Metallic pine nut taste: Industry hypotheses

Pine nuts are a popular addition to salads, and are also a crucial ingredient in pesto sauce. Reports of a metallic taste that can linger for up to two weeks after consumption of pine nuts circulated in Belgium in 2001, prompting the Poisons Centre to conduct a comparison of affected and unaffected nut batches. Although they concluded there was no safety threat, no chemical differences were found.

Although it is not a food safety issue, the UK’s FSA is taking up the challenge after incidents in that country.

Curiously, not everyone seems to be affected. Some people taste metal, while others emerge from eating from the same batch with their taste faculties unscathed.

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Rancid oils? ​

Bruce Johnson (company affiliation not supplied) suggested that the phenomenon could be down to rancidity. He noted that lipid peroxide tests for rancidity on safflower and flax seed oils, a near metallic taste has been identified that lasts for several hours.

“The contributing factors we have found to oil rancidity are time, heat and oxidizers. If you would like to discover the taste of rancid oils just purchase some Organic Flax Seed Oil and taste it at the end of its shelf-life,”​ he said.

Another respondent, who preferred not to be identified, wrote that “in addition to metallic flavors that are characteristic of some oxidized lipids, there is also a metallic flavor that results when lipids in the cell membranes of the taste receptors are oxidized”.​

Frans Remmerswaal, senior flavourist, sweet and beverages at Symrise also thought the problem could be down to stale oils

“Oxidation of linoleic acid will for typical 'rancid fat' chemicals like T,T-2,4-decadienal. Under certain circumstances this in turn can oxidize to 4,5-epoxy-T-2-decenal, which has a strong metallic character and has an extreme low flavour threshold.”​

Unfortunately, standard chemical analysis will normally not reveal this type of chemical, but Remmerswaal notes that they have been detected in several food products, oils, cereal products, dairy foods and beer.

Shared chemical? ​

Amanda Hewitt, product development manager for Nelson Farms, reported coming across the same phenomenon with an acidifier called Glucona Delta Lactone (GDL).

“Some people get the strangely metallic aftertaste in the center of their tongue that seems to last and others (myself included) cannot taste it,”​ she wrote. “Could it be a chemical the two have in common?”​

Rodentixides or sterilisation methods? ​

Raf Dahlquist of ChromaDex, a Nevada-raised pine nut aficionado, says he never experienced ‘metal mouth’ when eating native pine nuts. He has, however, experienced it from pine nuts sourced from China and South Korea and purchased from stores.

He suggests a pesticide survey be conducted as a matter of routine, but it is usually squirrels rather than insects that attack pine nuts – in Nevada at least. A check for the common rodenticides might therefore be productive. “Are there toxins in this application which produce as symptoms the metal mouth experience,” ​he said.

Other tests suggested could be a ICP/MS elemental survey. It could also be worth checking how the nuts were sterilized in bulk storage: “Was bromine fumigation used? Were they irradiated?” ​

Irradiation is not permitted by the US FDA, but this can be checked by scintillation counting. “If so, what might daughter products be?”​ he asked.

Original article - http://www.foodnavigator.com/Science-Nutrition/Metallic-pine-nut-mystery-stumps-food-analysts