魔芋微晶制备与再生中结构与性能研究
发布时间：2018-07-23 09:18
【摘要】：多糖微晶和纳米晶有着优良的性能和广泛的应用,如纳米复合材料、光电材料、阻气薄膜、乳液稳定剂等。在纤维素、甲壳素和淀粉等材料上,涉及提起、改性及特性研究已经较多。魔芋是我国的特色农业资源,目前关于魔芋葡甘聚糖(konjac glucomannan,KGM)的晶型研究只有零星报道、信息极不完整。本文从KGM品种、分子量、乙酰基含量、反应温度、反应介质极性等方面系统研究了KGM微晶的结构与性质,从而为葡甘聚糖晶型的人工调控奠定基础。此外,关注KGM微晶对外界因素(干燥温度、微波干燥、冻融循环、乙醇梯度洗脱)处理的敏感性,以及KGM微晶的溶解再生行为的研究,为KGM微晶的开发应用提供理论支持。通过本研究可为涉及KGM微晶的开发利用提供相对全面的基础性资料。本文主要研究结果如下:(1)KGM的水解反应分为两步。第一步为无定形区的水解,反应较快;第二步为结晶区的水解,速度较慢。这是因为无定形区结构松散,H+能快速渗入。结晶区结构相对紧密,且结晶区糖苷键的水解需要构象改变,从椅式转变为半椅式。固定硫酸浓度2.8 mol/L,KGM浓度2%,40oC条件下水解1 d,KGM微晶即可形成,结晶度达到约50%,在2θ=15.8°,20.9°,24°,25.5°等处出现特征衍射峰,KGM微晶的热稳定性从317oC提高到330oC。随着酸解的进行,KGM微晶的产率和粒径在不断减小,可通过控制水解温度或时间,来控制KGM微晶的粒径大小。不同来源KGM的理化指标(分子量、乙酰基含量、甘露糖和葡萄糖比例)并不存在明显差异。而酸解制备的花魔芋微晶、珠芽魔芋微晶、白魔芋微晶的晶型结构与热稳定性确有不同,可能是由种属不同所致。小角分析发现,珠芽魔芋晶体分子结构最为紧密(Lc=2.60 nm),分子刚性最强(Lp=23.07 nm),这与珠芽魔芋的低凝胶温度性质相关。KGM脱乙酰度越大,水解反应速率越慢,微晶粒径越大。不同脱乙酰度KGM酸解制备的KGM微晶在结晶形态上相似,均在2θ=11.8°,15.8°,20.6°出现明显的衍射峰,热降解温度提高到370oC附近。这说明KGM先经脱乙酰后再进行酸处理,结晶形态改变,热稳定显著提高。在分子尺寸上,由脱乙酰KGM制备的微晶(Rg=8.11 nm)比由天然KGM制备的微晶(Rg=9.03 nm)略小,这是由脱去的乙酰基引起的。在分子间距离和分子刚性上,脱乙酰样品会有明显增大,说明脱去乙酰基后分子间排斥力增加。KGM分子量越小,水解反应速率越快。低分子量KGM短时间水解产物与高分子量KGM长时间水解产物的结晶形态和热稳定性相似。然而,低分子量KGM的酸解产物中,分子间距离减小,刚性增强。在乙醇—酸反应介质中,酸解反应速率与乙醇浓度负相关。乙醇的添加会抑制KGM在水中的溶胀,使反应速率减慢。随着水解时间的延长,产物在2θ=11.8°处衍射峰强度不断降低,几近消失,而在2θ=15.8°、24.1°、25.8°等处衍射强度逐渐增大。可通过控制乙醇浓度或水解时间控制KGM的结晶形态。(2)采用不同物理方式作用于KGM微晶悬浮液,发现干燥温度、微波加热、冻融循环对KGM微晶的结晶形态没有影响。随着干燥温度的升高(50~100oC),结晶度逐渐下降。微波加热会使KGM微晶的结晶度先下降后上升,在640 w处出现拐点。冻融循环会破坏晶体的有序结构,随着冻融次数的增加,结晶度呈现递减趋势。采用化学方式乙醇梯度洗脱与水洗冷冻干燥进行比较发现,KGM微晶在结晶形态上差异显著,主要体现在峰的位置和强度上。KGM微晶的晶型或是结晶度的改变,会影响微晶的热稳定性。(3)KGM微晶几乎不溶于水,却能很好地溶解在氢氧化钠、硫脲、硫氰酸钾溶液中。透射电镜观察到KGM微晶为不规则的片状颗粒,易溶于碱液,说明酸解得到的KGM微晶属于甘露糖I结构。偏光显微镜显示,随着KSCN浓度提高,KGM微晶的双折射现象减弱。当Na OH浓度在0~0.4 mol/L范围内,刚果红与KGM微晶形成复合物,紫外吸收发生红移,说明KGM微晶具有螺旋结构。电导率和DSC实验证明KSCN与KGM微晶发生了结合,促进了KGM微晶的溶解。(4)KGM微晶溶解再生后,再生微晶re-KGM浓度、储藏时间、温度和p H值影响着re-KGM的溶液行为及聚集行为。随着re-KGM浓度增大,放置时间延长,温度提高,p H值降低,re-KGM粒径增大,分散指数增加,聚集行为明显。通过透射电镜和原子力显微镜观察,KGM微晶溶解再生后呈现丝状结构,长度为几微米。FT-IR表明re-KGM并没有发生衍生化。XRD和13C NMR表明re-KGM的晶型结构发生变化,结晶度明显下降。DSC表明re-KGM的有序结构遭到破坏,热降解温度从313oC降低到283oC。1H NMR证明re-KGM的糖苷键构型均为β-型。(5)re-KGM的流变学研究表明,re-KGM悬浮液为假塑性流体,对p H值、盐离子和氢键开裂剂等敏感。re-KGM悬浮液表观粘度与re-KGM浓度、温度正相关。随着温度升高,或进行超声处理,re-KGM悬浮液表观粘度增大。该特性有别于大多数亲水胶体的性质,其粘度随着温度升高,或超声处理的添加而降低。此外,浓度、温度及超声处理对re-KGM的动态粘弹性的影响与静态流变结果相似。该部分研究可为KGM微晶的开发与利用提供理论依据。
[Abstract]:Polysaccharides microcrystals and nanocrystals have excellent properties and extensive applications, such as nanocomposites, photoelectric materials, gas resistance films, emulsion stabilizers and so on. There are many studies on the modification and properties of cellulose, chitin and starch. Konjac is a characteristic agricultural resource in China. At present, konjac glucomannan (konjac GL) In this paper, the structure and properties of KGM microcrystals are systematically studied from the aspects of KGM, molecular weight, acetyl content, reaction temperature, and polarity of reaction medium, which lays the foundation for the artificial regulation of the crystal form of glucomannan. In addition, it is concerned about the external factors (drying temperature) of KGM microcrystals on the external factors (dry temperature). The sensitivity of microwave drying, freeze-thaw cycle, ethanol gradient elution and the study of the dissolution and regeneration of KGM microcrystals provide theoretical support for the development and application of KGM microcrystals. This study can provide relatively comprehensive basic data for the development and utilization of KGM microcrystals. The main results of this paper are as follows: (1) hydrolysis reaction of KGM It should be divided into two steps. The