Stem-end Chip Defect in Potatoes (Solanum tuberosum L.)

Global consumption of potato (Solanum tuberosum L.) continues to shift from fresh potatoes to value-added processed food products such as potato chips. One serious tuber quality defect of chipping potatoes is stem-end chip defect, which results in chips with dark-colored vasculature and adjacent tissues on the tuber stem end after frying at a high temperature. The influences of moderate water stress, alone or in combination with moderate heat stress, as well as maturity of tubers at harvest on the incidence and severity of stem-end chip defect were investigated. Treatments were imposed in controlled-environment greenhouses. Only temperature stress, daytime temperature at 30°C, in one of two years significantly changed the occurrence of stem-end chip defects. Biochemical analyses showed that more severe defects were associated with increased amounts of tuber stem-end glucose and increased stem-end acid invertase activity. Moderate environmental stresses and immaturity of tubers at harvest, however, were not sufficient to consistently cause stem-end chip defects.;Verticillium wilt, caused by a soil-borne fungal pathogen Verticillium dahliae, is a persistent potato disease that causes early plant senescence and yield reductions. A two-year field trial has been conducted to investigate the effects of V. dahliae on stem-end chip defect development and the underlying biochemical mechanism. Conditions that favored vascular infection with V. dahliae were more likely to cause a high incidence of severe stem-end chip defects than those that were less favorable for infection. Infection of V. dahliae was associated with an up-regulation of acid invertase activity and an accumulation of reducing sugars on the tuber stem end. High concentrations of reducing sugars are the direct cause of dark color on chips since reducing sugars produce dark-colored products in the Maillard reaction during frying.