TURBIDITY INVESTIGATION OF THE SOL-GEL TRANSITION IN CARRAGEENAN GELSUNDER PHYSIOLOGICAL CONDITIONS

A spectrophotometer was used to measure the turbidity of a carrageenan gel as a function of temperature. The optical transmission of the gel s was found to decrease as the gels undergo the sol-gel phase transiti on. The differential of transmission (I) with respect to temperature ( T), dI/dT, exhibits peaks for both the cooling and the heating runs wi th the peak. positions corresponding to temperatures of gelation and m elting, respectively. The full-width at half-height of the dI/dT peak obtained from the heating curve is about 2.5 times broader than that f rom the cooling curve. This indicates that the melting of gels may inv olve multiple relaxation mechanisms. The area of the hysteresis loop c overed by the cooling and the heating curves increases with a decrease in the scanning rate. The thermal cycling has little impact on the so l-gel transition in the gels. The experiments show that turbidity is a powerful tool for studying the sol-gel transition in carrageenan gels . (C) 1998 John Wiley & Sons, Inc.