first step is the hydrolysis of the amorphous region, the reaction is faster, the second step is the hydrolysis of the crystalline region, the speed is slow. This is because the amorphous structure is loose, the H+ can quickly infiltrate. The structure of the crystalline region is relatively tight, and the hydrolysis of the glycosidic bonds in the crystalline region needs conformation change from the chair type to the semi chair. The fixed sulphuric acid concentration is 2.8 mol/L, KGM Concentration 2%, 40oC hydrolysis 1 D, KGM microcrystal can form, the crystallinity can reach about 50%, 2 theta =15.8 degrees, 20.9 degrees, 24 degrees, 25.5 degrees and other characteristics of the diffraction peak, KGM microcrystal thermal stability from 317oC to 330oC. with acid solution, KGM microcrystal yield and particle size are constantly reduced, by controlling the hydrolysis temperature or time to control KGM The size of microcrystalline grain. There is no obvious difference in physical and chemical indexes (molecular weight, acetyl content, mannose and glucose ratio) of KGM from different sources. However, the crystal structure of Amorphophallus konjac microcrystals, Amorphophallus microcrystals and the thermal stability are different, which may be caused by different species. Small angle analysis found that the bead bud The molecular structure of the Amorphophallus crystal is the closest (Lc=2.60 nm), the molecular rigidity is the strongest (Lp=23.07 nm), which is related to the higher deacetylation degree of.KGM in the low gel temperature properties of the Amorphophallus. The slower the hydrolysis reaction rate is, the larger the microcrystalline particle diameter is. The KGM microcrystals with different deacetylation degree KGM acid solutions are similar in the crystalline form, all in 2 theta =11.8 degrees, 15.8 degrees, 20.6 degrees. It shows that the thermal degradation temperature increases near 370oC. This shows that KGM is treated with acid after deacetylation and the crystalline form changes, and the thermal stability is significantly improved. On the molecular size, the microcrystalline (Rg=8.11 nm) prepared by deacetylation KGM is slightly smaller than the microcrystalline (Rg=9.03 nm) prepared from natural KGM, which is caused by the removal of acetyl group. On the intermolecular distance and the molecular rigidity, the deacetylation samples will be significantly increased, indicating that the intermolecular repulsion force after removal of acetyl groups increases with the smaller.KGM molecular weight and the faster the hydrolysis reaction rate. The low molecular weight KGM short time hydrolysates are similar to the crystalline form and thermal stability of the long time hydrolysates of high molecular weight KGM. However, low molecular weight KGM In the acid solution, the intermolecular distance decreases and the rigidity increases. In the ethanol acid reaction medium, the rate of acid hydrolysis is negatively correlated with the concentration of ethanol. The addition of ethanol inhibits the swelling of KGM in the water and slows the reaction rate. With the prolongation of the hydrolysis time, the diffraction peak intensity of the product decreases at 2 theta =11.8 degrees and is almost disappeared, but at 2 theta =15.8. The diffraction intensity of 24.1 degrees and 25.8 degrees is gradually increased. The crystallization morphology of KGM can be controlled by controlling the concentration of ethanol or the time of hydrolysis. (2) the effect of different physical modes on the KGM microcrystalline suspension has been