球磨、超声和盐酸处理对几丁质的微观结构和酶促脱乙酰效率的影响

Effects of Ball Milling,Ultrosonic or Hydrochloric Acid Treatment on the Microstructure and Enzymatic Deacetylation Efficiency of Chitin

几丁质是地球上第二丰富的天然多糖,可经过脱乙酰生成壳聚糖。但是,其结晶度高、溶解性差,使其酶促脱乙酰效率很低。为研究不同处理对几丁质的微观结构和酶促脱乙酰效率的影响,本实验分别对几丁质进行了球磨、超声和盐酸改性处理。首先确定球磨和超声改性的最佳条件;然后使用傅里叶变换红外光谱、元素分析、X射线衍射、热重-差示扫描量热法和扫描电子显微镜对改性几丁质的微观结构进行表征;最后测定红球菌11-3的几丁质脱乙酰酶对改性几丁质的脱乙酰效率。结果表明,球磨和超声改性的最佳条件分别为1 800 r/min、45 min和400 W、45 min。3种几丁质改性方法中,球磨几丁质改性效果最好,与原几丁质相比,黏均分子质量降低了88.14%;几丁质分子间氢键网络被破坏,部分糖苷键断裂;脱乙酰度有所增加;结晶度由96.30%降低至73.04%;热稳定性被破坏;结构呈现堆叠现象,变得疏松多孔。此外,几丁质脱乙酰酶对球磨几丁质的脱乙酰效率更高,乙酸产量较原几丁质提高了2.40倍。综上,球磨处理可以更有效地改变天然几丁质的理化性质和微观结构,从而提高几丁质的酶促脱乙酰效率。

Chitin is the second most abundant natural polysaccharide on Earth,which can be deacetylated to produce chitosan.However,due to the high crystallinity and poor solubility of chitin,its efficiency of enzymatic deacetylation is very low.To investigate the effects of different treatments on the microstructure and enzymatic deacetylation efficiency of chitin,chitin was modified by ball milling,ultrasonic or hydrochloric acid treatment in this study.First,the optimum conditions of ball milling and ultrasonic treatments were determined.Then,the microstructure of modified chitins was characterized by Fourier transform infrared(FTIR) spectroscopy,elemental analysis,X-ray diffraction,thermogravimetricdifferential scanning calorimetry(TG-DSC) and scanning electron microscopy(SEM).Finally,the deacetylation efficiency of chitin deacetylase from Rhodococcus sp.11-3 for chitin was measured.The results showed that the optimum conditions of ball milling and ultrasonic modification were 1 800 r/min and 45 min,and 400 W and 45 min,respectively.Among the three treatments,ball milling had the best modification effect,resulting in an 88.14% reduction in the viscosity-average molecular mass of chitin.The intermolecular hydrogen bond network of chitin was destroyed and some glycosidic bonds were broken;the degree of deacetylation increased;the crystallinity decreased from 96.30% to 73.04%;thermal stability was destroyed;and the treated chitin showed a stacking structure and was more loose and porous.In addition,chitin deacetylase had higher deacetylation efficiency for ball-milled chitin,and the yield of acetic acid was 3.4 times higher than that from raw chitin.In conclusion,ball milling treatment can improve the enzymatic deacetylation efficiency of chitin by changing its physicochemical properties and microstructure.