The ascorbate system and lipid peroxidation in stored potato (Solanum tuberosum L) tubers

The changes in the components of the ascorbate-glutathione system during the storage of potato (Solanum tuberosum L. cv. Spunta) tubers for 40 weeks at both 3 degrees C and 9 degrees C were studied in relation to lipid peroxidation. The level of malondialdehyde was found to be higher at 3 degrees C than at 9 degrees C throughout storage. Thus, lipid peroxidation, which is the main cause of membrane deterioration, was accelerated at the lower temperature. Catalase activity increased throughout storage independently of temperature. The ascorbate content of tubers decreased during storage both at 3 degrees C and at 9 degrees C, as in other ageing processes. However, ascorbate peroxidase activity reached a maximum after about 8 weeks of storage, then declined at 9 degrees C, but held a higher level at 3 degrees C. The dehydroascorbic content also reached a maximum after about 8 weeks and was significantly higher in tubers stored at 3 degrees C. These findings indicate a greater utilization of ascorbate by ascorbate peroxidase at the lower temperature. Ascorbate free radical reductase, dehydroascorbate reductase and glutathione reductase, the enzymes involved in the regeneration of ascorbate, were not affected by temperature and remained quite unchanged throughout storage. It can be concluded that the ascorbate system is involved in the scavenging of the free-radicals responsible for lipid peroxidation in stored potato tubers, at least at low temperatures and in the first period of storage.