Cellulose nanocrystal/low methoxyl pectin gels produced by internal ionotropic gelation.

The biotechnological applications of cellulose nanocrystals (CNCs) continue to grow due to their sustainable nature, impressive mechanical, rheological, and emulsifying properties, upscaled production capacity, and compatibility with other materials, such as protein and polysaccharides. In this study, hydrogels from CNCs and pectin, a plant cell wall polysaccharide broadly used in food and pharma, were produced by calcium ion-mediated internal ionotropic gelation (IG). In the absence of pectin, a minimum of 4 wt% CNC was needed to produce self-supporting gels by internal IG, whereas the addition of pectin at 0.5 wt% enabled hydrogel formation at CNC contents as low as 0.5 wt%. Experimental data indicate that CNCs and pectin interact to give robust and self-supporting hydrogels at solid contents below 2.5 %. Potential applications of these gels could be as carriers for controlled release, scaffolds for cell growth, or wherever else distinct and porous network morphologies are required.

Formation of Cellulose-Based Composites with Hemicelluloses and Pectins Using Komagataeibacter Fermentation.

Komagataeibacter xylinus synthesizes cellulose in an analogous fashion to plants. Through fermentation of K. xylinus in media containing cell wall polysaccharides from the hemicellulose and/or pectin families, composites with cellulose can be produced. These serve as general models for the assembly, structure, and properties of plant cell walls. By studying structure/property relationships of cellulose composites, the effects of defined hemicellulose and/or pectin polysaccharide structures can be investigated. The macroscopic nature of the composites also allows composite mechanical properties to be characterized.The method for producing cellulose-based composites involves reviving and then culturing K. xylinus in the presence of desired hemicelluloses and/or pectins. Different conditions are required for construction of hemicellulose- and pectin-containing composites. Fermentation results in a floating mat or pellicle of cellulose-based composite that can be recovered, washed, and then studied under hydrated conditions without any need for intermediate drying.

Alginate and HM-pectin in sports-drink give rise to intra-gastric gelation in vivo.

The addition of gelling polysaccharides to sport-drinks may provide improved tolerability of drinks with high concentration of digestible carbohydrates (CHO), otherwise known to increase the risk of gastro-intestinal complaints among athletes under prolonged exercise. The physico-chemical properties of a drink containing 14 wt% of digestible CHO (0.7 : 1 fructose and maltodextrin-ratio), 0.2 wt% of HM-pectin/alginate and 0.06 wt%. sodium chloride were examined under in vitro gastric conditions using rheology and large deformation testing. The in vivo gelling behaviour of the drink was studied using magnetic resonance imaging of subjects at rest together with blood glucose measurements. The in vivo results confirm gelation of the test drink, with no gel remaining in the stomach at 60 min and blood glucose values were similar to control. The physico-chemical characterisation of the acidified test drink confirms the formation of a weak gel through which low Mw CHO can diffuse.

Adsorption isotherm studies on the interaction between polyphenols and apple cell walls: Effects of variety, heating and drying.

The adsorption capacity of principal phenolic compounds onto cell walls from three apple varieties was investigated. Isothermal adsorption modelled with Langmuir, Freundlich and Redlich-Peterson equations were carried out over a range of concentrations from 0.5 to 30 mM before and after cell walls were subjected to boiling, oven-drying or freeze-drying. The isotherm data were best fitted by the Langmuir model in all cases. Polyphenols selectively adsorbed onto cell walls with maximum binding capacities ranging from 140 to 580 µg/mg cell walls depending on surface charge. Increased pectin in apple cell walls caused a 129%-311% decrease in the adsorption of negatively charged polyphenols, presumably due to electrostatic repulsive forces. Boiling had limited effect on cell wall polysaccharides and polyphenol-cell wall interactions. However, more than twofold reduction in binding capacities of polyphenols was induced after drying by altering the structural (i.e. binding sites) and compositional (i.e. pectin degradation) characteristics of cell walls.

Cellulose-pectin composite hydrogels: Intermolecular interactions and material properties depend on order of assembly.

Plant cell walls have a unique combination of strength and flexibility however, further investigations are required to understand how those properties arise from the assembly of the relevant biopolymers. Recent studies indicate that Ca2+-pectates can act as load-bearing components in cell walls. To investigate this proposed role of pectins, bioinspired wall models were synthesised based on bacterial cellulose containing pectin-calcium gels by varying the order of assembly of cellulose/pectin networks, pectin degree of methylesterification and calcium concentration. Hydrogels in which pectin-calcium assembly occurred prior to cellulose synthesis showed evidence for direct cellulose/pectin interactions from small-angle scattering (SAXS and SANS), had the densest networks and the lowest normal stress. The strength of the pectin-calcium gel affected cellulose structure, crystallinity and material properties. The results highlight the importance of the order of assembly on the properties of cellulose composite networks and support the role of pectin in the mechanics of cell walls.

