydrated materials. 

Instant crystallization temperature (onset) for spray-dried and freeze-dried lactose as a function of water content, determined using DSC during heating at 5°C/min. 

The present study has shovm that spray-dried and freeze-dried lactose have different physical structures, thermal transitions, and time-dependent lactose crystallization behavior. Spray-dried lactose had round-shaped particles but freeze-dried lactose resembled broken glass or had a flakelike structure. Tg and Tq. of freeze-dried lactose were higher than those of... 

De Luca et al. [1.48] showed, that the addition of 5 % tertiary butyl alcohol (tBA) to aqueous sucrose and lactose solutions (up to 40 %) resulted in a frozen matrix, which could be easily freeze dried. De Luca demonstrated by DSC that the melting point rose distinctly (with 60 % solution to -10 °C), but the endothermic of melting returned to 25 %, indicating that not much water had frozen. In solutions with 5 % tBA the exothermic of crystallization became more visible and the melting of tBA could be recognized. 

Lactose may be obtained in two crystalline forms a-lactose and P-lactose (in addition to amorphous forms). The alpha form is obtained when water is incorporated into the lattice structure during crystallization (usually by supersaturation below 93.5°C) (5). Alternatively, the beta form does not contain water and exists as a non-hygroscopic and anhydrous form. Amorphous lactose is formed when either the crystallization is rapid or sufficient transient energy is introduced into the crystalline forms (74), i.e., spray drying (75), micronization and milling (76), freeze-drying, and anti-solvent crystallization (77). 

When a lactose solution is dried rapidly, its viscosity increases so quickly that crystallization cannot take place. The dry lactose is essentially in the same condition as it was in solution, except for removal of the water. This is spoken of as a concentrated syrup or an amorphous (noncrystalline) glass. Various workers have shown conclusively that lactose in milk powder (spray, roller, or freeze-dried) is noncrystalline and exists in the same equilibrium mixture of a- and /3-lactose as existed in the milk prior to drying (Zadow 1984). 

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