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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]

• A polysaccharide-Fe(III) complex, AGSP-Fe(III), was synthesized and characterized. • Fe release of AGSP-Fe(III) in simulated gastrointestinal digestion was exhibited. • Its iron supplementary efficiency was shown using Caco-2 cell model. • The solubility and stability of the complex were superior to FeCl 3. Using a sulfated polysaccharide from the gonad of pacific abalone (AGSP), a novel polysaccharide-Fe(III) complex, AGSP-Fe(III), was synthesized, and it was characterized by a series of methods including ultraviolet-visible (UV–vis) spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that AGSP-Fe(III) was formed by the Fe-O bond between sulfate, carboxyl, and hydroxyl groups in AGSP and Fe, its particle size reached a maximum of 200 nm after aggregating, and its surface morphology presented relatively regular columnar or spherical. Moreover, the iron release of AGSP-Fe(III) during simulated gastrointestinal digestion was exhibited, and its good iron supplementary efficiency was also shown using Caco-2 cells. In addition, compared to FeCl 3 , AGSP-Fe(III) showed better solubility and stability in the presence of polyphenol/trypsin. The present study demonstrated the potential of AGSP-Fe(III) as a novel iron supplement. [ABSTRACT FROM AUTHOR]