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Fundamental rheology, differential scanning calorimetry and infrared spectroscopy have been used to evaluate the effect of a cationic polysaccharide, chitosan, on the gelatinization, gel formation and retrogradation of maize starch samples, under acidic aqueous conditions. Moderate acidic conditions (0.1molL(-1) acetic acid) have shown a (slight) positive effect on starch gelatinization process and structure development. The presence of chitosan increased the DSC onset gelatinization temperature and also shifted the onset of the storage modulus increase to higher temperatures. Formation of the starch gel, mainly gelation of the leached-out amylose, is somehow hindered by the presence of the cationic polysaccharide and, therefore, the retrogradation of starch at very early stage can be delayed by addition of chitosan. However, long-term retrogradation was slightly increased. FTIR pectroscopy did not reveal any significant interaction between both polysaccharides what is in accordance with the observed rheological behavior. Small additions of chitosan to starch-rich systems may be a useful strategy to obtain new textures with novel phase transition behaviors.

The small amount of proteins in starch-rich food industry byproducts can be an advantage to crosslink with genipin and tailor the performance of biobased films. In this work, genipin was combined with non- purified starch recovered from industrial potato washing slurries and used for films production. Starch recovered from potato washing slurries contained 0.75% protein, 2 times higher than starch directly obtained from potato and 6 times higher than the commercial one. Starch protein-genipin networks were formed with 0.05% and 0.10% genipin, gelatinized at 75 °C and 95 °C in presence of 30% glycerol. Bluish colored films were obtained in all conditions, with the higher surface roughness (Ra, 1.22 μm), stretchability (elongation, 31%), and hydrophobicity (water contact angle, 127°) for 0.10% genipin and starch gelatinized at 75 °C. Therefore, starch-rich byproducts, when combined with genipin, are promising for surpassing the starch-based films hydrophilicity and mechanical fragilities while providing light barrier properties.

Oscillatory and steady-shear rheological methods as well as scanning electron microscopy were used to characterize silica (SiO 2 )/galactomannan dispersions. Particle loading and surface charge are found to strongly influence the composite structure and dynamics. When the particles were added above a minimum concentration, a sol–gel transition was induced. The SiO 2 /polysaccharide dispersions exhibited significant non-linearities, especially under ionic conditions that favor interparticle and particle–polysaccharide interactions, characterized by strong shear-thinning, diverging viscosities at low shear rates, apparent yield stress and high strain sensitivity. The mechanical spectra for the composite systems suggest that stress relaxation of these composites is effectively arrested by the presence of silica nanoparticles. Microstructural analysis revealed an ordering of the silica particles around the polymer chains. Polysaccharide chains act as templates for particle clustering leading to the formation of a particle-mediated transient biopolymer network, with particle clusters hindering polymer mobility and enhancing junction zones within the network.

A commercial gellan sample (Gelrite) and a gellan-like polymer (JB3) obtained by exposure of the producing strain to chemical mutagenesis were subjected to partial acid hydrolysis and the resultant oligosaccharides were identified by Electrospray Mass Spectrometry (ESI-MS) and Tandem Mass Spectrometry (ESI-MS/MS and MS n ). In both gellans, the main fragments were in accordance with the tetrasaccharide repeating unit, d -Glucose (Glc)- d -Glucuronic acid (GlcA)- d -Glucose (Glc)- l -Rhamose (Rha), described for the wild-type gellan, showing the higher acid lability of the Rha-(1 → 3)-Glc linkage when compared to the (1 → 4) of the other residues. Under the experimental conditions used in the study, as expected, no acyl substituents were observed in the commercial gellan but in JB3 oligosaccharides a glyceryl moiety was identified, substituted in the 3-linked Glc residue. Furthermore, the analysis of the MS/MS and MS n spectra of both gellans allowed the identification of structural details, some of them not yet reported for these exopolysaccharides. The presence of oligosaccharides with single Glc and Rha residues substituent of the tetrasaccharide unit of gellan may represent novel side chains of the backbone unit that to our knowledge have never been reported previously for the gellan exopolysaccharide.

The combination of the absorbance spectra in two infrared regions (1800–1500 and 1200–850 cm −1 ) was used to build a calibration model for the determination of the degree of methylesterification (DM) of pectic polysaccharides. The wavenumbers in the region 1800–1500 cm −1 are related to the carbonyl esters and carboxylates and those in the region 1200–850 cm −1 are related to the sugars composition. The model was done by means of a matrix of the outer product of the two regions and PLS1 regression, using cell wall pectic polysaccharide extracts from olive and pear pulps. The application of the Durbin–Watson criterion to the regression vector of OP-PLS1 gave an ‘optimal’ model with nine latent variables, with a RMSEP of 7.7% and a coefficient of determination ( R 2 ) of 0.95. The model explained 95% of the total variability present in the y vector. The results allowed the prediction of the DM of commercial standard pectic polysaccharides and of impure pectic polysaccharide extracts. A prediction error of 22% was found, which contrasted with the prediction error of 72% when only the region 1800–1500 cm −1 region was used.

The use of chitosan films has been limited due to their high degradability in aqueous acidic media. In order to produce chitosan films with high antioxidant activity and insoluble in acid solutions caffeic acid was grafted to chitosan by a radical mechanism using ammonium cerium (IV) nitrate (60 mM). Genipin was used as cross-linker. This methodology originated films with 80% higher antioxidant activity than the pristine film. Also, these films only lost 11% of their mass upon seven days immersion into an aqueous solution at pH 3.5 under stirring. The films surface wettability (contact angle 105°), mechanical properties (68 MPa of tensile strength and 4% of elongation at break), and thermal stability for temperatures lower than 300 °C were not significantly influenced by the covalent linkage of caffeic acid and genipin to chitosan. Due to their characteristics, mainly higher antioxidant activity and lower solubility, these are promising materials to be used as active films.