The crude polysaccharide UPOJ was extracted by ultrasound from <i> Ophiopogon japonicas </i> and purified by DEAE-cellulose52 column and Sephadex G-150 gel column. Purified polysaccharide UPOJ-DS was obtained. The thermal characteristics of UPOJ-DS were studied by using the thermal analysis system Q1000DSC LNCS FACS Q600SDT. The heating rate was 10 ° C/min and the test temperature was 20 ° C ~ 800 ° C. The results showed that there were three large mass losses in the process of heating, in which the maximum weight loss rate was 66.68% at 220 ° C ~ 330 ° C and the decomposition reaction took place in the polysaccharide itself, which indicated that the composition, water content, intermolecular interaction and aggregation behavior of UPOJ-DS were affected by temperature. The surface morphology of UPOJ-DS was observed by environmental scanning electron microscope (ESEM). The results indicated that the polysaccharide molecules were lamellar or clastic, with smooth surface, strong intermolecular interaction and close binding.
As a traditional Chinese medicine, the plant Ophiopogon japonicus is used for nourishing Yin and nourishing the heart, the treatment of dryness, dry cough, insomnia, constipation, etc [
Thermal analysis is the technology measuring the relationship of physical properties and temperature dependence under the program control temperature. The commonly used methods include thermogravimetric method (TG), derivative thermogravimetric method (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Thermal analysis technique can determine rapidly and accurately the transformation of crystal material type, melting, sublimation, absorption, dehydration and decomposition of change, is an important method to test the physical and chemical properties of inorganic, organic and polymer materials. Thermal analysis technology has been widely used in physics, chemistry, chemical industry, metallurgy, geology, building materials, fuel, textile, food and biology [
Thermogravimetry (TG) is the measurement of the weight change of sample during heating. Temperature is abscissa and the percentage of weight loss is ordinaten in TG curve. Composition, thermal stability, thermal decomposition and products generated could be obtained from TG curve. As well as the temperature range of decomposition and thermal stability could also be obtained from TG curve. The first derivative of the TG curve with respect to temperature is the thermogravimetry (DTG) curve, which reflects the relationship between the rate of change of sample mass and temperature [
Differential thermal analysis (DTA) is a thermal analysis method to measure the relationship between temperature between samples and reference materials under programmed temperature control [
Differential scanning calorimetry (DSC) is a technique for measuring the relationship between temperature and power difference of material and reference material under programmed temperature control. The DSC curve takes temperature or time as the horizontal coordinate, and the differential of enthalpy with respect to time (dH/dt) as the vertical coordinate. It has the characteristics of sensitive reaction and high resolution [
Environmental Scanning Electron Microscope (ESEM) is a new electronic optical instrument, which uses extremely thin electron beam to scan the sample surface, collects the generated secondary electron with the special detector, forms the electric signal to the picture tube, displays the object on the fluorescent screen. Three-dimensional images of the surface of cells and tissues could be photographed. It has been widely used in physics, chemistry, materials, geology, geography, biology, medicine and other disciplines, and metallurgy, ceramics, electronics, semiconductor and other industries, and promote the development of relevant disciplines, has wide application prospect [
Ophiopogon japonicus (produced in Zhejiang province) was purchased from the traditional Chinese medicine market of Wan Shou road, xi' an. Sodium chloride, concentrated sulfuric acid, phenol, 95% ethanol were all analytical pure reagents. DEAE-52 Whatman, Sephadex G-150 Pharmacia. The experimental water is double steamed water.
Thermal analysis system (Q1000DSC+LNCS+FACS Q600SDT, TA Co., USA), environmental scanning electron microscope (Quanta200, FEI Co., the Netherlands). Ultrasonic cell crusher (JY92-II, Ningbo Xinzhi Biological Scientific Technology Co., China). Ultraviolet and visible spectrophotometer (TU1810, Beijing’s General Instrument Co.). High-speed centrifuge (CF16RX, Hitachi Co., Japan). RE252AA type rotary evaporator, vacuum freezing dryer (FD-1, Beijing Boyikang Laboratory Instrument Co.). 2.5 × 60 cm series chromatography column (Shanghai Qite Analytical Instrument Co.) electronic balance (precision:1/105g, Beijing Sartorius Instrument System Co.).
