Membrane lipid dynamics and lipid peroxidation in the early stages of low‐temperature sweetening in tubers of Solanum tuberosum

Abstract

Sugar accumulation and membrane lipid parameters associated with membrane permeability in chilling injury and senescence were followed in the early stages of low‐temperature sweetening in Solanum tuberosum tubers to monitor their dynamics. Norchip, a low‐temperature sweetening‐susceptible potato cultivar, and North Dakota 860‐2, a low‐temperature sweetening‐tolerant selection, were stored for 55 days at 4 and 12°C. Sugar accumulations were not linear and were characterized by fluctuations or cycles over storage time. Sucrose cycling and accumulation were greatest for Norchip tubers stored at 4°C as compared to the other treatments. Increases in membrane permeability were not detected by increases in electrolyte leakage. No significant changes in the phospholipid, galactolipid, free sterol levels or phospholipid to free sterol ratio were observed. The double bond index obtained from the fatty acid profiles of the total lipid fraction decreased significantly (decreased unsaturation) for Norchip tubers at 4°C over time. Free fatty acid and diene conjugation values fluctuated and increased over time for all treatments with greater amplitude of fluctuations observed for Norchip tubers stored at 4°C. These latter effects may be due to the high levels of lipid acyl hydrolase and lipoxygenase found in potato tubers. When free fatty acid and diene conjugation values were plotted with glucose accumulation over time, a possible relationship among the variables was revealed. The observed peroxidation products could relate low‐temperature stress and the resultant low‐temperature sweetening to chilling injury and drought stress. The anti‐oxidative potential of potato tubers should be considered for future cultivar development as a mechanism to lessen the severity or rate of low‐temperature sweetening development.