Study On Irradiation Modification Of Xanthan Gum Molecular And Its Product Features And Functional Characteristics

Xanthan gum, a microbial exopolysaccharide produced aerobically by Xanthomonas campestris fermentation, is widely used as thickener, emulsifier and stabilizer agent in the food, pharmaceutical and oil industry. In order to make full use the excellent properties and resources of xanthan gum and expand the application scope of ionizing radiation technology in molecular modification of polysaccharide, in this paper, xanthan gum, was taken as raw materials, was modificated for degradation and grafted respectively by using ionizing radiation technology. The study will provide theoretical basis and technical support for application of radiation technology in xanthan gum modification and product development. In part of radiolysis of xanthan gum, through the study on the change of molecular weight and molecular weight distribution of xanthan gum irradiated in dry and aqueous state in different irradiation dose, the radiation degradation characteristics of xanthan gum irradiated in dry and aqueous state was revealed systematically; Through detection analysis means of X-ray diffraction (XRD), fourier-transform infrared spectra (FTIR), chroma and chromatism, pH and rheological behavior, the effect ofγ-ray irradiation on physical and chemical properties, such as structure, particles morphology, etc, of xanthan gum irradiated in dry state and aqueous state in different irradiation dose, was study systematically; Through analysing the changes of antioxidant activity, bacteriostatic activity and induce defense response of xanthan gum irradiated in dry and aqueous state, the effect ofγ-ray irradiation on biological activity of xanthan gum was study systematically and the dose-response relationship was revealed. In part of radiation grafting of xanthan gum, Xanthan gum-N-vinylpyrrolidone graft copolymer (XG-g-NVP) was prepared by irradiation. Xanthan gum was taken as the base material and NVP was taken as the single body. The effects of internal and external factors on the reaction of grafting polymerization were study systematically. The structure of graft copolymers was characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Thermo gravimetric analysis (TGA), Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD). In addition, the rheological behavior of soluble XG-g-NVP was investigated by the rheometer and the swelling property of unsoluble XG-g-NVP was also measured. Adsorption characteristics of XG-g-NVP on phenols and polyphenols was studied in static experiments and adsorption ability of XG-g-NVP was confirmed by application in clarification of tea beverage and apple juice. The main projects and research results are as follows:1.The radiation degradation characteristics of xanthan gum irradiated in dry state and aqueous state with or without H₂O₂ was different. For xanthan gum in dry state, irradiation effect ofγ-ray on Xanthan gum is show mainly for polymerization when irradiation dose is below 10kGy and the molecular weight and of xanthan gum increased at 10kGy; when irradiation dose is above 10kGy, irradiation effect ofγ-ray on Xanthan gum is show mainly for degradation and molecular weight of xanthan gum irradiated decreased. For xanthan gum irradiated in aqueous state with or without H₂O₂, irradiation effect ofγ-ray on Xanthan gum is show mainly for degradation and molecular weight of xanthan gum irradiated constantly decreased. From the perspective of efficiency of radiation degradation on xanthan gum, the radiolysis effect of xanthan gum in dry state 2O₂2O₂, so H₂O₂ is a kind of good radiation degrading additives for xanthan gum.2. For xanthan gum irradiated in dry state,γ-irradiation can act simultaneously on crystallization area and amorphous area of xanthan gum and xanthan gum molecules undergo degradation reactions through cleavage of glycosidic bond in main chain and branched chain and generates a great deal of fragments with intact crystal structure and different molecular weight. There is not notable change in crystallinity of xanthan gum when irradition dose is below 400kGy. But the xanthan gum particles gradually reduce and structures become coarser and loose. For xanthan gum irradiated in aqueous state with H₂O₂, when irradiation dose reach to 120kGy, the crystal structure of xanthan gum were destruction to some extent and generates a lot of small molecule monosaccharide. Though carbonyl groups or double bond was formed in irradiation, but chemical structure and crystal structure basic of xanthan gum remained stable.3. With increasing irradiation dose, molecular weight of xanthan gum decrease cause its apparent viscosity overall decrease and its rheological behavior changes dramatically. The results are as follows:(1)Apparent viscosity versus shear rate. For xanthan gum irradiated in dry state, its rheological behavior tend to typical non-Newtonian fluid when irradiation dose gradually increase to 10kGy. But when irradiation dose is above 10kGy, with increasing irradiation dose, its rheological behavior tend to gradually deviate from typical non-Newtonian fluid. For xanthan gum irradiated in aqueous state with H₂O₂, its rheological behavior tend to typical non-Newtonian fluid with increasing irradiation dose. But for xanthan gum irradiated in aqueous state without H₂O₂, its rheological behavior tend to gradually deviate from typical non-Newtonian fluid when irradiation dose is above 10kGy. (2)Apparent viscosity versus shear time. For xanthan gum irradiated in dry state, the change of the apparent viscosity of xanthan gum solution with shear time is positively correlated with radiation dose when irradiation dose is below 100kGy and take on negatively correlated with radiation dose when irradiation dose is above 100kGy. In addition, the rheological behavior of xanthan gum solution shift from thixotropic fluid to rheopexy fluid. And when the irradiation dose is 100kGy, the rheological behavior of xanthan gum solution take on characteristic of non-newtonian fluid without dependence on shearing time. For xanthan gum irradiated in aqueous state without