In view of the economic and technical limitations associated with diluted aqueous suspensions of cellulose nanofibrils, in the present contribution sorbitol was assayed as capping agent in the drying ...of bacterial nanocellulose (BNC) for the first time. The effect of different sorbitol:BNC mass ratios (1:1, 3:1 and 5:1), drying strategies (freeze-drying versus oven-drying), and redispersion methods (high-speed homogenization and mechanical stirring) on the water redispersibility of dried BNC was studied. Sedimentation, specific surface area and rheology assays all demonstrated the suitability of sorbitol for significantly limiting irreversible hydrogen bonding between adjacent cellulose nanofibrils during dehydration, leading to redispersed BNC suspensions with characteristics similar to those of never-dried ones. In the case of freeze-dried samples, results showed that the lowest sorbitol:BNC mass ratio assayed (i.e., 1:1) was enough to prevent irreversible hydrogen bonding between adjacent cellulose fibrils, whereas for oven-dried BNC samples full redispersion was achieved by mechanical stirring when sorbitol:BNC mass ratios of at least 3:1 were used. The feasibility of easily removing sorbitol from the dried product upon redispersion was also verified.
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•Sorbitol was used for the first time as capping agent in the drying of BNC.•Sorbitol addition proved to be successful in the prevention of BNC hornification.•A 1:1 sorbitol:BNC ratio was required to successfully redisperse freeze-dried samples.•A 3:1 sorbitol:BNC ratio was required to successfully redisperse oven-dried samples.•Sorbitol could be easily removed by washing with water at room temperature.
Bioactive packaging is gaining interest in food preservation as an alternative to the incorporation of additives to food formulations. Yeast cell wall is a good candidate for the formation of ...biodegradable films. In this context, enzymatically hydrolysed yeast cell wall (YCW-E) and fungal extracts, containing naphtho-γ-pyrones (NGPs), were used to develop bioactive materials with antioxidant activity. Two types of ethanol fungal extracts from
Aspergillus tubingensis
G131 were used; a crude (CE*3) and a semi-purified (EP) extract, which presented different antioxidant capacity. Initial degradation temperature of samples with 2% of CE*3 extract were decreased in comparison to the control. Mechanical properties were significantly affected by the incorporation of the fungal extracts, those samples with CE*3 extract presented higher elongation at break due to the presence of melanins, while samples with EP extract showed higher modulus and tensile strength because of the increase in macromolecules interactions product of the hydrophobic character of the extract. Barrier properties were improved due to the low affinity to water of the extract. Antioxidant capacity of films was confirmed by the ABTS method. The addition of fungal metabolites with antioxidant properties to yeast cell wall films is a promising solution for the development of active materials for food contact application increasing shelf life of the products.
The 1.8 Å resolution neutron structure of deuterated type III antifreeze protein in which the methyl groups of leucine and valine residues are selectively protonated is presented. Comparison between ...this and the 1.85 Å resolution neutron structure of perdeuterated type III antifreeze protein indicates that perdeuteration improves the visibility of solvent molecules located in close vicinity to hydrophobic residues, as cancellation effects between H atoms of the methyl groups and nearby heavy‐water molecules (D2O) are avoided.
The use of renewable resources to develop food contact materials, such as proteins or polysaccharides, and the use of industrial residues for alternative applications are trending topics for ...researchers and the industry. Yeast cell wall (YCW) is a very rich waste from the yeast extract industry. Due to this, the aim of this work is to develop new biodegradable films based on residual YCW and the study of the effect of plasticization on films properties. Residual YCW was used as base matrix and different concentrations of glycerol (0, 15, 25 and 35 wt%) were tested to obtain casted films. Homogeneous and yellow-brownish films, which allow seeing through them, were obtained from the YCW. Total soluble matter demonstrated that glycerol enhanced solubility of films but glycerol was retained in the polymer matrix. TGA studies indicated that YCW films exhibited substantial degradation at temperatures above 180 °C. FTIR spectra of the casted films were representative of yeast cell wall material and SEM photographs showed that cell wall maintained their shape after film formation. As expected, Young’s modulus and tensile strength values were decreased with the increasing amount of glycerol. However, elongation at break was not increased further with higher concentration of plasticizer and the addition of 15 wt% of glycerol seemed to be enough to improve mechanical properties. The linear increment of water vapour permeability with glycerol concentration was produced by the increase in water solubility in the film. Therefore, based on solubility in water, mechanical, and barrier properties, it is possible to propose yeast cells residues as film-forming material for biodegradable film developments.
