Study On The Konjac Glucomannan Molecule Stability

With the development of scientific technology, people are searching for intelligent materials of new properties and high functions, especially the macromolecule which has the respondent ability. Konjac Glucomannan (KGM) is the main content of the local resource Konjac as a kind of natural polymer. It is a water-soluble noninonic polysaccharide which now is successfully widely used in fields such as food, Pharmaceuticals, cosmetics, and materials. Properties of high molecular weight, good hydration capacity and without charge help with KGM excellent gel-forming ability. Factors like concentration, molecular weight, pH, temperature and H-bonds could strongly affect its gel strength. Under certain conditions, the temperature arising would enhance the gel strength. KGM can be deacetylated to form irreversible gel, under such conditions, it turns to be a solid or semi-solid gel. KGM also can be blended with other polymers such as carrageean, xanthan, and soybean protein to form gel. The synergistic interaction between them can improve properties of blend gel. Due to its structure, KGM gel is instable, so its structure should be studied. The study on polysaccharide is difficult because of its complex structure. Polysaccharide 3D structure was used to be studied by indirect methods, they need complex substrate but can not give visual structure image. In this text, molecular dynamics method was used to give visual molecule structure image, explain the experiment results and study the interaction between KGM and its reaction environment. Studies were as follows: firstly chemical study methods were used, the efficient way to purify the KGM was studied; secondly the biological study method was used, the purified KGM was enzymed, as well as effects of enzyme time and enzyme concentration on KGM molecular weight were studied, the molecular weight and distribution of enzymed KGM was determined by Size Exclusion Chromatography (SEC);And finally the theory study method was used, the effects of concentration, molecular weight, pH, reaction temperature and H-bonds on KGM gel stability were also studied. The details are specified as follows:1. Chemical method on KGM gel stability studyDifferent structures lead to different properties. So structure study is a key to study KGM gel stability. In order to well study its structure, purification was used. The SO₂ percentage of KGM is an important index. High percentage of SO₂ could affect its stability, so it was used as a reference index in purification. In KGM purifying, best results were obtained in following conditions: KGM 3g, reaction temperature 70℃, reaction time 1h, and pH=5 Na₂HPO₄ solution. By this way, the SO₂ removing rate could reach 90%. It is purely white and has no strange smell for its protein and starch are partly removed. Purified KGM is shown to be superior to the raw KGM in freeze-thaw stability and fungistasis.2. Biological method on KGM gel stability studyThe molecular weight means much to the structure and properties of polysaccharide. Different molecular weight polysaccharide has different physiological properties, so it needs to study effects of different molecular weight on KGM properties. In order to prepare different molecular weight KGM, they were made in following conditions: KGM 3g, reaction temperature 50℃, pH=6, 100mL water, reaction time were 10min, 20min and 30min. Using viscosity as a reference index. The results show that KGM gel stability and fungistasis decreasing as the molecular weight decreasing. The aboved KGM samples were dissolved to prepare 0.5% solution, centrifuged and ultra filtered. Their molecular weights were analyzed by SEC and GPC software. The results show that the Number Average Molecular Weight (Mn) of 0.5% KGM is between 204922～265322 while its Weight Average Molecular Weight (Mw) is between 538737～697832.3. Theory method on KGM gel stability studyEffects of factors, such as concentration, molecular weight, pH, temperature and hydrogen-bonds on KGM gel stability were studied by using molecular simulation and modern instruments. The results are specified as follows:(1) Effects of KGM concentration and its molecular weight on KGM gel stability were studied by two factors orthogonal experiments. The results show that the gel viscosity, gel strength, and freeze-thaw stability are all enhanced as the molecular weight increase. By molecular dynamics method, it shows that the increase of intra-molecular hydrogen bonds help with gel strength.(2) Effects of KGM/κ-carrageen concentration, KGM/κ-carrageen mixed ratio and KGM molecular weight on KGM gel stability were studied by three factors orthogonal experiments. The results showed that by increasing the KGM/κ-carrageen concentration and the KGM molecular weight while the KGM/κ-carrageen mixed ratio is 4:6, the gel stability could be enhanced. By molecular dynamics method, it shows that, compared with single gel, hydrogen-bonded function of blend gel is enhanced, the two polymers are compatible.(3) Effects of KGM concentration, KGM molecular weight and urea on KGM gel stability were studied by three factors orthogonal experiments. The results show that by increasing the KGM concentration and KGM molecular weight while decreasing the urea concentration, the gel stability could be enhanced. By molecular dynamics method, it shows that urea not only affect the formation of intra-molecular hydrogen bonds, but also change the position of hydrogen bonds and it destroys the KGM hydrogen bond network. That is because removing acetyl groups help with enhancing the intra-molecular hydrogen bond function.(4) Effects of KGM concentration, KGM molecular weight, pH, and reaction temperature on KGM gel stability were studied by four factors orthogonal experiments. The results show that by increasing the KGM concentration and KGM molecular weight when the reaction temperature is 90℃and pH=9, the gel stability is the best. By molecular dynamics method, it shows that, under alkaline conditions, the increase of intra-molecular hydrogen bond interaction improves gel strength.