Controllably Adjusting the Hydrophobicity of Collagen Fibers for Enhancing the Adsorption Rate, Retention Capacity, and Separation Performance of Flavonoid Aglycones.

Collagen fibers (CFs) were previously used as packing materials for the separation of flavonoids based on hydrogen bond and hydrophobic interactions. However, as for flavonoid aglycones, CFs presented unsatisfactory adsorption capacity and separation efficiency due to the fact that they include limited hydroxyls and phenyls. In order to improve the adsorption capacity and separation efficiency, the hydrophobic modification strategy was employed in this research to enhance the hydrophobic interaction of CF with flavonoid aglycones by using silane coupling agents with different alkyl chains (isobutyl, octyl, and dodecyl). FT-IR analysis, DSC, TG, SEM, EDS mapping, water contact angle, and absorption time of solvent proved the successful grafting of alkyl chains on the CF without disturbing its special fiber structure, leading to the significantly enhanced hydrophobicity of the CF. The dynamic adsorption and elution behavior of kaempferol and quercetin (the typical flavonoid aglycones) on the hydrophobic CF showed that the adsorption rate and retention rate were largely increased in comparison with the CF without modification. Molecular dynamic simulations indicated that the CF grafted with isobutyls could interact with flavonoid aglycones through the highest synergetic effect of hydrophobic and hydrogen bond interactions, which exhibited the strongest retention to flavonoid aglycones. On further increasing the alkyl length (octyl and dodecyl), the hydrophobic interaction was further enhanced, but the hydrogen bonds were significantly weakened by steric hindrance, which showed that the retention to flavonoid aglycones was appropriately increased but without causing peak tailing. In the column separation of kaempferol and quercetin, the CF with hydrophobic modification presented a greater separation efficiency, with the purity of kaempferol increased from 71.99 to 86.57-97.50% and the purity of quercetin increased from 82.69 to 88.07-99.37%, which was much better than that of polyamide and close to that of sephadex LH 20. Therefore, the hydrophobicity of the CF could be controllably adjusted to enhance the adsorption rate and retention capacity, specifically improving the separation efficiency of flavonoid aglycones.

Insights into the mechanism of flavor compound changes in strong flavor baijiu during storage by using the density functional theory and molecular dynamics simulation.

The aging procedure/storage is essential to enhance the organoleptic quality of strong flavor baijiu (SFB). How the storage affects flavor changes in SFB, that is, the aging mechanisms remains unclear. Herein, the physical and chemical effects on the main flavor compounds of SFB during storage were investigated using the density functional theory (DFT) and molecular dynamics (MD) simulation. DFT calculation results showed that the activation energy of ester alkyl-oxygen protonation was lower than that of acid hydroxyl-oxygen protonation, which explained the reason why the concentrations of acids increased and those of esters decreased during SFB storage. MD simulation results showed that electrostatic interaction was a major contributor to SFB and that the ethanol-water system containing acids had a stronger electrostatic energy and more hydrogen bonds than the ethanol-water system containing esters. These findings revealed that acids are prone to generating and strengthening associative structures in SFB during storage.