CALCIUM GELATION OF PECTIC POLYSACCHARIDES ISOLATED FROM UNRIPE TOMATO FRUIT

Cell-wall material was prepared from unripe tomato fruit, and a pectic polysaccharide extracted with cyclohexanediaminetetraacetic acid. The structure of the purified pectic polysaccharide was examined by sugar and methylation analysis, and was typical of a rhamnogalacturonan fro m the primary cell wall. The physicochemical properties of the isolate d polysaccharide were characterised by viscometry and size-exclusion c hromatography. The polysaccharide was polydisperse, but of large molec ular size as indicated by an intrinsic viscosity of 810 mL g(-1). At c oncentrations above similar to 0.2-0.6% w/w, coil entanglement was obs erved as an increase in the dependency of viscosity on concentration. For these concentrated solutions, clear elastic gels were formed on ad dition of calcium ions. At concentrations in the range 0.6-2.8% w/w th e shear modulus of the gel showed a c(1.9) dependence on concentration . The modulus of the gel increased linearly with absolute temperature in a rubberlike way, enabling an estimate of cross-link density to be made. (C) 1996 Elsevier Science Ltd.