Industrial Application of Dextransucrase Produced from Different Lactic Acid Bacteria

Synthesis and Application of Dextran

Dextran is a non-ionic homo-polysaccharide synthesized by enzymatic hydrolysis of sucrose molecules and has varying application at industrial level. The mechanism of dextran synthesis has been mentioned in Figure 9.1. Sephadex is the modified form of dextran used as packing material in chromatographic separation of biomolecules (Purama and Goyal 2005). Dextran can be considered as substitute for blood plasma, activating plasminogen and as anti-thrombogenic compound

Scanning electron micrograph of dextran at magnification of 1.5 Kx showing the porous surface morphology

FIGURE 9.3 Scanning electron micrograph of dextran at magnification of 1.5 Kx showing the porous surface morphology.

(Purama and Goyal 2005). Anaemia caused due to iron deficiency can be treated by forming dextran iron complex (Thayu and Mamula 2005). The lubricating effect of eye drops and the blood glucose levels can be enhanced by the addition of dextran. Trichosanthin coupled with dextran T40 inhibits the replication of human immunodeficiency virus (HIV) (Purama and Goyal 2005). It was reported that the growth and proliferation of HIV virus is controlled by the addition of sodium salt of dextran sulphate (Purama and Goyal 2005).

Dextran Hydrogels made of dextran are used in drug encapsulation, making contact lenses and in regeneration of spinal cord (Aumelas et al. 2007). Formation of water- insoluble dextran by S. mutans was regulated by producing water-soluble dextran in presence of W, cibaria CMU (Kang et al. 2009). Cancer drug doxorubicin was conjugated with dextran for targeted delivery (Oh et al. 2009). The emulsifying and texturizing activity of the dextran was reported by Tingirikari et al. (2014). The porous weblike nature of biopolymer dextran was studied by observing under a scanning electron microscope as mentioned in Figure 9.3.

Application of Dextran in Baking Industry

It was reported that some people are allergic to the gluten (protein) produced by wheat, barley and rye (Tingirikari et al. 2014). Tingirikari and Goyal (2013a) reported that 1% of the Western population is allergic to the gluten and causes celiac disease which involves severe immunological complications. During the fermentation of quinoa and sorghum-based sourdoughs, Weissella cibaria 10 M and Lacto bacillus reuteri LTH5448 produced levan and dextran (Tingirikari and Goyal 2013a). Good textured, soft bread with enhanced shelf life and free from gluten can be generated by using bacterial based exopolysaccharides, which can replace the nonbacterial hydrocolloids and cater the needs for celiac disease patients. Baker’s yeast cannot digest the dextran and oligosaccharides and are thermally stable (Tingirikari et al. 2014).

Dextran as Emulsifying Agent

Microbial exopolysaccharides are being used as bio-emulsifiers and flocculating agent (Tingirikari et al. 2014). They have unique biodegradable property and are less toxic in nature when compared to chemical emulsifiers. A stable emulsifier must retain minimum 50% of its strength after its formation (Tingirikari et al. 2014). As compared to guar gum and sodium alginate, the dextran from W. cibaria JAG8 displayed good emulsifying property (Tingirikari et al. 2014).

Generation of Prebiotic Oligosaccharide

Prebiotics are non-digestible but fermentable sugars which are selectively utilized by friendly microbes in the gut (Tingirikari et al. 2017). Commercially available prebiotics are gluco, fructo, galacto, manno, malto, isomalto, xylo oligosaccharides, arabinose, galactose, inulin, raffinose, mannose, lactulose, stachyose, palatinose, lac- tosucrose and soybean oligosaccharides (Bosscher et al. 2006). Prebiotic oligosaccharides can be produced by either acid or enzymatic treatment of dextran. It was reported that oligosaccharides generated by enzymatic hydrolysis method is considered to be more specific and the yields are also quite high (Tingirikari et al. 2017). The enzyme- mediated synthesis of prebiotic oligosaccharide has been mentioned in Figure 9.2.

It was reported that oligosaccharides are stable to salivary amylase, pancreatic juice, and digestive enzymes (Bosscher et al. 2006), which promotes the easy passage of non-digestible oligosaccharides through the stomach. They are utilized by bifido bacterial species present in the large intestine to produce short-chain fatty acids, thus decreasing pH and regulating the growth of harmful bacteria in the intestine (Morris and Morris 2012). Bosscher et al. (2006) have highlighted the significance of prebiotic oligosaccharides in gut health. Some of the benefits are prevention of diarrhoea and promoting the growth of healthy bacteria in the intestine by maintaining the homeostasis in the microbial population of the intestine.

