Liquid crystallinity of levan/water/starch solutions

Huber, Anne E.; Kaplan, David L.; Viney, Christopher

doi:10.1007/bf02067445

Cited by 5 publications

(4 citation statements)

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“…Thus, when levan is blended with plasticizer, such as glycerol, elastic and extrudable films can be formed (Barone and Medynets 2007) and nanocomposites with improved thermal and mechanical properties, composed of montmorillonite clay blended with levan, obtained (Chen et al 2014). Levan films suitable for food coatings and packaging materials were prepared using aqueous solutions of levan (5 ÷ 6% w/w) containing corn starch (0.05%) as a filler (Huber et al 1994). Similarly, edible films were produced by a casting procedure using aqueous solutions of levan (0.6 ÷ 0.9% w/w), cassava starch (2.1 ÷ 2.4%) and glycerol (6%) as a plasticizer (Mantovan et al 2018).…”

Section: Biomedical and Technological Applicationsmentioning

confidence: 99%

Extracellular polysaccharides produced by bacteria of the Leuconostoc genus

Zikmanis

Brants²,

Koļesovs

et al. 2020

World J Microbiol Biotechnol

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Structurally diverse biopolymers, including extracellular polysaccharides (EPS), synthesized by bacteria can possess physicochemical and functional properties that make them important products of microbial synthesis with a broad and versatile biotechnological potential. Leuconostoc spp. belongs to the group of lactic acid bacteria as one of the predominant members and are relevant not only in varied food fermentations, but also can be employed in the production of extracellular homopolysaccharides (HoPS) such as α-glucans (dextran, alternan) and β-fructans (levan,inulin) from the sucrose-containing substrates. EPS are synthesized by specific Leuconostoc spp. extracellular glycosyltransferases [dextran sucrase, alternansucrase (ASR)] and fructosyltransferases (levansucrase, inulosucrase) and enzymatic reactions can be performed in whole culture systems as well as using cell-free enzymes. Both α-glucans and β-fructans have a wide range of properties, mostly depending on their pattern of linkages, which, although differing in some respects, make suitable prerequisites for their versatile application in many fields, especially in the food industry and biomedicine. As a rule, these properties (polymer type, molecular mass, rheological parameters), as well as the overall EPS yield, are strain-specific for the selected producers and depend to a large extent on the nutritional and growth conditions used, which in many cases remain not sufficiently optimized for Leuconostoc spp. This review summarizes the current knowledge on the potential of Leuconostoc spp. to produce commercially relevant EPS, including information on their applications in various fields, producer strains, production methods and techniques used, selected conditions, the productivity of bioprocesses as well as the possible use of renewable resources for their development.

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Section: Biomedical and Technological Applicationsmentioning

confidence: 99%

Extracellular polysaccharides produced by bacteria of the Leuconostoc genus

Zikmanis

Brants²,

Koļesovs

et al. 2020

World J Microbiol Biotechnol

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“…The liquid-crystalline state (either solution or melt) offers several well-documented advantages in both of these respects. − It has been demonstrated , that aqueous solutions of cell-free and nominally pure bacterial levan 3 are able to form a nematic liquid-crystalline phase at low concentrations and at ambient temperatures (Figure ). Subsequent research has revealed how the addition of starch, a nonmesogenic filler, affects the stability of the nematic phase 2 Partial phase diagram for dilute aqueous solutions of cell-free and nominally pure levan.…”

Section: Introductionmentioning

confidence: 99%

“…Subsequent research has revealed how the addition of starch, a nonmesogenic filler, affects the stability of the nematic phase. 11 The phase diagrams for these systems were determined by turbidity measurements made with a UVvisible spectrophotometer. [10][11][12] Solution absorbance spectra show a large peak centered at around 260 nm (Figure 3); it is assignable to electronic transitions that are characteristic of the aromatic groups found in nucleic acid impurities.…”

Section: Introductionmentioning

confidence: 99%

“…11 The phase diagrams for these systems were determined by turbidity measurements made with a UVvisible spectrophotometer. [10][11][12] Solution absorbance spectra show a large peak centered at around 260 nm (Figure 3); it is assignable to electronic transitions that are characteristic of the aromatic groups found in nucleic acid impurities. 13 Since the levan molecule does not itself contain such groups, the large 260 nm peak should not be present in a molecularly pure sample.…”

Section: Introductionmentioning

confidence: 99%

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Chimeric Liquid Crystallinity: Noncovalent Association of DNA and Bacterial Levan

Huber

Viney

1997

Macromolecules

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The liquid-crystalline phase of cell-free and nominally pure bacterial levan in water is shown to depend on the presence of DNA. The necessary concentrations of DNA are 2 orders of magnitude lower than those needed to stabilize a mesophase in aqueous solutions of DNA on its own and are similarly small in comparison to the number concentration of the globular levan molecules. A partial phase diagram for liquid crystallinity in the ternary system water/levan/DNA is mapped out. A model is proposed in which the levan and DNA associate noncovalently, to produce supramolecular, rodlike aggregates. The term “chimeric liquid crystal” is coined to denote a mesophase based on such rods assembled from otherwise unrelated molecular species. The model can account for several characteristics of the liquid-crystalline phase of bacterial levan, including the unexpected observation that liquid crystal phase formation is accompanied by a continuous increase in viscosity.

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