Tailoring kappa/iota-hybrid carrageenan from Mastocarpus stellatus with desired gel quality through pre-extraction alkali treatment

Mastocarpus stellatus seaweeds were subjected to different alkali pre-treatments to investigate the effect of alkali type, concentration and treatment duration on the chemical structure and the gelling properties of extracted kappa/iota-hybrid carrageenan (KI). Increasing the concentration in KOH and the pre-treatment time gives KI with lower amounts of nu-carrageenan units, which have a direct impact on the improved gelling properties. However, excessive KOH concentration and pre-treatment duration give KI with smaller molecular mass and depressed gel properties. NaOH is more efficient in converting nu-carrageenan to iota-carrageenan, but no correlation between the chemical structure and gel properties was found. An interaction between the alkali concentration and the pre-treatment duration complicates the rationalization of NaOH efficiency. A set of KI with 60–75 mol% kappa-carrageenan and tailored gelling properties for a wide range of applications is delivered.

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► Kappa/iota-hybrid carrageenans with gel elasticity from 10 Pa to 8 kPa are produced.
► Longer alkali treatment and higher KOH concentration improve gel elasticity.
► The content in nu-carrageenan is negatively correlated with the gel elasticity.
► Less NaOH and shorter alkali treatment give gels with equivalent elasticity.
► Hybrid-carrageenan with 60–75 mol% kappa units and extraction yields of 40–50%.