Residual Cell Wall Research Articles

Effects of Wood Drying Temperatures on the Reduction in Mechanical Properties of Japanese Cedar (Cryptomeria japonica D. Don) Perpendicular to Grain

Wood drying is often accompanied by changes in mechanical properties due to external thermal energy. This study examined the influences of drying temperature on the mechanical properties of Japanese cedar based on the partial compression properties and bending properties. Two types of longitudinal specimens with quarter grain on both lateral surfaces were prepared under green conditions, followed by subsequent drying under each drying temperature (20 °C, 40 °C, 60 °C, 80 °C, and 100 °C). Then, the partial compression and bending tests were performed using the respective specimens. Young’s modulus perpendicular to grain, yield stress, and compressive strength obtained by the partial compressive test were highest for wood dried at 20 °C. It was considered that the decrease in mechanical properties was attributed to the thermal influences during drying at 100 °C and other factors such as compressive residual stress and cell walls collapsing at lower temperatures. The strain energy suggested that the effects of drying temperature became apparent, especially in the plastic region during loading in the direction perpendicular to the wood fiber. Bending properties showed little influence on drying temperatures compared to the partial compressive properties, whereas the fractures found under the loading point of the wood dried at 100 °C suggested a reduction in resistance to shear forces.

Microscopic and submicroscopic exploration of diplolepideae peristome structures in hygroscopic movement

BackgroundThe Diplolepideae are the larger group within the Arthrodontae mosses, characterized by peristomes formed from residual cell walls. It is now understood that these peristomes exhibit diverse hygroscopic movements, playing a crucial role in spore release. However, the exact mechanism behind this movement remains unclear, lacking direct evidence. This study investigated the microscopic and submicroscopic structures of the peristomes in three Diplolepideae species: Hypopterygium fauriei (Besch.), Pylaisia levieri (Müll. Hal.) Arikawa and Regmatodon declinatus (Hook.) Brid. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to reveal the differences in their hygroscopic movement mechanisms.ResultsThe three species exhibited distinct responses upon wetting: H. fauriei’s exostome closed inwards, P. levieri’ opened outwards, and R. declinatus’ elongated significantly. These differences are attributed to the varying microfibril deposition in the exostome layers. Uniform deposition in the inner layer and minimal deposition in the outer layer enabled exostome opening upon wetting and closing when dry. Our findings suggest that the diastole and contraction of fine microfibrils in the exostome plates and ridges are the key drivers of hygroscopic movement.ConclusionsThis study provides further evidence at both the structural and submicroscopic levels, contributing to the unraveling of the hygroscopic movement mechanism in Diplolepideae peristomes. This enhanced understanding sheds light on the relationship between peristome structure and function.

Tracking digestible and non-digestible cell wall components during protein concentrate production from grass-clover and alfalfa

AbstractGreen biomass from leguminous and gramineous forage crops, such as alfalfa and grass-clover, has been proposed as a potential new source of feed protein concentrates for non-ruminant livestock. However, the efficient separation of the protein fraction from the non-digestible cell components, primarily comprising cell walls (fiber) and starch, presents a significant technological challenge. Moreover, it is crucial to optimize the process to preserve the optimal nutritional value of the final product. This study comprehensively analyzed the non-digestible fiber content and composition across all biorefinery fractions using two different feedstocks: green biomass from alfalfa and grass-clover. The pilot scale refining process involved a combination of screw pressing, lactic acid fermentation, and protein separation via centrifugation. We observed variations in carbohydrate composition and abundance between alfalfa and grass-clover. The lactic acid fermentation led to a reduction in cellulose and total glucose content. Our findings indicate that the final protein concentrate still contains residual cell wall components, including lignin, indicating potential inefficiencies in the filtration, fermentation, and isolation steps. The presented analytical approach provides a valuable framework for optimizing processing conditions and tailoring enzyme cocktails for enhanced valorization of the by-products.

Promoting hierarchical porous carbon derived from Bamboo via copper doping for high-performance supercapacitors

Porous carbon obtained from biomass has emerged as a significant source of electrode materials for supercapacitors. However, the microporous structure of biomass itself and the low doping of elements limit its electrochemical performance. In this work, a Cu doped bamboo/polypyrrole (PPy) based derived porous carbon material was prepared by polymerization of one-dimensional linear polypyrrole in bamboo residual cell walls and synergistic catalysis of citric acid (CA) and copper sulfate (CuSO4) during hydrothermal carbonization. Thanks to the introduction of PPy and the synergistic catalytic effect of CA and CuSO4, the prepared carbon materials had a more moderate pore structure, good heteroatom doping degree, and a richer variety of photo energy groups. The optimized carbon material (HBC/N-CA-Cu) had a large specific surface area (1987.76 m2 g−1) and good capacitive performance (508.50 F g−1 at 0.5 A g−1). The assembled symmetric supercapacitors delivered an energy density of 17.42 Wh kg−1 at the power density of 5000 W kg−1 in Na2SO4 solution. After cycling for 12,000 at a current density of 5 A g−1, the initial specific capacitance could still be maintained at 94.1 %, demonstrating good practical application potential.

