Role of interfacial flexibility in emulsifying ability of coconut protein isolate remodeled by pulsed light coupled with weak alkali cycling treatment

The interfacial flexibility of proteins is a crucial factor that affects their functional properties. In this study, we investigated the role of interfacial flexibility in the emulsifying ability of coconut protein isolate (CPI) treated by pulsed light coupled with weak alkali cycling (pH 7 -> 9 -> 7). After treatment, the structure of CPI was unfolded and re-folded, which resulted in the exposure of hydrophobic groups and the formation of smaller aggregates, with the change of secondary structure. Additionally, the S-S bond content increased while the free -SH content decreased. The interfacial flexibility of CPI-based samples at the oil-water interface was evaluated by dissipative quartz crystal microbalance and interfacial dilatational rheology. Compared to CPI, PCPI-9 (CPI treated by pulsed light coupled with pH 9 cycling) possessed a greater viscoelastic modulus and a smaller relaxation time. Meanwhile, the anti-perturbation ability was better than CPI. Then, microstructure, centrifugal stability and emulsifying properties of the O/W emulsions stabilized by CPI-based samples were measured. The results showed that emulsion stabilized by PCPI-9 had significant advantages in long-term stability. The emulsification stability (ESI) increased by 25.45 times compared to CPI. In conclusion, moderate pulsed light coupled with weak alkali cycling treatment could improve the emulsifying ability of CPI by remodeling its structure to change the interfacial flexibility. These results could provide an in-depth insight into the relationship between interfacial flexibility and emulsifying properties of coconut protein isolate.