EFFECT OF NON‐ANTISCORBUTIC REDUCING SUBSTANCES UPON THE ASCORBIC ACID CONTENT OF BAKED POTATOES^a,b

Abstract

A large volume of information concerning the effect of heat on the ascorbic acid content of vegetables has been accumulated. Of the various values reported, the effect of baking on the potato shows the greatest variation. Olliver ( 6 ) found losses ranging froin 19-5970 in the ascorbic acid content of baked potatoes. EIollinger (2) found that 76% of the ascorbic acid in the raw sweet potato is present in the baked potato. On the other hand, Scoular and Eakle (11) found in three varieties of baked sweet potatoes a 0.1585% loss in ascorbic acid and in three other varieties, a 12-130%increase. Other investigators have found increases in ascorbic acid content of potatoes on baking (3,12).This study was undertaken to determine the effect of baking on the true ascorbic acid content of potatoes. In the beginning phase of this work, it was found that baked potatoes, assayed with their peelings, showed an apparent gain in ascorbic acid when compared with raw potatoes. In view of this, a critical evaluation of the ascorbic acid content of potatoes baked to a series of internal temperatures was undertaken. Three different chemical methods were chosen for measuring the ascorbic acid content of potatoes. By use of these methods, the effect of non-antiscorbutic reducing substances upon the true ascorbic acid content of potatoes has been determined. MATERIALS AND METHODSSecuring and handling of potatoes. Sweet potatoes, obtained from the experimental farm, Tuskegee Institute, were used in some of the experiments and white potatoes in others. White potatoes were not available at the school farm and were purchased, as needed, from local markets. Potatoes were cleaned, rinsed with glassdistilled water, wiped dry, weighed, and stored a t 2" C. until the time of assay. A t all times, analyses were made on both the raw and the baked potatoes.Cooking. Baking was done in an electric table oven preheated to 450" F. and maintained at this temperature throughout the baking period. Internal temperature was determined with a Leeds and Northrup Precision Potentiometer, using a thermocouple consisting of 30-gauge iron and constantan wires. For experiments in which the potatoes were to be cooked to a series of 6 internal temperatures, 8 potatoes were matched for shape and weight. One was analyzed raw. The remaining 7 potatoes were weighed precisely, the thermocouple was inserted into one of them, and the 7 potatoes were put into the oven a t the same time. Since the potatoes had been matched for shape and weight, it was assumed that the temperature of each potato was the same at all a A portion of a thesis submitted by Janet Wilson McAfee to the Graduate Committee of Tuskegee Institute in partial fulfillment of the requirements for the degree of Master of Science. 115 times during the cooking period. As the e m f . corresponding to the desired temperature was reached, one of the potatoes which did not contain the thermocouple was withdrawn and assayed as the sample for that particular temperature.For experiments in which the potato was to be c...