48 CARBOHYDRATES 



Lactose 



This sugar has been found only in the milk of mammals. It varies 

 from 1.5 to 8 per cent depending upon the species. Human milk con- 

 tains from 4 to 6.3 per cent and cow's milk about 5 per cent. Based 

 on the annual production of milk (more than 120,000,000,000 lb.), it 

 is estimated that the consumption of lactose in the United States is equiva- 

 lent to more than one-third that of sucrose. Lactose is obtained from 

 skim milk by removing the casein with acid or rennet and purifying 

 the resultant whey by heating and liming. The clear liquor from these 

 treatments is concentrated in a vacuum pan until crystallization begins. 

 The hot sirup is then transferred to cooling pans and stirred until crystalli- 

 zation is complete. The mush of yellow crystals is dropped into a 

 centrifuge, freed of excess sirup, and washed with cold water. The crude 

 sugar is refined by dissolving, bone-blacking, and recrystallizing. The 

 refined sugar is dried and ground to pass a 200 mesh sieve. The yield 

 of refined sugar averages about one-half the lactose contained in the 

 whey. Lactose production in 1949 amounted to 19,025,000 lb., but this 

 is only a small part of what could be produced if there were sufficient 

 demand for it. Smith and Claborn estimate that at least 2,700,000,000 

 lb. could be made from available skim milk, buttermilk, and whey. 

 Much of the highly purified lactose is used in infant feeding, and in the 

 manufacture of infant foods and pharmaceutical preparations. Large 

 quantities of pure lactose are also used in the production of penicillin. 



Lactose is not very soluble and is almost tasteless. It gives a faint 

 suggestion of sweetness, but this is slight in comparison with the sweet- 

 ness of glucose or sucrose. A more soluble and sweeter form of lactose 

 can be made by crystallizing the sugar at a temperature above 95°C. 

 This sugar is known as anhydrous beta lactose. The milk sugar of 

 commerce is hydrated alpha lactose. The anhydrous beta lactose appears 

 to be stable for a considerable time at ordinary conditions of tempera- 

 ture and moisture. Because of its greater solubility and sweetening 

 power, it appears that there should be a demand for this product. A 

 more general use of lactose has been advocated for the reason that the 

 ingestion of lactose helps to maintain a healthy condition of the intestinal 

 tract. Although many bacteria are unable to use lactose, others ferment 

 it readily and thus are favored in their development. Among the latter 

 are L. acidophilus, a lactic acid-producing microorganism, which is more 

 or less abundant in the intestinal tract. The growth of this desirable 

 organism is favored by an abundance of lactose, and its development 

 results in an acid, reaction that checks the growth of the troublesome 

 proteolytic bacteria. Lactose is not fermented by ordinary yeasts. 



Lactose reduces Fehling's solution and gives a characteristic osazone, 

 both of which tests indicate the presence of an aldehyde group in its 

 structure. This compound is shown in the following formula: 



