Available lysine (AL) content, weight-average molar mass (M w ) and kinetic of α helixes’ formation have been determined in thermally treated gelatin (75°C) during 2, 6 and 8 days. Quantification of available lysine in gelatin sample by LC–UV has been developed. Thermal treatment during 8 days led to a decrease of AL content from 3.1g/100g of gelatin to 2.3g/100g of gelatin. In the same time, M w increased from 6.7×10 5 gmol −1 to more than 2.0×10 6 gmol −1 and α helixes’ formation ability was strongly affected. Thermal treatment led to the reaction of available lysine group with other functions present in its environment. Intermolecular cross-links led to a high molar mass compounds’ formation and limited protein chain unfolding which is an essential step for helixes’ formation.