Justyna Cybulska

Sensing the structural differences in cellulose from apple and bacterial cell wall materials by Raman and FT-IR spectroscopy.

Raman and Fourier Transform Infrared (FT-IR) spectroscopy was used for assessment of structural differences of celluloses of various origins. Investigated celluloses were: bacterial celluloses cultured in presence of pectin and/or xyloglucan, as well as commercial celluloses and cellulose extracted from apple parenchyma. FT-IR spectra were used to estimate of the Iβ content, whereas Raman spectra were used to evaluate the degree of crystallinity of the cellulose. The crystallinity index (XCRAMAN%) varied from −25% for apple cellulose to 53% for microcrystalline commercial cellulose. Considering bacterial cellulose, addition of xyloglucan has an impact on the percentage content of cellulose Iβ. However, addition of only xyloglucan or only pectins to pure bacterial cellulose both resulted in a slight decrease of crystallinity. However, culturing bacterial cellulose in the presence of mixtures of xyloglucan and pectins results in an increase of crystallinity. The results confirmed that the higher degree of crystallinity, the broader the peak around 913 cm−1. Among all bacterial celluloses the bacterial cellulose cultured in presence of xyloglucan and pectin (BCPX) has the most similar structure to those observed in natural primary cell walls.

The relation of apple texture with cell wall nanostructure studied using an atomic force microscope

In this study, the relation of the nanostructure of cell walls with their texture was investigated for six different apple cultivars. Cell wall material (CWM) and cellulose microfibrils were imaged by atomic force microscope (AFM). The mean diameter of cellulose microfibrils for each cultivar was estimated based on the AFM height topographs obtained using the tapping mode of dried specimens. Additionally, crystallinity of cellulose microfibrils and pectin content was determined. Texture of apple cultivars was evaluated by sensory and instrumental analysis. Differences in cellulose diameter as determined from the AFM height topographs of the nanostructure of cell walls of the apple cultivars are found to relate to the degree of crystallinity and pectin content. Cultivars with thicker cellulose microfibrils also revealed crisper, harder and juicier texture, and greater acoustic emission. The data suggest that microfibril thickness affects the mechanical strength of cell walls which has consequences for sensory and instrumental texture.

Relation of Biospeckle Activity with Quality Attributes of Apples

Biospeckle is nondestructive optical technique based on the analysis of variations of laser light scattered from biological samples. Biospeckle activity reflects the state of the investigated object. In this study the relation of biospeckle activity (BA) with firmness, soluble solids content (SSC), titratable acidity (TA) and starch content (SC) during the shelf life of seven apple cultivars was studied. The results showed that the quality attributes change significantly during storage. Significant and pronounced positive correlation between BA and SC was found. This result shows that degradation of starch granules, which could be stimulated to vibration by intracellular cyclosis, causes a lesser number of laser light scattering centers and results in smaller apparent biospeckle activity.

Physicochemical characterization of exopolysaccharides produced by Lactobacillus rhamnosus on various carbon sources

The impact of five carbohydrate sources (glucose, maltose, galactose, sucrose, and lactose) on the chemical composition, structure, morphology, and physicochemical properties, as well as, viscosity of exopolysaccharides (EPSs) produced by Lactobacillus rhamnosus E/N was investigated. GLC-MS analysis and 2DNMR spectroscopy showed that the EPSs had the same primary structure independently of the carbon source used in the growth medium. The following EPS composition was elucidated: four rhamnose, two glucose, and one galactose residue with a pyruvate substituent. Molecular masses (M(w)) were determined by gel permeation chromatography, which revealed differences in M(w) distribution. EPS-Gal, EPS-Suc, and EPS-Lac showed heterogenic fractions of a high and low molecular weight, while EPS-Mal and EPS-Glc contained only a high-molecular-weight fraction. AFM microscopy revealed morphological differences in chain length, thickness, and branching. Differences in the Mw ratio and thickness of the polymer chain were correlated with high viscosity of EPS solutions. Our results indicate that a single bacterial strain, depending on the carbon source in the medium, can produce EPSs of different rheological properties.

Changes of pectin nanostructure and cell wall stiffness induced in vitro by pectinase

Structural modifications of fruit cell-wall pectins are controlled by various enzymes. In this in vitro study, the cell wall material (CWM) from pear fruit (Pyrus communis L.) was treated using pectinases in two concentrations. Water soluble (WSP), chelator soluble (CSP) and sodium carbonate soluble (DASP) pectin fractions were extracted from CWM. By visualization of enzymatic-induced changes of structure and CWM stiffness using an atomic force microscopy (AFM), the role of pectins in the mechanical properties of cell walls was shown. Galacturonic acid (GalA) content in pectin fractions was assayed as well. This experiment unveiled evidence of the structural degradation of molecules in pectin fractions extracted from CWM caused by in vitro pectinase action and softening of CWM due to pectin removal that might be related to the creation of empty spaces in the cellulose-hemicellulose network.

Rheological and chemical properties of pectin enriched fractions from different sources extracted with citric acid.

