Reducing Potato Tuber Discoloration

Discoloration or internal blackening or browning of the tuber is responsible for significant post-harvest losses. It is caused by the oxidation of phenolic substances, mainly tyrosine to melanin. Potassium, magnesium and boron can all have effects on discoloration and blackening.

Crop Nutrition and Potato Tuber Discoloration


Potassium affects enzymatic discoloration and after-cooking blackening and low levels of potassium can increase the incidence of after-cooking blackening.

Potassium influences the concentration of organic anions such as citric acid or ascorbic acid (i.e. vitamin C within the tuber). These two molecules have an antioxidative function, which decreases the incidence of enzymatic and non-enzymatic discoloration by slowing down the oxidation processes.

This trial from the USA shows the influence of potassium on enzymatic discoloration on two different varieties.


Low magnesium levels can increase susceptibility to enzymatic discoloration. This trial from the USA shows the influence of magnesium on enzymatic discoloration.


Boron reduces the oxidation of phenols that are responsible for enzymatic discoloration. Thus, a good supply of boron reduces the occurrence of enzymatic discoloration in potato tubers.

This trial from Holland shows the influence of boron on enzymatic discoloration in two different years.


Other Crop Management Practices Influencing Potato Tuber Discoloration

  • Selecting the right variety to meet dry matter production needs
  • Selecting quality seed with less risk of disease
  • Avoiding fields, with adverse factors such poor drainage or low water holding capabilities
  • Ensuring blight spray programs are effective
  • Scheduling irrigation to maximize quality characteristics
  • Harvesting early, thereby minimizing late disease ingress or tuber deterioration