The Acid Hydrolysis of Lactose and the Preparation of Hydrolyzed Lactose Sirup

Abstract

Summary 1.A study has been made of the factors affecting the hydrolysis of pure solutions of lactose by heat. The velocity constant (K · 10 4 ) for the reaction varied with the time and temperature of hydrolysis and the acid and lactose concentration of the solutions. Values for K · 10 4 ranged from 11 at 100° C. to 1904 at 165° C. Hydrochloric acid was used in concentrations of 0.001 to 1.0 mole per 1000 grams of solution and it was found to be a more effective catalyst than citric acid. 2.There was a progressive destruction of lactose and of the newly formed hexoses during hydrolysis. This destruction was accelerated by conditions of excessive or prolonged heating and when high sugar and acid concentrations were used. 3.Hexose sugars to the extent of 93 per cent of the theoretical yield were obtained by hydrolyzing a 30 per cent lactose solution using 0.007 mole of HC1 per 1000 grams of mixture and heating to 147° C. The process, conducted in a glass-lined pressure kettle required a total time of 65 minutes, of which 60 minutes were used to heat the batch to 147° C. A circulating heater which would quickly raise the sirup to the hydrolyzing temperature would shorten the process. 4.A solubility curve for galactose in aqueous glucose solutions at 25° C. has been presented. The solubility of glucose at 25° C. is 50.8 pev cent, galactose 32.09 per cent and a mixture of equal parts of both hexoses 42 per cent. The maximum concentration of the two hexoses which is soluble at 25° C. is 58.3 per cent, consisting of 49.8 per cent glucose and 8.5 percent galactose. 5.The lactose in skim milk, whey or crude lactose, cannot be hydrolyzed without the use of excessive quantities of acid and the production of undesirable protein decomposition products.