Crystallization, sugars lactose

When the model samples were stored in a 65.6% RVP environment, OD of the three systems was observed at 11-, 24-, and then at 24-h intervals up to 240 h, as shown in Figure 53.3d. OD in the trehalose/reactant system increased linearly from 11 h, which was followed by a leveled-off plateau. In lactose/reactant systems, from 11 to 24 h, rate constant was low, then started to increase linearly and rapidly because of the crystallization of lactose, and finally ended at the plateau stage. In agreement with the water-sorption results for the model systems at 65.6% RVP (Figure 53.1), crystallization of component sugars was observed from the loss of sorbed water at 5, 21, and 56 h for trehalose/reactant, lactose/reactant, and lactose/trehalose/reactant systems, respectively. The rapid linearly increasing region of OD in the trehalose/reactant and lactose/reactant systems seemed to be directly... 

We will illustrate the phenomenon for the crystallization of lactose. Lactose is a reducing sugar, and in solution the a and p anomers are in equilibrium with each other the ratio p over a is about 1.6. The crystallization of a-lactose monohydrate, the most common crystalline form, has been studied in detail. Figure 15.10 depicts a crystal as formed at... 

Lactose (milk sugar), C12H22O11.H2O, occurs in the milk of mammals, in which it is present to the extent of from three to five per cent. It is obtained as a b3 -product in the manufacture of cheese. When rennet is added to milk, the casein and fat which the milk contains are precipitated. The liquid, called whey, after separation from the solid material by pressure, is neutralized with calcium carbonate, filtered, and evaporated to crystallization. The lactose so obtained forms large, hard, rhombic crystals, which contain one molecule of water of crystallization. 

D-galactose, C HiiOe. Crystallizes in the pyranose form m.p. 1I8-120 C (monohydrate), 165-5" C (anhydrous). An isomer of glucose which is fairly widely distributed in plants. It is a constituent of raffinose and slachyose, of hemicelluloses, of pectin, of gums and mucilages, and of some glycosides. In animals it forms half the lactose molecule and is the sugar found in the brain. Chemically it is very similar to glucose. It has the structure... 

By pre-treating milk with lactase, all adults can enjoy milk and a whole range of other lactose-free dairy products can be made such as ice cream and yogurt. In the production of ice cream, lactose hydrolysis can also be used to improve certain properties such as the texture, sweetness and tendency to crystallize. The increased sweetness is also advantageous in the manufacture of flavored milk products because less sugar needs to be added. 

Lactitol. Lactitol (4-0-/ -D-galactopyranosyl-D-sorbitol), is a synthetic sugar alcohol produced on reduction of lactose, usually using Raney nickel. It can be crystallized as a mono- or di-hydrate. Lactitol is not metabolized by higher animals it is relatively sweet and hence has potential as a non-nutritive sweetener. It is claimed that lactitol reduces the absorption of sucrose, blood and liver cholesterol levels and to be anticariogenic. It has applications in low-calorie foods (jams, marmalade, chocolate, baked goods) it is non-hygroscopic and can be used to coat moisture-sensitive foods, e.g. sweets. 

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. 

FIGURE 11-43 Structure of the lactose transporter (lactose permease) of E. coli. (a) Ribbon representation viewed parallel to the plane of the membrane shows the 12 transmembrane helices arranged in two nearly symmetrical domains shown in different shades of blue. In the form of the protein for which the crystal structure was determined, the substrate sugar (red) is bound near the middle of the membrane where it is exposed to the cytoplasm (derived from PDB ID 1 PV7). (b) The structural changes postulated to take place during one transport... 

Further information on the kinetics of crystallization is helpful in designing improved processes for lactose recovery. Many potential food applications, such as in confectionary products, involve concentrated sugar solutions in which crystallization imparts the desired texture to the product. 

The candy industry uses lactose to achieve desirable characteristics in certain types of candies. It changes the crystallization habits of other sugars present and improves body, texture, chewiness, or shelf life. 

LACTOSE. CAS 63-42-3]. Also called milk sugar or sacchanmt laclis. formula CieHjjOn H.-O, While, hard, crystalline mass or white powder sweet taste odorless stable in air. D 1.525. mp decomposes at 203.5C. soluble in water insoluble in ether and chloroform scry slightly soluble in alcohol, formed from whey, by concentration and crystallization. Cows milk contains about 5 < lactose. 

Condensed milks are mostly condensed to one-third of their volume. Their composition varies somewhat, atcording to the degree of concentration and to the addition of sugar (see later). Good products should be slightly yellowish, should have no unpleasant smell or cheesy flavour and should be homogeneous and show no clots, fat drops or crystals (lactose). 

---