Research Results

Brown discoloration of green beans

In GreenCHAINge an innovative ‘smart chain’ is being developed. The overall goal is to improve the intrinsic quality of the produce on the shelf. To do this, it is imperative to understand all occurring quality issues of the fresh product at hand, in this case brown discoloration of green beans.

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Green beans are an important crop on the retail shelf. One of the main quality issues is brown discoloration during the post-harvest phase. The objective in this research is to test what the causes are for this discoloration. Three potential causes are investigated: 1) contact with free water, 2) low temperature and 3) microbial decay.

Experiment & results

Two cultivars of green beans were exposed to various conditions to test the hypotheses that brown discoloration results from contact with free water, low temperatures and/or microbial decay.

  • Contact with free water does not increase the amount of brown discoloration, in fact the amount of brown discoloration is lower. The effect shown in the beans that have been in contact with free water (washing or condensation) is that they were limper (loss of firmness) than the beans in the control group.
  • Low temperature did not increase the amount of brown beans. The beans stored at 18°C had most brown discoloration, more than in the samples stored at 9°C, 6°C or 3 °C.
  • Microbial decay is not causing brown discoloration, since treating the beans with chlorine to remove all microbial contaminations (not allowed in practice) had no effect on the amount of brown discolaration.

This means that all three hypotheses were rejected. The experiment showed that the two used cultivars have a clear difference in amount of discoloration.

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Defect distribution in green beans (cv. Domino) for 4 storage temperatures


The experiment showed that the three suspected causes of brown discoloration in green beans could not be upheld. The recommendation from this study is to cool green beans to temperatures below 9°C to prevent brown discoloration. Another measure could be to wash the beans, but the beans may then become limper.

Susceptibility to brown discoloration is partly cultivar dependent.