In the last decades, cellulose nanoparticles have been widely used to reinforce polymeric materials due to their strength and their wide availability in nature. Cellulose nanoparticles are entirely ...compatible to reinforce natural polymers, as performed in this study. The effect of rice husk cellulose nanofibers (RHCNF) and bacterial nanocellulose (BNC) on water vapor transfer and mechanical properties was studied in yeast biomass films, made from dispersions at pH 6 and 11. Water vapor permeability was reduced at 5 wt% in both reinforcements in films prepared at pH 11, although their influence was negligible at pH 6. Despite both cellulose nanofibres have similar aspect ratios, Young’s modulus, tensile strength, elongation and tensile toughness of films reinforced with BNC were significantly increased with respect to RHCNF films, and both were better than the pure matrix. In this way, the present study provides an interesting contribution regarding the effect of the mentioned nanocellulosic reinforcements on yeast biomass films used for packaging purposes.
Graphic Abstract
•By-product of Kombucha beverage as a resource of active materials.•Symbiotic Community Of Bacteria and Yeast SCOBY produced bacterial cellulose films.•Sugared herbal infusions provided the nutrients ...for cellulose synthase activation.•Kombucha native films showed high mechanical strength and low elongation at break.•Films from Kombucha fermented in yerba mate presented high antioxidant capacity.
The symbiotic community of bacteria and yeast (SCOBY) of Kombucha beverage produces a floating film composed of bacterial cellulose, a distinctive biobased material. In this work, Kombucha fermentation was carried out in six different herbal infusions, where SCOBY was able to synthesise cellulosic films. Infusions of black and green tea, yerba mate, lavender, oregano and fennel added with sucrose (100 g/l) were used as culture media. In all cultures, film production resulted in a maximum after 21 days. Yield conversion, process productivity and antioxidant activity were quantified. Macroscopic and microscopic features of films were determined based on electronic microscopy, calorimetric and mechanical properties and hydration behaviour. Native films from yerba mate had a remarkable antioxidant activity of 93 ± 4% of radical inhibition due to plant polyphenols, which could prevent food oxidation. Results revealed that films retained natural bioactive substances preserving important physicochemical properties, essential for developing active materials.
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•Innovative material based on the biomass of water kefir grains was developed.•Water kefir grains are constituted basically by the polysaccharide dextran.•The obtained films exhibited ...a great continuity, homogeneity and high transparency.•The addition of glycerol affected thermal, hydration, and water barriers properties.•The addition of 30 wt% glycerol improved significantly the elongation of the films.
Microorganisms’ biomass is a sustainable and innovative source of biopolymers, such as proteins and polysaccharides, which are suitable for development of biodegradable films. In this work, an alternative material based on the entire biomass of water kefir grains was developed. The whole biomass was submitted to physical treatments of ultrasonic homogenization separated by a thermal treatment at 90 °C. The effect of glycerol on film properties was evaluated. The films obtained exhibited high transparency and homogeneity without cracks. Infrared spectroscopy revealed that the material is constituted basically by the polysaccharide dextran. The increasing plasticiser content decreased glass transition temperature. Indeed, the presence of plasticiser increased the amount of hydration water and the water vapour permeability. Moreover, the addition of 30 wt% of glycerol improved significantly the elasticity of films to 275 ± 15%. Results revealed that water kefir grains biomass is a viable and innovative source of biodegradable materials.
