A pistachio shell can be bleached for looks. The unusual part is what may happen beyond the shell: chlorine-based treatment can meet fatty acids in the edible kernel and create new compounds.
USC researchers describe these reaction products as fatty acid chlorohydrins, a case of food-safety chemistry producing something new inside the food matrix rather than simply leaving a known contaminant on its surface. The USC account of the research explains that distinction.
A cosmetic treatment, a kernel reaction
In tests using 1 percent sodium hypochlorite, pistachios had the highest chlorohydrin concentrations among the nuts studied, ahead of hazelnuts and walnuts, according to Food Safety Magazine’s account.
That puts pistachios squarely in a study about a treatment intended for shell appearance. The result is a chemical finding, not a measurement of illness in consumers.
From a lab result to a food-safety question
The researchers also tested the compounds’ effects on cells. The available reporting does not establish a consumer dose or translate the lab results into a health-risk estimate; the study summary describes the work as an early step in understanding those compounds.
For pistachios, the detail worth keeping is the route of contact: a treatment applied to the shell may interact with fats in the kernel. That is a narrower question than whether bleaching is safe in every setting, and a more useful one for understanding what the experiment actually tested.