Different mechanical properties of the gamma-irradiated gelatin gels prepared through the different cooling processes

Here we have prepared gelatin gels with different mechanical properties using a combination of different cooling protocols and γ-irradiation. Young's modulus (E) values for the slow-cooled gels were only slightly higher than the fast-cooled gels except for the 20% (w/v) gel. After irradiation with γ-rays, the difference in E between the slow-cooled gel and the fast-cooled gel became clearer. The E values of the γ-irradiated gelatin gels were mostly decreased while the temperature was raised to 40 °C and 60 °C from 20 °C. The values for the slow-cooled gels with concentrated (15–20% (w/v)) gelatin were still significantly higher than the values for the fast-cooled gels. We also measured the dynamic viscoelasticity of the gelatin gels. The storage modulus (G′) values for the slow-cooled gels were higher than that of the fast-cooled gels, except for 10%(w/v) gelatin irradiated with γ-rays at a dose of 40 kGy. The loss modulus (G″) values for the slow-cooled gels were higher than the values for the fast-cooled gels. Circular dichroism spectra of the gelatin gels showed that the slow-cooled gels contained a higher amount of renatured helical structure in their molecules than the fast-cooled gels. We concluded that the slow-cooled gelatin gels had a higher amount of triple-helical structure, and higher efficiency of covalent crosslinking between gelatin molecules under γ-irradiation, which resulted in a larger number of network points than the fast-cooled gels.