Study On The Structure Modulation And Application Of Gelatin In Hofmeister Salts

As a kind of biopolymer,gelatin has been widely used in food,medicine and chemical industries due to its remarkable gelling properties.As a polyampholyte,the conformation of gelatin molecules is very sensitive to salts,which have an important effect on the physical gelation of gelatin.However,there is a lack of systematic studies on the effect of the salt type on the structure and properties of gelatin.In this work,the Hofmeister effect was applied to the gelatin system and its mechanism was studied in depth.Moreover,the modulation of gelatin molecular conformation and its triple helix structure was achieved based on the specific effect of Hofmeister salts.The main research contents and conclusions are as follows:1.Effect of Hofmeister salts on the viscosity properties of gelatin in dilute solutions:When the salt concentration is low(<0.1 mol/L),the electrostatic screening of salt ions plays a major role and the intrinsic viscosities of gelatin molecules decrease with the increasing of salt concentration;when the salt concentration is high(0.1～1 mol/L),the specific effect of salt ions plays a predominant role and the intrinsic viscosities of gelatin molecules conform to the order of Cit3-(citrate ion)<SO42-<H2PO4-<CH3COO-<Cl-<SCN-.Chaotropic anions such as SCN-can promote the unfolding of polymer molecular chains due to the fact that these anions can interact directly with the gelatin chains,causing an increase of gelatin molecular intrinsic viscosity.On the contrary,kosmotropic anions such as Cit3-are able to promote the intrachain aggregation of gelatin molecules through hydration effect,which reduces the intrinsic viscosity of gelatin molecules.In addition,these observations are confirmed by the results of optical rotation and dynamic light scattering.2.Effect of Hofmeister salts on the physical gelation of gelatin solutions and its properties:for kosmotropic salts(K2SO4 and KH2PO4),the gelling temperature of gelatin solutions increases linearly with increasing salt concentration,whereas the opposite trend is observed for chaotropic salts(KCl and KSCN).The order of gelling temperature in different salt ions is SO42->H2PO4->Cl->SCN-.Additionally,similar order of the influence of salt anions is also found for the melting temperature and triple helix content of hydrogels.Kosmotropic anions are able to facilitate the gelation of gelatin solutions through hydration effect,resulting in both increases of the length and content of triple helices.Contrarily,chaotropic anions tend to interact directly with gelatin molecules,which hinders the coil-helix transition of protein molecules and the physical gelation transition of gelatin solutions.3.Effect of Hofmeister salts on the structure and properties of soaked gelatin hydrogels:kosmotropic anions(Cit3-,SO42-,H2PO4-and S2O32-)enhance the interchain hydrogen bonds and hydrophobic interactions of gelatin molecules by strong hydration effect,which contribute to the increase of the length and content of triple helices of the protein,and thus the viscoelasticity,thermal stability and mechanical property of gelatin hydrogels are improved.Contrarily,chaotropic anions(Cl-,I-and SCN-)weaken the hydrogen bonds and hydrophobic interactions among polymer molecules by directly interacting with gelatin molecules,and thus the triple helix structure of hydrogels is destroyed and their properties reduce.The effect of salts on the triple helix content,melting temperature,storage modulus and tensile strength of gelatin hydrogels follows the Hofmeister series.4.Preparation and characterization of gelatin hydrogels enhanced by Hofmeister effect:polymer hydrogels with better mechanical properties were obtained by immersing original gelatin hydrogels in K3Cit(potassium citrate)solutions at appropriate concentrations.The interactions including hydrogen bonds and hydrophobic interactions among protein chains are remarkably strengthened by the strong hydration effect of kosmotropic Cit3-,resulting in the increase of triple helices and the superior mechanical properties of the immersed hydrogels.The study on the strengthening mechanism of gelatin hydrogels by kosmotropic anion is vital for the design and fabrication of protein materials with defined structures and properties.