Kow-Jen Duan

Production of galactooligosaccharides by β-galactosidase immobilized on glutaraldehyde-treated chitosan beads

β-Galactosidase from Aspergillus oryzae, immobilized on glutaraldehyde-treated chitosan beads, produced galactooligosaccharides (GOS) in a plug reactor. Maximum yields of GOS were 18, 21, 26 with lactose at 100, 200, 300 g/L, respectively. Yields of GOS in the immobilized enzyme system were always lower than that of free enzyme system. In a continuous reaction there was no significant loss of activity after 30 days of operation.

Production of high-content galacto-oligosaccharide by enzyme catalysis and fermentation with Kluyveromyces marxianus

Of three β-galactosidases from Aspergillus oryzae, Kluyveromyces lactis and Bacillus sp., used for the production of low-content galacto- oligosaccharides (GOS) from lactose, the latter produced the highest yield of trisaccharides and tetrasaccharides. GOS production was enhanced by mixing β-galactosidase glucose oxidase. The low-content GOS syrups, produced either by β-galactosidase alone or by the mixed enzyme system, were subjected to the fermentation by Kluyveromyces marxianus, whereby glucose, galactose, lactose and other disaccharides were depleted, resulting in up to 97% and 98% on a dry weight basis of high-content GOS with the yields of 31% and 32%, respectively.

Kinetic studies and mathematical model for enzymatic production of fructooligosaccharides from sucrose

Abstract The enzymatic reaction mechanism of fructooligosaccharides production from sucrose was investigated by use of a β-fructofuranosidase from Aspergillus japonicus . Competitive product inhibition by glucose was observed from kinetic analysis for the substrates sucrose, 1-kestose, and nystose. In addition, the reaction rate of sucrose was inhibited at concentrations greater than 20% (w/v). A mathematical model was proposed based on the kinetic observation to simulate fructooligosaccharides production from sucrose. The mathematical calculation agreed with the experimental data for the initial sucrose concentrations of 30% (w/v) and 50% (w/v) at 37°C.

Production of fructooligosaccharides in high yield using a mixed enzyme system of β-fructofuranosidase and glucose oxidase

A mixed enzyme system, with β-fructofuranosidase (obtained from Aspergillus japonicus) and commercial glucose oxidase (Gluzyme, Novo Nordisk), produced fructooligosaccharides (FOS) in high yield from sucrose. The reaction was performed in an aerated stirred tank reactor controlled at pH 5.5 by a slurry of CaCO3. Glucose, an inhibitor of β-fructofuranosidase, produced in the reaction was converted by glucose oxidase to gluconic acid, which was then precipitated to calcium gluconate in solution. The system produced more than 90% (w/w) FOS on a dry weight basis, the remainder was glucose, sucrose and a small amount of calcium gluconate. Most of the FOS and sucrose was hydrolyzed to fructose in the mixed enzyme system with glucose oxidase and β-fructofuranosidase from Asp. niger.

Immobilization of β-Fructofuranosidases from Aspergillus on Methacrylamide-Based Polymeric Beads for Production of Fructooligosaccharides

β‐Fructofuranosidases from Aspergillus niger ATCC 20611 and Aspergillus japonicusTIT‐KJ1 were purified and immobilized covalently onto methacrylamide‐based polymeric beads. The porous, oxriane‐containing support was reactive and could bind enzymes in a buffered solution at room temperature with a density up to 0.4 mg of protein g−1 of support with 100% immobilized yield. Neither the optimum temperature for the highest enzymatic activities nor the batch reaction pattern for fructooligosaccharides formation catalyzed by β‐fructofuranosidases was changed by immobilization. The amount of fructooligosaccharides produced from 50% (w/w) sucrose solution using the prepared immobilized enzymes was determined to be approximately 60% of the total sugars in the reaction mixtures. This level of fructooligosaccharides produced by the immobilized enzymes was comparable to that resulting from processes employing other immobilized biocatalysts as shown in the literature. The fraction of total fructooligosaccharides presented in the final mixture increased with the initial sucrose concentration, while fractions of glucose and fructose decreased with an increase sucrose concentration.

