Bacterial and plant cellulose modification using ultrasound irradiation

Cellulose nanocrystal iridescence: a new model

A homogeneous aqueous dispersion of cellulose nanocrystals (CNs) that is left to evaporate in a Petri dish self-organizes into smectic liquid crystals that are actually liquid multilamellar structures. As evaporation proceeds, the liquid multilamellar structures solidify to become a solid multilamellar film. Each solid lamella is in the submicrometer range, and its iridescence is easily explained by classical light interference. A careful inspection of each solid lamella revealed long, oriented arrays of colloids. Interestingly, the array orientation is generally the same for each superposed layer. This is exceptional because the stratification appears first in the liquid, and the solid colloids are formed in each stratum at the very end of the process. Our findings are supported by optical, atomic force, and electron microscope observations and by laser diffraction observations. The multilamellar solid film model is easier to engineer than the helical model currently used to explain the iridescence and optical activities of CN solid films. This new understanding should promote the industrial production of colorful CN coatings and inks as a green alternative for decades to come.

Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl(2)) and sodium carbonate (Na(2)CO(3)) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.

Evaluation of the effect of roasting on the structure of coffee galactomannans using model oligosaccharides

The roasting process induces structural changes in coffee galactomannans. To know more about the reaction pathways that occur during the roasting of coffee, mannosyl and galactomannosyl oligosaccharides, having a degree of polymerization (DP) between 3 and 4, were used as models for galactomannans. These compounds were dry-heated under air atmosphere from room temperature to 200 °C, being maintained at 200 °C for different periods of time. The roasted materials were analyzed by mass spectrometry (ESI-MS, MALDI-MS, and ESI-MSn) and methylation analysis. In the MS spectra were identified several [M+Na]+ ions belonging to a series from a single hexose to 10 hexose residues ([Hex1-10+Na]+). The ions corresponding to their respective mono- and tridehydrated derivatives ([Hex2-10-H2O+Na]+ and [Hex2-10-3H2O+Na]+, respectively) were also identified. ESI-MSn as well as deuterium-labeling and alditol derivatization experiments showed that the tridehydrations occur at the reducing end of the oligosaccharides. The identification of (1→2)- and (1→6)-linked mannose residues and (1→4)-linked glucose residues by methylation analysis allowed the conclusion that transglycosylation and isomerization reactions occur during dry thermal processing.