Acetan:glucomannan interactions—a molecular modeling study

Corncob-derived biodegradable packaging films: A sustainable solution for raspberry post-harvest preservation

Plastic food packaging, with its harmful migration of microplastics and nanoplastics into food, presents significant ecological imbalance and human health risks. In this regard, using food and agricultural byproducts as packaging materials reduces environmental and economic concerns and supports their sustainable management. Herein, cellulosic residue from corncob was employed as a renewable source for developing biodegradable packaging films. It was solubilized in ZnCl2 solution, crosslinked with Ca2+ ions, and plasticized with sorbitol to form films and used to improve the shelf-life of raspberries. The optimized film possesses water vapor permeability, tensile strength, and elongation at break of 1.8(4) x10-10 g-1 s-1 Pa-1, 4.7(1) MPa, and 15.4(7)%, respectively. It displays UV-blocking and antioxidant properties and biodegrades within 29 days at 24% soil moisture. It preserves raspberries for 7 and 5 more days at room temperature and refrigeration conditions, respectively, compared to polystyrene film. Overall, more value addition could be envisioned from agricultural residues to minimize post-harvest losses and food waste through biodegradable packaging, which also aids in mitigating plastic perils.

Role of metal chlorides in the gelation and properties of fucoidan/κ-carrageenan hydrogels

Metal ions play a crucial role in forming hydrogels, and their effects on fucoidan (FUC): κ-carrageenan (KC) mixed gels were investigated. The results indicated that the FUC: KC mixed gels (FC) were promoted by K⁺ and Ca²⁺ but destroyed by Fe³⁺. The gel strength of FC was enhanced by K⁺ and Ca²⁺, with G' and G″ being highest at 50 mmol/L KCl and 25 mmol/L CaCl₂, respectively. Water mobility was weakened after the addition of KCl and CaCl₂ in accordance with the decrease in T₂₃ relaxation time (free water, 100-1000 ms). After addition of KCl and CaCl₂, the FC groups presented a typical three-dimensional network structure in contrast to the lamellar, disordered, and broken structure of FUC. Moreover, the FT-IR spectrum certified the enhancement of hydrogen bonds and the occurrence of electrostatic interactions during gel formation by the red-shift of the OH stretching vibration of the Ca²⁺ group and the blue-shift of the COS vibrations. The XRD results confirmed that the binding of Ca²⁺ to FC was tighter than that of K⁺ at the same charge content. These results provide a theoretical basis for understanding the interaction mechanism of FC with metal ions.

Fucoidan hydrogels induced by κ-carrageenan: Rheological, thermal and structural characterization

Fucoidan (FUC) is a non-gelling polysaccharide but could interact with κ-carrageenan (KC) to form a stable gel blend. However, their interaction mechanism is unclear. Herein, FUC and KC blended gels are prepared by mixing FUC (10 and 20 mg/mL) and KC (6, 7 and 8 mg/mL) solutions, and characterized through LF-NMR, rheology, DSC, Cryo-SEM, and FTIR. The FTIR analysis confirms the formation of hydrogen bonds between FUC and KC chains. The KC addition to FUC significantly improves the water retention and frost resistance. The viscoelastic measurements reveal higher gelling nature of the FUC-KC binary mixtures, and the DSC results confirm the higher thermal stability. The Cryo-SEM images clearly reveal the gel network structure. The outcome of this study deemed to further the FUC use in food and non-food applications.

Visualisation of xanthan conformation by atomic force microscopy

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New AFM imaging methodology BlueDrive™ enabling resolution of xanthan’s helix.

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Visual evidence of the structural composition of xanthan’s helices.

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Confirmation of the effect of counterion screening on structural ordering.

Direct visual evidence obtained by atomic force microscopy demonstrates that when xanthan is adsorbed from aqueous solution onto the heterogeneously charged substrate mica, its helical conformation is distorted. Following adsorption it requires annealing for several hours to restore its ordered helical state. Once the helix state reforms, the AFM images obtained showed clear resolution of the periodicity with a value of 4.7 nm consistent with the previously predicted models. In addition, the images also reveal evidence that the helix is formed by a double strand, a clarification of an ambiguity of the xanthan ultrastructure that has been outstanding for many years.

Synergistic interactions between the genetically modified bacterial polysaccharide P2 and carob or konjac mannan

Rheological studies have confirmed that the bacterial polysaccharide P2, a genetically modified variant of the Acetobacter xylinum polysaccharide acetan, undergoes synergistic gelation with either of the plant polysaccharides carob or konjac mannan. X-ray fibre diffraction data shows that P2 can form a 5-fold helical structure of pitch 4.7nm and an axial rise per disaccharide repeat of 0.92nm. Optical rotation data demonstrate that P2 undergoes a coil-helix transition in solution and that deacylation enhances the stability of the helical structure in solution. Studies made on mixtures prepared at different temperatures and ionic strengths suggest that denaturation of the P2 helix favours interaction and gelation. Deacetylation of P2 enhances gelation. X-ray diffraction data for oriented fibres prepared from deacetylated P2-konjac mannan mixed films reveal a 6-fold helical structure of pitch 5.54nm with an axial rise per disaccharide repeat also of 0.92nm. This mixed helix provides direct evidence for binding between the two polysaccharides. P2 contains two sites of acetylation: one on the backbone and one on the sidechain. The former site of acetylation inhibits helix formation for P2. It is suggested that this site of acetylation also inhibits formation of the mixed helix, explaining the enhanced gelation of mixtures on deacetylation.