Lactose glass

The rate of nucleation is slow at low levels of supersaturation and in highly supersaturated solutions owing to the high viscosity of the solution. The stability of a lactose glass is due to the low probability of nuclei forming at very high concentrations. 

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. 

The tendency of lactose to form supersaturated solutions that do not crystallize readily causes problems in many dairy products unless adequate controls are exercised. The problems are due primarily to the formation of large crystals, which cause sandiness, or to the formation of a lactose glass, which leads to hygroscopicity and caking (Figure 2.9). 

Anhydrous Lactose Glass (Amorphous Noncrystalline Glass)... 

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. 

Other approaches use Laser-Raman spectra to differentiate five conformational states of lactose, including a-lactose monohydrate, /3-lactose, and lactose glass (Susi and Ard 1974). Differential thermal analysis has also been used to measure the concentration of crystalline lactose, especially a-lactose hydrate (Ross 1978B). The specialized equipment required by these procedures may limit their use. 

Concentrated lactose syrup "LACTOSE GLASS" (Non-crystalline)... 

Weigh all the ingredients separately. Iodine must be finely subdivided. Place the iodine in a glass mortar, add alcohol drop wise, and triturate until the iodine is reduced to a fine powder. Then add boric acid and lactose by geometric mixing until the alcohol evaporates. Dry the powder for about twenty minutes in the air and then pass through a 40 mesh sieve to break all the lumps. Transfer the powder into a wide-mouthed, four-ounce bottle. Label appropriately as Compounded Powder with the instructions of Apply to affected area twice daily as directed. ... 

Ice-cream. Crystallization of lactose in ice-cream causes a sandy texture. In freshly hardened ice-cream, the equilibrium mixture of a- and /1-lactose is in the glass state and is stable as long as the temperature remains low and constant. During the freezing of ice-cream, the lactose solution passes through the labile zone so rapidly and at such a low temperature that limited lactose crystallization occurs. 

Various thermal transitions can occur in rapidly cooled solutions, including glass transition, devitrification (ice formation on warming a rapidly-frozen solution) and melting of ice. The relationship between temperature, weight fraction of solids, solubility and glass transition of lactose is shown in Figure 7.16. 

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. 

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). 

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-... 

Lactose in the glass state may be used as a protective coating on certain materials, either to seal in components or to protect the material from the environment. Materials may be coated with lactose solution and dried, or a solution containing the material and lactose can be spray-dried. This latter application has been used to preserve enzymatic activity during spray drying and storage (Nickerson 1974). 

Sharma et al. [44] Lactose Milk and dairy products Lactase and galactose oxidase (GaO)/in Langmuir-Blodgett (LB) films of poly(3-hexyl thiophene) (P3HT)/stearic acid (SA) Indium-tin-oxide coated glass plates/0.4 V vs. Pt reference electrode ... 

Column Chromatography. Sepharose beads containing covalently linked gangliosides (0.2 ml packed volume) were placed into a pasteur pipette containing a small amount of glass wool. Columns were washed with HEM containing 50 ug/ml bovine serum albumin (3 ml). Interferon solutions in MEM-albumin (1 ml) were placed on the columns, which were eluted with MEM-albumin at a flow rate of no more than one drop per minute. Fractions of 1 ml were collected and interferon titers determined in each fraction after serial two-fold dilution. Columns onto which mouse fibroblast interferon had been loaded, were eluted with MEM-albumin first, then with 0.07 M N-acetylneuraminyl lactose at pH 2. 

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