Enzyme catalysis of insoluble cornstarch granules: Impact on surface morphology, properties and biodegradability
Enzyme catalysis of insoluble cornstarch granules: Impact on surface morphology, properties and biodegradability
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DOI：
10.1016/j.polymdegradstab.2006.08.021
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发表时间：
2006-12
影响因子：
5.9
通讯作者：
S. Imam;S. Gordon;A. Mohamed;R. Harry‐O'kuru;B. Chiou;G. Glenn;W. Orts
中科院分区：
文献类型：
--
作者：
S. Imam;S. Gordon;A. Mohamed;R. Harry‐O'kuru;B. Chiou;G. Glenn;W. Orts
将颗粒状玉米淀粉用微生物葡糖淀粉酶（50 mM乙酸钠缓冲液，pH 5.5，30°C，150 rpm）处理长达8小时。处理后的淀粉被回收，并评估颗粒形态，化学性质，热性能，结晶度和其生物降解性的影响的变化。随着酶处理的进行，还原糖开始在液体培养基中积累（在8小时内总共6%），并且颗粒在孵育的8小时内遭受大约6%的重量损失。虽然颗粒在形态上看起来完整，但由于酶处理，颗粒表面出现了许多小坑。即使在酶处理8小时后，有坑的颗粒也没有被破坏并且保持完整。X-射线衍射表明，没有损失的结晶度在酶处理的颗粒，而是增加相对结晶度，这表明，酶优先催化脱水葡萄糖单元在无定形区域的颗粒。FTIR数据进一步支持了这些发现，表明颗粒对酶的攻击更具抵抗力，因为无定形直链淀粉比结晶支链淀粉水解得更快。这些结果还表明，不同类型的淀粉的结晶度的变化有可能影响其生物降解速率。酶处理后的淀粉颗粒表现出抗生物降解性，且抗生物降解性的程度与酶处理时间的长短有关。与未处理的样品相比，用酶处理颗粒共7小时，并在土壤中进行生物降解，在闭路呼吸计中产生的CO2减少40-50%。差示扫描量热法（DSC）热分析图显示吸热反应，起始温度和峰值温度几乎没有变化，表明葡糖淀粉酶通过从表面降解淀粉颗粒开始。
Granular cornstarch was treated with microbial glucoamylase (50mM sodium acetate buffer at pH 5.5 at 30°C, 150rpm) for up to 8h. Treated starch was recovered and evaluated for changes in granular morphology, chemical properties, thermal properties, crystallinity and impact on its biodegradability. As the enzyme treatment progressed, reducing sugars began to accumulate in the liquid culture media (total of 6% in 8h) and the granule suffered roughly 6% weight loss within 8h of incubation. While the granules appeared intact morphologically, numerous small pits developed throughout the surface of the granules as a result of the enzyme treatment. Even after 8h of enzyme treatment, the pitted granules were not disrupted and remained intact. X-ray diffraction indicated no loss of crystallinity in the enzyme treated granules but rather an increase in relative crystallinity, suggesting that the enzyme preferentially catalyzed the anhydroglucose units in amorphous regions of the granule. These findings were further supported by FTIR data suggesting that granules become more resistant to enzyme attack as amorphous amylose is hydrolyzed faster than the crystalline amylopectin domains. These results also suggest that variations in the crystallinity of different types of starches have the potential to affect their rates of biodegradation. Enzyme treated starch granules exhibited resistance to biodegradation, and the degree of resistance was related to the length of enzyme treatment. Granules treated with enzyme for a total of 7h and subjected to biodegradation in soil produced 40–50% less CO2in a closed circuit respirometer compared to the untreated samples. Differential scanning calorimetry (DSC) thermograms showed an endothermic reaction with little change in the onset and peak temperatures indicating that glucoamylase started by degrading the starch granules from the surface.