Temperature, sample and time dependent structural characteristics of gelatine gels studied by near infrared spectroscopy

The aim of the present experiment was to investigate differences in the NIR spectra of gelatine gels and to relate spectral differences to structural characteristics. Spectral changes induced by temperature, maturation time and sample-related differences, like the Bloom strength, viscosity and sample origin. have been studied. The main conclusion is that the same or very similar spectral changes take place in gelatine gels at decreasing temperatures, increasing Bloom strengths and increasing maturation time, and that the changes are most clearly seen in the 2160-2210 nm region. It is suggested that the 2160-2170 nm region represents single chains (with or without helical parts), while bands 2180 and 2208 nm represent triple helices and beta-turns. In the region containing the first OH overtone of water, increased intensities were observed with increased maturation time at the 1414 and 1462 nm bands, along with a decrease at the 1492 nm band. No temperature- or sample-dependent spectral changes were observed in the 1400-1500 nm region that cannot be explained by temperature changes in bulk water. From the NIR spectra it was possible to distinguish hide gelatine gels from pigskin gelatine gels. The overall absorbance level was found to increase slightly with time, indicating that some aggregation takes place as a function of gel maturation time. (C) 2003 Elsevier Ltd. All rights reserved.