SUMMARY— Ontario potatoes, representing a variety that is very susceptible to precooking blackening, were grown in each of two consecutive years at different levels of potassium fertilization. In each of the two years of the study, the discoloration and total phenolic content of tubers decreased as potash applications were increased from 140 to 400 or 540 lb. per acre. The differences in discoloration were significant at the 1% level and the differences in phenolic content at the 5% level. Potatoes grown at high levels of potassium fertilization had higher cytochrome oxidase activity than those grown at lower levels. Potassium fertilization had no significant effect on polyphenol oxidase activity. A positive correlation (0.830) was found between the phenolic content and discoloration of potatoes as affected by potassium fertilizer.

SUMMARY Ontario and Pontiac potatoes, respectively representing varieties susceptible and resistant to precooking blackening, were examined for phenolic content and for cytochrome oxidase and polyphenol oxidase activities following storage at 4‐O and 50°F. The study was conducted for two consecutive years. In each of the two years the phenolic content of both varieties was significantly higher in potatoes stored at 40°F than in potatoes stored at 50°F. Both varieties had higher cytochrome oxidase and polyphenol oxidase activities when stored at 50°F than when stored at 40°F. The lower enzyme activities at 40°F may be responsible, in part, for the accumulation at that temperature of phenolic substances which serve as substrates for the enzymes. The higher phenolic content at lower temperatures may account for the greater discoloration of the potatoes.

SUMMARY The relationship of specific gravity to the phenolic content and enzymatic activity of Ontario potatoes grown in each of two consecutive years was studied. Phenolic content was found to be highest in tubers of highest specific gravity. Cytochrome oxidase activity tended to increase with increasing specific gravity up to the highest level, but, in each of the harvests studied, eytochrome oxidase activity dropped at the highest specific gravity level. Polyphenol oxidase, in relation to specific gravity, showed a trend opposite to that of cytochrome oxidase. Polyphenol oxidase activity decreased significantly with increasing specific gravity.