Exploring the lentil protein and onion skin phenolics interaction by fluorescence quenching method

In this paper, the effect of two phenolic extracts (red and yellow onion skin, RS and YS respectively) with different phenolic profiles on the fluorescence quenching of lentil protein isolate (LPI) was investigated. The quenching effect of YS at 4–30 μM concentrations on lentil proteins was in the range of 20.9–77.8%. A linear Stern-Volmer plot was obtained in agreement with static quenching for the LPI-YS complex while giving the blue shift at maximum emission between 8 and 30 μM YS concentrations. Thermodynamic parameters of the LPI-YS complex showed that the interaction was hydrophobic (ΔH>0 and ΔS>0), enthalpy driven (ΔH>ΔS), and non-spontaneous (ΔG>0) reaction. RS provided a more effective quenching effect at lower concentrations compared to YS and the quenching effect of RS at 1–16 μM concentrations was 24.5–92.8%. On the other hand, the red shift was observed between 0 and 16 μM RS concentrations, where the Stern-Volmer plot was non-linear, so there was a “sphere of action model” for LPI-RS complexes.