There is a strong public concern about plastic waste, which promotes the development of new biobased materials. The benefit of using microbial biomass for new developments is that it is a completely ...renewable source of polymers, which is not limited to climate conditions or may cause deforestation, as biopolymers come from vegetal biomass. The present review is focused on the use of microbial biomass and its derivatives as sources of biopolymers to form new materials. Yeast and fungal biomass are low-cost and abundant sources of biopolymers with high promising properties for the development of biodegradable materials, while milk and water kefir grains, composed by kefiran and dextran, respectively, produce films with very good optical and mechanical properties. The reasons for considering microbial cellulose as an attractive biobased material are the conformational structure and enhanced properties compared to plant cellulose. Kombucha tea, a probiotic fermented sparkling beverage, produces a floating membrane that has been identified as bacterial cellulose as a side stream during this fermentation. The results shown in this review demonstrated the good performance of microbial biomass to form new materials, with enhanced functional properties for different applications.
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•Hydration kinetics provided water solubility and diffusion coefficient in films.•Glycerol content increased water solubility and did not change diffusion.•Raising film thickness ...decreased water solubility but diffusion increased.•Effect of glycerol increasing permeability was due to the increase in solubility.•Effect of thickness increasing permeability was dominated by diffusion.
Research on biodegradable films is a topic of strategical interest in the field of food science and technology. These films are membranes conformed by biopolymers that interact strongly with water and they generally require the addition of plasticizer in order to improve its integrity and mechanical properties. The study of the hydration and water transfer properties through these films, as well as understanding in what way the thickness and the addition of the plasticizer affect these properties, is essential for a better knowledge and optimization of the required protective function of these membranes. In this work the hydration kinetics and water transport through biodegradable films obtained from yeast biomass were studied, in order to know the performance against changes in thickness and glycerol content. Hydration kinetics experiments allowed obtaining solubility of water in the matrix film, and the diffusion coefficient. Results demonstrated that when glycerol content was increased, the solubility of water increased while diffusion remained constant. Moreover, when the film thickness was grown, the solubility of water decreased but the diffusion increased. Experimental water vapour permeability obtained through traditional cup method was compared to the theoretical permeability calculated by multiplying diffusion coefficient and water solubility. The good agreement observed between both values allowed the analysis of how solubility and diffusion contributed to permeability. As a result this study revealed that the increment of permeability with the plasticizer content was due to the increase in solubility, while the effect of the thickness increasing permeability was dominated by diffusion.
•Characterization of GumB and GumC proteins involved in xanthan synthesis.•The recombinant GumB shows to be a tetrameric protein.•Native and recombinant GumC showed oligomeric conformation.•GumC ...expression, stability and/or oligomerization rely on transmembrane segments.
This study investigated the structural and biophysical characteristics of GumB and GumC, two Xanthomonas campestris membrane proteins that are involved in xanthan biosynthesis. Xanthan is an exopolysaccharide that is thought to be a virulence factor that contributes to bacterial in planta growth. It also is one of the most important industrial biopolymers. The first steps of xanthan biosynthesis are well understood, but the polymerization and export mechanisms remain unclear. For this reason, the key proteins must be characterized to better understand these processes. Here we characterized, by biochemical and biophysical techniques, GumB, the outer membrane polysaccharide export protein, and GumC, the polysaccharide co-polymerase protein of the xanthan biosynthesis system. Our results suggested that recombinant GumB is a tetrameric protein in solution. On the other hand, we observed that both native and recombinant GumC present oligomeric conformation consistent with dimers and higher-order oligomers. The transmembrane segments of GumC are required for GumC expression and/or stability. These initial results provide a starting point for additional studies that will clarify the roles of GumB and GumC in the xanthan polymerization and export processes and further elucidate their functions and mechanisms of action.