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Lactic Acid in Dairy Products. I. Application of the Hillig Method^*

Department of Dairying, Michigan Agricultural Experiment Station, East Lansing, Michigan

ABSTRACT

Quantitative determinations of lactic acid and lactates in milk and milk products as means of ascertaining the extent of microbiological spoilage have long been of interest and various methods have been proposed for such analyses. Recently, an intensification of interest in this question hasresulted because of the use of lactic acid values by Federal regulatory officials as a basis for judging quality in concentrated and dried milk.

At the present time there are two rather generally accepted quantitative methods for measuring lactic acid in milk: (a) The Troy-Sharp aldehyde procedure (7) and (b) the Hillig colorimetric procedure (1).

The aldehyde procedure involves the precipitation of the interfering substances with copper hydroxide at 45°C., oxidizing the filtrate under carefully controlled conditions with sulfuric acid, manganese sulfate and potassium permanganate, distilling the acetaldehyde produced into sodium bisulfite, and titrating the bound sulfite with iodine. The result is then corrected for the blank on fresh milk and for the lactic acid retained by the precipitate.

^* Journal Article No. 683, new series, Michigan Agricultural Experiment Station.