Lactose and Lactic Acid

Lactose has been made from casein whey for many years and used mainly in infant foods. The suddenly increased demand during the war for lactose to use in producing penicillin came at a time when domestic casein production was greatly reduced, but when cheese production was greatly increased. Consequently, cheese whey was much more readily available than casein whey. The Department had accumulated information on the making of lactose from cheese whey which was published as six practical methods, each adapted to some special condition or requirement. These processes differ in cost of operation, in the purity of the lactose produced, and in the solubility of the whey protein obtained as a byproduct. Several companies have been producing lactose from cheese whey and have thus bolstered the supply needed in making penicillin.

Fermentable sugar present in dairy byproducts can be utilized in the production of alcohol and organic acids. One plant in the United States is producing alcohol from whey and converting the alcohol into vinegar. The only organic acid being produced directly from whey by commercial fermentation is lactic acid. The Bureau of Dairy Industry devised a process whereby more than 90 percent of the lactose in whey is converted to lactic acid in 24 hours. This is a continuous process, in which raw whey flows in at one end of a tank and fermented whey flows out at the other. The commercial process is a batch process requiring a 48-hour turn-over. In brief, the whey is fermented by a bacterial culture, the lactic acid being neutralized from time to time by lime in order that the bacterial action may continue. When the sugar is all fermented, the whey is boiled to coagulate the whey protein and the clear liquid is evaporated to cause calcium lactate to crystallize. The calcium lactate is removed on a filter and, after purification, is treated with sulfuric acid to convert it to lactic acid.

If increased quantities of lactic acid are to be made, greater use for it must be found. To this end two bureaus of the Department have developed procedures for converting lactic acid to acrylates. These acrylates, when polymerized, are flexible, glass-like substances that have use as plastics and in waterproofing cloth, and that can be converted into rubber-like materials. But acrylates can be made more cheaply from other starting materials and this has aroused interest in ways of cheapening the present expensive method of refining which is the largest proportion of the cost of lactic acid. This acid cannot be crystallized or distilled by any method that is commercially practical, but it can be combined with alcohols to give lactates that can be easily distilled and thus purified. Three patents on such procedures have been issued to workers in commercial laboratories. These purified lactates can be shipped in undiluted form and in inexpensive containers, in contrast to dilute lactic acid that must be shipped in expensive, noncorrodible containers. At the point of use the lactates can be converted back to lactic acid of any desired concentration by boiling with water. It is reasonable to expect that some of the needed reduction in cost of lactic acid to the user can be attained by application of these methods of refining and handling.

Another use for lactic acid that is not yet commercialized is in lacquers and protective coatings. When a lactic acid solution is heated, water distills off and the lactic molecules combine with one another to form resinous substances of increasing viscosity and insolubility. Public service patents have been issued to Paul D. Watson of the Bureau of Dairy Industry who has discovered that these resins may be combined with oils or with small percentages of metals to give lacquers. Baked on glass or metal surfaces, these are tough, elastic, and firmly adherent coatings that resist the action of steam, acids, and dilute alkalies, and are affected only by strong alkalies and few organic solvents. These coatings have been tested with satisfactory results on milk cans, pails for cottage cheese, cans for evaporated milk, mechanical pencils, and cigarette lighters.

THE AUTHOR