Description and references
Present in milk of mammals: human 6.7%; cow's
4.5%. Milk at body temp contains lactose as an equilibrium mixture
of 2 parts of α-lactose and 3 parts of β-lactose. By-product of the
cheese industry, produced from whey: Davis, Can. Dairy and Ice Cream J. 19, 52 (1940); Milk Trade Gaz. 12, 4 (1941);
F. Ullmann, Encyklopdie der Technischen Chemie, VII, 579 (2nd ed., 1931). Structure and configuration:
Zemplén, Ber. 59, 2402
(1926); Levene, Sobotka, J. Biol. Chem. 71, 471 (1926); Levene, Wintersteiner, ibid. 75, 315 (1927); Haworth,
Long, J. Chem. Soc. 1927, 544; Hudson, J. Am. Chem. Soc. 52, 1712 (1930); Hassid, Ballou in The Carbohydrates, W. Pigman, Ed. (Academic Press, New York, 1957) p 495. Synthesis:
Haskins et al., J. Am. Chem. Soc. 64, 1852 (1942). Reviews: Whittier, Chem. Rev. 2, 85-125 (1926); J. Dairy Sci. 27, 505-537 (1944);
Weisberg, ibid. 37, 1106-1115 (1954); L. A. W. Thelwall, Dev.
Food Carbohydr. 2, 275-326 (1980). Comprehensive
description: H. G. Brittain et al., Anal. Profiles Drug Subs. 20, 369-398 (1991).
Derivative
α-Lactose monohydrate.
Properties
Is the usual milk sugar and the lactose of pharmacy.
Monoclinic sphenoidal crystals from water. Faintly sweet taste.
Stable in air, but readily absorbs odors. d20 1.53. Becomes anhydrous at
120°. mp 201-202° (rapid
heating). Shows mutarotation. [α]D20 +92.6° → +83.5° (10 min.) → +69° (50
min) → +52.3° (22 hrs, c = 4.5). The final value is obtained instantly in the presence of a trace
of NH3. U.S.P. requires +54.4° to +55.9° (c = 10). One
gram dissolves in 5 ml water, in 2.6 ml boiling water; very slightly
sol in alcohol. Insol in chloroform, ether. Ka at 16.5° = 6.0×1013. d420 of aq solns
calcd for the monohydrate: 5.2% = 1.018; 10.2% = 1.038; 20.0% = 1.078; 30.2% = 1.123; 50.9% = 1.226; 60.8% = 1.281; 69.1% = 1.330.Derivative
β-Lactose.
C
12H
22O
11; mol wt 342.30.
C 42.11%, H 6.48%, O 51.41%.
Properties
Obtained by crystallizing concd solns of α-lactose
above 93.5°. Somewhat sweeter than the α-form. [α]D25 +34° (3
min) → +39° (6 min) → +46° (1 hr) → +52.3° (22 hrs). One gram dissolves in 2.2 ml water at 15°, in 1.1 ml boiling water.
After a few days crystals of the less sol α-monohydrate appear from
satd solns.Both forms of lactose are employed, with the α-form
predominating: as a nutrient in preparing modified milk and food
for infants and convalescents (Whittier). In baking mixtures. Pharmaceutic
aid (tablet and capsule excipient and diluent). To produce lactic
acid fermentation in ensilage and food products. As chromatographic
adsorbent in analytical chemistry. In culture media. For many additional
uses
Weisberg.
Added to cow's milk for feeding orphan
foals.
