Blackening of Potato Tubers on Boiling

Abstract

IT has been shown that the black coloration which appears in some potato tubers after boiling cannot be melanin, as the colour disappears rapidly in acid solution at about pH 3.0; at this pH melanin is quite stable. The bleached pigment appears to be soluble in acid solution, but the grey coloration partially reappears on neutralizing the acid with buffer solution at pH 7.0. No correlation was observed between the development of the pigment and the activity of the enzyme tyrosinase as estimated by the Warburg technique. Neither could any correlation be found between the blackening and the tyrosine content of the potatoes. It was observed that among the varieties tested there appeared to be two distinct levels of tyrosine content: King Edward and Majestic with 40–60 mgm. per 100 gm. fresh weight, and Kerr's Pink and Arran Banner with 8–25 mgm.