Investigation of β-galactosidase production by microalga Tetradesmus obliquus in determined growth conditions

Abstract

β-Galactosidase is a commercially important enzyme widely used in the food industry for the manufacturing of lactose-hydrolyzed products and synthesis of probiotic food ingredients. It could also be used to reduce the environmental impacts of the dairy industry relative to lactose disposal. This enzyme has been isolated from different sources, with varying properties and potential for diverse applications. Several microalgae have been screened for β-galactosidase activity, among which the chlorophyte Tetradesmus obliquus showed significant levels. The production of enzymes from microalgae could emerge as a valuable avenue for the utilization of its biomass. In addition, this particular microalga can grow mixotrophically on lactose as an organic carbon source, offering additional possibilities for the utilization of lactose. This study investigates the production of β-galactosidase from T. obliquus under different trophic conditions and known media composition, in order to assess their influence on its productivity and selectivity. Results show that the photoautotrophic cultures provide a highest selectivity, while mixotrophic conditions provide higher productivities due to faster growth and higher biomass yields. Further studies on mixotrophic cultures using lactose revealed no significant differences on β-galactosidase production when varying the concentrations of organic carbon and nitrogen nutrients. The age of culture has a strong influence on the enzyme production, suggesting a dependence on the growth phase. Maximal enzyme productivities obtained in mixotrophic conditions on lactose reach about 12.35 U L−1 day−1 after 7 days, which is a realistic duration for producing the enzyme at larger scales in bioreactors.