Rheo-impedance behavior during gelation of the gelatin solution -Effect of cooling rate-

Abstract

“Purpose,” In our previous report, we evaluated the rheo-impedance behavior of a gelatin solution during the gelation process. No clear change was observed in the viscoelastic behavior from the sol to the sol-gel transition. However, the internal resistance of the system calculated from the impedance |Z| increased exponentially. We considered that the increase in the internal resistance corresponded to the increase in the molecular weight of the collagen molecules due to the progress of the cross-linking. In this study, the effect of the cooling rate on the rheo-impedance behavior of the gelatin was investigated.“Methods,” A 2.5wt% Gelatin B (alkali-treated, Nitta gelatin) solution was used, and was heated to 65°C and stirred. The solution was cooled to 5°C at a rate of 1°C to 4°C/min and then maintained at 5°C. For the rheo-impedance measurement, the rheometer (MCR302e, Anton Paar) and the impedance analyzer (IM-3536, Hioki) connected with BNC-SMB conversion cables.“Results,” The elastic moduli increased rapidly and reached constant as the gelatin solution was cooled. The apparent sol-gel transition point shifted to the shorter time side as the cooling rate increased. The elastic moduli, which reached constant, were higher at slower cooling rates. The internal resistance increased exponentially from the sol to the sol-gel transition at all cooling rates. The internal resistance, when the elastic moduli reached constant, was higher at slower cooling rates, which was consistent with the viscoelastic behavior. These results suggest that the progress of cross-linking of collagen molecules becomes faster as the cooling rate increases, but the degree of cross-linking when gelatinized becomes relatively lower.