Purification of Galacto-oligosaccharide (GOS) by fermentation with Kluyveromyces lactis and Interaction between GOS and casein under simulated acidic fermentation conditions

In the enzymatic synthesis of galacto-oligosaccharide (GOS), the primary by-products include glucose, galactose and unreacted lactose. This This study was aimed to provide a method to to purify GOS by yeat fermentation and explore the interaction between GOS and CAS with a view for expanding the prospects of GOS application in the food industry. The crude GOS(25.70 g/L) was purified in this study using the fermentation method with Kluyveromyces lactis CICC 1773. Optimal conditions for purification with the yeast were 75 g/L of the yeast inoculation rate and 50 g/L of the initial crude GOS concentration for 12 h of incubation. After removing ethanol produced by yeast by low-temperature distillation, GOS content could reach 90.17%. A study of the interaction between GOS and casein (CAS) in a simulated acidic fermentation system by D-(+)-gluconic acid δ-lactone (GDL) showed that the GOS/CAS complexes with higher GOS concentrations, e.g., 4% and 6% (w/v), was more viscoelastic with higher water-holding capacity, but decreased hardness, elasticity, and cohesiveness at 6% (w/v) of GOS. The addition of GOS to CAS suspension significantly caused (p<0.05) decreased particle sizes of the formed GOS/CAS complexes, and the suspension system became more stable. FT-IR spectra confirmed the existence of different forms of molecular interactions between CAS and GOS, e.g., hydrogen bonding and hydrophobic interaction, and the change of secondary structure after CAS binding to GOS.

Challenges and perspectives of the β-galactosidase enzyme

The enzyme β-galactosidase has great potential for application in the food and pharmaceutical industries due to its ability to perform the hydrolysis of lactose, a disaccharide present in milk and in dairy by-products. It can be used in free form, in batch processes, or in immobilized form, which allows continuous operation and provides greater enzymatic stability. The choice of method and support for enzyme immobilization is essential, as the performance of the biocatalyst is strongly influenced by the properties of the material used and by the interaction mechanisms between support and enzyme. Therefore, this review showed the main enzyme immobilization techniques, and the most used supports for the constitution of biocatalysts. Also, materials with the potential for immobilization of β-galactosidases and the importance of their biotechnological application are presented. KEY POINTS: • The main methods of immobilization are physical adsorption, covalent bonding, and crosslinking. • The structural conditions of the supports are determining factors in the performance of the biocatalysts. • Enzymatic hydrolysis plays an important role in the biotechnology industry.

Recent advances in β-galactosidase and fructosyltransferase immobilization technology

The highly demanding conditions of industrial processes may lower the stability and affect the activity of enzymes used as biocatalysts. Enzyme immobilization emerged as an approach to promote stabilization and easy removal of enzymes for their reusability. The aim of this review is to go through the principal immobilization strategies addressed to achieve optimal industrial processes with special care on those reported for two types of enzymes: β-galactosidases and fructosyltransferases. The main methods used to immobilize these two enzymes are adsorption, entrapment, covalent coupling and cross-linking or aggregation (no support is used), all of them having pros and cons. Regarding the support, it should be cost-effective, assure the reusability and an easy recovery of the enzyme, increasing its stability and durability. The discussion provided showed that the type of enzyme, its origin, its purity, together with the type of immobilization method and the support will affect the performance during the enzymatic synthesis. Enzymes' immobilization involves interdisciplinary knowledge including enzymology, nanotechnology, molecular dynamics, cellular physiology and process design. The increasing availability of facilities has opened a variety of possibilities to define strategies to optimize the activity and re-usability of β-galactosidases and fructosyltransferases, but there is still great place for innovative developments.

Whey permeate as the raw material in galacto-oligosaccharide synthesis using commercial enzymes

Galacto-oligosaccharides (GOS), molecules with prebiotic properties are considered promising in the food industry. Its synthesis can be performed by enzymatic pathway, using commercial microbial enzymes. The reaction, known as transgalactosylation, is mediated by the enzyme β-galactosidase and its catalysis is influenced during the process by substrate concentration present (in this case lactose), pH, and temperature, among others. The use of whey permeate, a by-product of the dairy industry, demonstrates the interest in making such processes viable from an economic and technological point of view. The main of this work was to use whey permeate as raw material in an enzymatic GOS synthesis, comparing three commercial enzymes of different microbial sources. For better performance, the results on lactose conversion, yield, and specific productivity were evaluated. The commercial enzyme of Kluyveromyces lactis (Lactozyme™ 2600 L) showed the best results for lactose conversion (89.27%), yield (25 g GOS/100 g lactose) and specific productivity (51 g GOS/g enzyme*h). Thus, it can be considered suitable for further technological development. Aspergillus oryzae commercial enzyme also showed good results and could be used for other studies either. However, the Escherichia coli commercial enzyme did not present good results in GOS synthesis, being more appropriate to lactose hydrolysis reactions. All the three enzymes showed a decrease in the production and even depletion of GOS molecules, and therefore, smaller reaction times should be established. New stages of optimization and processes development should be considered in future works, in order to obtain best yields and productivities.

Sodium bicarbonate-gelled chitosan beads as mechanically stable carriers for the covalent immobilization of enzymes

The poor mechanical stability of chitosan has long impeded its industrial utilization as an immobilization carrier. In this study, the mechanical properties of chitosan beads were greatly improved through utilizing the slow rate of the sodium bicarbonate-induced chitosan gelation and combining it with the chemical cross-linking action of glutaraldehyde (GA). The GA-treated sodium bicarbonate-gelled chitosan beads exhibited much better mechanical properties and up to 2.45-fold higher observed activity of the immobilized enzyme (β-D-galactosidase (β-gal)) when compared to the GA-treated sodium tripolyphosphate (TPP)-gelled chitosan beads. The differences between the sodium bicarbonate-gelled and the TPP-gelled chitosan beads were proven visually and also via scanning electron microscopy, elemental analysis, and differential scanning calorimetry. Moreover, the optimum pH, the optimum temperature, the apparent K_m , and the apparent V_max of the β-gals immobilized onto the two aforementioned types of chitosan beads were determined and compared. A reusability study was also performed. This study proved the superiority of the sodium bicarbonate-gelled chitosan beads as they retained 72.22 ± 4.57% of their initial observed activity during the 13^th reusability cycle whereas the TPP-gelled beads lost their activity during the first four reusability cycles, owing to their fragmentation. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:347-361, 2018.