Cell wall polysaccharide changes and involvement of phenolic compounds in ageing of Red haricot beans (Phaseolus vulgaris) during postharvest storage

Cell wall material was isolated from selected non-aged and aged Red haricot bean cotyledons using a texture-based classification approach. Pectin-depleted residual cell wall fractions were obtained by sequential pectin extraction and were characterized to investigate in situ cell wall related molecular changes upon ageing during adverse storage of the beans. Particularly, involvement of phenolic compounds in cell wall strengthening during the ageing process, resulting in the hard-to-cook defect, was evaluated. Results show that ageing induces substantial changes at a cell-wall-structural level in the Aged sample compared to the Non-aged sample, with mainly vanillin, 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde covalently bound with sugar side-chains of pectin and/or involved in lignification-like mechanisms. FT-IR spectroscopy coupled with chemometric analysis reveals that lignin-like phenolic-cell wall polymers, which are known to reinforce cell wall structure, are present in the cell wall polysaccharide network of the Aged sample, and are therefore contributing factors to the hard-to-cook development during Red haricot bean ageing.

Targeted pectin depletion enhances the potential of high-pressure homogenization to increase the network forming potential of tomato cell wall material

The current study addresses the influence of pectin depletion on the potential of high-pressure homogenization (HPH) to increase the network forming potential of the cell wall material (CWM) from tomato. Therefore, the microstructure, water binding capacity and viscoelastic properties of the alcohol-insoluble residue (AIR) and unextractable fractions (UFs) obtained after different levels and methods of pectin extraction were determined in suspension before and after functionalization by HPH. Before HPH, the AIR and the UFs obtained by solvent-based pectin extraction were all characterized by particles displaying cell-like morphology and the storage modulus (G′) of the respective suspensions was maximal at partial pectin depletion. The network forming potential of the CWM could only be increased by HPH when extensive disruption of the cell wall network was realized instead of mainly breakage. Even when higher pressure levels were applied (up to 80 MPa), preceding weakening of the cell wall network by pectin extraction was a prerequisite to favor efficient disruption of the CWM during HPH above deformation and breakage. Apart from the effect of partial pectin depletion as such on the cell wall strength, the impact of the extraction conditions (e.g., acid conditions at high temperature) weakening the residual cell wall seemed important. This had repercussions on the potential of HPH to functionalize the CWM. While the G’ decreased upon HPH (evaluated at 20 MPa) for non-pectin-depleted or partially pectin-depleted CWM generated by using mild extraction conditions, a clear increase was observed upon HPH of CWM which was partially or extensively pectin-depleted using harsher extraction conditions.

The Structure and Composition of Extracted Pectin and Residual Cell Wall Material from Processing Tomato: The Role of a Stepwise Approach versus High-Pressure Homogenization-Facilitated Acid Extraction.

In literature, different pectin extraction methods exist. In this study, two approaches starting from the alcohol-insoluble residue (AIR) of processing tomato are performed in a parallel way to facilitate the comparison of pectin yield and the compositional and structural properties of the extracted pectin and residual cell wall material obtained. On the one hand, pectin is extracted stepwise using hot water, chelating agents and low-alkaline conditions targeting fractionation of the pectin population. On the other hand, an industrially relevant single-step nitric acid pectin extraction (pH 1.6) is performed. In addition to these conventional solvent pectin extractions, the role of high-pressure homogenization (HPH) as a physically disruptive treatment to facilitate further pectin extraction from the partially pectin-depleted fraction obtained after acid extraction is addressed. The impact of HPH on the pectin cell wall polysaccharide interactions was shown as almost two thirds of the residual pectin were extractable during the subsequent extractions. For both extraction approaches, pectin obtained further in the sequence was characterized by a higher molecular mass and a higher amount of rhamnogalacturonan I domains. The estimated hemicellulose and cellulose content increased from 56 mol% for the AIR to almost 90 mol% for the final unextractable fractions of both methods.

Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS

AbstractErosion bacteria are the main degraders of archaeological wood excavated from waterlogged environments. Light microscopy and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were exploited to study waterlogged archaeological wood (Pinus sylvestrisL.) at different stages of bacterial decay. The research explored the biochemical changes related to erosion bacteria degradation of the secondary cell wall in the wood cells and the chemical changes related to abiotic processes induced by the long-term waterlogged burial environment. Erosion bacteria were demonstrated by chemical analysis to cause significant holocellulose depletion. Detailed analysis of the holocellulose and lignin pyrolysis products revealed only minor chemical changes in the residual structure even after heavy erosion bacteria decay. Chemical changes in the lignin polymer is associated to enzymatic unlocking of the lignocellulose to gain access to the holocellulose fraction of the cell wall. Chemical changes in the holocellulose fraction are suggested to stem from depolymerisation and from alterations in the polymer matrix of the residual wood cell wall structure. Interestingly, a difference was observed between the sound reference wood and the waterlogged archaeological wood without erosion bacteria decay, indicating that long-term exposure in waterlogged environments results in partial decay of the holocellulose even in absence of bacterial activity.

Surface Activity and Foaming Capacity of Aggregates Formed between an Anionic Surfactant and Non-Cellulosics Leached from Wood Fibers.

This study relates to the release of non-cellulosic components (cell wall heteropolysaccharides, lignin, and extractives) from swollen wood fibers in the presence of an anionic surfactant (sodium dodecyl sulfate, SDS) at submicellar concentrations. Highly surface-active aggregates form between SDS and the leached, non-cellulosic components, which otherwise do not occur in the presence of cationic or nonionic surfactants. The in situ and efficient generation of liquid foams in the presence of the leached species is demonstrated. The foaming capacity and foam stability, as well as the foam’s structure, are determined as a function of the composition of the aqueous suspension. The results indicate that naturally occurring components bound to wood fibers are extractable solely with aqueous solutions of the anionic surfactant. Moreover, they can form surface-active aggregates that have a high foaming capacity. The results further our understanding of residual cell wall components and their role in the generation of foams.

Reinforcing effect of poly(furfuryl alcohol) in cellulose-based porous materials

The mechanical reinforcement of porous materials made of microfibrillated cellulose by in situ polymerisation of furfuryl alcohol prior to freeze-drying from aqueous slurry was studied. Besides a slight improvement in the modulus of elasticity measured in compression testing, no beneficial effects of furfuryl alcohol addition on porous materials produced from microfibrillated cellulose derived from bleached softwood pulp were observed. By contrast, when microfibrillated cellulose containing substantial amounts of residual non-cellulosic cell wall polymers, termed microfibrillated lignocellulose, was used, clear mechanical reinforcement effects due to furfuryl alcohol addition were measured. By means of SEM, significantly improved wetting of the cellulosic fibrillary architecture of porous materials with furfuryl alcohol was observed for microfibrillated lignocellulose compared to microfibrillated cellulose. It is proposed that the specific surface-chemical character of microfibrillated lignocellulose enables wetting of fibrils with furfuryl alcohol, thus providing micron fibre-reinforced structures with improved strength after in situ polymerisation. Besides mechanical properties, the density and thermal stability of cellulose-based porous materials were found to increase with increasing amounts of furfuryl alcohol added to the initial reaction slurry.Graphical abstract

Use of Residual Yeast Cell Wall for New Biobased Materials Production: Effect of Plasticization on Film Properties

The use of renewable resources to develop food contact materials, such as proteins or polysaccharides, and the use of industrial residues for alternative applications are trending topics for researchers and the industry. Yeast cell wall (YCW) is a very rich waste from the yeast extract industry. Due to this, the aim of this work is to develop new biodegradable films based on residual YCW and the study of the effect of plasticization on films properties. Residual YCW was used as base matrix and different concentrations of glycerol (0, 15, 25 and 35 wt%) were tested to obtain casted films. Homogeneous and yellow-brownish films, which allow seeing through them, were obtained from the YCW. Total soluble matter demonstrated that glycerol enhanced solubility of films but glycerol was retained in the polymer matrix. TGA studies indicated that YCW films exhibited substantial degradation at temperatures above 180 °C. FTIR spectra of the casted films were representative of yeast cell wall material and SEM photographs showed that cell wall maintained their shape after film formation. As expected, Young’s modulus and tensile strength values were decreased with the increasing amount of glycerol. However, elongation at break was not increased further with higher concentration of plasticizer and the addition of 15 wt% of glycerol seemed to be enough to improve mechanical properties. The linear increment of water vapour permeability with glycerol concentration was produced by the increase in water solubility in the film. Therefore, based on solubility in water, mechanical, and barrier properties, it is possible to propose yeast cells residues as film-forming material for biodegradable film developments.

