Effect of electrohydrodynamic drying on bee pollen biochemical pathways

The mechanism of ionic wind and electric field of electrohydrodynamic (EHD) drying dehydration stress on the biochemical and molecular basis of bee pollen is still unclear. In this study, metabolomics and proteomics were employed to analyze the changes in biochemicals and small-molecule metabolic compounds of bee pollen during the drying process using needle-to-plate and plate-to-plate electrode system. The results show that ionic wind and electric field contributed 85.0% and 15.0% respectively to the dehydration characteristics, with the electric field having a greater effect on the quality parameters. As compared to ionic wind, the ribosome, the citric acid cycle (TCA cycle), and proteasome pathway played a positive role in regulating the abiotic and biochemical responses of electric field dehydration. Both ionic wind and electric field changed the expression of functional proteins related to amino acid metabolism pathways, resulting in a decrease in the expression of characteristic metabolites such as L-phenylalanine, L-aspartic acid, and L-pyroglutamic acid from 114.27 x 107, 5.31 x 107, and 142.55 x 107 in fresh rape bee pollen to 57.46 x 107, 3.32 x 107, and 57.46 x 107 in needle-to-plate (N-P) electrode treated and 61.25 x 107, 2.47 x 107, as well as 33.82 x 107 in plate-to-plate (P-P) electrode treated samples. Additionally, the differential expression of proteasome pathway and the destruction of the structural integrity of the cell wall storing phenolic compounds resulted in the further interaction of protein-phenolic supercomplexes, which in turn changed the content of free phenolic acids in rape bee pollen. These findings elucidated the biochemical regulation strategy and protein-phenolic compound interaction mechanism of rape bee pollen during EHD drying processing, and further emphasized the synergistic mechanism of ionic wind and electric field.