Deciphering the Origin and Fate of the Natural Plant Hormone Indole-3-Acetic Acid in Coffee

Indole-3-acetic acid (IAA) is a natural hormone found in all plants and can also be used as a plant growth regulator, which is banned in the EU. To differentiate between its natural presence and pesticide usage, the origin and fate of IAA during coffee roasting were studied. Green beans from the Coffea arabica and Coffea canephora varieties were spiked with a stable isotope precursor, ¹³C₁₁-tryptophan, and roasted to different degrees. Liquid and gas chromatography coupled with mass spectrometry were used to analyze the degradation products. Alkaline hydrolysis determined free and bound IAA proportion in the coffee samples. The study found that IAA levels increased during roasting, forming indole-3-acetaldehyde and further degrading into 3-methylindole. Hydrolysis experiments showed that IAA was released from the coffee matrix, with higher amounts released during longer roasting times. These results indicate that IAA naturally occurs in green coffee and is not likely due to pesticide use.