Structural and rheological properties of diluted alkali soluble pectin from apple and carrot.

Pectin, a complex polysaccharide found in plant cell walls, plays a crucial role in various industries due to its functional properties. The diluted alkali-soluble pectin (DASP) fractions that result from the stepwise extraction of apples and carrots were studied to evaluate their structural and rheological properties. Homogalacturonan and rhamnogalacturonan I, in different proportions, were the main pectin domains that composed DASP from both materials. Atomic force microscopy revealed that the molecules of apple DASP were longer and more branched. A persistence length greater than 40 nm indicated that the pectin molecules deposited on mica behaved as stiff molecules. The weight-averaged molar mass was similar for both samples. Intrinsic viscosity values of 194.91 mL·g-1 and 186.79 mL·g-1 were obtained for apple and carrot DASP, respectively. Rheological measurements showed greater structural strength for apple-extracted pectin, whereas carrot pectin was characterized by a higher linear viscoelasticity limit. This comparison showed that the pectin fractions extracted by diluted alkali are structurally different and have different rheological properties depending on their botanical origin. The acquired insights can enhance the customized use of pectin residue and support further investigations in industries relying on pectin applications.

Apple metabolism under oxidative stress affects plant cell wall structure and mechanical properties.

Several studies have shown beneficial effects of short exposure to oxidative stress on stored fruit, such as better preservation, increased firmness, preservation of polyphenolic compounds, and reduced risk of postharvest disorders such as bitter pit and superficial scald in apples. In this study the effect of short-term oxidative stress conditions on the physiology of apple fruit was investigated. Apple fruit of three cultivars were exposed to hypoxic storage conditions of various lengths to induce anaerobiosis. The response of apple fruit to short-term oxidative stress was evaluated by means of cell wall immunolabeling and atomic force microscopy. In addition, the antioxidant capacity and antioxidative activity of apple peels was assessed. Through various techniques, it was shown that short-term oxidative stress conditions promote specific enzymatic activity that induces changes in the cell wall of apple fruit cells. Exposure to short-term stress resulted in the remodeling of cell wall pectic polysaccharides, observed as an increase in the size and complexity of extracted oxalate pectin. Structural changes in the cell wall were followed by an increase in Young's modulus (compressive stiffness of a solid material, expressed as the relationship between stress and axial strain) of the cell wall material. The data presented in this paper show in a novel way how storage under short-term oxidative stress modifies the cell wall of apple fruit at the molecular level.

Influence of pectin and hemicelluloses on physical properties of bacterial cellulose.

The properties of bacterial cellulose (BC)-based films produced by in situ biosynthesis with various polysaccharides (water-soluble pectin, arabinan, rhamnogalacturonan I, arabinoxylan, xyloglucan, glucomannan) were investigated. The addition of the polysaccharides to the bacterial growth environment changed the composition of the films by incorporating characteristic monosaccharides. BC-based films contained up to 26.7 % of non-cellulosic polysaccharides. The applied modification had a clear impact on water sorption and caused a decrease in the thermal stability of most BC films, which was connected with the depletion of geometrical dimensions of cellulose nanofibers observed with AFM. The FT-IR and Raman spectra demonstrated a decrease in % Iα of cellulose films, most notably for xyloglucan and glucomannan, as well as a change in their degree of crystallinity and the length of cellulose chains. The addition of xyloglucan had the most pronounced effect on film hardening; the other additives had a similar but lesser effect.

A mini-review on the plant sources and methods for extraction of rhamnogalacturonan I.

Rhamnogalacturonan type I (RG-I) is one of the pectin family member abundant in plant cell walls. Process of RG-I extraction from cell walls, either as a one-step or several-stage process, conditions the structure and properties of obtained polysaccharides. In this paper, we provide comprehensive overview of the factors related to the source and extraction techniques that determine the yield and chemical composition of pectin belonging to RG-I. The role of the source material, solvent, pH, temperature, time and additional factors related to applied techniques, such as microwaves, ultrasounds, high and low pressure or enzymatic treatments are discussed.

