Amorphous lactoses

Physical state of lactose—amorphous lactose protects free fat from being extracted while crystalline lactose promotes extraction. 

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. 

LIG. 37 Stability map for dairy powders containing amorphous lactose. The critical water activity (0.37 aw) corresponds to the water activity of amorphous lactose with Tg of 24 °C (and a moisture content of 6.8 g water/100 g solids) [reproduced with permission from Roos (2003)]. 

Lactose Hexanitrate, C12H1605(0N02)6 a white amorphous material with mp about, 70°, was isolated from the ale mother liquors in the crystn of the octanitrate (Ref 6). It is a less powerful expl than the octa-compd... 

Yromans H, Bolhuis GK, Lerk CF, Kussendrager KD, Bosch H. Studies on tableting properties of lactose. VI. Consolidation and compaction of spray-dried amorphous lactose. Acta Pharmaceutica Suecica 1986 23(4) 231-240. 

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). 

Lactose glass. When a lactose solution is dried rapidly, viscosity increases so quickly that crystallization is impossible. A noncrystalline form is produced containing a- and /J-forms in the ratio at which they exist in solution. Lactose in spray-dried milk exists as a concentrated syrup or amorphous glass which is stable if protected from air, but is very hygroscopic and absorbs water rapidly from the atmosphere, becoming sticky. 

Dried milk and whey. Lactose is the major component of dried milk products whole-milk powder, skim-milk powder and whey powder contain c. 30, 50 and 70% lactose, respectively. Protein, fat and air are dispersed in a continuous phase of amorphous solid lactose. Consequently, the behaviour of lactose has a major impact on the properties of dried milk products. 

Thermoplasticity of lactose. Unless certain precautions are taken during the drying of whey or other solutions containing high concentrations of lactose, the hot, semi-dry powder may adhere to the metal surfaces of the dryer, forming deposits. This phenomenon is referred to as thermoplasticity. The principal factors influencing the temperature at which thermoplasticity occurs ( sticking temperature ) are the concentrations of lactic acid, amorphous lactose and moisture in the whey powder. 

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). 

Cooling solutions to below their freezing point results in the formation of ice. If solutions of sugars are cooled rapidly, non-equilibrium ice formation occurs. This is the most common form of ice in frozen dairy products (e.g. ice-cream). Rapid freezing of ice-cream mixes results in the freeze concentration of lactose and other sugars, resulting in supersaturated solutions if the temperature is too low to permit crystallization. The rapid cooling of lactose results in the formation of a supersaturated, freeze-concentrated amorphous matrix. 

Lactose normally occurs naturally in either of two crystalline forms— a-monohydrate and anhydrous /3—or as an amorphous glass mixture of a- and /3-lactose. Several other forms may be produced under special conditions. 

Anhydrous Lactose Glass (Amorphous Noncrystalline Glass)... 

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). 

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. 

As mentioned previously, alcohol greatly reduces the solubility of lactose, but the glass or amorphous form dissolves in alcoholic solutions to form supersaturated solutions. This has been used to extract lactose from whey or skim milk powder with methanol or ethanol. A high-grade lactose subsequently crystallizes from the alcoholic solu-... 

It has been demonstrated in the laboratory that by careful manipulation of alcohol concentration, amorphous lactose high in the /3 anomeric form could be precipitated (Majd and Nickerson 1976 Ross 1978A Olano and Rios 1978). Parrish et al. (1980B) have formed /3-lactose from stable forms of anhydrous a-lactose and have prepared /3-lactose from a-lactose monohydrate with potassium methoxide (1979B). None of these processes have been commercialized. 

Berlin, E., Kliman, P. G., Anderson, B. A. and Pallansch, M. J. 1971. Calorimetric measurement of the heat of desorption of water vapor from amorphous and crystalline lactose. Therm. Acta 2, 143-152. 

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°. 

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