Tingirikari et al. (2017) described several applications of oligosaccharides; some of them has been listed below: (1) In food industry, they act as functional ingredients for making different juices, soft drinks, confectionery items, and desserts. (2) In dairy industry, milk products such as ice cream and yoghurt are mixed with oligosaccharides. The application of oligosaccharides is expanded in pharma and cosmetic industry.

Application in Dairy Industry

Recent study of dextransucrase in solidification of skimmed milk containing sucrose as supplement has been employed. Kim et al. (2008) have cultivated Weissella hellen- ica SKKimchi3 strain comprising skim milk supplemented with 10% sucrose. Instead of using the bacterial culture, Tingirikari et al. (2014), employed crude dextransucrase for solidification of skimmed milk. It indicated that solidification of milk was mediated only in presence of dextransucrase and the solidification of milk increased with the increase in concentration of sucrose. The textural properties of dairy products depend upon type of EPS (branching, glycosidic linkages and molecular mass) and their interaction with the milk proteins (Tingirikari et al. 2014). Thus, EPS produced by lactic acid bacteria can be employed in the food industry to increase the textural properties of milk and confectioneries.

Potential Biomedical Applications

Dextransucrase-mediated polysaccharide synthesis takes place with the direct involvement of mono or disaccharide sugars (Tingirikari and Goyal 2013b). The polysaccharides thus produced can be used as biomaterials for different biomedical applications and can be used in preparing glycocalyx-like biomimetic surfaces for detecting specific saccharides-protein interaction. It was reported that dextransu- crase from S. mutans produces water-insoluble polysaccharide that attaches to the dental enamel, which results in plaque formation (Decker et al. 2014). Lee and Park (2015) have employed the hydrolysed product of high molecular weight chitosan ranging from three to eight kilo Daltons, which inhibited the activity of dextransucrase. Thereby the above compounds could serve as the cheapest antibacterial agent which can inhibit the activity of dextransucrase and help maintain the oral health.

Application in Agro Industry

Fruits are great sources of sugars. Drinking fruit juices rich in sugars causes several diseases (Johansson et al. 2016). Intake of fruit juices can be enhanced by decreasing the sugar levels without hampering its quality. Production of prebiotic oligosaccharides using commercial substrates is relatively more expensive than fruit juice (Figure 9.4) because, in commercial process, analytical grade sugars are used for the reaction and require a lot of purification steps, which further enhances the cost

Production of prebiotic oligosaccharides in fruit juice using immobilized dextransucrase

FIGURE 9.4 Production of prebiotic oligosaccharides in fruit juice using immobilized dextransucrase (DS) and co-immobilized dextransucrase + dextranase (DS+DSN). Degree of polymerization (DP), Sucrose (S), Fructose (F) and Glucose (G).

of the product in the market. Thus, prebiotic oligosaccharides can be produced by employing fruit rich in sugars (Johansson et al. 2016). The fruit juices rich in sugars may be used as substrate to produce oligosaccharides and the resultant prebiotic juice can be consumed directly without any purification step. Recently, prebiotic oligosaccharides are synthesized by employing fruit juice such as cashew apple, pineapple, orange and apple in presence of dextransucrase (Tingirikari et al. 2017). The resultant fruit juice not only contains lesser amounts of sugars but also is fortified with non-digestible but fermentable prebiotic oligosaccharide. It is a great boon to agro industry.

Conclusions and Future Prospects

The present chapter has highlighted about the production, purification, characterization and application of dextransucrase. It is a commercially important enzyme induced by sucrose. Low cost and fast purification of dextransucrase was mediated by employing different molecular weights of polyethylene glycol. With the advancement in recombinant DNA technology dextransucrase can now be induced and expressed in E. coli in large quantities without sucrose in the medium and free from dextran contamination. Genetic engineering approach can be employed for enhancing the enzyme production and easing the purification process. Immobilization of enzyme by alginate encapsulation (or) covalent method has increased the efficiency and stability of dextransucrase. With increase in huge demand for dietary fibers (dextran and oligosaccharides) as prebiotics and food supplement in baking and dairy industry, the need to produce the enzyme will also increase tremendously. The main hurdle in commercialization of dextransucrase is its thermo-sensitive nature and production cost, which are creating hurdles in the bulk production. In order to address the above problem, there should be advancement in recombinant DNA technology and exploitation of microbial species which can easily metabolize the available industrial and agricultural waste as substrates and produce the enzyme.

ACKNOWLEDGEMENT AND CONFLICT OF INTEREST

The authors declare that they have no conflict of interest with anyone.

 
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