Novel polysaccharide and polysaccharide-peptide conjugate from Rosa rugosa Thunb. pseudofruit - Structural characterisation and nutraceutical potential.

A novel bioactive polysaccharopeptide (C1) and polysaccharide (C2) with an average molecular weight of 180 kDa and 70 kDa were isolated from R. rugosa pseudofruit. The composition of the macromolecules was established using 1H NMR, FT-IR, GC-MS, SDS-PAGE coupled with enzymatic cleavage, and proteomic analyses (LC-MS). C1 was found to contain 60.56 ± 1.82 % of sugars and 21.17 ± 0.47 % of uronic acids. Its main neutral monosaccharides were arabinose, rhamnose, galactose, glucose, fucose, and mannose. C1 was found to be a polysaccharopeptide containing pectinesterase-like protein. C2 was composed of 32.85 ± 0.97 % of sugars and 48.77 ± 1.15 % of uronic acids. Its main neutral monosaccharides were galactose, glucose, rhamnose, arabinose, and mannose. A promising nutraceutical value of the polysaccharides was revealed. Assays showed strong α-glucosidase inhibitory activity of both macromolecules and considerable antiradical potential and moderate lipoxygenase inhibitory activity of the crude polysaccharide. Moreover, antiproliferative activity of C2 was observed.

Microencapsulated Red Powders from Cornflower Extract-Spectral (FT-IR and FT-Raman) and Antioxidant Characteristics.

Although the health benefits of cornflower extracts are known, their application in food production has not been widely investigated. This study assessed microencapsulated red powders (RP) prepared from the aqueous extract of blue cornflower petals. Microencapsulation was performed by freeze-drying using various stabilizers, such as maltodextrin, guar gum, and lecithin. The microencapsulated RP were characterized by spectral (FT-IR and FT-Raman), mineral, structural, and antioxidant analyses. The FT-IR and FT-Raman band related to guar gum, lecithin, and maltodextrin dominated over the band characteristic of anthocyanins present in the cornflower petal powders. The main difference observed in the FT-Raman spectra was attributed to a shift of bands which is reflection of appearance of flavium cation forms of anthocyanins. The microencapsulated RP had total phenolic content of 21.6-23.4 mg GAE/g DW and total flavonoid content of 5.0-5.23 mg QE/g. The ABTS radical scavenging activity of the tested powders ranged from 13.8 to 20.2 EC50 mg DW/mL. The reducing antioxidant power (RED) of the powders was estimated at between 31.0 and 38.7 EC50 mg DW/mL, and OH• scavenging activity ranged from 1.9 to 2.6 EC50 mg DW/mL. Microencapsulated cornflower RP can be valuable additives to food such as sweets, jellies, puddings, drinks, or dietary supplements.

Structure and functionality of Rhamnogalacturonan I in the cell wall and in solution: A review.

Rhamnogalacturonan I (RG-I) belongs to the pectin family and is found in many plant cell wall types at different growth stages. It plays a significant role in cell wall and plant biomechanics and shows a gelling ability in solution. However, it has a significantly more complicated structure than smooth homogalacturonan (HG) and its variability due to plant source and physiological state contributes to the fact that RG-I's structure and function is still not so well known. Since functionality is a product of structure, we present a comprehensive review concerning the chemical structure and conformation of RG-I, its functions in plants and properties in solutions.

Chemical Changes in the Broccoli Volatilome Depending on the Tissue Treatment.

