Production of thermostable beta-galactosidase from tyhermophilic fungi for use in low-lactose milk production

Soydan, Meltem
The aim of this research was the production of beta-galactosidase from thermophilic fungi for use in low lactose milk production or other possible applications. For this purpose, three thermophilic fungi Humicola insolens, Torula thermophila and Thermomyces lanuginosus were screened for lactase production. Highest lactase activity was observed in Thermomyces lanuginosus. The carbon source inducing highest extracellular lactase production in Thermomyces lanuginosus was determined as arabinose. When grown on arabinose T. lanuginosus produced two major lactase activity peaks, one being at day 4 (beta-galactosidase-A) and second starting following the initiation of biomass degradation at day 3 suggesting the existence of a cell wall-bound beta-galactosidase (beta-galactosidase-B). Maximum activity of the second enzyme was at day 10. Crude enzyme stored at 4ºC and -20ºC was stable over a period of one month. Optimum pH and temperature of crude enzyme were found as pH 6.8 and 65ºC. For concentration of extracellular enzyme, fractional ammonium sulfate precipitation with 60-85% salt was applied. Comparisons with commercial lactase obtained from Kluyveromyces lactis revealed that partially purified lactase from Thermomyces lanuginosus was 1.3 times more efficient in hydrolysis of lactose even at 30ºC which is optimum for Kluyveromyces lactis. Lactose hydrolysis was enhanced at higher temperatures and reached maximum at 50-60ºC giving 4.7 fold higher hydrolysis than Kluyveromyces lactis beta-galactosidase. Molecular weight of the second enzyme was determined as 156 kDa by gel filtration. Being an extracellular enzyme with optimum pH suitable for dairy processes, high thermotolerance and stability, this enzyme has a potential for commercial use.


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Citation Formats
M. Soydan, “Production of thermostable beta-galactosidase from tyhermophilic fungi for use in low-lactose milk production,” M.S. - Master of Science, Middle East Technical University, 2006.