H₂O₂, its rheological behavior take on characteristic of non-newtonian fluid without dependence on shearing time. For xanthan gum irradiated in aqueous state with H₂O₂, its rheological behavior take on characteristic of thixotropic fluid when irradiation dose is below 10kGy and take on non-newtonian fluid without dependence on shearing time at 10kGy and take oncharacteristic of rheopexy fluid. (3)Apparent viscosity versus temperature. For xanthan gum irradiated in dry state, the trend of decrease of apparent viscosity far outclass those of samples unirradiated. With increasing irradiation dose, xanthan gum solution will be deprived of characteristics of three stage change of apparent viscosity with temperature increaseing. For xanthan gum irradiated in aqueous state, the trend of decrease of apparent viscosity and lose of characteristics of three stage change of apparent viscosity with temperature increaseing is more rapidly. 4. Irradiation can lead to significant changes of antioxidant activity of Xanthan gum. For xanthan gum irradiated in dry state, below 10kGy, its reducing power and scavenging effect on DPPH·and O2-·were negative correlated with irradiation dose and when irradiation dose was higher than 10kGy, its reducing power and the scavenging effect on DPPH·and O2-·of irradiated samples were postive correlated with irradiation dose. The scavenging capacity to·OH of xanthan gum is negative correlation with irradiation dose below 400kGy. For xanthan gum irradiated in aqueous state with or without H₂O₂, its reducing activity and scavenging effect on DPPH·were postive correlated with irradiation dose. For xanthan gum irradiated in aqueous state without H₂O₂, its scavenging effects on O2-·were negative correlated with irradiation dose overlly and its scavenging effects on·OH were negative correlated with irradiation dose when irradiation dose was below 10kGy, and were postive correlated with irradiation dose when irradiation dose was higher than 10kGy. The reducing power and scavenging effect on DPPH·of xanthan gum irradiated in aqueous state with or without H₂O₂ is higher than that of xanthan gum irradiated in dry state.5. Irradiation can enhance the antibacterial activity of Xanthan gum to Xanthomonas campestris pv. campestris. For xanthan gum irradiated in dry state, it shows bacteriostatic activity when irradiation dose rise to 10 kGy and it is postive correlated with irradiation dose. The diameter of inhibition zone can rise to 10mm at 400kGy. For xanthan gum irradiated in aqueous state without H₂O₂, its diameter of inhibition zone rise to maximum 8mm at 10kGy. For xanthan gum in aqueous state with H₂O₂, its diameter of inhibition zone is 17mm and with increasing irradiation dose, its diamenter of inhibition zone increase to 19mm at 5kGy, then decrease. The bacteriostatic activity of xanthan gum irradiated in aqueous state with H₂O₂ is higher than that of xanthan gum irradiated in dry state or in aqueous state without H₂O₂.6. The ability of inducing defense response in soybean cotyledon of xanthan gum were changed significantly when it were irradiated. The ability are both postive correlated with irradiation dose whether xanthan gum was irradiated in dry state or in aqueous state with H₂O₂. But for xanthan gum irradiated in aqueous state without H₂O₂, its ability of inducing defense response in soybean cotyledon is postive correlated with irradiation dose when irradiation dose is below 60kGy and is negative correlated when irradiation dose is above 60kGy. Its ability of inducing defense response in soybean cotyledon is higher than that of xanthan gum irradiated in dry state and in aqueous state with H₂O₂.7. The grafting degree was affected markedly by absorbed dose, NVP/XG mass ratio and xanthan gum concentration. Under the certain xanthan gum concentration and NVP/XG mass ratio situations, the grafting degree increased with absorbed dose and gradually achieved to the balance; under the certain absorbed dose and mass ratio conditions, the grafting degree reached maximum at the xanthan gum concentration of 10g/L; under certain irradiation and xanthan gum concentration situations, grafting degree reached the maximum at mass ratio 10 of NVP/XG.8. FTIR picture showed that grafting reaction occurred in NVP vinyl part and lactam structure was retained. After grafting, particles morphology, crystallinity, thermal stability, rheological properties and swelling performance of xanthan gum were changed significantly. SEM photographs showed that, after grafting, the structure of xanthan gum gradually became grain-like in shape from flake-like, of which the inner part was slice-like in shape. Thermo gravimetric analysis showed that XG-g-NVP enhanced thermal stability of xanthan gum and the carbonization temperature of xanthan gum went up. XRD showed the crystallinity increased after grafting and the grafting reaction may be occurred at the side chain of XG. The XG-g-NVP copolymer with low grafting degree was dissolvable and its viscosity behavior correspond well with power law equation of Ostwald-de Wale and its temperature and shear resistance was better than xanthan gum. And the XG-g-NVP copolymer with high grafting degree showed swelling performance. XG-g-NVP had the best swelling performance at grafting degree of 623%, and its swelling degree was 62.1 g/g at 25℃.9. The reaction of phenols with XG-g-NVP was taken place at the lactam group of NVP. The most suitable pH of absorbing phenol was at pH5.0. The pH value of adsorbing polyphenol material should be controlled in the weak acidity environment, which pH value was at 4.0⁶.0. At grafting degree of 623%, XG-g-NVP had the maximum adsorption capacity for phenol and tea polyphenol and tea polyphenol was more easily absorbed than phenol by XG-g-NVP. The isotherm data of adsorbing phenols and tea polyphenol were fitted to Freundlich model, which means that the adsorption was a single molecule layer adsorption and the process was a physical adsorption and the adsorption isotherm to phenols and tea polyphenol is the optimal adsorption isotherm.10. XG-g-NVP have excellent effect of clarification on the tea soup and apple juice.