found. It is found that the drying temperature, microwave heating, and freezing and thawing cycles have no effect on the crystalline form of KGM microcrystals. With the increase of drying temperature (50~100oC), crystallization The degree of microwave heating will decrease the crystallinity of KGM microcrystals first and then rise and turn to the point at 640 w. The freezing thawing cycle will destroy the ordered structure of the crystal. With the increase of the freezing and thawing times, the crystallinity decreases gradually. The crystallization morphology of KGM microcrystals is compared with the water washing and freezing drying by chemical ethanol gradient elution. The difference is remarkable, mainly reflected in the position and strength of the peak, the crystalline form of.KGM microcrystalline or the change of crystallinity, which will affect the thermal stability of microcrystalline. (3) KGM microcrystals are almost insoluble in water, but can be dissolved in sodium hydroxide, thiourea and potassium thiocyanate solution. The transmission electron microscope shows that KGM microcrystals are irregular flaky particles and easy to dissolve in alkali The solution showed that the KGM microcrystals obtained by the acid solution belonged to the mannose I structure. The polarization microscope showed that the birefringence of KGM microcrystals weakened as the concentration of KSCN increased. When the concentration of Na OH was in the 0~0.4 mol/L, the complex of Congo red and KGM microcrystals and the red shift of the UV absorption showed that the KGM microcrystal had a spiral structure. Conductivity and DSC experiment proved KS The combination of CN and KGM microcrystal promotes the dissolution of KGM microcrystals. (4) after the dissolution and regeneration of KGM microcrystals, the concentration of re-KGM, storage time, temperature and P H influence the behavior of solution and aggregation behavior of re-KGM. As re-KGM concentration increases, the placement time is prolonged, the temperature is higher, P H decreases, re-KGM particle size increases, dispersion index increases, aggregation index increases. Through transmission electron microscopy and atomic force microscopy, the KGM microcrystal showed a filamentous structure after its dissolution and regeneration. The length of the microcrystal was a few microns.FT-IR indicating that re-KGM had no derivative.XRD and 13C NMR showed that the crystal structure of re-KGM was changed, and the crystallinity decreased.DSC showed that the ordered structure of re-KGM was destroyed and the thermal degradation temperature was from 313oC was reduced to 283oC.1H NMR to prove that the glucoside configuration of re-KGM was beta type. (5) the rheological study of re-KGM showed that the re-KGM suspension was a pseudoplastic fluid. The apparent viscosity of the sensitive.Re-KGM suspensions, such as P H, salt ions and hydrogen bond dehiscence agents, was positively related to the re-KGM concentration and temperature. As the temperature increased, the ultrasonic treatment, re-KGM suspension was carried out. The apparent viscosity increases. This characteristic is different from the properties of most hydrophilic colloids. The viscosity decreases with the increase of temperature or the addition of ultrasonic treatment. In addition, the influence of concentration, temperature and ultrasonic treatment on the dynamic viscoelasticity of re-KGM is similar to that of static rheology. This part of the study can provide a theoretical basis for the development and utilization of KGM microcrystals.
