Influence of the method of purification on some solution properties of welan gum

Optimization of welan gum extraction and purification using lysozyme and alkaline protease

Welan gum, a natural polysaccharide produced by Sphingomonas sp. ATCC 31555, has attracted considerable attention in the scientific community due to its desirable properties. However, challenges, such as high viscosity, residual bacterial cells, carotenoids, and protein complexation, hinder the widespread application of welan gum. In this study, we established a method for the extraction and purification of welan gum using a synergistic approach with lysozyme and alkaline protease. Lysozyme hydrolysis conditions were optimized by applying response surface methodology, and the best results for bacterial cell removal were achieved at 11 000 U/g, 44 °C, and pH 9 after 3 h of treatment. Subsequently, we evaluated protein hydrolysis through computer simulation and identified alkaline protease as the most suitable enzyme. Through experimental investigations, we found that the optimal conditions for alkaline protease hydrolysis were 7500 U/g, 50 °C, pH 10, and 600 rpm. These conditions resulted in a sugar recovery rate of 76.1%, carotenoid removal rate of 89.5%, bacterial removal rate of 95.2%, and protein removal rate of 87.3% after 3 h of hydrolysis. The purified welan gum exhibited high transparency and purity. Structural characterization and antioxidant activity evaluation revealed that enzymatically purified welan gum has potential application prospects. Our study provides valuable insights into the optimal method for the enzymatic extraction and purification of welan gum. Such a method is conducive to the development of the multiple potential applications of welan gum. KEY POINTS: • A novel process for the synergistic purification of welan gum using lysozyme and alkaline protease was established. • In silico virtual digestion was employed to select the purification enzyme. • Welan gum with high transparency and purity was obtained.

NMR analysis of the side-group substituents in welan gum in comparison to gellan gum

The physicochemical properties and applications of polysaccharides are highly dependent on their chemical structures, including the monosaccharide composition, degree of substitution, and position of substituent groups in the backbone. The occurrence of side groups or side chains in the chain backbone of polysaccharides is often an essential factor influencing their conformational and physicochemical properties. Welan gum produced by the fermentation of Sphingomonas sp. ATCC 31555 microorganisms has been widely used in food, construction, and oil drilling fields. While understanding the physicochemical properties of welan gum solution has been highly developed, there is still little information about the determination strategy of the glycosyl side groups in welan gum. In this study, the NMR method was established to quantitatively determine the substituent groups in the chain backbone of welan gum. The delicate chemical structures of welan gum obtained at different fermentation conditions were clarified. The composition and content of side substituents were also identified by high-performance liquid chromatography to confirm the accuracy of NMR analysis. The quantitative determination of substituent groups in gellan gum based on NMR analysis was also elaborated for comparison. This work provides insights for profoundly understanding the structure-function relationship of welan gum.

Identification of the Key Enzymes in WL Gum Biosynthesis and Critical Composition in Viscosity Control

As an important microbial exopolysaccharide, the sphingan WL gum could be widely used in petroleum, food, and many other fields. However, its lower production is still limiting its wider application. Therefore, to gain insights into the bottlenecks of WL gum production by identifying the key enzymes in the WL gum biosynthesis pathway, more than 20 genes were over-expressed in Sphingomonas sp. WG and their effects on WL gum production and structure were investigated. Compared to the control strain, the WL gum production of welB over-expression strain was increased by 19.0 and 21.0% at 36 and 84 h, respectively. The WL gum production of both atrB and atrD over-expression strains reached 47 g/L, which was approximately 34.5% higher than that of the control strain at 36 h. Therefore, WelB, AtrB, and AtrD may be the key enzymes in WL production. Interestingly, the broth viscosity of most over-expression strains decreased, especially the welJ over-expression strain whose viscosity decreased by 99.3% at 84 h. Polysaccharides' structural features were investigated to find the critical components in viscosity control. The uronic acid content and total sugar content was affected by only a few genes, therefore, uronic acid and total sugar content may be not the key composition. In comparison, the acetyl degrees were enhanced by over-expression of most genes, which meant that acetyl content may be the critical factor and negatively correlated with the apparent viscosity of WL gum. This work provides useful information on the understanding of the bottlenecks of WL gum biosynthesis and will be helpful for the construction of high WL gum-yielding strains and rheological property controlling in different industries.

Positron emission tomography in multiple sclerosis - straight to the target

Following the impressive progress in the treatment of relapsing-remitting multiple sclerosis (MS), the major challenge ahead is the development of treatments to prevent or delay the irreversible accumulation of clinical disability in progressive forms of the disease. The substrate of clinical progression is neuro-axonal degeneration, and a deep understanding of the mechanisms that underlie this process is a precondition for the development of therapies for progressive MS. PET imaging involves the use of radiolabelled compounds that bind to specific cellular and metabolic targets, thereby enabling direct in vivo measurement of several pathological processes. This approach can provide key insights into the clinical relevance of these processes and their chronological sequence during the disease course. In this Review, we focus on the contribution that PET is making to our understanding of extraneuronal and intraneuronal mechanisms that are involved in the pathogenesis of irreversible neuro-axonal damage in MS. We consider the major challenges with the use of PET in MS and the steps necessary to realize clinical benefits of the technique. In addition, we discuss the potential of emerging PET tracers and future applications of existing compounds to facilitate the identification of effective neuroprotective treatments for patients with MS.