Identification and feeding characteristics of the mixotrophic flagellate Poterioochromonas malhamensis, a microalgal predator isolated from outdoor massive Chlorella culture

Chlorella is a strong candidate as a potential production organism for future biofuels and other algal-derived products, but contamination by grazing protozoa is a major constraint to its commercial production on a large scale. In this study, a mixotrophic flagellate chrysophyte that targeted Chlorella in mass culture was observed in samples from outdoor massive photobioreactor systems. Data from field studies demonstrated that once the predatory flagellate was observed in the algal culture, there was a dramatic reduction in Chlorella cell concentration. The grazer was identified as Poterioochromonas malhamensis, based on both morphology and molecular barcoding employing 18S rDNA gene sequences. Transmission electron microscopy revealed that P. malhamensis digested the ingested Chlorella sorokiniana cells within a food vacuole, with residual cell wall from the prey being observed in the final phase. It was noted that during the process of ingesting and digesting the C. sorokiniana cells, the chloroplast of P. malhamensis reduced in size, whereas the number and volume of mitochondria increased. After the prey had been completely digested, the chloroplast and mitochondria of P. malhamensis returned to their pre-feeding status. Feeding experiments in the laboratory demonstrated that cell concentrations of C. sorokiniana and P. malhamensis were negatively correlated. Furthermore, once P. malhamensis reached 5×105cellsmL−1 and the ratio of C. sorokiniana to P. malhamensis was in the range 15:1 to 30:1, the cell concentration of the C. sorokiniana culture decreased dramatically. The optimal temperature for P. malhamensis grazing on C. sorokiniana was 25°C; the grazing ability of P. malhamensis in light conditions was higher than that in dark conditions; and P. malhamensis preferred weakly acidic conditions. In addition, it was demonstrated that this flagellate could graze on other common microalgae of commercial value. On the basis of its capacity to ingest a wide spectrum of phytoplankton, and its wide environmental range and global distribution, this contaminant has the potential to be a common problem in microalgal mass cultures and warrants further study.

Complementary effects of cell wall degrading enzymes together with lactic acid fermentation on cassava tuber cell wall breakdown

Entrapment of starch granules within cassava parenchyma cells constitutes a major challenge in starch extraction from cassava tuber. This was addressed by applying cellulolytic and hemicellulolytic enzymes coupled with spontaneous lactic acid bacteria fermentation in the pre-treatment of wet milled cassava. The hydrolytic activities of the enzymes and pH lowering by the fermentation resulted in fragmentation of the cassava cell walls, with an improved release of free starch granules. The residual cell wall material after the treatments was characterized by microscopy and gas chromatography. Lignified material was resistant to hydrolysis. Material that was not hydrolysed by the enzymes consisted of arabinose, galactose, rhamnose, xylose and glucose, with the latter two the most abundant. It appears that the gums and hemicelluloses were hydrolysed first, enabling subsequent hydrolysis of the cellulosic materials. The complementary effects of these treatments could improve wet milling extraction of cassava starch.

Effects of diverse food processing conditions on the structure and solubility of wheat, barley and rye endosperm dietary fibre

The effects of archetypal food processing conditions (dough formation, baking, extrusion, and cooking/boiling) on dietary fibre structure and extractability from the endosperm flours of rye, hull less barley and wheat are reported. For all flours and processes, the distributions of soluble/insoluble cell wall dietary fibre as well as the chemical composition (arabinoxylan (AX) branching patterns, β-glucan DP3/DP4 (DP = degree of polymerisation) ratios) of solubilised fractions were characterised. The results show that overall the total amounts of AX and β-glucan (BG) were not significantly affected by processing but that there were similar increases in the soluble fibre fraction (20–29%) for baked, extruded, and boiled/cooked processes for each flour, with lower (10–15%) increases for all flours processed into dough. In all cases, solubilised fractions of AX and BG had very similar chemical structures to the starting flour, suggesting that increased solubilisation was not due to specific chemical fractions. Confocal images illustrate loosely-held associations of β-glucan with the cell walls of processed foods in contrast to some of the arabinoxylans which appear more tightly held within the residual cell walls. The similarities in behaviour across the three grains are consistent with mechanical treatments during food preparation resulting in similar extents of disentanglement of physically-constrained AX and BG leading to their partial solubilisation.

