Food Hydrocolloids vol.l no.l pp.89-93, 1986 SHORT COMMUNICATION Comparative studies of the mechanical properties of mixed gels formed by kappa carrageenan and tara gum or carob gum P.Cairns, V.J.Morris, M.J.Miles and G.J.Brownsey AFRC Food Research Institute (Norwich), Colney Lane, Norwich NR4 7UA, UK Abstract. Tara gum has been considered as a possible replacement for carob gum in the formation of kappa carrageenan - galactomannan mixed gels. The mechanical properties of tara - carrageenan mixed gels have been measured and compared with the mechanical properties of carob-carrageenan mixed gels. Introduction Polysaccharides are important gelling agents used by the processed food industry. Synergistic interactions between food-approved polysaccharides are attractive commer- cially and may be exploited technologically. Such mixtures may be used to replace ex- pensive polysaccharides by cheaper alternatives leading to savings in cost, and they offer the possibility for creating new textures or for manipulating the rheology and tex- ture of foods. The mixtures kappa carrageenan - carob and xanthan - carob have been successfully exploited by the food industry. This article is concerned with possible replacements for the kappa carrageenan -carob system. The galactomannan carob gum is extracted from the seeds of Ceratonia siliqua, a tree which may only be cultivated in a few areas of the world. Climatic changes could restrict the supply of carob gum, leading to an increase in price. There is a need to continually develop new polysaccharides or polysac- charide mixtures as alternatives in applications which at present use carob gum. There are several short-term solutions to the reduced supply and increased cost of carob gum. Firstly, the kappa carrageenan -carob gum mixture could be replaced by a new polysac- charide. Microbial polysaccharides grown by fermentation offer the prospect of a con- trolled and stable cost and supply. Gellan gum has been developed as a broad spectrum gelling agent (1) and it has been demonstrated (1) that it may be used to replace the kappa carrageenan -carob gum mixtures in typical food applications. However, gellan gum has not, as yet, been cleared for food use. Should such approval be granted, then the cost of gellan gum will ultimately determine whether it is adopted as a replacement for kappa carrageenan -carob gum by the food industry. Secondly, other galactomannans could be modified to replace carob gum. It has been demonstrated (2) that the rheological properties of the galactomannan and kappa carrageenan mixture depend on the galactose - mannose ratio of the galactomannan. Enzymatic removal of galactose from guar gum yields a modified guar gum which forms mixed gels with kappa carrageenan (3). However, enzyme-modified guar gum would also require testing before clearance could be given for food use. Thirdly, other galactomannans may have sufficiently low © IRL Press Limited, Oxford, England 89