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Chitosan (CTS) and chitosan oligosaccharides (COS) have been widely applied in food industry due to their bioactivities and functions. However, CTS and COS with positive charges could interact with proteins, such as whey protein isolate (WPI), influencing their digestion. Interaction among CTS/COS, FUC, and WPI/enzymes was studied by spectroscopy, chromatography, and chemical methods in order to reveal the role of FUC in relieving the inhibition of protein digestibility by CTS/COS and demonstrate the action mechanisms. As shown by the results, the addition of FUC increased degree of hydrolysis (DH) and free protein in the mixture of CTS and WPI to 3.1-fold and 1.8-fold, respectively, while raise DH value and free protein in the mixture of COS and WPI to 6.7-fold and 1.2-fold, respectively. The interaction between amino, carboxyl, sulfate, and hydroxyl groups from carbohydrates and protein could be observed, and notably, FUC could interact with CTS/COS preferentially to prevent CTS/COS from combining with WPI. In addition, the addition of FUC could also relieve the combination of CTS to trypsin, increasing the fluorescence intensity and concentration of trypsin by 83.3 % and 4.8 %, respectively. Thus, the present study demonstrated that FUC could alleviate the inhibitory effect of CTS/COS on protein digestion., Competing Interests: Declaration of competing interest The authors declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Excessive protein consumption (EPC) could increase the gastrointestinal burden and impair gut motility. The present study was designed to explore the improvement of chitosan (CTS) and chitosan oligosaccharide (COS) on colonic motility and serum metabolites in rats after EPC. The results of in vivo experiments fully proved that CTS and COS could improve gut motility and reverse the serum metabolites in rats as indicated by LC-MS/MS analysis, and the COS group even showed a better effect than the CTS group. Furthermore, short-chain fatty acids (SCFAs), which could promote gut motility, were also increased to alleviate EPC-induced constipation after supplementation with CTS or COS. In addition, CTS and COS could decrease the concentration of ammonia in serum and down-regulate the levels of H 2 S and indole. In summary, the present study revealed that CTS and COS could produce SCFAs, improve the colonic motility in rats, reverse the levels of valine, adenosine, cysteine, 1-methyladenosine, indole, and uracil, and enhance aminoacyl-tRNA biosynthesis and valine, leucine and isoleucine degradation. The present study provides novel insights into the potential roles of CTS and COS in alleviating the adverse effects of EPC., Competing Interests: Declaration of competing interest The authors declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

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., Competing Interests: Declaration of competing interest The authors declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

Chitosan (CTS) and its oligosaccharide (COS) can protect against excessive protein consumption (EPC)-induced constipation by regulating gut microbiota and metabolites. The imbalanced gut microbiota was observed in whey protein isolate (WPI) group by 16S rRNA gene sequencing. However, CTS and COS treatments reversed the abundance changes of several gut microbiota, which led to the balance in the production of metabolites. Interestingly, some metabolites associated with constipation were also regulated by CTS and COS in in vitro colonic fermentation model and EPC-induced constipated rats, including nicotinamide, glutamine, proline, cysteine, choline, tryptophan, and pipecolic acid, which were mainly associated with aminoacyl-tRNA biosynthesis, arginine biosynthesis, and d -glutamine and d -glutamate metabolism pathways. In conclusion, the present study shed light on the effects of CTS and COS on EPC by regulating gut microbiota and metabolites and explored the correlation between gut microbiota and metabolites, reinforcing its potential application as a prebiotic in maintaining intestinal health. CTS and COS could relieve the adverse effects of EPC by regulating gut microbiota and metabolite profiles. [Display omitted] [ABSTRACT FROM AUTHOR]