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Chitosan (CTS)/chitosan oligosaccharide (COS) and whey protein isolate (WPI) have been frequently used as food supplements, but notably, the interaction between the carbohydrate and the protein may affect the digestibility of protein. Thus, the present study focused on effects of the interaction between CTS/COS and WPI on the protein digestibility. A series of chemical and spectroscopic techniques including gel electrophoresis, gel permeation chromatography, Fourier transform-infrared (FT-IR) spectroscopy, intrinsic fluorescence (IF) spectroscopy, and circular dichroism (CD) spectroscopy were applied. According to the findings, both CTS and COS dramatically reduced intestinal digestibility of WPI, resulting in a decrease of DH by 43.33 % and 52.31 %, respectively. The substitution degree of WPI on CTS was 0.87 g WPI/g CTS, and the electrostatic interaction between amine groups of CTS and carboxyl groups of WPI caused changes in WPI's stability, microstructure, and fluorescence intensity. Notably, CTS affected the digestibility of WPI by precipitating protein and enzyme, whereas COS altered WPI's digestibility by decreasing or inactivating enzyme activity. The present study offered a solid scientific foundation for the rational formulations of carbohydrates and proteins in food industry. [Display omitted] • Chitosan (CTS) and its oligosaccharide (COS) influenced protein digestibility. • CTS decreased protein digestibility by partially precipitating protein and protease. • COS influenced protein digestibility by decreasing the activity of protease. • The electrostatic interaction occurred between -NH 3 + of CTS and -COO− of protein. [ABSTRACT FROM AUTHOR]

It is a challenge to degrade sulfated polysaccharides without stripping sulfate groups. In the present study, a photocatalytic method was applied to degrade fucoidan, a sulfated polysaccharide from brown algae. The degradation with varying addition amounts of H2O2 and TiO2 were monitored by high performance gel permeation chromatography (HPGPC) and thin layer chromatography (TLC), and fucoidan was efficiently degraded with 5% TiO2 and 0.95% H2O2. A comparison of the chemical compositions of 2 products obtained after 0.5 h and 3 h illumination, DF-0.5 (average Mw 90 kDa) and DF-3 (average Mw 3 kDa), respectively, with those of fucoidan indicates the photocatalytic degradation did not strip the sulfate groups, but reduced the galactose/fucose ratio. Moreover, 12 oligosaccharides in DF-3 were identified by HPLC-ESI-MSn and 10 of them were sulfated. In addition, DF-0.5 showed anticoagulant activity as strong as fucoidan while DF-3 could specifically prolong the activated partial thromboplastin time. All samples exerted inhibition effects on the intrinsic pathway FXII in a dose-dependent manner. Thus, photocatalytic degradation demonstrated the potential to prepare sulfated low-molecular-weight fucoidan with anticoagulant activity. [ABSTRACT FROM AUTHOR]