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.