This study made use of a novel totally chlorine-free (TCF) bleaching approach to prepare bleached shellac. Some single factor experiments were employed to investigate the effects of the main factors in the H₂O₂ bleaching method. A new chlorine-free bleached shellac resin was obtained in the Box–Behnken design responsive surface optimal experimental conditions (pH, 9.0–11.0; 1.33 mL g⁻¹, concentration of 30% hydrogen peroxide; 2.0 h, dropping time of hydrogen peroxide; 7.2 h, bleaching time; 90 °C, temperature). The yield and color index of the bleached shellac obtained under the optimal experimental conditions were 80.84% and 0.5675 respectively. The result of the physicochemical property test, IR spectrum and DSC characterization indicate that the properties of H₂O₂ bleached shellac are similar to commercially refined shellac resin. Moreover, it is noteworthy that the H₂O₂ bleached shellac was remarkable in alcohol solubility and thermal lifetime tests. It had a higher acid value and a lower softening point compared with commercially refined shellac resin, which can be applied safely in many fields including food and medical industries without chlorine residues.

To investigate the binding properties of 3,4-dihydroxybenzaldehyde with human serum albumin, as well as the structural changes of human serum albumin under a simulated physiological pH value (a pH of 7.4) and a high 3,4-dihydroxybenzaldehyde concentration, a series of techniques, i.e., fluorescence, synchronous fluorescence, ultraviolet-visible absorption, Fourier-transform infrared spectroscopy, and molecular docking simulation, were employed. Steady state fluorescence showed that 3,4-dihydroxybenzaldehyde quenched the intrinsic fluorescence of human serum albumin via a static mechanism. The 3,4-dihydroxybenzaldehyde-human serum albumin complex had a strong affinity (Kb = 105 M-1) at various temperatures. It was shown that 3,4-dihydroxybenzaldehyde was bound to the IB subdomain of human serum albumin primarily via hydrogen bonding and van der Waals forces at high 3,4-dihydroxybenzaldehyde concentrations, based on the results of the thermodynamic and molecular docking. Furthermore, the fluorescence emission spectrum and Fourier-transform infrared spectroscopy results indicated that the binding distance between 3,4-dihydroxybenzaldehyde and human serum albumin was 4.42 nm. In addition, 3,4-dihydroxybenzaldehyde induced conformational changes of human serum albumin. These findings provide reasonable evidence for further understanding the distribution of 3,4-dihydroxybenzaldehyde when it spreads into human blood serum, which may be helpful in food and medicine research.