Abstract
β-Galactosidase was immobilized on chitosan-coated magnetic Fe3O4 nanoparticles and was used to produce galactooligosaccharides (GOS) from lactose. Immobilized enzyme was prepared with or without the coupling agent, tris(hydroxymethyl)phosphine (THP). The two immobilized systems and the free enzyme achieved their maximum activity at pH 6.0 with an optimal temperature of 50 °C. The immobilized enzymes showed higher activities at a wider range of temperatures and pH. Furthermore, the immobilized enzyme coupled with THP showed higher thermal stability than that without THP. However, activity retention of batchwise reactions was similar for both immobilized systems. All the three enzyme systems produced GOS compound with similar concentration profiles, with a maximum GOS yield of 50.5% from 36% (w·v−1) lactose on a dry weight basis. The chitosan-coated magnetic Fe3O4 nanoparticles can be regenerated using a desorption/re-adsorption process described in this study.
Highlights
Galactooligosaccharides (GOS), which can stimulate the proliferation of Bifidobacteria and Lactobacilli in the intestine, are important food additives for health promotion
The acceptor can be a monosaccharide such as glucose or galactose, or a disaccharide, mainly lactose [1]. β-Galactosidases can be produced from various microbial sources [2,3], such as Aspergillus oryzae [4], Bacillus sp. [5], Escherichia coli [6], Kluyveromyces lactis [7], Kluyveromyces fragilis [8], Lactobacillus reuteri [9], Thermus aquaticus YT-1 [10], and Thermotoga maritima [11]
The results showed thermal stability of β-galactosidase immobilized on the porous chitosan beads was better than that on the nanoparticles of this investigation
Summary
Galactooligosaccharides (GOS), which can stimulate the proliferation of Bifidobacteria and Lactobacilli in the intestine, are important food additives for health promotion. (1) a higher specific surface area permitting the binding of a larger amount of enzymes; (2) the mass transfer resistance being relatively low; and (3) easy and selective separation of the immobilized enzyme from a reaction mixture by the application of a magnetic field [20,21]. The binding of enzyme to magnetic nanoparticles is commonly accomplished through the coupling agent, or surface coating using polymers such as chitosan, alginate, carrageen. The coupling agent most often used between enzymes and chitosan is glutaraldehyde. Enzymes can be immobilized onto the surface of chitosan beads via a coupling agent such as glutaraldehyde. THP is a water-soluble substance and can react with chitosan to form a P–CH2–N linkage at room temperature This P-CH2-N linkage has improved hydrolytic resistance for covalent immobilization of enzymes. We compared various properties of the two immobilized and the free enzyme systems
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