Detection of 3-N-oxalyl-l-2,3-diaminopropanoic acid in thermally processed foods by reverse phase high performance liquid chromatography

Grasspea (Lathyrus sativus), because of its low cost and ease of cultivation, is often an adulterant of other legumes. The seeds—albeit rich in protein (～20–32% of dry seed weight)—contain a neurotoxin, 3-N-oxalyl-l-2,3-diaminopropanoic acid (β-ODAP). An efficient and sensitive RP-HPLC method for detecting β-ODAP by pre-column derivatisation with O-phthalaldehyde (OPA) was developed in our laboratory. The usefulness of this method for measuring the β-ODAP content of thermally processed legume-based foods with various substitution levels of grasspea flour is demonstrated. The β-ODAP content of dehulled grasspea flour used was 5.26 ± 0.11 mg/g. The method shows a clear resolution between β-ODAP and its non-toxic α-isomer. At 1% (w/w) substitution it was possible to detect and distinguish the two isomers. Among the unit heat operations deep-frying results in the β-ODAP content being lowered by ～80% irrespective of the substitution level. The decrease in β-ODAP content by fermentation was ～58%, which was further decreased on steaming. The results indicate that levels as low as 0.01 mg of β-ODAP/g of product are measurable. Therefore this method is a useful tool in detecting the unwarranted use of grasspea flour in processed foods that pose health risks to unsuspecting customers.