Effect of storage temperature on potato (Solanum tuberosum L.) tuber glycoalkaloid content and the subsequent accumulation of glycoalkaloids and chlorophyll in response to light exposure

Tubers from six potato cultivars were placed into either 10 or 4 degrees C stores immediately postharvest. Replicated tuber samples were analyzed for glycoalkaloid (TGA) content immediately postharvest, after 6 and 14 weeks storage at 10 degrees C and after 6 weeks storage at 4 degrees C. Subsamples from the 10 degrees C store were removed after 1, 2, 3, 4, and 8 weeks, respectively, stored for a further 6 weeks at 4 degrees C, and again analyzed for TGA content. After each sampling date, tubers were exposed for 96 h to light and analyzed for both chlorophyll and TGA concentrations. The results indicated that the exposure of tubers from some cultivars, such as Brodick and Pentland Crown, to low temperatures within 2 weeks of harvest resulted in a relatively rapid accumulation of glycoalkaloids to levels close to or exceeding the recommended safe maximum level of 200 mg of TGA per kilogram of fresh weight, while other cultivars, such as Eden and Torridon, appeared insensitive to cold stress. Storage for 6 weeks at both 10 and 4 degrees C resulted in a greater accumulation of glycoalkaloids in response to light exposure relative to that observed immediately postharvest, with the tubers from all six cultivars stored at 4 degrees C producing over twice the amount of TGA as those stored at 10 degrees C. Storage at 10 degrees C prior to 6 weeks storage at 4 degrees C resulted in smaller photoinduced increases in TGA content but even after 8 weeks at 10 degrees C followed by 6 weeks at 4 degrees C, the photoinduced increases in all cultivars were significantly higher than that recorded for tubers stored continually at 10 degrees C, which had values comparable to those obtained immediately postharvest. In all cultivars photoinduced chlorophyll accumulation was little affected by storage temperature but was slightly, although significantly, reduced as time in storage increased from 6 to 14 weeks. The significance of these results in relation to consumer safety and plant breeding are discussed.