Synthesis of Lactulose in Continuous Stirred Tank Reactor With β-Galactosidase of Apergillus oryzae Immobilized in Monofunctional Glyoxyl Agarose Support

• Published in: Frontiers in bioengineering and biotechnology 2020-06, Vol.8, p.699-699
• Main Authors: Ubilla, Claudia, Ramírez, Nicolás, Valdivia, Felipe, Vera, Carlos, Illanes, Andrés, Guerrero, Cecilia
• Format: Article
• Language: English
• Subjects: agarose support; Bioengineering and Biotechnology; galacto-oligossacharides; immobilization; lactulose; prebiotic; β-galactosidase
• ISSN: 2296-4185; 2296-4185
• DOI: 10.3389/fbioe.2020.00699

Lactulose synthesis from fructose and lactose in continuous stirred tank (CSTR) reactor operation with glyoxyl-agarose immobilized Aspergillus oryzae β-galactosidase is reported for the first time. The effect of operational variables: inlet concentrations of sugar substrates, temperature, feed substrate molar ratio, enzyme loading and feed flow rate was studied on reactor performance. Even though the variation of each one affected to a certain extent lactulose yield (Y Lactulose ), specific productivity (π Lactulose ) and selectivity of the reaction (lactulose/transgalactosylated oligosaccharides molar ratio) (S Lu/TOS ), the most significant effects were obtained by varying the inlet concentrations of sugar substrates and the feed substrate molar ratio. Maximum Y Lactulose of 0.54 g⋅g –1 was obtained at 50°C, pH 4.5, 50% w/w inlet concentrations of sugar substrates, feed flowrate of 12 mL⋅min –1 , fructose/lactose molar ratio of 8 and reactor enzyme load of 29.06 IU H ⋅mL –1 . At such conditions S Lu/TOS was 3.7, lactose conversion (X Lactose ) was 0.39 and total transgalactosylation yield was 0.762 g⋅g –1 , meaning that 76% of the reacted lactose corresponded to transgalactosylation and 24% to hydrolysis, which is a definite advantage of this mode of operation. Even though X Lactose in CSTR was lower than in other reported modes of operation for lactulose synthesis, transgalactosylation was more favored over hydrolysis which reduced the inhibitory effect of galactose on β-galactosidase.