Piedad Gañán

Bacterial cellulose produced by a new acid-resistant strain of Gluconacetobacter genus.

A bacterial strain isolated from the fermentation of Colombian homemade vinegar, Gluconacetobacter medellensis, was investigated as a new source of bacterial cellulose (BC). The BC produced from substrate media consisting of various carbon sources at different pH and incubation times was quantified. Hestrin-Schramm (HS) medium modified with glucose led to the highest BC yields followed by sucrose and fructose. Interestingly, the microorganisms are highly tolerant to low pH: an optimum yield of 4.5 g/L was achieved at pH 3.5, which is generally too low for other bacterial species to function. The cellulose microfibrils produced by the new strain were characterized by scanning and transmission electron microscopy, infrared spectroscopy X-ray diffraction and elemental analysis. The morphological, structural and chemical characteristics of the cellulose produced are similar to those expected for BC.

Gluconacetobacter medellinensis sp. nov., cellulose- and non-cellulose-producing acetic acid bacteria isolated from vinegar.

The phylogenetic position of a cellulose-producing acetic acid bacterium, strain ID13488, isolated from commercially available Colombian homemade fruit vinegar, was investigated. Analyses using nearly complete 16S rRNA gene sequences, nearly complete 16S-23S rRNA gene internal transcribed spacer (ITS) sequences, as well as concatenated partial sequences of the housekeeping genes dnaK, groEL and rpoB, allocated the micro-organism to the genus Gluconacetobacter, and more precisely to the Gluconacetobacter xylinus group. Moreover, the data suggested that the micro-organism belongs to a novel species in this genus, together with LMG 1693(T), a non-cellulose-producing strain isolated from vinegar by Kondo and previously classified as a strain of Gluconacetobacter xylinus. DNA-DNA hybridizations confirmed this finding, revealing a DNA-DNA relatedness value of 81 % between strains ID13488 and LMG 1693(T), and values <70 % between strain LMG 1693(T) and the type strains of the closest phylogenetic neighbours. Additionally, the classification of strains ID13488 and LMG 1693(T) into a single novel species was supported by amplified fragment length polymorphism (AFLP) and (GTG)5-PCR DNA fingerprinting data, as well as by phenotypic data. Strains ID13488 and LMG 1693(T) could be differentiated from closely related species of the genus Gluconacetobacter by their ability to produce 2- and 5-keto-d-gluconic acid from d-glucose, their ability to produce acid from sucrose, but not from 1-propanol, and their ability to grow on 3 % ethanol in the absence of acetic acid and on ethanol, d-ribose, d-xylose, sucrose, sorbitol, d-mannitol and d-gluconate as carbon sources. The DNA G+C content of strains ID13488 and LMG 1693(T) was 58.0 and 60.7 mol%, respectively. The major ubiquinone of LMG 1693(T) was Q-10. Taken together these data indicate that strains ID13488 and LMG 1693(T) represent a novel species of the genus Gluconacetobacter for which the name Gluconacetobacter medellinensis sp. nov. is proposed. The type strain is LMG 1693(T) ( = NBRC 3288(T) = Kondo 51(T)).

Sustainable optically transparent composites based on epoxidized soy-bean oil (ESO) matrix and high contents of bacterial cellulose (BC)

Production of transparent composites from totally renewable resources with extraordinary potential for different applications can be made possible using cellulose. Composites of epoxidized soybean oil (ESO)/bacterial cellulose (BC) nanofibers have been prepared with high fiber content. Due to the nano-order scale network-like structure of BC nanofibers, composite films present high transparency even at high BC content. Transparency of films has been analyzed by UV–visible spectroscopy observing that only 15% of matrix transmittance is lost in the nanocomposites. ESO/BC composites show better mechanical properties with increasing BC content. Composites combine high stiffness and good ductility due to the incorporation of BC network structure in ESO matrix.

Influence of the acid type in the production of chitosan films reinforced with bacterial nanocellulose.

Chitosan films reinforced with bacterial cellulose (BC) nanoribbons were studied to understand the influence of acid (acetic and lactic acids) on the reinforcing effect. For both acids, the maximum concentration of the reinforcing constituent was 5wt% with respect to the dry weight of chitosan. The infrared spectra, mechanical properties, morphology and antimicrobial activity of the films were analyzed. The results showed a difference between the acids in their behavior and effect on the reinforcement, with a tensile strength of 12.3MPa for the acetic acid films and 3.3MPa for the lactic acid films. Additionally, the bacterial inhibition tests were shown to be positive for the lactic acid films and negative for the acetic acid films. Therefore, exchanging the acid used in these films may be desirable for certain applications.

Effect of Fiber Treatments on Mechanical Behavior of Short Fique Fiber-reinforced Polyacetal Composites

Different types of natural fiber composites with thermoplastic matrices have been extensively investigated, especially with polyolefins. However, the ability of these fibers as reinforcement of technical matrices has been less studied. This study evaluates the possibilities of using fique fibers (hard fibers) obtained from leaves to reinforce technical matrices such as polyoxymethylene (POM). The mechanical behavior of fique fiber-POM matrix composites has been analyzed as a function of the fiber length, the fiber content, and the surface modification of the fiber. The treatments used correspond to alkalization, and using of formaldehyde, glycidyl methacrylate, and an isocyanate compound. The mechanical properties of these treated fiber composites are higher than those of the untreated ones, due to the enhancement of the fiber-matrix adhesion, observed by the reduction on the hydrophilic tendency of fique fibers. The hydrophilicity has been analyzed by following the variation of the polar component of the free surface energy, calculated by the Owens-Wendt method.

