Interfacial behavior and emulsifying properties of coconut protein glycated by polygalacturonic acid with different molecular weight

Glycosylation can be used to improve the emulsifying properties of protein by covalently binding with sugar. In this study, we prepared coconut protein (CP) -polygalacturonic acid (PA) conjugates by dry-heat method, studied the effect of PA with different molecular weight on the structure and functionality of CP, and characterized the interfacical behavior of CP at the oil-water interface to establish the relationship between interfacial behavior and emulsion stability. The results showed that different molecular weights of PA (28.4 ± 2.01 kDa, 20.3 ± 3.09 kDa, 16.3 ± 3.07 kDa, 11.6 ± 2.33 kDa) significantly affected the grafting degree between CP and PA (14.57 % ± 0.98 %, 53.74 % ± 0.1 %, 45.5 % ± 1.81 %, 36.54 % ± 0.38 %, respectively). The results of scanning electron microscopy (SEM) and Fourier infrared spectroscopy (FT-IR) confirmed the successful preparation of PA-CP conjugates. The dynamic interfacial tension of the conjugate was lowest (11.03 ± 0.07 mN/m) at the lowest PA molecular weight (11.6 ± 2.33 kDa), which increased with the increase of molecular weight. The diffusion, penetration and rearrangement rates of the conjugate were the highest when the molecular weight of PA was 20.3 ± 3.09 kDa. Compared to mixtures, conjugates tended to form a more elastic and stable interfacial film at the oil-water interface. In addition, the glycosylation reaction could improve the emulsion stability, resulting in smaller droplets size and higher zeta potential. With the decrease of molecular weight of PA, the emulsifying performance of CP was also improved. In conclusion, this work can further expand the application of coconut protein in the food industry and indicate the direction for further development of pectin with different molecular weights in the food industry.