Mixtures of hydrocolloids are commonly used to impart novel and improved rheological characteristics to food products and an added incentive is a reduction in costs. The nature of the synergy can be due to association of the different hydrocolloid molecules or to non-association. If the two hydrocolloids associate then precipitation or gelation can occur. Oppositely charged hydrocolloids (e.g., a protein below its isoelectric point and an anionic polysaccharide) are likely to associate and form a precipitate while there is evidence to show that for some stiff polysaccharide molecules (e.g., locust bean gum and kappa carrageenan) association results in gel formation.
Hot solutions of kappa carrageenan-locust bean gum form strong elastic gels with low syneresis when cooled below 50-60oC. Locust bean gum is a galactomannan with a level of substitution of one part mannose to four units of galactose. However, this substitution is not regular and regions of the locust bean gum are unsubstituted. The mannose-free regions of the locust bean gum are able to associate with the repeating helical structure of carrageenan dimmers to form gels. The maximum interaction, and hence peak rupture gel strength, occurs at a ratios between 60:40 and 40:60 kappa carrageenan to locust bean gum.
These polymer combinations are used in very large quantities in cooked meats and in gelled pet foods. Kappa carrageenan and clarified locust bean gum mixtures can be used for cake glaze and flan gels or formulated to give clear water dessert gels with an elastic cohesive gel texture like gelatin. Recent improvements in formulations of kappa and iota carrageenan blends are also able to give elastic cohesive gels similar to gelatin in texture. Konjac flour (E425i) interacts even more strongly than locust bean gum to form strong elastic gels with kappa carrageenan, which are at least four times the rupture strength of kappa carrageenan alone. Iota carrageenan, in combination with starch, gives dessert products with a body that is equivalent to four times that of starch alone.
Further information on carrageenan structure, sources, production and protein interaction can be accessed using the arrows in the Further Reading box below.