After‐cooking Discoloration of Potatoes: Possible Involvement of Polyphenolic Constituents

Abstract

After-cooking discoloration of potatoes has been a serious problem in several growing areas east of the Mississippi River for more than 20 years.This problem was acute with the 1953 crop but occurred in only rare lots of the 1954 crop. Several hundred samples of potatoes from the 1954 Maine crop were screened by staff members of the Maine Agricultural Experiment Station but little incidence of this type of discoloration was found. Blackening of cooked potatoes was again troublesome with the 1955 crop.The extensive literature on after-cooking discoloration of potatoes was recently reviewed by E. Yanovsky (22), and will not be considered in detail here. This type of discoloration usually occurs as greying or blackening, in greatest intensity at the stem end just beneath the skin. Flesh of affected tubers typically appears normal in the raw state.After-cooking discoloration is not only encountered in home and restaurant cooked products but in all types of processed potato products. This discoloration can cause difficulties to processors, particularly in canned potatoes, frozen products, and dehydrated potato products. Caldwell ef al.(3) reviewed thoroughly the various types of discoloration encountered in the processing and use of dehydrated potatoes.Water blanching and acid dipping treatments of the raw, peeled stock are of limited value in inhibiting after-cooking discoloration. Sulfiting is of some help but cannot be used with potatoes to he processed with meat, since foodst.uffs containing meat must be sulfite-free for shipment in interstate commerce.In the past 10 years, at least two investigations have been made of a colorless, fluorescent substance extracted from potatoes \vith acidified alcohol. Lewis and Doty (12) believed this substance to be the precursor of the pigment causing potato blackening, since it \zas readily converted to a black pigment by heating above 35" C. However, Bowman and Hanning (2) concluded that there was no clear relationship bet\veen the extent of fluorescence obtained with this substance and the tendency for potatoes to blacken. Many possible causes have been suggested for after-cooking discoloration, but few facts have been established and much of the published data are contradictory when compared. Some of the factors proposed as being related to after-cooking discoloration are : potato variety ; soil pH and composition ; growing conditions ; storage conditions ; ratio of protein nitrogen to nonprotein nitrogen ; and the amounts of tyrosinase, iron, phosphorus, and manganese in the tubers.

Effect of pre-soaking treatments on the nutritional profile and browning index of sweet potato and yam flours

“…Organic acids other than ascorbic acid were found to yield flours with low browning indices, possibly due to partial inhibition of the PPO under acid pH. The bivalent iron in potato was reported to combine with O-dihydroxyphenol resulting in a lightcolored substance, which oxidized to form a dark-colored ferric compound on exposure to air (Hunter, Heisler, Scillano, Treadway, & Woodward, 1957). A direct relation between chlorogenic acid group of phenols and darkening in potatoes and inverse relation with citric acid have been suggested (Bate-Smith, Hughs, & Swain, 1958).…”

THE EFFECT OF MATURITY AND STORAGE ON PHENOLIC CONTENT, ENZYMATIC ACTIVITY AND DISCOLORATION OF POTATOESa

“…9, 10). Varietal differences in phenolic content have been reported by several workers (5,6,8). Craft, Siegelman and Butler (6) found that the total phenolic content in two varieties of potatoes did not change significantly after storage.…”

Cooking Methods and Storage Treatments of Potato: Effects on Carotenoids, Antioxidant Activity, and Phenolics

“…The phenolic acids (chlorogenic acid, caffeic acid, vanillic acid, p-coumaric acid, and t -cinnamic acid) and flavonoids (rutin, myricetin, (-) epicatechin, and quercetin dihydrate) accounted for 67 % and 33 % of the phenolics detected, respectively. Chlorogenic acid was determined to be the most abundant phenolic compound in potato, which has previously been reported (Hale et al, 2008;Hanson and Zucker 1963;Hunter et al 1957;Reddivari et al 2007a). The average concentrations of chlorogenic and caffeic acids, 34 and 33 μg/gfw, were within range of previous reports (Hale 2003) and accounted for 37 and 36 % of the phenolic acids, respectively.…”