Study On Physical Gelation Of Gelatin In Salt Solutions And Its Thermal Stability

Gelatin is widely used in food,biological,and pharmaceutical fields.In this work,the physical gelation of gelatin in different salt solutions was systematically studied.A series of gelatin hydrogels containing salts were prepared,and the effects of the type and valence of salts on the thermal stability of the these gels have been explored.1.The addition of NaCl and CrCl₃ in the gelatin solution hinders the physical gelation;CaCl₂ promotes the transition of the gelatin molecules from a random coil to a helical conformation at low concentrations,while high concentrations of CaCl₂ inhibit the gelation transition process.The gelation process?coil-to-helix conformational transition?of gelatin at early stage in these three salt solutions can be described by first-order kinetic equations,and their rate constants decrease with increasing salt concentrations.2.During the physical gelation of gelatin,increasing the polymer concentration or methanol content increase the gelling temperature of the polymer solution.On the contrary,the addition of NaCl or urea results in a decrease of gelling temperature.In addition,the values of solution pH deviation from isoelectric point will increase the gelling temperature.For the storage modulus of the gelatin gel,it is consistent with the changing trend of the gelling temperature at various gelation conditions.3.In gelatin/salt solutions,chaotropic salts?KCl,KNO₃,and KSCN?can hinder the formation and growth of triple helices;kosmotropic salt?KH₂PO₄?promotes gel formation,and a low concentration of K₂SO₄ contributes to the transformation of gelatin molecules from a random coil to a helical conformation,while a high concentration of K₂SO₄ is not conducive to the formation of gels.The effect of these five salts?KCl,KNO₃,KSCN,K₂SO₄,KH₂PO₄?used in the experiment on gelation process of gelatin does not follow the Hofmeister series completely.4.In various preparation conditions of the polymer gel,the polymer concentration,annealing time and pH have insignificant effect on its melting temperature.However,an increase in annealing temperature will result in an increase in gel melting temperature and an improvement in the thermal stability of the system.The thermal stability of gelatin hydrogels in different valence salt solutions follows the following rule:CrCl₃>CaCl₂>NaCl.