Potato skins help distinguish organic from conventional varieties

Organically and conventionally grown potatoes may be told apart by flavour, say researchers in the Journal of the Science of Food and Agriculture this month – but only if the potato skins are left on.

A panel of fifteen taste testers was asked to evaluate boiled samples of potatoes that had been grown organically with compost, organically without compost or conventionally.

Dark Red Norland potatoes – the most popular redskin potato in the US – were evaluated.

The scientists used the ‘triangle test’ method to evaluate the panel’s responses, which involves tasting three samples, two of which are identical and one of which is different. The test is repeated to ensure that the panellist is not identifying the ‘odd one out’ by luck.

However the panellists were merely looking for taste differences – they did not know how the potatoes had been grown. When the potatoes had been peeled prior to cooking, panellists could not distinguish between the conventionally and organically grown potatoes.

However when the skins were left on, the panellists tended to be able to identify a difference between the conventionally and organically grown potatoes. However, in similar tests, fewer panellists differentiated between organic potatoes grown with / without compost.

“The data suggest that, in this study, the ability of panellists to consistently differentiate samples depended on whether the skin of the tubers had been removed before boiling,” said lead researcher Dr Matthew Kleinhenz of the Department of Horticulture and Crop Science.

In addition, the chemical make-up of potatoes differed significantly when the crops were grown using different methods. Measure of the mineral and glycoalkaloid contents showed that glycoalkaloids (natural protective agents in potato plants and tubers) and levels of potassium, magnesium, phosphorous and sulphur were higher in organic potatoes, whereas iron and manganese levels were higher in conventional potatoes.

According to Dr Kleinhenz, it may be the glycoalkaloids, which can impart a bitter taste, that are responsible for the perceived flavour differences, as glycoalkaloids are thought to move from outer (such as skin) to inner (such as flesh) layers of potatoes during boiling.

“The results provide additional evidence that linkages exist between the methods used to grow crops and the responses consumers may have when eating them,” added Dr Kleinhenz, “and they could encourage growers and scientists alike to explore these linkages within the context of management systems, including organic. The goal would be to design cultivation systems that optimise the quality – sensory and nutritional properties – of vegetables and other crops.”

“Many factors influence the eating quality of potatoes and other vegetables. Some factors relate to the methods used to grow crops. In this study, we found evidence that the flavour of organically and conventionally grown redskin potatoes may differ, but only if the skin remains on the tubers during boiling,” he said.