The root of Ophiopogon japonicas was crushed after drying at 60˚C, and then 200 g dry powder was put into 1000 ml beaker, added 4 times the volume of 95% ethanol to degrease, stirring 20 min, centrifuge, collect precipitate and dry after repeated three times. It was added to distilled water according to the ratio of 1:10 to extract polysaccharide by used of ultrasound. The extraction conditions as follows: ultrasonic power: 80 W, ultrasonic time: 10 s, ultrasonic frequency: 90 times, interval time: 15 s, extract twice, respectively. The twice extract was combined, and added to four times the amount of 95% ethyl alcohol to precipitate polysaccharide after vacuum concentration, then centrifuge, dialyze three days by running water and vacuum freeze―drying. Crude polysaccharide UPOJ was obtained. No absorption was observed at 280 nm and 260 nm in the UV absorption spectra of UPOJ, which demonstrated the absence of protein and nucleic acid in the polysaccharides.
The polysaccharide UPOJ was eluted in succession with doubly distilled water by DEAE-52 cellulose column equilibrated with distilled water (2.5 × 60 cm). The eluate was detected by phenol?sulfuric acid method. Only one component obtained, which was named UPOJ-D. The sample of UPOJ-D was purified by Sephadex G-150 gel column (2.5 × 60 cm) using doubly distilled water as eluent. Only one component was obtained, named UPOJ-DS. Then UPOJ-DS was concentrated, dialyzed and lyophilized for further study.
With reference to literature [
A proper amount of polysaccharide sample powder was glued to the conductive adhesive of the experimental bench. The floating sample was blown off with rubber suction bulb and placed in a gold conductive layer of 10 nm thickness in a vacuum plating instrument. The accelerating voltage of the electron gun was 20 KV, observed by use of ESEM.
As shown in
process of 20˚C ~ 100˚C, which was the process of loss of the adsorption of water. In 220˚C ~ 330˚C, the weight loss ratio was 66.68%, suggesting that polysaccharide decomposition reaction happened. In 330˚C ~ 700˚C, the weight loss ratio was 18.68%. Thereafter until heated to 800˚C, the weight of UPOJ-DS had been continuously decreasing, but the weight loss ratio significantly smaller than before. These results indicated that these change of UPOJ-DS was related to its composition, water content, molecular interaction and aggregation behavior. DTG curves reflected the relationship between the mass-change rate and temperature. The mass-change rate also has two peaks in
The above conclusion indicated that the molecular structure of Ophiopogon japonicas polysaccharide UPOJ-DS will change with the change of temperature. The experiments of TG, DTA and DSC were used to study the thermal characteristics of UPOJ-DS. The analysis results showed that the UPOJ-DS was relatively
stable under 200˚C, and rapid decomposition occurred at about 280˚C. There were three times mass loss and two endothermic peaks in the heating process, suggesting the composition, water content and the intermolecular of UPOJ-DS were affected by temperature. It resulted in the change of the state of aggregation behavior of UPOJ-DS. From several above experiments, we could know the DTG curve is the first derivative of the TG curve with respect to temperature, enhanced the accuracy and could accurately determine the changes of thermogravimetric process. The DSC analysis was used to calculate quantitatively accurately, and was more sensitive, high resolution, and good reproducibility. But the highest determination temperature of DSC was only about 750˚C, differential thermal analysis method could be used when determination temperature was higher than the temperature 750˚C. The scanning electron microscopy showed that the polysaccharide molecules were lamellar or clastic, with smooth surface, strong intermolecular interaction and close binding. In conclusion, the results provided theoretical and experimental foundation for the thermal properties and morphology of the polysaccharide extracted by ultrasound from Ophiopogon japonicas.
This research was financially supported by the Natural Science Foundation of Shaanxi Province (Grant Numbers, 2018JQ1091); the Fundamental Research Funds for Xi’an Aeronautical University (Grant Numbers, 2016KY1215); undergraduate innovation and entrepreneurship training program of Xi’an Aeronautical University (Grant Numbers, DCX2018042).
Wang, X.M., Zhang, T.Z., Zhang, W.F., Wang, M., Hao, D.P. and Ding, Q. (2018) Morphology and Thermal Characteristics of Polysaccharide Extracted by Ultrasound from Ophiopogon japonicus. American Journal of Plant Sciences, 9, 1699-1707. https://doi.org/10.4236/ajps.2018.98123