Lactose crystal shape

In dairy products, crystallization is more complex. The impurities (e.g., other milk components), as far as lactose is concerned, may interfere with the crystalline habit. As a result, the crystals tend to be irregularly shaped and clumped, instead of yielding the characteristic crystals obtained from simple lactose solutions. In some instances, the impurities may inhibit the formation of nuclei and thus retard or prevent lactose crystallization (Nickerson 1962). 

The crystals of a-hydrate lactose usually occur in a prism or tomahawk shape. The latter is the basic shape and all other shapes are derived from it by different relative growth rates of the various faces. The shape of an a-hydrate lactose crystal is shown in Figure 4-17. The crystal has been character-... 

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... 

Figure 49.2 shows the rate of NEB as a function of RH for lactose and lactose-gelatinized starch (3 1) systems incubated at 70°C. Since lactose is a reducing sugar, NEB rate values were higher in the lactose systems than in the lactose-starch ones as a result of a dilution effect of the reactants. As previously indicated the purpose was to compare the shape of the curves and the location of the maximum in the RH scale. The maximum NEB rate for the lactose system was observed at 43% RH, in which the sample was completely crystalline. The kinetics of lactose crystallization was delayed by the incorporation of starch. However, the RH value at which crystallization started was the same as the lactose system, and the rate of NEB decreased only slighly above 52% RH (Figure 49.2). Several other studies have also indicated that the addition of a polymer to an amorphous matrix delayed the crystallization of the sugar (Roos and Karel, 1991 O Brien, 1996 Gabarra and Hartel, 1998 Mazzobre et al., 2001 Biliaderis et al., 2002). At higher RH, the NEB rate dramatically decreased for lactose, which was completely crystalline and where water had an inhibitory effect on the reaction. In the...

In optical microscopy the contrast between different components arises from differences in their refractive indices. Ice cream is too opaque for its structure to be observed. However, samples can be prepared so that the ice crystals, air bubbles and fat droplets can be visualized separately. Lactose crystals, if any are present, can be clearly observed using crossed polars. They have a characteristic arrowhead shape that makes them easily distinguishable. 

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. 

Figure 6.2. The crystalline habit of lactose a-hydrate. (A) Prism, formed when velocity of growth is very high. (B) Prism, formed more slowly than prism A. (C) Diamond-shaped plates transition between prism and pyramid. (D) Pyramids resulting from an increase in the thickness of the diamond. (E) Tomahawk, a tall pyramid with bevel faces at the base. (F) Tomahawk, showing another face which sometimes appears. (G) The form most commonly decribed as fully developed. (H) A crystal having 13 faces. The face shown in F is not present. (I) A profile view of H with the tomahawk blade sharpened. (From van Krevald and Michaels 1965. Reprinted with permission of the Journal of Dairy Science 48(3), 259-265.)...

Fig. 47 Particle shape (left) and surface differences (right) of crystallized a-lactose monohydrate [(A), Pharmatose (Trade name of DMV, Veghel, The Netherlands) 325 M] and roller-dried P-lactose [(B), DCL 21) (Trade name of DMV, Veghel, The Netherlands).]...

The product contains 440/260 = 1.69 kg sucrose per kg water and, according to Table 2.2, the solubility of lactose then is close to 200 g per kg water. This implies that about 58 g of lactose will eventually crystallize. Assuming that the number of crystals formed equals the number of seed crystals added, the volume of a seed crystal must be at most 0.3/58 times the volume of a crystal eventually formed. Assuming the crystals to be of the same shape, the maximum diameter of a seed crystal should then be (0.3/58)1/3 x 8 pm = 1.38 pm. 

FIGURE 15.5 Variation in crystal morphology for identical unit cells, (a) Crystals in the rhombohedral system that only have faces present in the unit cell (001), (010), and (100). (b) Cubic system the leftmost picture is a cube, the rightmost one a regular octahedron in between are intermediate shapes, (c) Examples of the various shapes that an ot-lactose monohydrate crystal (monoclinic) can assume in practice. In (a) and (b) the shapes are shown in perspective. In (c) we have projections (all in the same direction with respect to the axes of the unit cell). 

FIGURE 15.10 Common shape of an a-lactose monohydrate crystal. The crystallographic axes (a, b, and c) and the Miller indices of the faces are given. 

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