A highly viscose, thermally stable hydrogel was produced by treating agar and kappa-carrageenan with the natural crosslinker genipin, according to research published online in the journal Food Hydrocolloids.
"This genipin cross-linked blend presents an immense potential for food applications and in other pH-specific applications as well," wrote lead author Ramavatar Meena from Central Salt and Marine Chemicals Research Institute in Gujarat, India.
Hydrogels are liquid or semisolid materials composed of long-chain molecules cross-linked to one another to create many small empty spaces that can absorb water or other liquids like a sponge.
If the spaces are filled with a bioactive compound, for example, the hydrogel can release it gradually as the structure biodegrades.
Previous production methods have been limited by low productivity, they require high temperatures, and also require effluent treatment for environmental protection, according to the Indian researchers.
The new study however suggests that stable food-grade hydrogels can be produced, and are "yet another example of value addition of these hydrocolloids with emerging new applications, obtainable from a renewable bioresource."
According to Meena and co-workers, hydrogels could be prepared by blending agar and kappa carrageenan and using genipin as the crosslinker.
Optimal conditions were reported as 75 per cent carrageenan, 25 per cent agar, and 0.8 per cent. Under such conditions, the resulting hydrogel could sweel by 8600 and 9380 per cent at pH 1.2 and 7.0, respectively, stated the researchers.
"This result is significant especially when viewed against the fact that parent kappa-carrageenan is readily dispersible in water and that it degrades rapidly in acidic pH," they added.
According to mass spectrometry analysis, the genipin was fixed chemically and not physically in the hydrogel.
"The seaweed hydrocolloids blend of agar and kappa carrageenan generated a crosslinked hydrogel network assembly on reaction with genipin, showing remarkable swelling capacity and solution stability in wide range of pH. This hydrogel can be utilized in specific food applications as well as other applications which demand pH- resistance," concluded the researchers.
Both agar and carrageenan are prepared from red seaweed. Agar is a gelatinous substance used as a natural vegetarian gelatin replacement in icings, glazes, processed cheeses, jelly and sweets.
Carrageenan is a polysaccharide used in desserts, ice cream, sauces, beer, pates, processed meat and soy milk.
Source: Food Hydrocolloids (Elsevier)
Published online ahead of print 25 March 2008, doi: 10.1016/j.foodhyd.2008.03.008
"Development of a stable hydrogel network based on Agar-kappa-carrageenan blend cross-linked with genipin"
Authors: R. Meena, K. Prasad, A.K Siddhanta