The storage of plant samples as well as sample preparation for extraction have a significant impact on the profile of metabolites, however, these factors are often overlooked during experiments on vegetables or fruit. It was hypothesized that parameters such as sample storage (freezing) and sample pre-treatment methods, including the comminution technique or applied enzyme inhibition methods, could significantly influence the extracted volatile metabolome. Significant changes were observed in the volatile profile of broccoli florets frozen in liquid nitrogen at -20 °C. Those differences were mostly related to the concentration of nitriles and aldehydes. Confocal microscopy indicated some tissue deterioration in the case of slow freezing (-20 °C), whereas the structure of tissue, frozen in liquid nitrogen, was practically intact. Myrosinase activity assay proved that the enzyme remains active after freezing. No pH deviation was noted after sample storage - this parameter did not influence the activity of enzymes. Tissue fragmentation and enzyme-inhibition techniques applied prior to the extraction influenced both the qualitative and quantitative composition of the volatile metabolome of broccoli.

Changes of pectin structure and microbial community composition in strawberry fruit (Fragaria × ananassa Duch.) during cold storage.

Strawberry is very perishable fruit with rapid postharvest loss of quality and high susceptibility to microbial infections. In this work we study pectin modifications and microbiota and mycobiota composition in strawberry in conventional and organic cultivation systems. The enzymatic activity during postharvest storage of both types of strawberry was divided at the fifth day of storage into two phases: postharvest changes and rotting. Pectin molecules extracted from organic strawberries were longer and more branched compared to the conventional strawberries; however a more noticeable reorganization of molecular structure occurred. The sequential action of the pectinolytic enzymes had a direct effect on the molecular structure of pectin fractions. The observed changes in pectin structure relate to the synergistic activity of pectinolytic enzymes and some microorganisms. The organic system was characterized by a greater number and variety of bacteria and fungi during storage as compared to the conventional system.

Structural properties of diluted alkali-soluble pectin from Pyrus communis L. in water and salt solutions.

The self-assembly and gelation of low-methoxyl diluted alkali-soluble pectin (LM DASP) from pear fruit (Pyrus communis L. cv. Conference) was studied in water and salt solutions (NaCl and CaCl2, constant ionic strength) without pH adjustment at 20 °C. The samples at different LM DASP concentrations were characterized using rheological tests, Fourier-transform infrared spectroscopy, dual-angle dynamic light scattering and atomic force microscopy. LM DASP from pear fruit (Pyrus communis L.) showed gelling ability. The indices (aggregation index and shape factor) based on light scattering may be useful for the characterization of structural changes in polysaccharide suspension, particularly for the determination of a gel point. The results obtained may be important for the food, cosmetic and pharmaceutical industries where pectin is used as a texturizer, an encapsulating agent, a carrier of bioactive substances or a gelling agent.

Aggregation and weak gel formation by pectic polysaccharide homogalacturonan.

This study presents a novel model of homogalacturonan (HG) based on the dissipative particle dynamics (DPD). The model was applied to investigate the mechanism of self-aggregation of low-methoxylated homogalacturonan in aqueous solutions in the absence of cations. The coarse-grained model provided new insights into the structural features of HG aggregates and networks in aqueous solutions. Depending on the properties and concentration of polysaccharides, two major patterns of self-assembly were observed for HG - ellipsoidal aggregates and a continuous three-dimensional network. Simulations showed that a decrease in the degree of dissociation of HG results in a higher rate of self-aggregation, as well as facilitating the formation of larger assemblies or thicker nanofilaments depending on the type of final self-assembly. Simulations of polysaccharides of different chain lengths suggested the existence of a structural threshold for the formation of a spatial network for HG consisting of less than 35 GalA units.

The primary, secondary, and structures of higher levels of pectin polysaccharides.

