Molecular structure-affinity relationship of selected phenolic compounds for lupin seed γ-conglutin

The molecular basis underlying the interaction between proteins and phenolic compounds are still not fully understood. The specific structural properties of proteins, as well as phenolics, strongly determine the complex formation. In this work, the interactions between γ-conglutin, a unique lupin seed protein, and twenty-one different phenolic compounds representing six different classes of phenolics that differ in their structures were investigated. The interactions were studied based on a fluorescence quenching experiment, and the determined binding constant (Ka) ranged from 6.88 × 102 (protocatechuic acid) to 5.06 × 106 (hesperidin), while the number of binding sites of phenolic compound molecules to the protein (n) was on average 1.14 ± 0.16. Within the analysed compounds, phenolic acids interacted the weakest with the protein, while flavonoids showed considerable higher affinity strength to γ-conglutin. Notably, flavanones and flavones were the phenolics that formed the complex with markedly higher values of Ka (1-3 orders of magnitude) and n. Additionally, principal component analysis allowed to formulate the general regularities of phenolic compounds preferences for γ-conglutin. Finally, the obtained results also indicate that phenolic compounds' binding preferences for γ-conglutin can result from their native occurrence in lupin seeds