The Effects of Low Oxygen on Chlorophyll and Glycoalkaloid Concentrations in Potato Tubers

Light stimulates both chlorophyll and glycoalkaloid synthesis in potatoes through independent biochemical processes.  Green potatoes are rejected by markets because of the expectation that the potatoes also have higher glycoalkaloid contents. To reduce potato losses caused by light exposure, the use of controlled atmospheres was investigated.  Potato tubers (white skin varieties) were held in chambers with air or controlled atmospheres with four oxygen concentrations (i.e. 0%, 0.5%, 1%, and 3%) for 8 days with continuous light exposure at 3,000 lux and compared to potatoes held in chambers in the dark.  Glycoalkaloid concentrations (determined spectrophotometrically on freeze-dried potato slices) in light-exposed potatoes increased from an average of 6 mg/g FW on day 0 to 18 mg/g FW on day 8.  Glycoalkaloid concentrations of potatoes held in the dark or in any of the low oxygen atmospheres did not exceed 8 mg/g FW after 8 days.  Only oxygen concentrations of 1% or lower were effective to inhibit greening (spectrophotometric determination of chlorophyll in peels). Although controlled atmospheres with oxygen lower than 1% inhibited both greening and glycoalkaloid synthesis, these atmospheres caused unacceptable anaerobic conditions (mainly increased ethanol concentrations with little change in acetaldehyde concentrations) and decay. The 3% oxygen treatment, though providing less inhibition of greening, caused no increase in fermentative volatiles.  It appears that glycoalkaloid synthesis is more sensitive to lowering oxygen concentration than is chlorophyll synthesis.