Adaptation of the Barker-Summerson Lactic Acid Method to Ice Cream and Ingredients for Ice Cream

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Abstract
This method gives accurate values for a wide variety of dairy products. When a constant allowance is made for the lactic acid value of the sugar present, it can be used for sweetened products, such as ice cream. The method consists of precipitation of protein with Na tungstate and sulfuric acid, removal of interfering substances from the protein-free filtrate with CuSO4 and Ca(OH)2, converting the lactic acid to acetaldehyde by heating in coned. H2SO4, development of color through the reaction of the acetaldehyde and p-hydroxy-diphenyl in the presence of Cu ions, measurement of the color in a photoelectric colorimeter, and reading the lactic acid from a standard curve. Flavorings which do not contain propylene glycol cause no difficulty, and corrections for propylene glycol in extracts can be made when the amt. present is known. Neutralizers do not interfere with detn. of developed lactic acid, nor do common sample preservatives.