Sweetening responses of potato tubers of different maturity to conventional and non-conventional storage temperature regimes

Low storage temperatures stimulate the accumulation of glucose and fructose (sweetening) in potato (Solanum tuberosum L.) tubers, resulting in unacceptably dark processed products during frying. Information on how tubers respond to unorthodox storage temperature regimes is lacking, especially for the relatively new frozen-processing cultivars, ‘Umatilla Russet’ and ‘Ranger Russet’. Such knowledge could greatly facilitate the ability to manage immature, over-mature, or otherwise stressed potatoes. This study characterizes the sweetening responses of ‘Russet Burbank’, ‘Ranger Russet’ and ‘Umatilla Russet’ tubers of different maturity, over a range of conditioning and holding storage temperatures. Tubers from early- and late-planted crops were wound-healed (12 °C) for 17 d after harvest (DAH), conditioned for a month (17–48 DAH) at 4.5, 6.7, or 9 °C, and subsequently stored (48–230 DAH) at 4.5, 6.7 or 9 °C (nine temperature regimes) for an additional 182 d before reconditioning at 16 °C for 21 d. Reconditioning hastens catabolism of reducing sugars and restoration of processing quality. On average, tubers from the early planting had lower rates of respiration during wound-healing and emerged from dormancy sooner than those planted later, indicating relative immaturity of the latter. The early-planted crop of ‘Ranger Russet’ was more sensitive to low temperature sweetening than the late-planted crop, reflecting a tendency of tubers to become over-mature and reinforcing the benefit of a ‘green’ harvest for this cultivar. All cultivars sweetened rapidly when conditioned at 4.5 °C. Conditioning at 6.7 and 9 °C, however, decreased the extent of low temperature sweetening during subsequent storage at 4.5 °C through most of the storage season, expanding the options for managing potatoes with lower than normal temperature later in storage. The processing quality of ‘Ranger Russet’ was maintained for 230 d with higher conditioning/holding temperature regimes. Reducing sugar concentrations in cold-sweetened ‘Ranger Russet’ and ‘Russet Burbank’ tubers decreased more than in ‘Umatilla Russet’ tubers in response to reconditioning at 16 °C. Following an interval of wound-healing, the use of combinations of non-conventional conditioning and holding temperatures that do not stimulate excessive sweetening broadens the management options for storing potatoes for the frozen-processing industry.