Thermal transitions in gelatin: Optical rotation and enthalpy changes

Enthalpy changes [as determined by differential scanning calorimetry (DSC)] and optical rotation changes over the helix → coil transition were measured for various gelatin solutions and films. From these studies it has been concluded that: (1) a linear correlation between Δ H and Δ[α] exists for gelatin solutions, independent of the temperature at which gelation occurred; (2) the amount of triple helical structure regained when a melted gelatin solution is quenched can be calculated from DSC data, but the values obtained will be dependent on assumptions about the number and strength of hydrogen bonds; (3) the anomalously high levorotation values found for cold‐dried films of gelatin do not reflect the presence of an extraordinarily large amount of triple helical structure; rather, the large rotations appear to be the result of orientation of helices in the plane of the film.