Stem End Chip Defect In Tubers Used for Potato Chip Production.

Stem-end chip defect (SECD) is a serious tuber quality concern that affects chipping potatoes (Solanum tuberosum). SECD defect is characterized by dark-colored vascular tissues and adjacent cortical tissues at the tuber stem-end portion of potato chips after frying. Chips with SECD are unattractive to consumers and raw product may be rejected at processing facilities if SECD exceeds specifications. A multi-year research project has investigated the potential for moderate environmental stresses, such as those that cause sugar end defects in potatoes used for French fry production, to cause SECD in chipping potatoes. Plants were grown in controlled-environment greenhouses in the UW Biotron and field plots at the research station in Hancock, WI. Our Biotron data indicate that moderate environmental stresses including soil moisture deficit and high daytime temperature (30°C), alone or in combination, as well as immaturity of plants at harvest, had little affect on the percentage of severe SECD. Immaturity at harvest greatly affected tuber bud-end and stem-end sucrose contents at harvest, with sucrose being significantly greater (p <0.01) in tubers harvested from immature rather than mature plants. Vine maturity at harvest, however, changed the percentage of tubers that had severe defects by only 2%. More severe SECD corresponded with higher rates of vacuolar acid invertase activity and it is likely that this enzyme produces the reducing sugars that cause dark color formation during frying. Defects in chips cut through the tuber stem attachment point were uncommon in field plots in 2010 at early sampling times but were common at harvest and in storage, as they were throughout the upper Midwest that year. Defect incidence differed between cultivars and for three of four cultivars in these small-scale trials, defect severity decreased slowly during storage at 13°C.