title: Influences of operating conditions on continuous lactulose synthesis in an enzymatic membrane reactor system: A basis prior to long-term operation.
abstract: Lactulose synthesis was performed in a continuous stirred enzymatic membrane reactor. Each investigated operating condition (agitation, pH, feed molar ratio of lactose to fructose (mL/mF ratio), hydraulic residence time (HRT)) had an influence on reaction performances, in terms of lactulose concentration, productivity and selectivity. Lactulose concentration was maximum at an mL/mF ratio of 1/2. Higher than this ratio, synthesis of galactooligosaccharides was promoted rather than lactulose. At mL/mF ratios lower than 1/2, enzyme inhibition was pronounced to the detriment of lactulose production. At 7 or 9h HRT, higher lactulose concentrations were obtained than at shorter HRTs. Applying an mL/mF ratio of 1/2 and an HRT of 9h in a long-term operation, nearly constant lactulose concentration was reached after 23h and lasted up to 32h with a mean concentration of 14.51±0.07g/L and a reaction selectivity of 0.075-0.080mollactulose/molcons.lactose. After 7d, lactulose concentration reduced by 31%. A continuous synthesis of lactulose at lab-scale was shown to be amenable using a membrane reactor process. Moreover, for process evaluation, this study can bridge the gap between batch laboratory scale and continuous full-scale operation regarding lactulose synthesis.
authors.affiliation: Chair of Chemical and Process Engineering, Technische Universität Berlin, Ackerstraße 76, 13355 Berlin, Germany; Department of Food Science and Technology, Bogor Agricultural University, Raya Darmaga St, Kampus IPB Darmaga Bogor 16680, West Java, Indonesia. Electronic address: azis.b.sitanggang@mailbox.tu-berlin.de.
authors.forename: Azis Boing
authors.initials: AB
authors.lastname: Sitanggang
authors.affiliation: HTW Berlin - University of Applied Science, Engineering II, School of Life Science Engineering, Wilhelminenhofstraße 75A, 12459 Berlin, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Drews
authors.affiliation: Chair of Chemical and Process Engineering, Technische Universität Berlin, Ackerstraße 76, 13355 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kraume
mesh_terms: D005632:Fructose / Q000737:chemistry*; D007716:Kluyveromyces / Q000201:enzymology; D007785:Lactose / Q000737:chemistry*; D007792:Lactulose / Q000737:chemistry*; D001616:beta-Galactosidase / Q000737:chemistry*
chemical_list: D005632:Fructose; D007792:Lactulose; D001616:beta-Galactosidase; D007785:Lactose
keywords: Enzymatic membrane reactor (EMR); Lactulose; Process intensification; Transgalactosylation; β-galactosidase