Inhibitory effects of xanthohumol from hops (Humulus lupulus L.) on human hepatocellular carcinoma cell lines

Xanthohumol is one of the main flavonoids in hop extracts and in beer. Very few investigations of xanthohumol have studied hepatocellular carcinoma. In this study, the inhibitory effects of xanthohumol on human hepatocellular carcinoma cell lines were investigated. The IC50 values of xanthohumol for two hepatocellular carcinoma cell lines and one normal hepatocyte cell line were 108, 166 and 211 µm, respectively. Normal murine hepatocyte cell line had more resistance to xanthohumol than hepatocellular carcinoma cell lines. Besides, the inhibitory effects of xanthohumol on human hepatocellular carcinoma cell lines were attributed to apoptosis as indicated in the results of flow cytometry, fluorescent nuclear staining and electrophoresis of oligonucleosomal DNA fragments. Hop xanthohumol was more efficient in the growth inhibition of hepatocellular carcinoma cell lines than the flavonoids silibinin and naringin from thistle and citrus. It was shown for the first time that xanthohumol from hops effectively inhibits proliferation of human hepatocellular carcinoma cells in vitro. Copyright

Continuous Production of High-Content Fructooligosaccharides by a Complex Cell System

A complex biocatalyst system with a bioreactor equipped with a microfiltration (MF) module was employed to produce high‐content fructooligosaccharides (FOS) in a continuous process initiated by a batch process. The system used mycelia of Aspergillus japonicus CCRC 93007 or Aureobasidium pullulans ATCC 9348 with β‐fructofuranosidase activity and Gluconobacter oxydans ATCC 23771 with glucose dehydrogenase activity. Calcium carbonate slurry was used to control pH to 5.5, and gluconic acid in the reaction mixture was precipitated as calcium gluconate. Sucrose solution with an optimum concentration of 30% (w/v) was employed as feed for the complex cell system, and high‐content FOS was discharged continuously from a MF module. The complex cell system was run at 30 °C with an aeration rate of 5 vvm and produced more than 80% FOS with the remainder being 5–7% glucose and 8–10% sucrose on a dry weight basis, plus a small amount of calcium gluconate. The system worked for a 7‐day continuous production process with a dilution rate of 0.04 h−1, and the volumetric productivity for total FOS was more than 160 g L−1 h−1.

Immobilization of β-fructofuranosidase from Aspergillus japonicus on chitosan using tris(hydroxymethyl)phosphine or glutaraldehyde as a coupling agent

A partially purified β-fructofuranosidase from Aspergillus japonicus was covalently immobilized on to chitosan beads using either glutaraldehyde or tris(hydroxymethyl)phosphine (THP) as a coupling agent. Compared with the glutaraldehyde-immobilized and the free enzyme, the THP-immobilized enzyme had the highest thermal stability with 78% activity retained after 12 days at 37 ° C. The THP-immobilized enzyme also had higher reusability than that immobilized by glutaraldehyde, 75% activity was retained after 11 batches (or 11 days) at 37° C for the THP immobilized enzyme system. Less yield (48%) of fructooligosaccharides (FOS) were produced by the THP-immobilized enzyme compared with the free enzyme system (58%) from 50 (w/v) sucrose at 50 ° C.

Production of fructooligosaccharides by immobilized mycelium of Aspergillus japonicus

β-Fructofuranosidase (EC 3.2.1.26) in Aspergillus japonicus mycelium was immobilized by entrapment in calcium alginate gel. After immobilization, the enzyme was active over a wider pH range, and had improved thermostability. The total amount of fructooligosaccharides produced by immobilized enzyme was similar to that produced by a free enzyme system. A packed-bed reactor was employed for production of fructooligosaccharides at 42°C using the immobilized enzyme. The reactions were continued for 35 days and only 17% of enzyme activity was lost during this period.

Reaction mechanism of isomaltooligosaccharides synthesis by α-glucosidase fromAspergillus carbonarious

SummaryAn α-glucosidase fromAspergillus carbonarious CCRC 30414 was employed for investigating the enzymatic synthesis of isomaltooligosaccharides from maltose. The enzyme transferred a glucose unit from the nonreducing end of maltose and other α-linked glucosyl oligosaccharides to glucose and other glucosyl oligosaccharides which function as accepting co-substrates. The transfer of a glucose unit occurs most frequently to the 6-OH position of the nonreducing end of acceptor, but transfer to 4-OH position also occurs. Treatment of 30 % (w/v) maltose with the enzyme under optimum conditions afforded more than 50% isomaltooligosaccharides.