Flow Properties of Lambda Carrageenan in Aqueous Systems

Small amplitude oscillatory and steady shear measurements at 25°C were used to investigate the rheological behavior of λ‐carrageenan solutions at pH 7.0 ± 1.0 without and with added sodium counterion. The dynamic moduli, G′(ω) and G″(ω), show the typical behavior of macromolecular solutions in which the viscous character predominates. The steady shear flow exhibits a Newtonian zero‐shear viscosity (η0) region followed by a shear‐thinning zone. Viscosity data can be well described by the Carreau‐Yasuda model. Without added Na+, the intrinsic viscosity, [η], and the critical overlap concentration, C*, are 204 dL/g and 0.21%, respectively. With 20 mmol/dm3 Na+, [η] = 14.7 dL/g and C* = 0.38%. For concentrations below C*, the viscous character is more sensitive to the presence of added Na+, and the opposite occurs when the concentration exceeds C*. The dynamic moduli and viscosity increase with the increase of polysaccharide concentration, but they decrease with added Na+, confirming the polyelectrolyte nature of λ‐carrageenan. Empirical shift factors were used to obtain master curves for the dynamic moduli and apparent viscosity for different polysaccharide and added Na+ concentrations

Chemoenzymatic synthesis of polypeptides in neat 1,1,1,2-tetrafluoroethane solvent

Chemoenzymatic polypeptide synthesis offers several advantages over chemical or other biological routes, however, the use of aqueous-based media suffers from reverse hydrolysis reactions that challenge peptide chain propagation. Herein, the protease from subtilisin Carlsberg biocatalyzed the synthesis of poly-L-PheOEt, poly-L-LeuOEt, and the copolymers poly-L-PheOEt-co-L-LeuOEt from their amino acid ethyl ester substrates in a neat liquid 1,1,1,2-tetrafluoroethane solvent. The products, achieved in acceptable yields (ca. 50%), were fully characterized showing relatively high molar mass (ca. 20 000 Da for poly-L-PheOEt). This non-toxic low-boiling hydrofluorocarbon enhances enzymatic peptide propagation by limiting hydrolysis owing to its hydrophobic and relatively polar characteristics that sustain the protease activity and solubilize substrates and products. Computational molecular dynamic calculations were used to assess the L-PheOEt/L-LeuOEt-solvent and polypeptide-solvent interactions in this system. Additionally, the homopolypeptides displayed higher crystallinity than the copolypeptides with random incorporation of amino acid ethyl esters, notwithstanding the significantly highest specificity for Phe in this system. Interestingly, secondary structure characterization of the products by FTIR and circular dichroism suggests a non-common peptide folding

Physicochemical characterization of sodium stearoyl lactylate (SSL), polyoxyethylene sorbitan monolaurate (Tween 20) and κ-carrageenan

Surfactant-polymer mixtures are common in food, cosmetic and pharmaceutical products. These components can interact with each other. The interactions depend on the type of polymer and surfactant, the purity of the ingredients, the ionic content and their concentration. Therefore, the data presented here provide valuable information that could be useful for those working with these mixtures in different applications, particularly in blends with polyelectrolytes and their counterions. This article contains experimental data about the physicochemical characterization of sodium stearoyl lactylate (SSL), polyoxyethylene sorbitan monolaurate (Tween 20) and κ-carrageenan. Techniques included atomic absorption, DSC, FTIR-ATR, NMR, and surface tension. Keywords: Sodium stearoyl lactylate, Tween 20, κ-carrageenan, Surface tension, Calorimetry, IR, NM

Removal of Heavy Metal Ions from Wastewater with Poly-ε-Caprolactone-Reinforced Chitosan Composite

Currently, the requirements for adsorbent materials are based on their environmentally friendly production and biodegradability. However, they are also related to the design of materials to sustain many cycles in pursuit of low cost and profitable devices for water treatments. In this regard, a chitosan reinforced with poly-ε-caprolactone thermoplastic composite was prepared and characterized by scanning electron microscopy; Fourier transforms infrared spectroscopy, X-ray diffraction analysis, mechanical properties, as well as erosion and swelling assays. The isotherm and kinetic data were fitted with Freundlich and pseudo-second-order models, respectively. The adsorption equilibrium capacities at pH 6 of Zn(II), Cu(II), Fe(II), and Al(III) were 165.59 ± 3.41 mg/g, 3.91 ± 0.02 mg/g, 10.72 ± 0.11 mg/g, and 1.99 ± 0.22 mg/g, respectively. The adsorbent material lost approximately 6% of the initial mass in the adsorption-desorption processes

Inhibition of Listeria monocytogenes in Fresh Cheese Using Chitosan-Grafted Lactic Acid Packaging

A chitosan from biologically obtained chitin was successfully grafted with d,l-lactic acid (LA) in aqueous media using p-toluenesulfonic acid as catalyst to obtain a non-toxic, biodegradable packaging material that was characterized using scanning electron microscopy, water vapor permeability, and relative humidity (RH) losses. Additionally, the grafting in chitosan with LA produced films with improved mechanical properties. This material successfully extended the shelf life of fresh cheese and inhibited the growth of Listeria monocytogenes during 14 days at 4 °C and 22% RH, whereby inoculated samples with chitosan-g-LA packaging presented full bacterial inhibition. The results were compared to control samples and commercial low-density polyethylene packaging