Lactose in milk powders

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). 

Knoop, E. and Samhammer, E. 1962. Roentgenographic studies on the crystal structure of lactose in milk powder. Milchuiissenschaft 17, 128-131. 

Around 70°C, the gelatinization of finely divided flours (starches) mixed with water can be observed. Retrogradation, for instance bread staling, can also be studied [97]. Crystallization of amorphous sugars (e.g., crystallization of amorphous lactose in milk powders [98]) can be detected in reconstituted foods. However, protein denaturation is no longer detected elearly when studying liquid whole milk products containing lipids, lactose, caleium, etc. 

To ensure that the correct wavelength was chosen, a spectral scan of a few different milk powders and of its isolated constituents protein, fat, and lactose was carried out using an InfraAlyzer 500 (Figure 20.3 and Figure 20.4). The most useful interference filters for analyzing fat, protein, moisture, and lactose in milk powders are shown in Figure 20.4 and given in Table 20.5. 

Problems arising from the crystallization of lactose in milk and whey powders may also be avoided or controlled by pre-crystallizing the lactose. Essentially, this involves adding finely divided lactose powder which acts as nuclei on which the supersaturated lactose crystallizes. Addition of 0.5 kg of finely ground lactose to the amount of concentrated product (whole milk, skim milk or whey) containing 1 tonne of lactose will induce the formation of c. 106 crystals ml-1, about 95% of which will have dimensions less than 10/an and 100% less than 15 /an, i.e. too small to cause textural defects. 

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). 

One problem arises with sugar-free toffees. What about the lactose Lactose is a native component of skim milk solids and if the product is to be sugar-free then lactose-free milk powder will have to be used. If lactose is acceptable, as it would be in a reduced calorie product, then by replacing the sugar and glucose acceptable products can be made. 

Mutarotation has limited, rather diagnostic, significance in food chemistry and technology. Practical use of this reaction is demonstrated in milk powder manufacture. Evaporation of milk at a rate lower than mutarotation of lactose yields a product with less a-lactose isomer, which crystallizes in prism- or pyramid-like form. Fast milk evaporation gives an amorphous mixture of a- and [3-lactose (5.7b). 

Crystallization can be accounted for by the moisture dependence of Tg according to Roos and Karel (1991b). Crystallization releases water, which in closed containers is absorbed by the amorphous portion of the food. As a result when Tg drops, T-Tg increases and rapid crystallization follows. Products, which have high moisture transfer rates in the environment, will lose water, but the moisture content in the amorphous part remains fairly constant. Crystallization proceeds at a rate defined by a constant T-Tg. Crystallization leads to a complete change in physical structure. It may considerably decrease stability. Lactose crystallization in milk powders... 

The most stable form is a-lactose monohydrate, C12H22O11 H2O. Lactose crystallizes in this form from a supersaturated aqueous solution at T < 93.5 °C. The crystals may have a prism-or pyramid-like form, depending on conditions. Vacuum drying at T > 100 °C yields a hygroscopic a-anhydride. Crystallization from aqueous solutions above 93.5 °C provides water-free P-lactose (P-anhydride, cf. Formula 10.10). Rapid drying of a lactose solution, as in milk powder production, gives a hygroscopic and amorphous equilibrium mixture of a- and P-lactose. 

Dehydrated milk-based foods is the major source of D-lactulose-amino acids in human nutrition. The dairy industry widely uses milk dehydration to manufacture powdered milk as a base for numerous dairy products, such as infant formulas, confectionaries, reconstituted milk etc. During the process of heating, drying and storage, lactose in milk can readily interact with amino compounds that are naturally present, primarily lysine residues in milk proteins. Estimated contents of D-lactulose-amino acids in selected products are compiled in Table 2. Commercial dairy products may contain, therefore, up to 40% of protein lysine in form of lactulose-lysine. Dietary availability of D-lactulose-amino acids is similar to that of the fructosamine derivatives. An ample evidence exists that the Amadori-type lysine glycoconjugates are not available to mammals as a nutrient and that lactulose-lysine is partially absorbed into the bloodstream and excreted unchanged. ... 

Milk powder contains several useful components, namely protein and lactose. Lactose is a reducing sugar that undergoes the Maillard reaction to produce flavour and colour. The proteins as well as participating in the Maillard reaction have useful emulsifying abilities. These benefits are only obtained if the lactose is dissolved and the proteins dissolved or dispersed. 

Fungal and other microbial lactase preparations have also been formulated into tablet form, or sold in powder form. These can be ingested immediately prior to the consumption of milk or lactose-containing milk products, or can be sprinkled over the food before eating it. Such lactose preparations are available in supermarkets in many parts of the world. 

Field Pea Flour in Other Baked Products. When McWatters (44) substituted 8% field pea flour and 4.6% field pea concentrate for milk protein (6%) in baking powder biscuits, sensory attributes, crumb color, and density of the resulting biscuits were adversely affected. No modifications were made in recipe formulation when pea products were incorporated. The doughs were slightly less sticky than control biscuits that contained whole milk. This might be due to lack of lactose or to the different water absorption properties of pea protein or starch. Panelists described the aroma and flavor of these biscuits as harsh, beany and strong. Steam heating the field pea flour improved the sensory evaluation scores, but they were never equivalent to those for the controls. 

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. 

Josephson (1943) reported that butterfat prepared from butter heated to 149°, 177°, and 204.5°C was extremely stable to oxidation, while that heated to 121 °C oxidized readily when stored at 60°C. When butter oil itself was heated from 121 to 204.5 °C, it also oxidized rapidly. However, the addition of 1% skim milk powder to butter oil prior to heating at 204.5°C for 10 min also resulted in a significant antioxidative effect, which Josephson concluded was the result of a protein-lactose reaction (carmelization). Wyatt and Day (1965) reported that the addition of 0.5% nonfat milk solids to butter oil followed by heating at 200 °C and 15 mm Hg for 15 min caused the formation of antioxidants which protected the butter oil against oxidative deterioration for 1 year, surpassing the effectiveness of many synthetic antioxidants tested. 

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-... 

The crystallization principles previously discussed are applied in processing dairy products, such as sweetened condensed milk, instant milk powder, stabilized whey powders, lactose, and ice cream. 

Lactose Disaccharide (Glu + Gal) Found naturally only in milk and dairy products used as a dusting powder for some baked goods... 

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