【学位授予单位】：华中农业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TS201.23
本文编号：2138938
[Abstract]:Polysaccharides microcrystals and nanocrystals have excellent properties and extensive applications, such as nanocomposites, photoelectric materials, gas resistance films, emulsion stabilizers and so on. There are many studies on the modification and properties of cellulose, chitin and starch. Konjac is a characteristic agricultural resource in China. At present, konjac glucomannan (konjac GL) In this paper, the structure and properties of KGM microcrystals are systematically studied from the aspects of KGM, molecular weight, acetyl content, reaction temperature, and polarity of reaction medium, which lays the foundation for the artificial regulation of the crystal form of glucomannan. In addition, it is concerned about the external factors (drying temperature) of KGM microcrystals on the external factors (dry temperature). The sensitivity of microwave drying, freeze-thaw cycle, ethanol gradient elution and the study of the dissolution and regeneration of KGM microcrystals provide theoretical support for the development and application of KGM microcrystals. This study can provide relatively comprehensive basic data for the development and utilization of KGM microcrystals. The main results of this paper are as follows: (1) hydrolysis reaction of KGM It should be divided into two steps. The first step is the hydrolysis of the amorphous region, the reaction is faster, the second step is the hydrolysis of the crystalline region, the speed is slow. This is because the amorphous structure is loose, the H+ can quickly infiltrate. The structure of the crystalline region is relatively tight, and the hydrolysis of the glycosidic bonds in the crystalline region needs conformation change from the chair type to the semi chair. The fixed sulphuric acid concentration is 2.8 mol/L, KGM Concentration 2%, 40oC hydrolysis 1 D, KGM microcrystal can form, the crystallinity can reach about 50%, 2 theta =15.8 degrees, 20.9 degrees, 24 degrees, 25.5 degrees and other characteristics of the diffraction peak, KGM microcrystal thermal stability from 317oC to 330oC. with acid solution, KGM microcrystal yield and particle size are constantly reduced, by controlling the hydrolysis temperature or time to control KGM The size of microcrystalline grain. There is no obvious difference in physical and chemical indexes (molecular weight, acetyl content, mannose and glucose ratio) of KGM from different sources. However, the crystal structure of Amorphophallus konjac microcrystals, Amorphophallus microcrystals and the thermal stability are different, which may be caused by different species. Small angle analysis found that the bead bud The molecular structure of the Amorphophallus crystal is the closest (Lc=2.60 nm), the molecular rigidity is the strongest (Lp=23.07 nm), which is related to the higher deacetylation degree of.KGM in the low gel temperature properties of the Amorphophallus. The slower the hydrolysis reaction rate is, the larger the microcrystalline particle diameter is. The KGM microcrystals with different deacetylation degree KGM acid solutions are similar in the crystalline form, all in 2 theta =11.8 degrees, 15.8 degrees, 20.6 degrees. It shows that the thermal degradation temperature increases near 370oC. This shows that KGM is treated with acid after deacetylation and the crystalline form changes, and the thermal stability is significantly improved. On the molecular size, the microcrystalline (Rg=8.11 nm) prepared by deacetylation KGM is slightly smaller than the microcrystalline (Rg=9.03 nm) prepared from natural KGM, which is caused by the removal of acetyl group. On the intermolecular distance and the molecular rigidity, the deacetylation samples will be significantly increased, indicating that the intermolecular repulsion force after removal of acetyl groups increases with the smaller.KGM molecular weight and the faster the hydrolysis reaction rate. The low molecular weight KGM short time hydrolysates are similar to the crystalline form and thermal stability of the long time hydrolysates of high molecular weight KGM. However, low molecular weight KGM In the acid solution, the intermolecular distance decreases and the rigidity increases. In the ethanol acid reaction medium, the rate of acid