A novel process for the production of high-purity galactooligosaccharides (GOS) using consortium of microbes

Enhancing the synthesis efficiency of galacto-oligosaccharides of a β-galactosidase from Paenibacillus barengoltzii by engineering the active and distal sites

Previously, a glycoside hydrolase (GH) family 2 β-galactosidase (PbBGal2A) from Paenibacillus barengoltzii is characterized for its high transglycosylation capability. Here, the cryo-electron microscopy (cryo-EM) structure of PbBGal2A was determined, revealing an enlarged acidic catalytic pocket that facilitate the binding of carbohydrate substrates. Three structure-based strategies as well as machine learning MECE platform (method for enhancing the catalytic efficiency) were employed to identify active and distal mutations with enhanced galacto-oligosaccharides (GOS) synthesis and their synergistic effects were evaluated. The best H331V mutation yielded a maximum GOS production of 76.57 % at 4 h when 35 % (w/v) of lactose was used as a substrate. Molecular dynamics (MD) simulation analysis further indicated that distal mutations increase the rigidity of the loops surrounding the catalytic pocket. This research sheds light on the structural and catalytic mechanisms of PbBGal2A, highlighting the importance of both active and distal mutations in the efficient design of customized β-galactosidases.

Synthesis of novel lactose-derived oligosaccharides by two-step enzymatic reactions and structural characterization of the oligomers

Exploitation of the added value of lactose by enzymatic synthesis of novel lactose-derived oligosaccharides has been a subject of increasing research interests. In this study, a strategy of two-step enzymatic reactions was designed to first synthesize galacto-oligosaccharide (GOS) from lactose by β-galactosidase, and then the novel oligosaccharides were synthesized by inulosucrase (IS) using the obtained GOS and sucrose as the substrates. The recombinant IS was initially expressed by employing the IS gene from Lactobacillus gasseri DSM 20604. The appropriate synthesis conditions by the IS were determined as: reaction time of 12 h, the concentration of IS at 25 U/mL, GOS to sucrose ratio of 1:2, and the total substrate concentration of 500 g/L. Purification of the synthesized oligosaccharides in the reaction mixture was done by fermentation with Kluyveromyces lactis CICC 1773 to remove the carbohydrate by-products, and HPLC on an oligosaccharide column. The purified oligosaccharides, namely, Oligo-1, Oligo-2, and Oligo-3 were determined for their monosaccharide components to be galactose and glucose in the molar ratios of 0.230:0.770, 0.522:0.478 and 0.637:0.363, respectively. These three oligosaccharides had relative molecular masses of 666.18, 990.26, and 1314.43, corresponding to the degree of polymerization (DP) value of 4, DP6, and DP8, respectively. NMR spectroscopic studies of the oligosaccharides revealed a common branched structure consisting of three glucosides, one of which was linked with one (Oligo-1), three (Oligo-2) and five galactosides (Oligo-3), respectively. These lactose-derived oligosaccharides with the structural patterns that were not reported earlier represented novel potential prebiotic agents for use in functional foods.

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.

Recent developments in microbial production of high-purity galacto-oligosaccharides

Galacto-oligosaccharides (GOS) are used as prebiotic ingredients in various food and pharmaceutical formulations. Currently, production of GOS involves the enzymatic conversion of lactose by transgalactosylation using β-galactosidase. The purity of the resulting product is low, typically limited to up to 55% GOS on total carbohydrate basis due to the presence of non-reacted lactose, and the formation of by-products glucose and galactose. In industrial practice high-purity GOS is manufactured by removing the unwanted mono- and disaccharides from raw GOS with simulated moving bed (SMB) chromatography. This purification step is associated with high processing cost that increases the price of pure GOS and limits its marketability. The last decades have witnessed a growing interest in developing competitive biotechnological processes that could replace chromatography. This paper presents a comprehensive review on the recent advancements of microbial GOS purification, a process commonly referred to as selective fermentation or selective metabolism. Purification strategies include: (i) removal of glucose alone or together with galactose by lactose negative yeast species, that typically results in purity values below 60% due to remaining lactose; (ii) removal of both mono- and disaccharides by combining the fast monosaccharide metabolizing capacity of some yeast species with efficient lactose consumption by certain lactose positive microbes, reaching GOS purity in the range of 60-95%; and (iii) the application of selected strains of Kluyveromyces species with high lactose metabolizing activity to achieve high-purity GOS that is practically free from lactose and monosaccharides.

