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Extraction Route Controls the Microstructure and Rheological Performance of Sodium Alginate from Beach-Cast Sargassum spp.
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DOI：10.3390/polysaccharides7030074.png)
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Abstract
En 中文
Sodium alginate was extracted from beach-cast Sargassum spp. collected along the coast of Puerto Progreso, Yucatán, Mexico, using two established pretreatment routes based on formaldehyde and ethanol. This study evaluates how extraction methodology controls alginate recovery, molecular structure, hydrogel rheology, macroscopic integrity, swelling behavior, and preliminary inorganic contaminant profiles. The ethanol-based route provided the highest extraction yield, reaching 19.87 ± 0.79% w/w for AE-5, whereas the formaldehyde route reached a maximum of 15.60 ± 0.62% w/w for AF-12; statistical analysis confirmed significant differences among extraction conditions (ANOVA, p < 0.05). Despite its lower yield, the formaldehyde route produced alginate with higher intrinsic viscosity (2.13 dL/g) and viscosity-average molecular weight (1.00 × 105 g/mol) than the ethanol-derived sample (1.33 dL/g and 0.62 × 105 g/mol), indicating better preservation of polymer chain length. 1H NMR analysis showed that AE-5 had higher guluronic acid content (FG = 0.60), lower M/G ratio (0.67), and higher G-block fraction (FGG = 0.54), favoring Ca2+-mediated junction zone formation. Consequently, AE-5-derived hydrogels exhibited the highest storage modulus at 1 Hz (G′ = 23,650 Pa), compared with AF-12-derived hydrogels (13,160 Pa) and the commercial reference (14,480 Pa). However, visual inspection and swelling analysis showed that the higher small-amplitude stiffness of AE-5 did not translate into superior macroscopic integrity; these hydrogels showed greater fragmentation during handling and higher long-term swelling. In contrast, AF-12-derived hydrogels showed lower stiffness but better apparent cohesion and a more restricted swelling profile, consistent with enhanced long-range network connectivity derived from higher molecular weight. FTIR confirmed preservation of the characteristic functional groups of sodium alginate, whereas XRD provided qualitative evidence of residual crystalline inorganic phases. Selected-metal analysis by MP-AES detected Cu in both extracted alginates, while As was detected but not quantified only in AF-12; Cd and Pb were not detected under the analytical conditions employed. Overall, the results establish a route-dependent structure-property relationship in which extraction conditions govern yield, chain preservation, block architecture, viscoelastic response, swelling behavior, and preliminary contaminant profile. These findings support beach-cast Sargassum as a promising source of research-grade sodium alginate, while emphasizing that further purification, expanded contaminant profiling, arsenic speciation, biological evaluation, and direct mechanical testing are required before any food, biomedical, pharmaceutical, or environmental application can be proposed.
Keywords:
sodium alginate
beach-cast sargassum
extraction route
<sup>1</sup>H NMR
rheology
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IF:
5.5
Papers:
228
Citations:
696
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