| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程技術研究所 === 86 ===
In this work, the thermal stability of Rhizopus arrhizus,Candida rugosa, and Mucor miehei lipase in organic solvent was investigated. The effects of tempetature,water content,solution pH, and lactose addition on the stability of lipase were studied and an inactivation model for the thermal inactivation of lipases was proposed.
The thermal inactivation of Rhizopus arrhizus,Candida rugosa, and Mucor miehei lipases both in free and immobilized forms can be described by the series type model with biphassic nature (a1< 1,a2=0 ,k1>k2). Activation energy of inactivation, Ea ,can be obtained if the thermal inactivation is assumed to the first order. The Ea of free and immobilized R. arrhizus lipase is 1630.45 KJ/mole (60°C∼75°C) and 53.37KJ/mole (55°C∼85°C),respectively.The corresponding value for C. rugosa lipase is 127.6 KJ/mole (35°C∼65°C) and 120.68 KJ/mole (70°C∼ 85°C), respectively. For M. miehei lipase, it is 175.23 KJ/mole(55C°∼70C°) and 128.56 KJ/mole (70°C∼85°C)，respectively.
Thermostability of free lipase is sensitive ot variation of temperature, water content and pH. For the thermal inactivation of lipase, a1 decreases with increasing temperature and water content,while k1 imcreases with increasing temperature and warer content. The changes of k2 with temperature and water content is irregular. k2 is small compared to k1 and its effect on the thermal inactivation is insignificant. The thermostability of immobilized lipase is better than that of the free lipase. Temperature, water content and pH have important influences on the activity of immobilized lipase, but not on its thermostanbility. This indicates that after immobilization.lipase conformation is more rigid and does not change easily under changes of environment.
The addition of lactose has little effect on the thermal stability of both free and immobilized lipases. This contradicts the results of literatures. The reason is propably that the thermal inactivatons of lipase were carried out in hydrophobic organic solvent in this work, while in literatures the reactions were carried out in hydrophilic solvent.
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