Phthalimide Residue in Coffee: Does It Solely Derive from Folpet?

Folpet, a fungicide used on several crops, easily degrades into phthalimide (PAI) at high temperatures and basic pH. The maximum admitted limit for Folpet in foodstuffs as coffee is defined by the sum of its amount and that of PAI. Noteworthy, PAI can also arise from the reaction between ubiquitous phthalate derivatives and NH3. This work aims to demonstrate that the detection of PAI in roasted coffee is not necessarily diagnostic for Folpet as it can also originate from the reaction between phthalic anhydride (PAA), derived from phthalates, and amino acids (AAs), as a NH3 source. Thermal treatment of AAs with PAA confirmed that PAI generation follows a temperature-dependent path. Experiments with diethyl phthalate (DEP) and AAs have shown that maximum PAI generation via heating occurs at 200 °C for 60 min. PAI generation has also been proven for Folpet-free green coffee beans that were heated under laboratory and industrial roasting conditions.