Pectin is a heteropolysaccharide abundant in the cell wall of plants and is obtained mainly from fruit (citrus and apple), thus its properties are particularly prone to changes occurring during ripening process. Properties of pectin depend on the string-like structure (conformation, stiffness) of the molecules that determines their mutual interaction and with the surrounding environment. Therefore, in this review the primary, secondary, and structures of higher levels of pectin chains are discussed in relation to external factors including crosslinking mechanisms. The review shows that the primary structure of pectin is relatively well known, however, we still know little about the conformation and properties of the more realistic systems of higher orders involving side chains, functional groups, and complexes of pectin domains. In particular, there is lack of knowledge on the influence of postharvest changes and extraction method on the primary and secondary structure of pectin that would affect conformation in a given environment and assembly to higher structural levels. Exploring the above-mentioned issues will allow to improve our understanding of pectin functionality and will help to tailor new functionalities for the food industry based on natural but often biologically variable source. The review also demonstrates that atomic force microscopy is a very convenient and adequate tool for the evaluation of pectin conformation since it allows for the relatively straightforward stretching of the pectin molecule in order to measure the force-extension curve which is directly related to its stiffness or flexibility.

The Effect of Cultivation Method of Strawberry (Fragaria x ananassa Duch.) cv. Honeoye on Structure and Degradation Dynamics of Pectin during Cold Storage.

The high quality and long shelf life of strawberry fruit are largely dependent on the cultivation method. The goal of this experiment was to study the effect of different cultivation methods on molecular structure and rheological properties of pectin extracted from strawberry quality parameters during cold storage. Three methods of cultivation of strawberry cv. Honeoye were tested: organic cultivation on raised beds, organic cultivation with the flat-planted method and conventional cultivation with the flat-planted method. The nanostructure of pectin (AFM), its chemical structure (FT-IR) and rheological properties were studied. The fruits were also tested by size, dry matter, firmness, acidity and the content of soluble solids, anthocyanin, phenolics, vitamin C and galacturonic acid. Pectin isolated from organic strawberries was more rapidly degraded than conventional strawberry pectin, which limits the possibilities for their processing and use as gelling or stabilizing agents at 20 °C. The differences in fruit quality were particularly noticeable with respect to the anthocyanin content, which was significantly higher for organic strawberry. The organic fruit also had better sensory properties because of its lower acidity and higher soluble solid content (SSC). These and other results from this experiment showed that strawberries produced by organic farming methods had better biochemical properties compared to conventional fruit; however, pectin transformation undergone faster limits their further technological applications.

Effect of different conditions of synthesis on properties of silver nanoparticles stabilized by nanocellulose from carrot pomace.

The silver nanoparticles (AgNPs) can exhibit different optical properties depending on their size and shape as a result of synthesis method and the stabilizer used. In this research the synthesis of AgNPs in the presence of nanocellulose obtained from carrot pomace was investigated. The influence of silver nitrate concentration, temperature and mechanical agitation on size and shape of AgNPs was studied. The mixing of reagents during synthesis, regardless temperature, led to obtain AgNPs of various sizes and shapes. It was confirmed by different colors of samples with absorbance maximum from 334 to 779 nm, the transmission electron microscopy images and dynamic light scattering results. In unmixed samples only spherical nanoparticles with absorbance maximum at 408 nm were observed. Obtained results have demonstrated that mechanical agitation and an appropriate silver nitrate concentration combined with stabilizing effect of nanocellulose allow to obtain AgNPs in different shapes and sizes.

An Atomic Force Microscopy Study on the Effect of ß-Galactosidase, α-L-Rhamnosidase and α-L-Arabinofuranosidase on the Structure of Pectin Extracted from Apple Fruit Using Sodium Carbonate.

The enzyme driven changes in plant cell wall structure during fruit ripening result in debranching, depolymerization and solubilization of pectin polysaccharides, which has an effect in terms of the postharvest quality losses in fruit. Atomic force microscopy (AFM) has revealed that diluted alkali soluble pectins (DASP) from fruit and vegetables have an interesting tendency to self-assemble into regular structures. However, the mechanism is not yet fully understood. The current study is aimed at investigating the role of neutral sugars, namely galactose, rhamnose and arabinose in the formation of the branched structure of DASP. ß-galactosidase, α-L-rhamnosidase and α-L-arabinofuranosidase enzymes were used for the treatment of DASP extracted from Golden Delicious apple flesh (Malus domestica cv. Golden Delicious). The effects of the selective degradation of pectic polysaccharides after 15, 30, 60, 90 and 120 min of incubation were observed using AFM. The α-L-rhamnosidase enzyme activity on pectin extracted with Na2CO3 did not cause any visible or measurable degradation of the molecular structure. The moderate effects of ß-galactosidase enzymatic treatment suggested the possible role of galactose in the branching of DASP molecules deposited on mica. Data obtained for α-L-arabinofuranosidase indicated the crucial role of arabinose in the formation and preservation of the highly branched structure of the DASP fraction.

