鲢鱼皮明胶提取方法和谷氨酰胺转氨酶改性对明胶结构和膜性能的影响

Effect of Extraction Methods and Transglutaminase Modification on Film Properties and Structure of Gelatin

研究鲢鱼皮明胶的酶法、酸法、热水法3种常用的工业提取方法对其凝胶强度、黏度以及膜性能指标的影响,在此基础上进一步使用谷氨酰胺转氨酶(transglutaminase,TG)改性以达到改善膜性能的效果。同时以市售猪皮明胶为对照,采用圆二色谱、红外光谱分析3种提取方法对明胶高级结构的影响;通过红外光谱、原子力显微镜分析了鲢鱼皮明胶TG改性前后明胶高级结构和表面结构变化。结果表明,3种提取方法中酶法明胶的比黏度和凝胶强度最大,成膜后的酶法明胶膜抗拉强度最大、断裂延伸率最大、水蒸气透过率最低。继续经过TG改性后,抗拉强度、断裂延伸率指标显著增加(P<0.05),接近猪皮明胶膜,水蒸气透过率进一步降低。圆二色谱及红外光谱结果发现酶法明胶α-螺旋相对含量增加、无规卷曲相对含量减少,并可保留更多的分子内氢键。而TG改性后明胶分子内氨基转变为亚氨基,同时增强了肽链间相互作用。原子力显微镜图像分析结果证明,TG改性的明胶膜具有更为致密均匀的表面结构。明胶膜的机械强度与明胶结构中α-螺旋的含量呈正相关。因此,酶法提取并通过TG改性是一种提高可食性明胶膜性能的有效方法。

The present study was conducted to improve the membrane properties of silver carp skin gelatin and dissect the mechanism involved by examination of protein structure.The gel strength,viscosity and mechanical properties of silver carp skin gelatin extracted by three extraction methods(acid extraction,hot water extraction and enzymatic extraction)were comparatively studied.Then the enzymatically prepared gelatin was modified with transglutaminase(TG),and the amino acid composition was determined and compared with that of a commercial product and that of the unmodified gelatin.At the same time,circular dichroism(CD)spectroscopy and infrared(IR)spectroscopy were employed to estimate the secondary and tertiary structure,and IR spectroscopy and atomic force microscopy(AFM)were employed to examine the change of protein structure before and after TG addition.The results showed that the enzymatically prepared gelatin had the highest viscosity and strongest gel strength.Its membrane had the strongest mechanical properties and lowest water vapor permeability.Furthermore,after TG modification,its tensile strength and elongation at break were increased significantly to levels equivalent to those of type A pigskin gelatin membrane,accompanied by a decrease in water vapor permeability.CD and IR spectra showed that,compared with the samples prepared by two other methods,the enzymatically obtained gelatin had higherα-helix content and lower random coil content and thus retained more hydrogen bonds between gelatin chains.After TG modification,the-NH2group in gelatin was changed to-NH-,consequently improving the interaction between peptide chains.The results of AFM showed that the surface microstructure of the modified gelatin membrane was more even and compact.A positive correlation existed between theα-helix content and mechanical properties of the gelatin membrane.In conclusion,pepsin-assisted extraction combined with TG modification is an effective method to improve the membrane properties of gelatin.