Carrier-Free Immobilization of α-Galactosidase as Nano-Biocatalysts for Synthesizing Prebiotic α-Galacto-Oligosaccharides

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%.

Protective effects of α-galacto-oligosaccharides against a high-fat/western-style diet-induced metabolic abnormalities in mice

In this study, we investigated the effects of a newly synthesized α-galacto-oligosaccharide mixture (α-GOSg), 0.5% in drinking water, on high-fat/western-style diet (HFWD)-induced metabolic abnormality in mice in a study of 13 weeks. Raffinose family oligosaccharides (RFOs) were included as a comparison. Mice treated with α-GOSg had significantly lower body weight and body fat (p < 0.05), while RFOs were less effective. Both α-GOSg and RFOs significantly reduced serum levels of total cholesterol and low-density lipoprotein cholesterol, alanine aminotransferase and liver lipids. However, only α-GOSg significantly decreased the histopathological score for liver steatosis and downregulated hepatic fatty acid synthesis gene acetyl CoA carboxylase-α. α-GOSg also significantly reduced the content of bile acids in the small intestine and significantly increased the abundance of gut Bifidobacterium and decreased the abundance of Clostridium leptum. These actions are proposed to be key mechanisms contributing to the beneficial health effects of α-GOSg.