| Alginate is safe and non-toxic,and is widely used in food,pharmaceutical,textile and biomedical fields due to its good biocompatibility,biodegradability,nonimmunogenicity and gel properties.The binding behavior between alginate and calcium ions is an important theoretical basis for gelation and application of alginate.Therefore,it is significant for food science research and technology application to explore the influence of monovalent metal ions on gel mechanism of alginate,in order to enrich the theory of alginate gelation and expand the application scope of alginate.In this study,alginates with different monovalent metal ions types were selected as research objects,the binding behavior between lithium alginate(Li-ALG),sodium alginate(Na-ALG),potassium alginate(K-ALG)and calcium ions,and its gel kinetics and gel properties were studied.We also further studied the gel kinetics and gel properties of different alginate mixed systems.The main conclusions of this study are as follows:1.A method to prepare alginates with different monovalent metal ions types was established by ion exchange.The molecular weight and molecular weight distribution,ions contents,molecular structure and block degree,groups distribution,hygroscopicity and intrinsic viscosity of Li-ALG,Na-ALG and K-ALG were characterized by infrared spectrum,nuclear magnetic resonance,relative viscosity and other detection means.The results indicated that the preparation method was successful,the prepared Li-ALG,Na-ALG and K-ALG were up to standard.2.The binding behavior between alginate with different monovalent metal ion types and calcium ions and its gel kinetics and gel properties were detected and analyzed.The results showed that monovalent ions affected the lateral aggregation rate of the “egg-box” dimers,the affinity between lithium ions and alginate molecular chain is higher than sodium ions and potassium ions.The critical concentrations of Li-ALG,Na-ALG and K-ALG for gelation are from 0.2% to 0.3% when they cross-link with calcium ions,and the critical gel R values for 0.5% Li-ALG,Na-ALG,and K-ALG are located in 0.25 when time tends to infinity.Li-ALG has faster gel kinetics rate,higher equilibrium storage modulus and better water holding capacity than Na-ALG and KALG under the same conditions.When R > 0.6,Li-ALG and K-ALG had stronger gel network structures and higher average height of microstructure than Na-ALG.3.The gel kinetics and gel properties of different alginate mixed systems with different compound proportions were detected and analyzed.The results showed that replacing part of Na-ALG with Li-ALG can effectively improve the gel kinetics rate of Na-ALG gelation system and maintain its stability,meanwhile improve the rupture strength and water holding capacity of Na-ALG gel to some extent.We replace part of K-ALG with Li-ALG and found that it can effectively improve the gel kinetics rate of K-ALG gelation system,and can improve the stability,rupture strength and water holding capacity of K-ALG gel to some extent.Replacing part of Na-ALG with K-ALG can effectively improve the gel kinetic rate of Na-ALG gelation system and maintain its stability,meanwhile,the water holding capacity of Na-ALG gel can be significantly improved when mixed ratio was 1:1. |