Yield, properties and functionality of pectins depend on the source material and method of extraction. The objective of this work was to compare pectinolytic enzyme activity in fresh pulp as well as the physicochemical and rheological properties of polysaccharides extracted with citric acid from six new potential sources: fruit materials - peach, blackcurrant, raspberry, strawberry, plum and a vegetable Source: carrot. The uronic acid content of polysaccharides extracted in citric acid depended on pectinolytic enzymes activity in fresh plant tissues and ranged between 16.5 and 37.1%; which are slightly lower values than those of commercial pectins isolated from citrus and apple. The values of examined rheological parameters (viscosity, thixotropic effect, flow behaviour) demonstrated quality and possibility of pectin enriched fraction application as a food texture modifier. Pectin enriched fractions extracted from seasonal fruit and carrot with citric acid showed considerable potential as thickeners and gelling agents.

Simulation of Force Spectroscopy Experiments on Galacturonic Acid Oligomers

Pectins, forming a matrix for cellulose and hemicellulose, determine the mechanics of plant cell walls. They undergo salient structural changes during their development. In the presence of divalent cations, usually calcium, pectins can form gel-like structures. Because of their importance they have been the subject of many force spectroscopy experiments, which have examined the conformational changes and molecular tensions due to external forces. The most abundant unit present in the pectin backbone is polygalacturonic acid. Unfortunately, experimental force spectroscopy on polygalacturonic acid molecules is still not a trivial task. The mechanism of the single-molecule response to external forces can be inferred by theoretical methods. Therefore, in this work we simulated such force spectroscopy experiments using the Enforced Geometry Optimization (EGO) method. We examined the oligomeric (up to hexamer) structures of α-D-galacturonic acid exposed to external stretching forces. The EGO simulation of the force spectroscopy appropriately reproduced the experimental course of the enforced conformational transition: chair →inverted chair via the twisted boat conformation(s) in the pyranose ring of α-D-galacturonic acid. Additionally, our theoretical approach also allowed to determine the minimum oligomer size adequate for the description of nano-mechanical properties of (poly)-α-D-galacturonic acid.

Effects of fatigue on microstructure and mechanical properties of bone organic matrix under compression.

The aim of the study was to investigate whether a fatigue induced weakening of cortical bone was revealed in microstructure and mechanical competence of demineralized bone matrix. Two types of cortical bone samples (plexiform and Haversian) were use. Bone slabs from the midshaft of bovine femora were subjected to cyclical bending. Fatigued and adjacent control samples were cut into cubes and demineralized in ethylenediaminetetraacetic acid. Demineralized samples were either subjected to microscopic quantitative image analysis, or compressed to failure (in longitudinal or transverse direction) with a simultaneous analysis of acoustic emission (AE). In fatigued samples porosity of organic matrix and average area of pores have risen, along with a change in the pores shape. The effect of fatigue depended on the type of the bone, being more pronounced in the plexiform than in Haversian tissue. Demineralized bone matrix was anisotropic under compressive loads in both types of cortical structure. The main result of fatigue pretreatment on mechanical parameters was a significant decrease of ultimate strain in the transverse direction in plexiform samples. The decrease of strain in this group was accompanied by a considerable increase of the fraction of large pores and a significant change in AE energy.

New image analysis method for the estimation of global and spatial changes in fruit microstructure

Abstract A new image analysis method for the spatial characterization of microscopy images of fruit microstructure is proposed in order to analyse the heterogeneous microstructure of unprocessed fruit and the possible inhomogeneous effects of various technological treatments on this microstructure. The micro-structure of tissue samples was characterized using the global statistics of size and shape parameters calculated for all visible objects. Global analysis was supported by a novel algorithm that allowed for drawing of the maps of the cell wall fraction from microscopy images and for the analysis of both global and local compaction or loosening of tissue. The spatial distribution of the cell wall fraction was visualised in the convenient form of bivariate histograms. To test the developed image analysis protocols, structural changes resulting from ultrasonic and osmotic treatments of apple tissue samples were studied. Peeled and cored apples were submersed in a liquid medium (distilled water or 60 °Bx sucrose solution) for 45 and 90 min with and without ultrasonic treatment. After these treatment procedures, tissue samples were cut into slices, stained and imaged using a microscope. The proposed method allowed to characterise the effects of different sample treatments.

Structure-Related Gelling of Pectins and Linking with Other Natural Compounds: A Review

Pectins are polysaccharides present commonly in dicotyledonous and non-grass monocotyledonous plants. Depending on the source, pectins may vary in molecular size, degrees of acetylation and methylation and contents of galacturonic acid and neutral sugar residues. Therefore, pectins demonstrate versatile gelling properties and are capable of forming complexes with other natural compounds, and as a result, they are useful for designing food products. This review focuses on the structure-related mechanisms of pectin gelling and linking with other natural compounds such as cellulose, hemicellulose, ferulic acid, proteins, starch, and chitosan. For each system, optimal conditions for obtaining useful functionality for food design are described. This review strongly recommends that pectins, as a natural biocomponent, should be the focus for both the food industry and the bioeconomy since pectins are abundant in fruits and may also be extracted from cell walls in a similar way to cellulose and hemicellulose. However, due to the complexity of the pectin family and the dynamic structural changes during plant organ development, a more intensive study of their structure-related properties is necessary. Fractioning using different solvents at well-defined development stages and an in-depth study of the molecular structure and properties within each fraction and stage, is one possible way to proceed with the investigation.