Abstract
α-Galacto-oligosaccharides (α-GOSs) have great functions as prebiotics and therapeutics. This work established the method of batch synthesis of α-GOSs by immobilized α-galactosidase for the first time, laying a foundation for industrial applications in the future. The α-galactosidase from Aspergillus niger L63 was immobilized as cross-linked enzyme aggregates (CLEAs) nano-biocatalyst through enzyme precipitating and cross-linking steps without using carriers. Among the tested agents, the ammonium sulfate showed high precipitation efficacy and induced regular structures of α-galactosidase CLEAs (Aga-CLEAs) that had been analyzed by scanning electron microscopy and Fourier-transform infrared spectroscopy. Through optimization by response surface methodology, the ammonium sulfate-induced Aga-CLEAs achieved a high activity recovery of around 90% at 0.55 U/mL of enzymes and 36.43 mM glutaraldehyde with cross-linking for 1.71 h. Aga-CLEAs showed increased thermal stability and organic solvent tolerance. The storage ability was also improved since it maintained 74.5% activity after storing at 4 °C for three months, significantly higher than that of the free enzyme (21.6%). Moreover, Aga-CLEAs exhibited excellent reusability in the α-GOSs synthesis from galactose, retaining above 66% of enzyme activity after 10 batch reactions, with product yields all above 30%.
Highlights
Accepted: 20 February 2021Prebiotics are non-digestible food fibers that beneficially affect the host health by selectively increasing the growth and activity of gut microbes, especially Bifidobacteria and Lactobacilli, and by their effects on system-wide metabolic and physiological readouts [1]. α-Galacto-oligosaccharides (α-GOSs) have attracted particular attention due to the prebiotic role as strong Bifidus growth factors in maintaining gut microflora balance
The insoluble biocatalysts of Aga-cross-linked enzyme aggregates (CLEAs) were prepared by precipitating the crude enzyme with various precipitant agents followed by glutaraldehyde-mediated cross-linking
The preparation of ammonium sulfate-induced Aga-CLEAs was further optimized by the statistical response surface methodology (RSM), which had an overall consideration of the interactive effects among various factors in the cross-linking process
Summary
Prebiotics are non-digestible food fibers that beneficially affect the host health by selectively increasing the growth and activity of gut microbes, especially Bifidobacteria and Lactobacilli, and by their effects on system-wide metabolic and physiological readouts [1]. α-Galacto-oligosaccharides (α-GOSs) have attracted particular attention due to the prebiotic role as strong Bifidus growth factors in maintaining gut microflora balance. Α-Galacto-oligosaccharides (α-GOSs) have attracted particular attention due to the prebiotic role as strong Bifidus growth factors in maintaining gut microflora balance They significantly stimulate the growth of intestinal probiotics, resulting in a series of beneficial effects such as enhanced intestinal health, improved immune activities, alleviation of inflammatory response, reduction of cancer risk, and so on [2,3,4,5,6]. The immobilized nano-biocatalyst was characterized and found to have higher thermal stability and organic solvent tolerance as well as longer service life than the free enzyme It had been successfully applied in the batch synthesis of α-GOSs
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