Pectin impacts cellulose fibre architecture and hydrogel mechanics in the absence of calcium.

Pectin is a major polysaccharide in many plant cell walls and recent advances indicate that its role in wall mechanics is more important than previously thought. In this work cellulose hydrogels were synthesised in pectin solutions, as a biomimetic tool to investigate the influence of pectin on cellulose assembly and hydrogel mechanical properties. Most of the pectin (60-80%) did not interact at the molecular level with cellulose, as judged by small angle scattering techniques (SAXS and SANS). Despite the lack of strong interactions with cellulose, this pectin fraction impacted the mechanical properties of the hydrogels through poroelastic effects. The other 20-40% of pectin (containing neutral sugar sidechains) was able to interact intimately with cellulose microfibrils at the point of assembly. These results support the need to revise the role of pectin in cell wall architecture and mechanics, and; furthermore they assist the design of cellulose-based products through controlling the viscoelasticity of the fluid phase.

Binding of arabinan or galactan during cellulose synthesis is extensive and reversible.

Arabinans and galactans are major components of the side-chains of pectin in plant cell walls. In order to understand how pectin side-chains interact with cellulose, in this work we studied the interaction of de-branched arabinan (from sugar beet) and linear galactan (from potato) during the synthesis of cellulose by Gluconacetobacter xylinus (ATCC 53524) to mimic in muro assembly. The binding studies reveal that arabinan and galactan are able to bind extensively (>200mg/g of cellulose) during cellulose deposition, and more than pectin (from apple) in the absence of calcium. (13)C NMR revealed that associated arabinan, galactan or apple pectin molecules were neither rigid nor affected cellulose crystallinity, and there was no apparent change in cellulose architecture as reflected in scanning electron micrographs. De-binding of arabinan, galactan or apple pectin occurred as a result of washing, indicating a reversible binding to cellulose, which was modelled in terms of a surface-controlled process. Implications for structural models of primary plant cell walls and possible roles for cellulose binding of arabinan- and galactan-rich pectins in biological processes are discussed.

Comprehensive metabolomics to evaluate the impact of industrial processing on the phytochemical composition of vegetable purees.

The effects of conventional industrial processing steps on global phytochemical composition of broccoli, tomato and carrot purees were investigated by using a range of complementary targeted and untargeted metabolomics approaches including LC-PDA for vitamins, (1)H NMR for polar metabolites, accurate mass LC-QTOF MS for semi-polar metabolites, LC-MRM for oxylipins, and headspace GC-MS for volatile compounds. An initial exploratory experiment indicated that the order of blending and thermal treatments had the highest impact on the phytochemicals in the purees. This blending-heating order effect was investigated in more depth by performing alternate blending-heating sequences in triplicate on the same batches of broccoli, tomato and carrot. For each vegetable and particularly in broccoli, a large proportion of the metabolites detected in the purees was significantly influenced by the blending-heating order, amongst which were potential health-related phytochemicals and flavour compounds like vitamins C and E, carotenoids, flavonoids, glucosinolates and oxylipins. Our metabolomics data indicates that during processing the activity of a series of endogenous plant enzymes, such as lipoxygenases, peroxidases and glycosidases, including myrosinase in broccoli, is key to the final metabolite composition and related quality of the purees.

Rheology and microstructure of carrot and tomato emulsions as a result of high-pressure homogenization conditions.

High-pressure homogenization, as a way to further mechanically disrupt plant cells and cell walls compared to conventional blending, has been applied to thermally treated and comminuted carrot and tomato material in the presence of 5% olive oil. Mixes of both vegetables in a 1:1 ratio were also included. Both the effect of homogenization pressure and the effect of multiple process cycles were studied. The different microstructures generated were linked to different rheological properties analyzed by oscillatory and steady state measurements. The results showed that while carrot tissue requires a high shear input to be disrupted into cells and cell fragments, tomato cells were broken across the cell walls already at moderate shear input, and the nature of the tomato particles changed to amorphous aggregates, probably composed of cell contents and cell wall polymers. All the plant stabilized emulsions generated were stable against creaming under centrifugation. While for tomato a low-pressure multiple cycle and a high-pressure single-cycle process led to comparable microstructures and rheological properties, carrot showed different rheological properties after these treatments linked to differences in particle morphology. Mixes of carrot and tomato showed similar rheological properties after homogenizing in a single or in a split-stream process. Practical Application: Following consumers' demand, the food industry has shown a growing interest in manufacturing products free of gums and stabilizers, which are often perceived as artificial. By tailored processing, fresh plant material could be used to structure food products in a more natural way while increasing their nutritional quality.