Effect of molecular weight reduction by gamma irradiation on the antioxidant capacity of chitosan from lobster shells

Abstract This study assessed the effect of molecular weight (MW) reduction by gamma irradiation on the antioxidant capacity of chitosan with potential application in the preservation of foodstuffs. Two batches of chitosan were obtained by heterogeneous chemical N-deacetylation of chitin from common lobster (Panulirus argus). Irradiation of chitosan was performed using a 60Co source and applying doses of 5, 10, 20 and 50 kGy with a dose rate of 10 kGy/h. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy was used to identify main chemical features of chitosan. The average viscosimetric MW was determined by the viscosimetric method while the deacetylation degree by a potentiometric method. Thermogravimetric analysis and differential scanning calorimetry were conducted to evaluate the thermal degradation behavior of the chitosan samples, both under nitrogen flow. The antioxidant activity of chitosan solutions at 1% (w/v) in lactic acid at 1% (v/v) and Tween 80 at 0.1% (v/v) was evaluated through the ABTS assay and scavenging of DPPH radical by chitosan. The increase of irradiation dose with 60Co until 50 kGy decreased significantly the MW of chitosan through the scission of glycosidic bonds without affecting its functional groups, while the DD (72–75 %) did not vary (p > 0.05). The AC of the chitosan solutions increased with the reduction of MW of chitosan by gamma irradiation.

In-situ glyoxalization during biosynthesis of bacterial cellulose

A novel method to synthesize highly crosslinked bacterial cellulose (BC) is reported. The glyoxalization is started in-situ, in the culture medium during biosynthesis of cellulose by Gluconacetobacter medellensis bacteria. Strong crosslinked networks were formed in the contact areas between extruded cellulose ribbons by reaction with the glyoxal precursors. The crystalline structure of cellulose was preserved while the acidic component of the surface energy was reduced. As a consequence, its predominant acidic character and the relative contribution of the dispersive component increased, endowing the BC network with a higher hydrophobicity. This route for in-situ crosslinking is expected to facilitate other modifications upon biosynthesis of cellulose ribbons by microorganisms and to engineer the strength and surface energy of their networks.

Off-axis Flexure Test: A New Method for Obtaining In-plane Shear Properties

Off-axis three-point flexure test for unidirectional composites is proposed as a new method for obtaining in-plane shear modulus and in-plane shear strength. The method of determination of the in-plane shear modulus GLT has been explained in a previous work where the displacement field of an off-axis flexure test was analyzed. In the present work, besides summarizing the calculation equations of GLT, the condition of small displacements is analyzed. Otherwise, an error analysis is carried out in order to study the influence of the calculated value of GLT on the other elastic parameters. Normal and shear stresses in the fiber–matrix interface change from point to point in the specimen depending on the fiber orientation angle and specimen geometry. A critical point of failure that depends on the fiber orientation angle is determined and optimum conditions for obtaining in-plane shear strength are discussed. Experiments for different fiber orientations and geometric conditions have been carried out for IM7/8552 epoxy matrix based carbon fiber reinforced unidirectional composite material.

Synthesis of thermoplastic starch-bacterial cellulose nanocomposites via in situ fermentation

In this paper, a nanocomposite based on thermoplastic starch (TPS) reinforced with bacterial cellulose (BC) nanoribbons was synthesized by in situ fermentation and chemical crosslinking. BC nanoribbons were produced by a Colombian native strain of Gluconacetobacter medellinensis; the nanocomposite was plasticized with glycerol and crosslinked with citric acid. The reinforcement percentage in the nanocomposites remained constant throughout the fermentation time because of the TPS absorption capability of the BC network. Nanocomposites produced after fermentation for seven days were characterized using thermogravimetric analysis (TGA); Fourier transformed infrared spectroscopy with attenuated total reflectance (FTIR-ATR), mechanical testing and scanning electron microscopy (SEM). The new TPS/BC nanocomposites exhibit strong interfacial adhesion, improved thermal behavior, water stability and enhanced mechanical properties. These findings support the applications of starch in the packaging industry.

Development of composite films based on thermoplastic starch and cellulose microfibrils from Colombian agroindustrial wastes

Composite materials are produced using thermoplastic starch reinforced with cellulose microfibrils. The cellulose microfibrils are isolated from two different sources and their reinforcement capacity was evaluated. Vegetable cellulose (VC) microfibrils are isolated from vascular bundles of banana rachis, while bacterial cellulose (BC) microfibrils are produced by Gluconacetobacter genus bacteria using pineapple peel juice as the culture media. For this study, both the materials were obtained from Colombian agroindustrial wastes. Composite films were characterized using different techniques, including mechanical tensile testing, attenuated total reflection Fourier transform infrared spectroscopy, and thermogravimetric analysis. The purpose of this study is to assess the effect of different processing methods and cellulose microfibrils content in the composite material behavior. The results showed that the mechanical properties were increased when cellulose microfibrils were added before gelatinization. Significant increments in Young’s modulus and tensile strength of both VC and BC composites were obtained with respect to starch matrix.