hydrolysis is negatively correlated with the concentration of ethanol. The addition of ethanol inhibits the swelling of KGM in the water and slows the reaction rate. With the prolongation of the hydrolysis time, the diffraction peak intensity of the product decreases at 2 theta =11.8 degrees and is almost disappeared, but at 2 theta =15.8. The diffraction intensity of 24.1 degrees and 25.8 degrees is gradually increased. The crystallization morphology of KGM can be controlled by controlling the concentration of ethanol or the time of hydrolysis. (2) the effect of different physical modes on the KGM microcrystalline suspension has been found. It is found that the drying temperature, microwave heating, and freezing and thawing cycles have no effect on the crystalline form of KGM microcrystals. With the increase of drying temperature (50~100oC), crystallization The degree of microwave heating will decrease the crystallinity of KGM microcrystals first and then rise and turn to the point at 640 w. The freezing thawing cycle will destroy the ordered structure of the crystal. With the increase of the freezing and thawing times, the crystallinity decreases gradually. The crystallization morphology of KGM microcrystals is compared with the water washing and freezing drying by chemical ethanol gradient elution. The difference is remarkable, mainly reflected in the position and strength of the peak, the crystalline form of.KGM microcrystalline or the change of crystallinity, which will affect the thermal stability of microcrystalline. (3) KGM microcrystals are almost insoluble in water, but can be dissolved in sodium hydroxide, thiourea and potassium thiocyanate solution. The transmission electron microscope shows that KGM microcrystals are irregular flaky particles and easy to dissolve in alkali The solution showed that the KGM microcrystals obtained by the acid solution belonged to the mannose I structure. The polarization microscope showed that the birefringence of KGM microcrystals weakened as the concentration of KSCN increased. When the concentration of Na OH was in the 0~0.4 mol/L, the complex of Congo red and KGM microcrystals and the red shift of the UV absorption showed that the KGM microcrystal had a spiral structure. Conductivity and DSC experiment proved KS The combination of CN and KGM microcrystal promotes the dissolution of KGM microcrystals. (4) after the dissolution and regeneration of KGM microcrystals, the concentration of re-KGM, storage time, temperature and P H influence the behavior of solution and aggregation behavior of re-KGM. As re-KGM concentration increases, the placement time is prolonged, the temperature is higher, P H decreases, re-KGM particle size increases, dispersion index increases, aggregation index increases. Through transmission electron microscopy and atomic force microscopy, the KGM microcrystal showed a filamentous structure after its dissolution and regeneration. The length of the microcrystal was a few microns.FT-IR indicating that re-KGM had no derivative.XRD and 13C NMR showed that the crystal structure of re-KGM was changed, and the crystallinity decreased.DSC showed that the ordered structure of re-KGM was destroyed and the thermal degradation temperature was from 313oC was reduced to 283oC.1H NMR to prove that the glucoside configuration of re-KGM was beta type. (5) the rheological study of re-KGM showed that the re-KGM suspension was a pseudoplastic fluid. The apparent viscosity of the sensitive.Re-KGM suspensions, such as P H, salt ions and hydrogen bond dehiscence agents, was positively related to the re-KGM concentration and temperature. As the temperature increased, the ultrasonic treatment, re-KGM suspension was carried out. The apparent viscosity increases. This characteristic is different from the properties of most hydrophilic colloids. The viscosity decreases with the increase of temperature or the addition of ultrasonic treatment. In addition, the influence of concentration, temperature and ultrasonic treatment on the dynamic viscoelasticity of re-KGM is similar to that of static rheology. This part of the study can provide a theoretical basis for the development and utilization of KGM microcrystals.
【学位授予单位】：华中农业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TS201.23
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