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The Value of the Chemical Titration Method in Determining the Vitamin C Potency of Certain Food Substances¹

Department of Agricultural and Biological Chemistry, Pennsylvania State College, State College

A study has been made concerning the value of the chemical titration method for determining the vitamin C potency of certain food substances. In these studies, the ascorbic acid content of certainfruit and vegetable juices was determined by titrating against a standard solution of 2, 6-dichlorophenol-indophenol. In order to ascertain the accuracy of the data obtained through the chemical titration method, biological assays were also made on a number of the fruit juices used in this study. From the results obtained it appears that:

1. The chemical titration method for the estimation of ascorbic acid is of material value in determining the vitamin C potency of certain fruit and vegetable juices. By means of this method, it is possible at least to approximate the antiscorbutic activity of the juices before the biological assay is started, thus saving time and expense.

2. The accuracy of the results obtained by the chemical titration method appears to depend to an appreciable degree upon the nature of the juice that is being titrated. Some juices contain interfering substances that react with the dye, thus complicating the titration results and leading to erroneous conclusions.

3. For lemon juice, orange juice, grapefruit juice and fresh pineapple juice, the values obtained by the chemical titration method are in close agreement with those obtained by the usual biological assay method.

4. Fresh pineapple juice, when evaluated for its antiscorbutic potency by the chemical method, gives values in closer agreement with those obtained by the biological method than does the canned pineapple juice, owing to the presence of interfering substances in the latter.

Manuscript received 14 December 1934.