High-performance starch biocomposites with celullose from waste biomass: Film properties and retrogradation behaviour

In this work, the effects of relative humidity (RH) pre-conditioning (53% vs. 85% RH) and incorporation of cellulose fillers (from Posidonia waste biomass) on the properties and retrogradation of melt compounded starch biocomposites were investigated. Pre-conditioning at 85% RH promoted starch gelatinization during processing, leading to more amorphous materials with reduced stiffness but better barrier properties. Furthermore, these films were less stable upon storage due to greater starch retrogradation. Cellulose incorporation improved significantly the mechanical and water barrier performance, especially in the films pre-conditioned at 85% RH due to enhanced filler dispersion. Although incomplete gelatinization of the starch pre-conditioned at 53% RH led to films with bigger cellulose aggregates, their mechanical and water barrier properties were better, outperforming starch-cellulose biocomposites typically reported in the literature. Moreover, the presence of cellulose limited the degree of starch retrogradation upon storage, highlighting the potential of Posidonia biomass as a cheap source of high-performance fillers.

Rheological and structural properties of complex arabinoxylans from Plantago ovata seed mucilage under non-gelled conditions

Two gel-forming arabinoxylan (AX) fractions with very similar linkage composition and molecular weight distributions have been isolated from Plantago ovata seed mucilage. Both isolated fractions have distinct gel properties attributed to differences in intermolecular hydrogen bonding. This study probes the effect of hydrogen bonding on molecular interactions of P. ovata AX fractions under non-gelled conditions achieved using a mild hydrogen bonding inhibitor, 0.2 M KOH. Chain conformation, relaxation dynamics and interactions between AX molecules are investigated using a combination of rheological techniques and small angle X-ray and neutron scattering. The scattering data confirm similar molecular dimensions and chain rigidity for both fractions, while showing distinct patterns of molecular interactions which result in the formation of a self-associated polymer network. The relationship between molecular associations, chain relaxation time and entanglement behaviour of P. ovata AX solutions are corroborated though the analysis of flow profiles and small amplitude oscillatory shear rheology.

Self-assembled gelatin-ι-carrageenan encapsulation structures for intestinal-targeted release applications

In this work, natural biopolymeric encapsulation structures were developed through the self-assembly of gelatin and ι-carrageenan in aqueous solutions. The interactions of this binary system and of a ternary system containing a polyphenol-rich extract were deeply explored for the development of intestinal delivery systems. The processing of the structures (extrusion vs. freeze-drying) greatly influenced release properties, explained by the specific interactions between gelatin and polyphenols, thus allowing for tuning the processing conditions depending on the desired target application. Release was further controlled by incorporating a divalent salt, giving raise to extract-loaded ι-carrageenan/gelatin capsules with adequate release profiles for intestinal targeted delivery. These results demonstrate the potential of exploiting biopolymer interactions for designing bioactive delivery systems using environmentally friendly processes which do not involve the use of toxic or harsh solvents or cross-linkers.

Nanostructuring Biopolymers for Improved Food Quality and Safety

Food-grade biopolymers, apart from their inherent nutritional properties, can be tailored designed for improving food quality and safety, either serving as delivery vehicles for bioactive molecules, or as novel packaging components, not only improving the transport properties of biobased packaging structures, but also imparting active antibacterial and antiviral properties. In this chapter, the potential of different food-grade biopolymers (mainly proteins and carbohydrates but also some biopolyesters) to serve as encapsulating matrices for the protection of sensitive bioactives or as nanostructured packaging layers to improve transport properties and control the growth of pathogenic bacteria and viruses are described based on some developments carried out by the authors, as well as the most prominent works found in literature in this area.