Contrasting effects of extracellular polymeric substances on the surface characteristics of bacterial pathogens and cell attachment to soil particles

Extracellular polymeric substances (EPSs) have been confirmed to affect bacterial surface properties and cell attachment to minerals. However, no systematic work has been done to clarify the contrasting roles of EPS in cell attachment to natural soil between different pathogenic strains. This study compared the different surface properties and attachment behaviors of two bacterial pathogens (with full or partial EPS) using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, potentiometric titration, zeta potential, hydrophobicity analysis, DLVO theory, and attachment tests. Cation exchange resin (CER) was employed to remove the EPS on Streptococcus suis and Escherichia coli such that the contribution of EPS to cell attachment to soil could be determined. ATR-FTIR confirmed the binding sites differed between S. suis and E. coli EPS. Notably, after partial EPS removal the absorption bands of S. suis between 1800cm−1 and 800cm−1 shifted or disappeared, whereas the lack of EPS did not affect the infrared absorption peaks for E. coli. This result suggests the overall surface site types within the E. coli EPS were similar to the residual EPS fractions or cell wall. The partial removal of EPS also changed the proton-active site concentrations of both cell types, and reduced the bacterial surface charge densities by 7%–17%. The negative charges on bacterial surfaces followed the order of full EPS-S. suis<partial EPS-S. suis<partial EPS-E. coli<full EPS-E. coli (ionic strength 1–100mM; pH5.6–5.8). With the removal of EPS, the average hydrophobicities of S. suis increased by 5% while those of E. coli decreased by 11%. EPS removal inhibited the attachment of S. suis to soil particles (<2mm) but enhanced E. coli attachment across the IS range of 1–100mM, which was attributed to the alteration in electrostatic repulsion. At IS 60–100mM, a sudden reduction in the attachment was observed only for full EPS-S. suis, which could be ascribed to the steric hindrance derived from EPS. However, full EPS-E. coli and partial EPS-E. coli showed similar increasing attachment trends at IS 1–100mM. This study clearly showed the distinct contribution of EPS to pathogen attachment to soil as a function of cell type and EPS present.

The influence of proteolytic and cytolytic enzymes on starch degradation during mashing

The objective of this research was to investigate the impact of proteolysis and cytolysis on starch degradation over the course of the mashing process. A proteolytic enzyme (Neutrase 0.8L, Novozymes) and a number of cytolytic enzymes (barley β-glucanase from Megazyme, Shearzyme 500L and Ultraflo Max from Novozymes) were used to test their efficiency on starch degradation during mashing. The proteolytic and cytolytic enzymes had positive effects on the levels of starch-degrading enzymes and starch solubilization during mashing, resulting in higher levels of wort sugar compared with the control, indicating that proteins and residual non-starchy polysaccharides limited the digestibility of starch during mashing. Moreover, the proteolytic enzyme showed a significantly greater improvement than the cytolytic enzymes, yielding a 57% increase in β-amylase, a 173% increase in limit dextrinase, rapid starch solubilization during mashing and a higher percentage of fermentable sugars in resultant wort. The increases in limit dextrinase and β-amylase promoted by the protease suggest that sufficient proteinaceous inhibitor existed in the wort during mashing to inhibit their activities, leading to the unavailability of β-amylase and especially limiting dextrinase. Furthermore, Ultraflo Max, which contained a β-glucanase–xylanase mixture, showed a greater improvement than either the individual β-glucanase or the xylanase on starch hydrolysis. These findings suggest that β-glucanase is the major enzyme responsible for the degradation of cell walls, and that the complete hydrolysis of the residual cell walls depends on the synergistic effect of β-glucanase and xylanase. The results suggest that brewers should adjust the degradation of the cell walls and correct the degree of protein modification in order to obtain the desired wort composition. Copyright © 2014 The Institute of Brewing & Distilling

Investigation into the deterioration process of archaeological bamboo strips of China from four different periods by chemical and anatomical analysis

