A Colorimetric Picric Acid Method for Determining Lactose

Abstract

The picric acid colorimetric method, for the estimation of carbohydrates, owes its origin to Dehn and Hartman (1) who worked with purified sugars and lactose in milk; and to Lewis and Benedict (2) who worked on glucose in blood. The method is based upon the fact that reducing sugars, in alkaline (when heated) reduce picric acid which is yellow in color, to picramic acid which is a deep mahogany red. The original methods have been improved and modified for application to various sugar containing materials. Several different modifications, as applied to milk, have been published. Folin and Denis (3), report a modification using saturated picric acid and a standard which must have a color value within 20 per cent of the color value of the unknown. Pacini and Russell (4) use more complicated technique and solid picric acid with no restriction on the comparative colors of the standard and unknown. Boch (5), reports a study on the reaction of lactose on picric acid using Benedict's (6), three times saturated solution, which is in reality sodium picrate. The method of Folin and Denis was used by Lisk (7) in her work on milk. To our knowledge, no one has applied any picric acid method to dairy products, other than milk.