Legume crops constitute a promising alternative to reduce meat proteins in the human diet and fulfill both the nutritional
needs of the world population and agro-environmental sustainability goals. One of the challenges to their use is the
presence of polyphenols. Condensed tannins (polyphenol polymers) are usually contained in the testa and participate in
plant defense against both biotic and abiotic stressors. During alimentary processing steps (e.g., flour grinding, protein
precipitation), some condensed tannins can be processed with kernels. When flour grinding breaks down cell organelles,
polyphenol oxidase comes into contact with its substrates, creating quinones through an enzymatic process. Additionally,
high pH conditions during protein precipitation can trigger polyphenol autoxidation, leading to quinone formation.
Quinones are highly reactive and can carry out nucleophilic attacks (e.g., Michael addition or imine formation) on
proteins. As a result of this reactivity, adducts are formed, which modify the organoleptic properties of legume flours or
protein isolates. While some changes can be positive (e.g., increased solubility, foaming, and emulsification), many result
in off-flavors (bitterness, beany taste), browning, and instabilities.