The chemical and the anatomical features of the archeological bamboo strips of China from four different periods were compared with the non-degraded fresh bamboo to understand the deterioration process. Unprocessed bamboo strips, isolated hemicelluloses and lignin fractions were analyzed with wet chemical analysis, GC, FTIR, UV and XRD to investigate the chemical degradation. It was found that the crystalline cellulose and the polyxylose degraded with increasing age, leaving the amorphous cellulose and the lignin with syringyl moieties modified as the main residual cell wall materials. Serious degradation of p-coumaric acid and ferulic acid were detected and indicated the cleavage of the linkage between the lignin and the carbohydrate, which might facilitate the degradation of carbohydrate. The anatomical analysis with SEM and TEM revealed the vanishing of the parenchymatous ground tissue and vessels and the cellulose microfibrils in the multilayered secondary wall. The differences in lignin content and in tissue density (cell thickness/cell size) between the parenchyma cells and the sclerenchymatous fiber cells fundamentally led to the formation of the unique anatomical structure of the archeological bamboo strips which was composed of parallel solid bundles. The effects of the chemical and the anatomical degradation on the mechanical properties were also discussed.

Characterisation of soluble and insoluble cell wall fractions from rye, wheat and hull-less barley endosperm flours

Within cereal endosperm flours, arabinoxylan and β-glucan molecules exist in either a soluble or an insoluble form. From a nutritional functionality viewpoint, soluble and insoluble forms offer different potential health advantages, so it is important to define both the features controlling solubilisation and the properties of each of the soluble and insoluble fractions. Factors known to affect the stability of arabinoxylan (AX) and β-glucan (BG) solutions include AX branching extent and type, and the ratio of cellotriose to cellotetraose units (DP3/DP4) in BG. Through studying the solubilisation of AX and BG from wheat, rye, and hull less barley endosperm under conditions that avoid the use of alkali or ethanol during the solubilisation process, we report (a) similar A/X ratios and fine structures for extracted soluble arabinoxylan and the corresponding insoluble AX within the cell walls for rye and wheat endosperm flours, (b) comparable DP3/DP4 ratios for soluble β-glucan, flour and insoluble β-glucan within the endosperm cell wall of hull less barley, and (c) evidence for enrichment of β-glucan at the exterior of residual insoluble cell walls. Therefore, the factors determining solubilisation of AX and BG from endosperm cell walls are different to those that determine the stability of aqueous solutions of the same polymers, and β-glucan may show limited solubilisation by being trapped within restraining cross-linked arabinoxylans in the cell wall.

Separation and Purification of Soluble Polymers and Cell Wall Fractions from Wheat, Rye and Hull less Barley Endosperm Flours for Structure-Nutrition Studies

The nutritional values associated with the cell walls of cereal endosperm flours are due to a combination of solubilized arabinoxylan and (1-3,1-4)-β-d-glucan as well as residual nonsolubilized cell wall material. In order to investigate structure-nutrition relationships, an appropriate method for the complete functional and structural characterization of cell wall polysaccharides in various cereal endosperm flours is described. This involves the separation of soluble polymers and the residual cell wall fraction without using organic solvents, and the fractionation of soluble polymers into arabinoxylan- and (1-3,1-4)-β-d-glucan-rich fractions for subsequent analysis. This methodology is applied to endosperm flours from wheat, hull-less barley and rye, and could be extended to include studies on the effects of food processing with respect to yield and characteristics of the three fractions in order to better understand the structural basis for nutritional functionality.

Effect of residual lignin and heteropolysaccharides in nanofibrillar cellulose and nanopaper from wood fibers

Unbleached (UN), oxygen-delignified and fully-bleached (FB) birch fibers with a residual lignin content of ca. 3, 2 and <1 %, respectively, were used to produce nanofibrillated cellulose (NFC) and nanopaper by using an overpressure device. The tensile index, elongation and elastic modulus of nanopaper were compared and the effect of residual cell wall components accessed. Under similar manufacturing conditions, UN NFC produced nanopaper with a density of 0.99 g/cm3, higher than that from FB NFC (0.7 g/cm3). This translated in much lower air permeability in the case of UN nanopaper (1 and 11 mL/min for UN and FB samples, respectively). Fundamentally, these observations are ascribed to the finer fibrils produced during microfluidization of UN fibers compared to those from lower yield counterparts (AFM roughness of 8 and 17 nm and surface areas of 124 and 98 m2/g for NFC from UN and FB fibers, respectively). As a result, values of stress at break and energy absorption of nanopaper from high yield fibers are distinctively higher than those from fully bleached NFC. Interactions of water with the surface and bulk material were affected by the chemical composition and structure of the nanofibrils. While UN nanopaper presented higher water contact angles their sorption capacity (and rate of water absorption) was much higher than those measured for nanopaper from FB NFC. These and other observations provided in this contribution are proposed to be related to the mechanoradical scavenging capacity of lignin in high shear microfluidization and the presence of residual heteropolysaccharides.