Pine nut syndrome: a simple test for genome size of 12 pine nut–producing trees links the bitter aftertaste to nuts of P. armandii Zucc. ex Endl

Genome sizes of 12 pines that produce edible nuts were investigated by flow cytometry with propidium iodide. Results were compared with the genome size and taste of 11 commercial samples of pine nuts to determine which species is the cause of a lingering bitter aftertaste (“pine nut syndrome”). Each nut sample was visually separated into two to six subsets. From a single nut, the embryo and the endosperm were measured. On the basis of nuclear DNA content, pine species could be matched with their nuts. Seven out of the 11 commercial samples contained only a single pine species: P. koraiensis Sieb.& Zucc., P. pinea L., P. armandii Zucc. ex Endl., or P. gerardiana Wall. ex Don, but the other four samples were a mix of two species. Tasting showed definitively that P. armandii is the origin of the bitter aftertaste. Nuclear DNA content can be measured using flow cytometry in less than 5 min, including the calculations. This makes it easy to identify the problem-causing nuts. With hindsight, it is now also possible to identify the species of four common edible pine nuts.