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

This paper reports an investigation of factors concerned in the hydrolysis of lactose by acids, including a study of the solubility of mixtures of glucose and galactose and of methods for the production of hydrolyzed lactose sirups. By hydro!yzing lactose into its more soluble hexose constituents, higher sugar concentrations could be obtained in some dairy products which otherwise might develop a"sandy" texture. However, the destructive effect of acid hydrolysis on proteins precludes this treatment on dairy products such as milk or whey. The milder method of enzyme hydrolysis is impractical because there are no known methods of econ(;mically preparing and concentrating large quantities of lactose. Browne and Ramsdell in a recent study (2) found the enzyme prepared from lactosefermenting yeasts to be unstable and weak in hydrolytic power. EXPERIMENTAL U.S.P. grade lactose was used unless otherwise stated. Most of the samples were hydrolyzed by batch heating but a few were hydrolyzed in a high-temperature circulating heater. For one method of batch heating i50-ml, portions of the lactose test solutions were sealed in small, well-tinned cans coated with an acid-resisting lacquer. The cans were heated in a pilot evaporated-milk sterilizer with the reel revolving at 4 r.p.m. Fifteen minutes was used to bring the cans to the required temperature and this time was not included in the reported holding times. The other method of batch heating involved the use of a 2-gallon, glass-lined, steam-jacketed, reaction kettle equipped with an agitator and with an outlet valve for removing samples. The highest hydrolysis temperatures used in this work were attained in a Mallory (5, 10) heating unit. When holding periods longer than the time required for passage of the liquid through the heater were needed, the sirup was recirculated until the desired heating time was reached. The flow time through the different parts of the heater were : heating unit--3 seconds, holding pipe--1 minute, cooling unit---3 seconds.