Carbon Dioxide and Ethylene: A Combined Influence on Potato Fry Color

Abstract

For many years, the accepted wisdom among potato storage researchers and industry personnel linked the accumulation of CO2 in the storage atmosphere to darkening of potato fry color. Dark fry color is undesirable in the potato processing industry, as consumers prefer light-colored finished products. Previous research to elucidate the effect of CO2 has presented conflicting results. In three consecutive years of storage trials, the effects of elevated CO2 concentrations, reduced O2 concentrations and ethylene gas on the fry color and sugar content of `Russet Burbank' potato (Solanum tuberosum L.) tubers were evaluated. The potatoes were stored in modified atmosphere chambers and selected atmosphere mixtures were supplied from compressed gas cylinders. Four 3-week trials were conducted in 2002 and two 9-week trials were conducted in each of 2003 and 2004. Fry color and tuber sugars were assessed at the start of each trial and after several weeks of exposure to the treatment atmospheres. Compared with untreated controls, increased CO2 alone or in combination with decreased O2 had little or no effect on fry color or tuber sugars. During the second and third years, only selected treatments were repeated, with or without the addition of 0.5 μL·L–1 ethylene gas. Ethylene is known to affect potato fry color and reducing sugars. In three of four trials, tubers exposed to ethylene alone had darker fry color and higher reducing sugars compared with controls. Applied treatments had little or no effect on fry color and sugars in the fourth trial. Interestingly, in the same three of four trials, fry color of tubers exposed to both elevated CO2 and ethylene gas was not only darker than controls but also darker than tubers treated with ethylene alone. Similarly, reducing sugar concentrations were higher in tubers exposed to both ethylene and CO2 than with ethylene alone. No similar interaction between ethylene and oxygen concentration was observed. The results suggest a synergistic negative effect of trace ethylene and elevated CO2 on fry color, which may explain the apparently contradictory findings of some published research examining the effects of CO2 on potato fry color.