Lactose hydrate

Lactose (hydrated). Lactose (anhydrous) 2031 223 + 52-5 200 — Octa-acetate, a- 152, P- 90 mucic acid, 213... 

Figure 2.7 The most common crystal form of a-lactose hydrate.

Sweetened condensed milk. Crystallization of lactose occurs in sweetened condensed milk (SCM) and crystal size must be controlled if a product with a desirable texture is to be produced. As it comes from the evaporators, SCM is almost saturated with lactose. When cooled to 15-20°C, 40-60% of the lactose eventually crystallizes as a-lactose hydrate. There are 40-47 parts of lactose per 100 parts of water in SCM, consisting of about 40% a-and 60% /1-lactose (ex-evaporator). To obtain a smooth texture, crystals with dimensions of less than 10 /an are desirable. The optimum temperature... 

Crystalline Habit. a-Lactose hydrate crystals are observed in a wide variety of shapes, depending on conditions of crystallization. The principal factor governing the crystalline habit of lactose is the precipitation pressure, the ratio of actual concentration to solubility (Herrington 1934A). When the pressure is high and crystallization is forced rapidly, only prisms form. As precipitation pressure lessens, the dominant crystal form changes to diamond-shape plates, then to pyramids and tomahawks, and finally, in slow crystallization, to the fully developed crystal. These types of crystals are illustrated in Figure 6.2. 

Riboflavin also may adsorbed on growing lactose crystals and alter the crystalline habit. Since it is naturally present in the whey from which lactose hydrate is made and is present in all dairy foods, its influence on lactose crystallization may be of special interest. Adsorption is dependent upon concentration of riboflavin in solution, on degree of lactose supersaturation and on temperature (Leviton 1943, 1944 Michaels and Van Krevald 1966). No adsorption occurs below a certain minimum (critical) concentration of riboflavin (2.5 uglml), but adsorption increases linearly with riboflavin concentration above this critical level. Increasing the temperature of crystallization results in reduced riboflavin adsorption. Adsorption is favored at lower supersat-... 

The water of crystallization can be moved from a-hydrate by refluxing it in a high-boiling organic solvent that is immiscible with water. For example, the moisture in lactose hydrate has been determined by the toluene distillation method that is often used to determine moisture in milk powder with lactose, prolonged distillation (5 hr) is necessary to remove the hydrate moisture. The powder remaining after distillation in a stable anhydrous form (Nickerson 1974). 

Several methods have been developed for preparation of /3 lactose. a-Lactose hydrate has been converted to /3-lactose in nearly quantitative yield by refluxing in methanol containing small amounts of sodium hydroxide (Olano and Rios 1978) ethanol, n-propanol and n-buta-nol were also effective as solvents (Olano 1978). Similarly, a-lactose hydrate was converted to /3-lactose with potassium methoxide or potassium hydroxide as the base (Parrish et al. 1979B). /3-Lactose was also prepared from the anhydrous forms of a-lactose if small amounts of /3-lactose were present (Parrish et al. 1980A). 

Mutarotation also manifests itself in the solubility behavior of lactose. When a-lactose hydrate is added in excess to water, with agitation a definite amount dissolves rapidly, after which an additional amount dissolves slowly until final solubility is attained. 

Estimation of water of crystallization. When lactose is crystallized as the a-lactose hydrate in a product, the fraction crystallized can be determined from the weight of water of crystallization lost. Water of crystallization accounts for 5% by weight of the crystalline lactose. 

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. 

Olano, 0. and Rios, J. J. 1978. Treatment of lactose with alkaline methanolic solutions Production of beta-lactose from alpha-lactose hydrate. J. Dairy Sci. 61, 300-302. 

If n is the total dilution to which the original filtrate is subjected to obtain the solution used in the Fehling titration, and a the number of c.c. of the diluted solution required to decolorise the 50 c.c. of Fehling solution, the lactose (hydrated) L contained in 100 grams of the milk analysed is given by the formula ... 

For maltose, lactose (hydrated) and raffinose (hydrated), the normal weights are respectively 12-55 (or 12-58) grams, 37-88 (or 32-95) grams,2 and 16-545 (or 16-576) grams, according as the volume is measured in true (or Mohr) c.c. 

Lactose (Hydrate) corresponding with the Copper weighed (Soxhlet)... 

Zurich 1998, Nobel Prize in Chemistry 1975), he published the first of the many landmarks in stereochemistry that are identified with his name the resolution of Troger s base 1 into its mirror-image components by chromatography on a column of lactose hydrate (44HCA1127). 

You have a bottle containing finely crystallized lactose, but you don t know whether it is a-lactose hydrate or (3-lactose. How can you find out You have no other equipment than laboratory glassware and a balance. 

In Section 15.2.2 it was argued that the linear growth rate of a-lactose hydrate crystals is very much smaller than that of sucrose crystals, because in the former case fierce competition with 3-lactose occurs, and nothing like that can occur for sucrose. Can you now give additional causes for the crystallization rate of a lactose solution being far smaller than that of a sucrose solution at the same supersaturation, especially at low temperature Tip also consult Section 2.2. 

When a solution of a racemate (dt) is brought into contact with a crystal built from chiral molecules, d, e.g. lactose, preferential adsorption takes place d may be more readily adsorbed than I or vice-versa again pointing to a difference between d-i> and /-d. A number of racemates have been resolved on columns of lactose. Moeller and Gulyfas (1958) for example, resolved [Co(aca)3]° and [Cr(acac)3]° on lactose hydrate by passing a solution of the complexes in benzene-petroleum through the column. [See also Henderson and Rule (1939), Lecoq (1943), Prelog and Wieland (1944)]. 

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