Effect of maturity and storage on ascorbic acid and tyrosine concentrations and enzymatic discoloration of potatoes

Ontario and Pontiac potatoes, representing cultivars susceptible and resistant to enzymatic discoloration, were examined for the effect of maturity and maturity-storage interactions on the concentrations of ascorbic acid and tyrosine. Both cultivars were harvested 7, 9, 11, 13, 15, and 17 weeks following planting and stored for 0, 4, 8, 12, and 24 weeks at 5 degrees C and 95% relative humidity prior to analyses. Ascorbic acid concentrations, of both cultivars increased significantly (p 0.05) up to 11 weeks following planting and decreased thereafter. Following 24 weeks of storage tubers harvested at 1 1 weeks showed greatest decreases while those harvested at 7 weeks showed least decreases in ascorbic acid, suggesting significant maturity-storage interactions. Tyrosine decreased significantly (p 0.05) up to 9 weeks following planting and increased thereafter. Following 24 weeks of storage tyrosine showed greatest increases in tubers harvested at 7 (Ontario) and 9 weeks (Pontiac). No consistent correlation between ascorbic acid and discoloration was observed. Although tyrosine was positively correlated with discoloration within a cultivar, it did not appear to be a predominant factor determining blackspot susceptibility of potatoes. The blackspot-susceptible cultivar, Ontario, had higher ascorbic acid and lower tyrosine concentrations than the resistant cultivar, Pontiac