Abstract
Establishment of the determination method of lactic acid and lactate in milk was investigated. A colorimetric method derived from Davidson was pursued. This method involves the precipitation of fat, protein and lactose by the combined action of copper sulfate and calcium hydroxide, oxidation of the lactic acid into acetaldehyde by sulfuric acid in the presence of copper sulfate and a colorimetric determination using p-hydroxydiphenyl. Oxidation and colorimetric procedures were studied on the following items: concentration and quantity of p-hydroxydiphenyl solution to be added, stability of color developed as well as the maximal absorbance wavelength of the color developed. From experiment it revealed that the omission of the addition of copper sulfate to the sulfuric acid resulted in a decrease of the optical density of about 50%. So far as the clarification procedure was concerned, the addition of 25% copper sulfate was simplified to a single successive addition with calcium hydroxide without warming. No significant difference was observed compared with control carried out by the Davidson method.
This method can be applied for the detection of neutralizers. It is also available for the grading of condensed milk and milk powder.
