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Calcium β-hydroxy-β-methylbutyrate (CaHMB), a functional calcium salt, is used to maintain and improve muscle health. Here, a new hydrogel material prepared from alginate (ALG) with three M/G ratios (1:1, 2:1, and 1:2) and CaHMB (0-2 mg/mL) was investigated. CaHMB regulates the formation and properties of ALG hydrogels through chelation and hydrogen bonding. When the M/G ratio was 2:1, the anionic groups of CaHMB containing carboxyl and hydroxyl groups formed hydrogen bonds with the polysaccharide chains, hindering the capture of Ca 2+ by the G-residue fragments of ALG, which in turn retarded the gelation process. The noncalcium cross-linked polysaccharide chain structure of ALG and the anionic group of CaHMB also affected the water distribution in the hydrogel, especially when M residue content ≥G residue content. Lower M/G ratios and higher CaHMB concentrations could increase the number of "egg box" crosslinking junctions of calcium alginate, and the microstructure was denser in the gel pores, resulting in a stronger gel strength and more free water bound in the gel matrix. This study provides a theoretical and methodological basis for the design of novel hydrogels by studying the crosslinking features of ALG/CaHMB., Competing Interests: Declaration of competing interest The authors declare that they 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.)

Gel properties of hydrogel-forming by Ala-Lys dipeptide (AK) and iota-carrageenan (ι-C) were investigated by rheological behavior, fourier transform infrared analysis, cryo-scanning electron microscopy, low field-NMR relaxometry and magnetic resonance imaging. Iota-carrageenan was changed from a liquid to a gel with the addition of AK, and the existence of AK significantly increased the storage modulus (G') of ι-C from 590.4 to 1077.8 Pa. In the ι-C/AK gel, the blue-shift of OH stretching and water deformation were observed, meanwhile, the presence of amide I band at 1682 cm -1 was observed. The network of ι-C/AK gel showed a dense honeycomb structure with flocculating continuous phase and rough entanglement morphology. After adding AK, the water free in the pores of ι-C entered the ι-C/AK gel matrix, and the binding capacity of bound water was enhanced. These scenarios proved that the AK as the cationic dipeptide could control the conversion of negatively charged ι-C from an original random structure to a helical structure due to electrostatic interactions and hydrogen bonds. This study provides a new opportunity for the peptides into carbohydrate-based gel matrices, which could provide insights for the further application of ι-C/AK gels in the fields of food industry, tissue engineering and drug delivery., (Copyright © 2021 Elsevier B.V. All rights reserved.)