Biotechnological approaches for the production of designer cheese with improved functionality

Cheese is a product of ancient biotechnological practices, which has been revolutionized as a functional food product in many parts of the world. Bioactive compounds, such as peptides, polysaccharides, and fatty acids, have been identified in traditional cheese products, which demonstrate functional properties such as antihypertensive, antioxidant, immunomodulation, antidiabetic, and anticancer activities. Besides, cheese-making probiotic lactic acid bacteria (LAB) exert a positive impact on gut health, aiding in digestion, and improved nutrient absorption. Advancement in biotechnological research revealed the potential of metabolite production with prebiotics and bioactive functions in several strains of LAB, yeast, and filamentous fungi. The application of specific biocatalyst producing microbial strains enhances nutraceutical value, resulting in designer cheese products with multifarious health beneficial effects. This review summarizes the biotechnological approaches applied in designing cheese products with improved functional properties.

Production of high-purity galacto-oligosaccharides by depleting glucose and lactose from galacto-oligosaccharide syrup with yeasts

Galacto-oligosaccharides (GOS) are prebiotic compounds, widely used as ingredients in various food, nutraceutical and pharmaceutical products. Enzymatic synthesis of GOS results in low-purity products that contain high amounts of glucose and lactose beside the valuable GOS. In this study, a systematic approach was used to develop yeast-based fermentation strategies to purify crude GOS. Potentially applicable yeast strains were identified based on an extensive search in literature databases followed by a series of laboratory-scale fermentation tests. Single- and two-step fermentation processes were designed for the removal of glucose alone or together with lactose from crude GOS syrup. Single-step fermentation trials with two strains of previously unreported species, Cyberlindnera jadinii NCAIM Y.00499 and Kluyveromyces nonfermentans NCAIM Y.01443, resulted in purified products free of both glucose and ethanol from a crude GOS syrup diluted to 15 and 10 w/v%, respectively. Simultaneous removal of glucose and lactose was achieved by Kluyveromyces marxianus DMB Km-RK in a single-step fermentation process with a yield of 97.5% and final purity of 100%. A two-step fermentation approach was designed to allow conversion of a glucose-free product into a high-purity GOS by removing glucose with C. jadinii Y.00499 in the first step, and lactose by Kluyveromyces lactis DMB Kl-RK in the second step, resulting in a final product with a yield of 100% and a final purity of 92.1%. These results indicate that the selected nonconventional yeasts are promising candidates for the removal of non-GOS components from commercial crude GOS products by selective fermentation.

Lactic acid bacteria-fermented product of green tea and Houttuynia cordata leaves exerts anti-adipogenic and anti-obesity effects

Obesity is associated with higher risks of developing diabetes and cardiovascular disease. Green tea, rich in polyphenolic compounds such as epigallocatechin gallate (EGCG) and epigallocatechin (EGC), has been shown to display anti-obesity effects. Houttuynia cordata leaves have also been shown to exhibit anti-obesity effects due to their chlorogenic acid content. Lactic acid bacteria are able to increase the production of polyphenolic compounds. This study aims to develop a novel anti-obesity fermentation product by combining H. cordata leaf tea with green tea, using Lactobacillus paracasei subsp. paracasei NTU 101 (NTU 101) for fermentation due to the advantages of bioconverting the poly-phenolic compounds. The regulation of adipogenesis factors and the anti-obesity effect of the NTU 101-fermented tea were evaluated in an in vitro 3T3-L1 pre-adipocyte model and an in vivo obese rat model, respectively. The results show that the NTU 101-fermented tea, which contained higher EGCG, EGC, and chlorogenic acid levels than unfermented tea, was able to inhibit the lipogenesis of mature 3T3-L1 adipocytes by the stimulation of lipolysis. Furthermore, the body weight gain, body fat pad, and feeding efficiency of obese rats, induced with a high fat diet, were decreased by the oral administration of NTU 101-fermented tea. The significant anti-obesity effect was probably due to lipolysis. However, NTU 101 bacteria cells and EGCG may also act as functional ingredients to contribute to the anti-obesity effects of NTU 101-fermented products.