The Effect of Concentration on the Cross-Linking and Gelling of Sodium Carbonate-Soluble Apple Pectins.

The cross-linking and gelation of low-methoxy pectins are basic processes commonly used in different industries. The aim of this research was to evaluate the cross-linking process of the sodium carbonate-soluble pectins (named DASP) extracted from apples, characterized by a low degree of methylesterification as a function of its concentration in water (CDASP). The cross-linking process was studied with a dynamic light scattering method, atomic force microscope (AFM), viscosity and pH measurements. An increase in CDASP above 0.01% resulted in a decrease in the aggregation index (AI) and the change of its sign from positive to negative. The value of AI = 0 occurred at CDASP = 0.33 ± 0.04% and indicated the formation of a pectin network. An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with AFM, which confirmed results obtained. The hydrogen bonds were involved in the cross-linking process.

Analysis of AGP contribution to the dynamic assembly and mechanical properties of cell wall during pollen tube growth.

Arabinogalactan proteins as cell wall structural proteins are involved in fundamental processes during plant development and growth. The aim of this study was to evaluate AGP function in the distribution of pectin, cellulose and callose along Fragaria x ananassa pollen tube and to associate the cell wall structure with local mechanical properties. We used Yariv reagent which interacts with AGPs and allows the observation of the assembly of cell walls without AGPs performing their function. Cytochemical, immunofluorescence labelling and atomic force microscope have been used to characterize the changes in cell wall structure and stiffness. It was shown that disordering of the structure of AGP present in cell walls affects the localization of cellulose, pectins and the secretion of callose. Changes in cell wall assembly are relevant to pollen tube mechanical properties. The stiffness gradient lengthwise through the axis of the pollen tube has demonstrated a significantly higher Young's modulus of the shank region than the growth zone. It has been revealed that the apex of the pollen tube cultured in the presence of Yariv reagent is stiffer (1.68 MPa) than the corresponding region of the pollen tube grown under control conditions (0.13-0.27 MPa). AGP affects the structure of the cell wall by changing the distribution of other components and the modification of their localization, and hence it plays a significant role in the mechanical properties of the cell wall.

Distribution of arabinogalactan proteins and pectins in the cells of apple (Malus × domestica) fruit during post-harvest storage.

Background and Aims: Changes in the arrangement of cell wall components determine cell wall properties (integrity, stiffness), thereby affecting the macro-scale properties of fruits, which are important for consumers and industry. Arabinogalactan proteins (AGPs) are ubiquitous components of the plant cell, in which they have various functions. Currently, AGPs are considered to be one of the less well-known, enigmatic proteoglycans, a consequence of their heterogeneous structure and unclear mechanism of activity. Methods: An immunocytochemical study was conducted to elucidate the distribution of AGPs and pectic polysaccharides contained in apple (Malus × domestica) fruit during senescence. De-esterified homogalacturonan (LM19), methyl-esterified homogalacturonan (LM20), processed arabinan (LM16) and three AGP epitopes (JIM13, JIM15, MAC207) were identified in the fruit at three stages: fresh fruit, and fruit at 1 and 3 months of post-harvest storage. Key Results: Microscopy revealed spatio-temporal changes in the localization of all examined epitopes. Changes of fruit cell wall assembly and its degradation were confirmed by determination of the galacturonic acid content in the WSP (water soluble pectins), CSP (chelator soluble pectins) and DASP (dilute alkali soluble pectins) fractions. