Cross-linked α-galactosidase aggregates: optimization, characterization and application in the hydrolysis of raffinose-type oligosaccharides in soymilk

Immobilization of α-galactosidase in polyvinyl alcohol-chitosan-glycidyl methacrylate hydrogels based on directional freezing-assisted salting-out strategy for hydrolysis of RFOs

Raffinose family oligosaccharides (RFOs) in food are the main factors causing flatulence in Irritable Bowel Syndrome (IBS) patients and the development of effective approaches for reducing food-derived RFOs is of paramount importance. In this study, polyvinyl alcohol (PVA)-chitosan (CS)-glycidyl methacrylate (GMA) immobilized α-galactosidase was prepared by the directional freezing-assisted salting-out technique, aimed to hydrolyze RFOs. SEM, FTIR, XPS, fluorescence and UV characterization results demonstrated that α-galactosidase was successfully cross-linked in the PVA-CS-GMA hydrogels, forming a distinct porous stable network through the covalent bond between the enzyme and the carrier. Mechanical performance and swelling capacity analysis illustrated that α-gal @ PVA-CS-GMA not only had suitable strength and toughness for longer durability, but also exhibited high water content and swelling capacity for better retention of catalytic activity. The enzymatic properties of α-gal @ PVA-CS-GMA showed an improved Km value, pH and temperature tolerance range, anti-enzymatic inhibitor (melibiose) activity compared to the free α-galactosidase and its reusability was at least 12 times with prolonged storage stability. Finally, it was successfully applied in the hydrolysis of RFOs in soybeans. These findings provide a new strategy for the development of α-galactosidase immobilization system to biological transform the RFOs components in the food for diet intervention of IBS.

Cross-linked enzyme aggregates immobilization: preparation, characterization, and applications

Enzymes are commonly used as biocatalysts for various biological and chemical processes. However, some major drawbacks of free enzymes (e.g. poor reusability and instability) significantly restrict their industrial practices. How to overcome these weaknesses remain considerable challenges. Enzyme immobilization is one of the most effective ways to improve the reusability and stability of enzymes. Cross-linked enzyme aggregates (CLEAs) has been known as a novel and versatile carrier-free immobilization method. CLEAs is attractive due to its simplicity and robustness, without purification. It generally shows: high catalytic specificity and selectivity, good operational and storage stabilities, and good reusability. Moreover, co-immobilization of different kinds of enzymes can be acquired. These CLEAs advantages provide opportunities for further industrial applications. Herein, the preparation parameters of CLEAs were first summarized. Next, characterization of structural and catalytic properties, stability and reusability are also proposed. Finally, some important applications of this technique in: environmental protection, industrial chemistry, food industry, and pharmaceutical synthesis and delivery are introduced. Potential challenges and future research directions, such as improving cross-linking efficiency and internal mass transfer efficiency, are also presented. This implies that CLEAs provide an efficient and feasible technique to improve the properties of enzymes for use in the industry.

Intra-Laboratory Validation of Alpha-Galactosidase Activity Measurement in Dietary Supplements

INTRODUCTION

Alpha-galactosidase (α-Gal) is an enzyme responsible for the hydrolyzation of glycolipids and glycoprotein commonly found in dietary sources. More than 20% of the general population suffers from abdominal pain or discomfort caused by intestinal gas and by indigested or partially digested food residuals. Therefore, α-Gal is used in dietary supplements to reduce intestinal gases and help complex food digestion. Marketed enzyme-containing dietary supplements must be produced in accordance with the Food and Drug Administration (FDA) regulations for Current Good Manufacturing Practice (cGMPs).

AIM

in this work we illustrated the process used to develop and validate a spectrophotometric enzymatic assay for α-Gal activity quantification in dietary supplements.

METHODS

The validation workflow included an initial statistical-phase optimization of materials, reagents, and conditions, and subsequently a comparative study with another fluorimetric assay. A final validation of method performance in terms of specificity, linearity, accuracy, intermediate-precision repeatability, and system precision was then executed.

RESULTS AND CONCLUSIONS

The proven method achieved good performance in the quantitative determination of α-Gal activity in commercial food supplements in accordance with the International Council for Harmonisation of Technical Requirements for Pharmaceuticals (ICH) guidelines and is suitable as a rapid in-house quality control test.

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%.

Combined Cross-Linked Enzyme Aggregates of Monoamine Oxidase and Putrescine Oxidase as a Bifunctional Biocatalyst for Determination of Biogenic Amines in Foods

In order to determine total biogenic amines in fermented foods, the combined cross-linked enzyme aggregates of a monoamine oxidase and a putrescine oxidase (combi-CLEAs) and the cross-linked enzyme aggregates (CLEAs) of the fused enzyme of two amine oxidases (MonoAmine Putrescien Oxidase, MAPO) were prepared. The effects of various parameters were examined to optimize the CLEAs formation. Biochemical characterization and stability of free and the CLEAs enzymes were performed. Through optimization of the CLEAs formation condition, the combi-CLEAs and the CLEAs-MAPO were prepared with 82% and 78% of residual activities relative to the activities of the subjected enzymes were in a preparative scale. The optimal pH for tyramine-activities of the CLEAs enzymes were shifted to relatively basic pH, leading to synchronization of the optimal performances of combi-CLEAs over pH for tyramine and putrescine. In addition, thermostability of the CLEAs enzymes were improved with almost double half-lives at 65 °C in comparison to the free enzymes. The catalytic efficiencies of combi-CLEAs for tyramine, histamine and putrescine were reduced by 41%, 56%, and 31%, respectively, and the inhibition potency by the substrate was reduced by two-fold in comparison of the mixed free enzymes. In conclusion, combi-CLEAs are a promising catalyst with the improved stability and the same optimum pH for dual activities in enzymatic determination of biogenic amines in foods.