Interaction mechanism of pea proteins with selected pyrazine flavors: Differences in alkyl numbers and flavor concentration

The mechanism of pea protein (PPI) adsorbing flavor components of cooked beef (pyrazine flavor compounds with different concentrations and different numbers of alkyl groups) was researched by spectroscopic and molecular docking approaches. The binding ability results showed that the concentration of pyrazines and the number of alkyl groups in pyrazine strongly influenced the adsorbing ability of PPI. The binding ability of PPI to the pyrazines decreased in the order 2,3,5-trimethyl-pyrazine (TRP) > 2,5-dimethyl pyrazine (DP) > 2-methylpyrazine (MP). The increase in the concentration of pyrazine flavor compounds promoted the enhancement of the adsorption capacity of PPI. Fluorescence and time-resolved fluorescence analysis showed that different molecular structures caused by the amount of alkyl groups on a pyrazine ring showed different quenching types: MP and DP were mainly subjected to static quenching, and TRP with more alkyl groups was mainly subjected to dynamic quenching. During the adsorption of pyrazine flavor compounds, the structure on the peptide bond of pea protein is destroyed. The conformation of pea protein expanded gradually, and the protein changed from ordered structure to disordered structure with lower ΔH. The interactions between pyrazine and pea protein were spontaneous from thermodynamic analysis. Combined with the results of molecular docking, hydrophobic interactions were dominant in the noncovalent interactions between MP and pea protein, whereas hydrogen bonding was dominant between DP/TRP and pea protein. TRP with more alkyl groups could generate new interactions with PPI (π-π stacking interaction) to improve the adsorption capacity of PPI. Pyrazine with more alkyl groups showed a stronger binding force with pea protein to improve the ability of pea protein to adsorb pyrazine flavor compounds, and they displayed different fluorescence quenching mechanisms. This study could provide a theoretical basis for flavor selection and control in the production of pea protein-based meat analogs and thus improve the overall flavor of plant protein-based meat analog products.