Effects of harvesting time and modified atmosphere packaging on biochemical changes in potato tubers

Undamaged potato tubers (cv. 'Marfona') grown in Tokat, Turkey, were used in this study. The tubers were cured for two weeks at 15 degrees C and 75-85% relative humidity. The tubers were sorted for size, shape and physical damage and were divided into two groups. One group was left unwrapped and the other was placed on polystyrene trays and heat-sealed in 30, 40 or 60 mu m low density polyethylene (LDPE) film or 38 mu m c-polypropylene (CPP) film. The samples were kept in temperature-controlled rooms at 5 +/- 1 degrees C and 75-85% RH for eight months. Samples were taken every month during storage, and the internal colour, ascorbic acid, titratable acidity, pH and total soluble solids were determined. Results indicate that the harvesting time and storage period significantly affected quality parameters. The highest increases in total soluble solids, minimum change in pH, lowest titratable acidity and ascorbic acid values were found in tubers in 38 mu m CPP harvested on July 25th. The lowest pH and ascorbic acids were found in the 40 mu m LDPE packaged tubers, while maximum titratable acidity was found in the unwrapped tubers harvested on 20th September. The L* values indicate that the internal lightness of the tubers generally decreased during the storage period, indicating that they became a bit darker during storage.