Long Jie, Li Xingfei, Zhan Xiaobei, Xu Xueming, Tian Yaoqi, Xie Zhengjun, Jin Zhengyu
School of Food Science and Technology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, China.
The State Key Laboratory of Food Science and Technology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, China.
Bioprocess Biosyst Eng. 2017 Jun;40(6):821-831. doi: 10.1007/s00449-017-1747-5. Epub 2017 Feb 27.
Pullulanase was sol-gel encapsulated in the presence of magnetic chitosan/FeO nanoparticles. The resulting immobilized pullulanase was characterized by scanning electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the addition of pullulanase created a more regular surface on the sol-gel matrix and an enhanced magnetic response to an applied magnetic field. The maximal activity retention (83.9%) and specific activity (291.7 U/mg) of the immobilized pullulanase were observed under optimized conditions including an octyltriethoxysilane:tetraethoxysilane (OTES:TEOS) ratio of 1:2 and enzyme concentration of 0.484 mg/mL sol. The immobilized enzyme exhibited good thermal stability. When the temperature was above 60 °C, the immobilized pullulanase showed significantly higher activity than the free enzyme (p < 0.01); enzyme immobilized by simple sol-gel encapsulation and co-immobilized by crosslinking-encapsulation retained 52 and 69% of their initial activity after 5 h at 62 °C, respectively, compared to 11% for the free enzyme. Moreover, the stability of the pullulanase was improved by crosslinking-encapsulation, as the enzyme retained more than 85 and 81% of its original activity after 5 and 6 consecutive reuses, respectively, compared to 80 and 72% of its original activity for simple sol-gel encapsulated enzymes. This indicated the leakage of enzyme molecules through the pores of the gel was substantially abated by cross-linking. Such immobilized pullulanase provides high stability and ease of enzyme recovery, characteristics that are advantageous for applications in the food industry that involve continuous starch processing.
普鲁兰酶在磁性壳聚糖/FeO纳米颗粒存在的情况下被溶胶-凝胶包封。通过扫描电子显微镜、振动样品磁强计、傅里叶变换红外光谱和热重分析对所得固定化普鲁兰酶进行了表征。结果表明，普鲁兰酶的添加在溶胶-凝胶基质上形成了更规则的表面，并增强了对施加磁场的磁响应。在优化条件下，包括辛基三乙氧基硅烷：四乙氧基硅烷（OTES:TEOS）比例为1:2和酶浓度为0.484 mg/mL溶胶，观察到固定化普鲁兰酶的最大活性保留率（83.9%）和比活性（291.7 U/mg）。固定化酶表现出良好的热稳定性。当温度高于60°C时，固定化普鲁兰酶的活性明显高于游离酶（p < 0.01）；通过简单溶胶-凝胶包封固定的酶和通过交联-包封共固定的酶在62°C下5小时后分别保留了其初始活性的52%和69%，而游离酶仅保留11%。此外，交联-包封提高了普鲁兰酶的稳定性，因为该酶在连续5次和6次重复使用后分别保留了其原始活性的85%和81%以上，而简单溶胶-凝胶包封的酶分别为80%和72%。这表明通过交联大大减少了酶分子通过凝胶孔的泄漏。这种固定化普鲁兰酶具有高稳定性和易于酶回收的特点，这些特性有利于在涉及连续淀粉加工的食品工业中的应用。
