Crystallization of amorphous lactose

KNUDSEN J c, ANTANUSE H s, RisBO j and SKIBSTED L H (2002) Induction time and kinetics of crystallization of amorphous lactose, infant formula and whole milk powder as studied by isothermal differential scanning calorimetry, Milchwissenschaft, 57, 543-546. 

The sorption behaviour of a number of dairy products is known (Kinsella and Fox, 1986). Generally, whey powders exhibit sigmoidal sorption isotherms, although the characteristics of the isotherm are influenced by the composition and history of the sample. Examples of sorption isotherms for whey protein concentrate (WPC), dialysed WPC and its dialysate (principally lactose) are shown in Figure 7.13. At low aw values, sorption is due mainly to the proteins present. A sharp decrease is observed in the sorption isotherm of lactose at aw values between 0.35 and 0.50 (e.g. Figure 7.13). This sudden decrease in water sorption can be explained by the crystallization of amorphous lactose in the a-form, which contains one mole of water of crystallization per mole. Above aw values of about 0.6, water sorption is principally influenced by small molecular weight components (Figure 7.13). 

An example of a reaction that can be induced by the presence of water vapor is the crystallization of amorphous lactose, a subject that has been reviewed by Buckton and Darcy (34). After a period of exposure to any particular RH amorphous lactose exhibits a crystallization exotherm (Fig. 8) (35). It can be shown that the rate of onset of crystallization varies with... 

FIGURE 8.4 Schematic microcalorimetric heat flow curve for crystallization of amorphous lactose. (Reproduced from Sebhatu et al., 1994. With permission.)... 

Net Area under the Curve for the Crystallization of Amorphous Lactose at Different Temperatures and Humidities... 

Around 70°C, the gelatinization of finely divided flours (starches) mixed with water can be observed. Retrogradation, for instance bread staling, can also be studied [97]. Crystallization of amorphous sugars (e.g., crystallization of amorphous lactose in milk powders [98]) can be detected in reconstituted foods. However, protein denaturation is no longer detected elearly when studying liquid whole milk products containing lipids, lactose, caleium, etc. 

The presence of amorphous lactose in the excipient may have a negative effect on compactibility and product stability. Direct compression grades of lactose monohydrate are available as granulated/agglomerated particles from multiple vendors. These physical properties are listed in Table 7.4. Commercial products combine the good flowability of coarse lactose crystals and the good compressibility... 

A suspension of a-lactose monohydrate crystals in a lactose solution is atomized and dried in a spray drier. Approximately 10-20% of the total amount of lactose is in solution and the remaining 80-90% is present in the crystalline form. The spray-drying process predominantly produces spherical particles. The compactibility of the material and its flow characteristics are a function of the primary particle size of the lactose monohydrate and the amount of amorphous lactose. " ... 

Newell HE, et al. The use of inverse phase gas chromatography to study the change of surface energy of amorphous lactose as a function of relative humidity and the processes of collapse and crystallization. Int J Pharm 217(1-2) 45-56, 2001. 

During the storage of amorphous lactose powder, no crystallization is observed for Ow < 0.35. Above 0.35, the glass transition temperature Tg decreases to values below the ambient temperature, leading to crystallization at a rate depending on... 

JouppUa K, Kansikas J, Roos YH. Water induced crystaUization of amorphous lactose dehydrated lactose and lactose in skim milk powder. Crystal Growth of Organic Materials 4,4th International Workshop, Bremen, 17-19 September 1997 pp. 317—324. 

In vacuum oven methods for moisture determination, such as the official method of the Association of Official Analytical Chemists, lactose solutions are dried at about 100°C for 2 to 6 hr. The result in the dried product is amorphous lactose glass. Since lactose glass is very hygroscopic, the dried sample must be protected from moisture until final weighing. If a-hydrate crystals are present in the product to be analyzed, the sample is diluted with water to dissolve the crystals, since slow removal of the water of crystallization under the temperature and vacuum conditions of the moisture test unduly prolongs the moisture determination. 

Lactose hexanitrate, C12Hie05 (0N02) , has been found in the alcoholic mother liquors from the crystallization of the octonitrate, white, amorphous material melting not sharply at about 70°. 

Both lactose and sucrose have been shown to crystallize in an amorphous form at moisture contents close to the glass transition temperature (Roos and Karel 1991a,b Roos and Karel 1992). When amorphous lactose is held at constant water content, crystallization releases water to the remaining amorphous material, which depresses the glass transition temperature and accelerates crystallization. These authors have done extensive studies on the glass transition of amorphous carbohydrate solutions (Roos 1993 Roos and Karel 1991d). 

The crystalline type of lactose can be of technological importance, for example, managing water release for control of MaiUard reaction products via crystallization of an amorphous matrix. 

A faulty batch of tablets can sometimes be recovered by grinding up the tablets and recompressing them, a process which is known as reworking and is analogous to the dry granulation method of tablet manufacture. This can sometimes cause problems with a direct compression formulation. Many direct compression diluent particles are in the form of aggregates, e.g., spray-dried lactose is composed of small crystals of lactose embedded in amorphous lactose. If these aggregates are compressed, their structure may be broken down to such an extent that subsequent recompression will result in impaired tablet quality. 

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