Alkali-modification of carrageenans: mechanism and kinetics in the kappa/iota-, mu/nu- and lambda-series
The cyclization reaction (formation of 3,6-anhydro-α-d-galactose units from α-d-galactose 6-sulfate) of carrageenans follows a pseudo first-order kinetics, being 20-60 times faster for carrageenans of the kappa-family than for those of the lambda-family. In lambda-carrageenans the clustering of the...
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| Autores principales: | , , , |
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| Formato: | JOUR |
| Materias: | |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_01448617_v20_n2_p95_Ciancia |
| Aporte de: |
| Sumario: | The cyclization reaction (formation of 3,6-anhydro-α-d-galactose units from α-d-galactose 6-sulfate) of carrageenans follows a pseudo first-order kinetics, being 20-60 times faster for carrageenans of the kappa-family than for those of the lambda-family. In lambda-carrageenans the clustering of the sulfate groups around the hydroxyl on C-3 of the α-unit shields it from polarization or ionization, reducing the cyclization reaction rate. Furthermore, molecular models of lambda-carrageenans suggest an adequate geometry for the interaction between the hydroxyl group on C-3 of the α-unit and the sulfate group on C-2 of the β-unit. These observations also explain the lack of cyclized derivatives of lambda-carrageenans in nature. The ease with which the cyclization reaction occurs for carrageenans of the kappa-family indicates that the alkaline treatments used industrially could be carried out under milder conditions, giving products of high gel strength. © 1993. |
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