Hierarchical architecture of bacterial cellulose and composite plant cell wall polysaccharide hydrogels using small angle neutron scattering

Small angle neutron scattering (SANS) has been applied to characterise the structure of pure bacterial cellulose hydrogels, and composites thereof, with two plant cell wall polysaccharides (arabinoxylan and xyloglucan). Conventional published models, which assume that bacterial cellulose ribbons are solid one-phase systems, fail to adequately describe the SANS data of pure bacterial cellulose. Fitting of the neutron scattering profiles instead suggests that the sub-structure of cellulose microfibrils contained within the ribbons results in the creation of regions with distinct values of neutron scattering length density, when the hydrogels are subjected to H2O/D2O exchange. This may be represented within a core-shell formalism that considers the cellulose ribbons to comprise a core containing impermeable crystallites surrounded by a network of paracrystalline cellulose and tightly bound water, and a shell containing only paracrystalline cellulose and water. Accordingly, a fitting function comprising the sum of a power-law term to account for the large scale structure of intertwined ribbons, plus a core-shell cylinder with polydisperse radius, has been applied; it is demonstrated to simultaneously describe all SANS contrast variation data of pure and composite bacterial cellulose hydrogels. In addition, the resultant fitting parameters indicate distinct interaction mechanisms of arabinoxylan and xyloglucan with cellulose, revealing the potential of this approach to investigate the role of different plant cell wall polysaccharides on the biosynthesis process of cellulose.

Antimicrobial Poly(lactic acid)-Based Nanofibres Developed by Solution Blow Spinning

The present study reports on the development of hybrid poly(lactic acid) (PLA) fibres loaded with highly crystalline bacterial cellulose nanowhiskers (BCNW) by the novel solution blow spinning method. Furthermore, fibres with antimicrobial properties were generated by incorporating carvacrol and THC as antimicrobial agents and the biocide effect against Listeria monocytogenes was studied. Initially, PLA blow spun fibres containing BCNW were optimized in terms of morphology and thermal properties. The addition of BCNW was seen to significantly increase the viscosity and surface tension of solutions, restricting the capacity to form fibres for concentrations greater than 30 wt.-% BCNW. 15 wt.-% BCNW was selected as the optimum nanofiller loading as it led to the most uniform fibres morphology, with BCNW homogeneously distributed along the fibres' axis. Subsequently, carvacrol and THC were incorporated into the fibres to confer them with antimicrobial properties, although the hydrophobic PLA matrix did not provide an efficient release of the antimicrobials. Thus, hydrophilic substances were added in order to trigger the antimicrobials release through water sorption mechanisms. The addition of the BCNW filler was not seen to significantly increase the antimicrobial capacity of the fibres by itself and, hence, gelatin was added to help promoting further the hydrophylicity and biocide performance of the fibres. Nevertheless, for the more hydrophilic THC, the biocide capacity of the fibres with gelatin was accentuated further by the presence of the BCNW.

Optimization of the dispersion of unmodified bacterial cellulose nanowhiskers into polylactide via melt compounding to significantly enhance barrier and mechanical properties

In the present study, property-enhanced polylactide (PLA) nanocomposites containing bacterial cellulose nanowhiskers (BCNW) were prepared by melt compounding. With the aim of improving the nanocrystals' dispersion in the final melt processed nanocomposites, these were preincorporated either into PLA nanostructured fibers by electrospinning or into an ethylene vinyl-alcohol copolymer (EVOH) by solution precipitation. An optimized dispersion of the nanofiller in the nanocomposites produced by applying these preincorporation methods, when compared to the direct melt mixing of the freeze-dried nanowhiskers with the polymeric matrix, was confirmed by morphological studies. Enhanced dispersion of BCNW was critical for enhancing the barrier and mechanical properties of the nanocomposites. Thus, for concentrations around the percolation threshold, that is, 2-3 wt % BCNW, nanocomposites produced by the electrospinning preincorporation method showed increased elastic modulus and tensile strength, preserving the ductility of the pure PLA. Moreover, in the optimized nanocomposites the water permeability of PLA was reduced by 43% and the oxygen barrier also decreased to a significant extent. This paper provides a successful route to solve the long-standing issue related to the dispersion of highly polar unmodified cellulose nanowhiskers into PLA via the industrially meaningful melt compounding processing.