Fluctuation-optical method for determining gelation point of biopolymer systems

Method for determining temperature of the transition of biopolymer systems to gellike state was developed using the earlier discovered effect of decay ing amplitude of spontaneous fluctuations of system optical density, which significantly exceed the level of intrinsic noise of measuring devices of S pecord M40 and Specord M400 spectrophotometers. These fluctuations are caus ed by the thermal convection resulting in the emergence of randomly distrib uted regions with different optical properties in the analyzed systems. The inhomogeneity can by amplified by the fraction of supermolecular particles (SMP). The effect of convection markedly decreases as a result of the loss of fluidity during the system gelation, thus underlying the instrumental r egistration of the sol-gel transition whose efficiency was confirmed in thi s work using aqueous preparations of plant polysaccharides (pectin, agar, f urcellaran, and kappa -carrageenan). It was shown that, in the cases of ini tially optically homogeneous systems, the role of the SMPs can be played (i f necessary) by the relatively small amounts of the particles of chemically inert compounds (for example, cellulose) at slight mixing of a system usin g magnetic stirrer. This method was applied for constructing the fragment o f the phase diagram of the furcellaran-water system during its cooling. The interpretation of its semi-logarithmic transformation in terms of the Eldr idge-Ferry theory resulted in the estimation of the amount of heat evolved during the formation of gel network junctions (presumably, due to the pair associations of double helixes), which appeared to be equal to -63 kJ mol(- 1).