1961 年 81 巻 2 号 p. 227-230
A rapid determination of lactose in milk and powdered milk, and of lactose and sucrose in condensed milk, using 3, 6-dinitrophthalic acid was established. Diluted solution of milk or its products is deproteinized by heating for a short time with basic zinc carbonate and colored by 3, 6-dinitrophthalic acid in the previously established method for reducing sugars. The lactose content is read from the calibration curve. The sucrose in condensed milk is inverted and colored by the same reagent.
To deproteinize the solution, the sample is diluted with water to 1% solution for milk, 0.1% solution for powdered milk, and 0.25% solution for condensed milk. Two cc. of this solution is diluted with 3cc. of water, deproteinized with about 150mg. of basic zinc carbonate, and diluted to 20cc., except for condensed milk, which solution is diluted to 100cc. The lactose is determined by developing 2cc. of the diluted solution.
For the determination of sucrose in condensed milk, 2cc. of 10% solution is deproteinized with about 300mg. of basic zinc carbonate, hydrolysed with hydrochloric acid, neutralized, and diluted to 2000cc. Two cc. of this solution is developed and total sugar is read from the calibration curve of glucose. Lactose gives the coefficient of 0.785 when it is read on the curve of glucose and sucrose is calculated from the following equation:
This method of determination is simple and rapid for treating a larger number of sample, and the determined value agrees with the macro methods within the largest deviation of ±3%.