Surface attachment of fucoidan through electrostatic interaction alleviates chitosan/chitosan oligosaccharide‐induced reduction in protein digestion

BACKGROUND: Chitosan (CTS) and chitosan oligosaccharides (COS) are widely used in the food industry due to their bioactive properties. However, their cationic nature enables interaction with whey protein isolate (WPI), affecting protein digestibility. Fucoidan (FUC), a naturally occurring anionic sulfated polysaccharide from brown algae, can form electrostatic complexes with CTS and COS to partially alleviate this effect; however, this process requires optimization. RESULTS: Chitosan-fucoidan (CTS-FUC) and chitosan oligosaccharide-fucoidan (COS-FUC) complexes were successfully prepared and characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and other analytical instruments, confirming that complexation occurred via electrostatic interactions between amino groups of CTS and COS and the sulfate groups of FUC. Subsequently, the impact of these carbohydrates on WPI's digestibility was assessed during simulated gastrointestinal digestion. The CTS-FUC and COS-FUC complexes mitigated the inhibition of protein digestion caused by CTS and by COS alone. Specifically, the addition of the CTS-FUC complex increased the degree of hydrolysis of WPI by 24.6% compared with the corresponding mixed group, whereas the COS-FUC complex increased it by 22.6% compared with its corresponding mixed group. Furthermore, compared with the group containing CTS + FUC or COS + FUC, both preformed complexes increased protein concentration to 1.08-fold. The free trypsin concentration in the CTS-FUC + WPI group was 1.11 times that in the CTS + FUC + WPI group, whereas the concentration in the COS-FUC + WPI group was 1.06 times that in the COS + FUC + WPI group. Spectroscopic and chemical methods further revealed that the complexes reduced the binding of CTS and COS to protein and trypsin. CONCLUSION: Overall, this study demonstrates that CTS-FUC and COS-FUC complexes effectively alleviated the negative impact of CTS and COS on protein digestion, offering new insights into mitigating their adverse nutritional effects in food systems. © 2026 Society of Chemical Industry.