Role of Substituents on the Properties of Some Polysaccharides

This paper concerns the influence of the chemical structure on the physical properties of some polysaccharides. Especially, we proposed to discuss the role of the substituents on these properties. In some cases, non-carbohydrate substituents play a minor role on rheological properties in the presence of a salt excess as shown on xanthan and succinoglycan. The rheology of aqueous solution of these stereoregular polysaccharides is controlled by the conformation (helical conformation) whose stability is not largely influenced by these substituents. On the other hand, the interaction between galactomannan and xanthan depends on the presence of acetyl substituents on xanthan but also on the xanthan conformation. However, for polymers such as gellan, XM-6 or BEC 1615, complete deacetylation induces the ability to form physical gels in given thermodynamic conditions. The presence of carbohydrate substituents or short side chains was also examined. Especially in the gellan family, the role of position of substitution (position 3 on the glucose unit C or position 6 on the A glucose) was presented. It is concluded that the substituents giving the higher stability for the helical conformation (higher DeltaH and Tm values) also cause a lower salt sensitivity for the helical stability. The role of the substituents on the properties is also described for natural polymers and their chemically or enzymatically modified derivatives.

Studies on neutral exopolysaccharides produced by the ectomycorrhiza Thelephora terrestris

The ectomycorrhizal hymenomycete Thelephora terrestris was grown in synthetic pure culture and the production of extracellular polysaccharide was monitored. The exopolysaccharides were prepared by ethanol precipitation and then fractionated into two components using a DEAE-Sepharose column. A neutral fraction (NeP) was fractionated on Sepharose CL-6B, which resulted in three peaks: NeP1, NeP2 and NeP3. NeP1 was filtered through an exclusion membrane and two polysaccharides were obtained (fractions: NeA, NeB). Fraction NeB was submitted to methylated derivatives and 1H-, 13C- and 2D NMR spectroscopic analyses. These analyses showed a main chain of a (1-->6)-linked alpha-D-Manp units substituted at O-2 by a variety of side chains containing alpha-Fucp, beta-Xylp and beta-Galp residues. The main fraction corresponds to mannan as shown by methylation analysis. Size exclusion chromatography (HPSEC-MALLS) of fraction NeB showed a main component of 15.0 kDa. It contained mannose, galactose, fucose and xylose in a molar ratio of 50:29:11:10. The fractions NeP2 and NeP3 were characterised as a (1-->6)-linked beta-glucan (pustulan) and (1-->3)-linked beta-glucan, respectively.

Role of galactomannan composition on the binary gel formation with xanthan

The influence of the galactomannan characteristic ratios (M/G) on the temperature of gelation (Tg) and the gel strength of mixtures of galactomannan with xanthan is reported. Two galactomannans were investigated: one highly substituted from the seeds of Mimosa scabrella (M/G = 11), and the other, less substituted, from the endosperm of Schizolobium parahybae, with (M/G = 30) [Ganter JLMS, Zawadzki-Baggio SF, Leitner SC, Sierakowski MR, Reicher F. J Carbohydr Chem 1993;12:753]. The xanthan:galactomannan systems (4:2 g l(-1), in 5 mM NaCl) showed a temperature of gel formation (Tg) of 24 degrees C for that of S. parahybae [Bresolin TMB, Milas M, Rinaudo M and Ganter JLMS. Int J Biol Macromol 1998;23:263] and 20 degrees C for the galactomannan of M. scabrella, determined by viscoelastic measurements and microcalorimetry. A Tg of 40-50 degrees C was found by Shatwell et al. [Shatwell KP, Sutherland IW, Ross-Murphy SB, Dea ICM. Carbohydr Polym 1991;14:29] for locust bean gum-LBG (M/G = 43). Lundin and Hermansson [Lundin L, Hermansson AM. Carbohydr Polym 1995;26:129] reported a difference of 13 degrees C for Tg of two LBG samples with M/G = 3 (40 degrees C) and 5 (53 degrees C), in mixtures with xanthan. It appears that the more substituted galactomannans have lower temperatures of gelation in the presence of xanthan. The mechanism of gelation depends also on the M/G ratio. For the lower values it involves only disordered xanthan chains in contrast to M/G ratios higher than 3. In addition, the presence of the galactomannan from M. scabrella increased slightly the temperature of the conformational change (Tm) of xanthan probably due to the ionic strength contribution of proteins (3.9%) present in the galactomannan. On the other hand, the galactomannans from S. parahybae, with 1.5% of proteins and M. scabrella, with 2.4% of protein, did not show this effect, the Tm of xanthan alone or in a mixture being practically unchanged.