Preserving Color in `Michigan Purple' Potatoes

The objective of this study was to evaluate preharvest fertilizer application and postharvest storage temperature and duration as they affect the intensity and stability of color in red and purple potato cultivars during storage. `Michigan Purple', `Dakota Rose', and `Chieftain' were stored at 4 °C and hue angle (h°) was measured weekly. The initial `Michigan Purple' h° of 1.1° changed to 23.2° after 18 weeks of storage (a shift in h° from 350° to 30° changes from purple to red) while the initial hue angle of 18.5° and 34.1° for red-skinned cultivars, `Dakota Rose' and `Chieftain', changed to 27.2° and 43.2°, respectively. Hence, the degree of color shift was greater in `Michigan Purple' although all the cultivars in this experiment underwent significant color change during storage. Hue angle of `Michigan Purple' tubers stored at 4°, 10°, and 20 °C for 8 weeks changed 19.4°, 12°, and 14.2° toward the redder h°, respectively. Thus, the color of `Michigan Purple' tubers changed the least at 10°C. Hue angle of `Michigan Purple' tubers fertilized with 180 lbs/acre slow-releasing nitrogen, 180 lbs/acre nitrogen, 270 lbs/acre nitrogen, and 2.5 lbs/acre poultry manure was measured after 5 weeks at 4 °C. Hue angles were 0.92°, 11.65°, 3.99°, and 1.34°, respectively. The hue of the first three treatments differed significantly from one another, but the hue of the potatoes treated with 180 lbs/acre slow-releasing nitrogen and 2.5 lbs/acre poultry manure did not differ. Preharvest factors like plant nutrition can influence tuber color in storage and `Michigan Purple' tuber color is particularly sensitive to storage temperature.