Pine nut study fails to solve mystery of 'pine mouth'

By Nathan Gray

- Last updated on GMT

Related tags Pine nut

New research investigating the composition of pine nuts has failed to fully uncover a reason behind the mystery of why thousands of people around the world have experienced taste disturbances – known as ‘pine mouth’.

The report – published in the Journal of Agricultural & Food Chemistry ​– analysed the composition of fatty acids of pine nut products, including some products that have been associated with ‘pine mouth’. The researchers said that the findings leave the decade-old mystery of why thousands of people around the world have experienced disturbances in taste after eating pine nuts partially unsolved.

The research team from the US Food and Drug Administration (FDA) reported that fatty acid and DNA analysis of pine nut products found them to often be made up of several different species of pine nut. In particular, they reported that samples from products that had been associated with ‘pine mouth’ contained traces of Chinese white pine.

Pine mouth

‘Pine mouth’ was first reported in Belgium in 2000. The ‘condition’ is a bitter metallic taste that develops within one to two days of eating certain pine nuts, and can last from one to two weeks.

In 2009, the French Food Safety Administration reported a possible link between ‘pine mouth’ and consumption of nuts of Chinese pine – a species whose nuts are not traditionally eaten by humans.

Chinese pine

Last year the Danish food authority released a report stating that ‘counterfeit’ pine nuts from China were the reason for ‘pine mouth’. The authority warned that  ‘illegitimate' Chinese pine nuts have a different fatty acid profile than 'genuine' pine nuts – and are responsible for the bitter metallic tastes.

They outlined two species of Chinese pine to be related to the incidence of ‘pine-mouth’ – Pinus armandii ​(Chinese white pine) and Pinus massoniana ​(Chinese red pine). 

Both species have smaller, round or triangular nuts that are only occasionally exported for use in pine nut products. However, with a growing demand for pine nuts, they Danish authority reported that these species of nut are being increasingly mixed with 'real' pines.

Since the Danish report, Codex has also recently classified P. armandii ​as unfit for human consumption.

Research details

The FDA researchers – led by Sara Handy – identified certain fatty acids with varying levels among pine species – so making them a potentially useful tool for telling different species apart. They then determined the source of pine nuts sold by measuring the ratio of these compounds to the overall amount of fatty acids in the nuts.

Using fatty acid composition and a fatty acid diagnostic index along with DNA analysis, they found that most pine nuts sold in the US are mixtures of nuts from different pine species, including Pinus armandii.

“Although the exact cause of pine nut associated dysgeusia is still not known, we found that 15 of 15 samples from consumer complaints contained at least some Pinus armandii, confirming the apparent association of this species with taste disturbances,”​ they said.

Handy and her team added that combining the fatty acid diagnostic index and DNA analysis was a useful way to determine which products contained pine nuts from several species. However, they said that such information had failed to fully indentify the cause of ‘pine mouth’ – adding that the technique cannot definitively predict which pine nuts may cause the metallic taste reaction.

Source: Journal of Agricultural of Food Chemistry
Volume 59, Issue 20, Pages 10995–11002, doi: 10.1021/jf203215v
Title: “Use of the Chloroplast Gene ycf1 for the Genetic Differentiation of Pine Nuts Obtained from Consumers Experiencing Dysgeusia”
Authors: S.M. Handy, M.B. Parks, J.R. Deeds, A. Liston, L.S. de Jager, et al

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