Determination of Glucose,Galactose,and Lactose in a Mixture of the Three Sugars

Abstract

Harding and coworkers 1 have devised a method of estimating a number of the common sugars when present in a mixture. They utilized Proteus vulgaris, M. krusei, S. marxianus, and M. tropicalis for the differential removal of sugars in a mixture of glucose, fructose, galactose, sucrose, maltose and lactose. This procedure combined with reduction values before and after hydrolysis provided a reasonably satisfactory method of determining the individual sugars in the mixture.

The writers have found it possible to determine glucose, galactose, and lactose in a mixture by a similar, though simplified technique which avoids the use of organisms other than baker's yeast. An improved method for the hydrolysis of lactose was devised which gives complete decomposition as compared with the 72% hydrolysis by the method of Harding and Grant. 2

Galactose or lactose mixed with glucose were satisfactorily recovered after fermentation with washed baker's yeast. Table I shows recoveries of different quantities of glucose, galactose and lactose from solutions of all three. The data are not selected and represent all determinations made. The recoveries of galactose and lactose are not quite as good as those for glucose as might be expected due to the greater number of procedures involved in their estimation. 1. The titration values for the mixture are determined by a Shaffer-Somogyi 3 reagent (79.5 gm. Na₂Co₃, 1 gm. of K1, and 21 gm. of NaHCO₃, per 1) both (A) before and (B) after fermentation using 5 cc. of a 15% suspension of washed baker's yeast 4 (Fleischmann) and 14 cc. of the sugar solution made first just acid to congo with a drop of H₂SO₄.