The widespread occurrence of discoloration in potatoes after cooking has warranted study over a period of many years. The possible combination of iron and phenolic compounds was mentioned in the early work of Tinkler (11) and again more recently by Juul (3) and Mulder (5) as possible causative agents of the discoloring pigment.A synthetic chelating agent, ethylene diamine tetra acetate or EDTA, was reported by Leonard and Stewart ( 4 ) to prevent iron chlorosis in citrus trees in 1953. Various sprays of EDTA were used on the Katahdin variety of potatoes by Smith and Muneta (10) who noted a decrease in the discoloration in such potatoes after cooking.The plan of this study included attempts to modify the development of the pigment by spraying plants of a variety of potatoes, Ontario, known to discolor seriously after cooking and observing the effect on the color scores and on the phenol and iron content of juice from the light and dark areas, or by dipping the newly harvested tubers in solutions of chelates, sodium EDTA and sodium citrate, before placing them in cold storage and making the same observations as for the sprayed samples, or by evacuating slices of Ontario potatoes in solutions which might be expected to increase or decrease the phenol or iron content of the tissue.
EXPERIMENTALOntario potatoes grown under controlled conditions were given certain plant spray treatments : iron sulfate, iron, sodium, magnesium, calcium ethylene diamine tetra acetate, EDTA, or sodium citrate. The design of the field plots included checks for the various treatments. Dip samples consisted of composites of control tubers placed in sodium citrate and sodium EDTA for hour before being placed in cold storage. Halves of 24 o r 27 potatoes of each treatment were cooked and the degree of after-cooking darkening was observed by 5 to 8 judges. The procedure for the cooking and scoring are reported in a paper by Hanning and Hunsader (1) and details of plant sprays by Hunsader (2). After being scored, the potato halves from the 1955 treatments were carefully matched with the corresponding raw halves. The dark and light areas were cut from the cooked halves and similar areas were cut symetrically from the raw halves. Composites were made of dark and light areas of each spray and dip treatment and a single composite of the checks. Juice was pressed from the tissue and aliquots were taken for iron and phenol determinations.Sixty-four potatoes from the check samples of the 1955 crop were divided into lots of 8 potatoes each. Each lot was peeled and cut into 2 mm. slices. Four of the lots were wrapped in aluminum foil and baked after evacuation. The slices were evacuated in 0.5% solutions of benzoic, boric, caff eic, chlorogenic, tannic, and citric acids ; or of ethylene diamine tetra acetate or EDTA; or of iron sulfate. Two controls were used; (a) some slices were not given any treatment, and (b) some slices were evacuated in distilled water. Iron and phenol
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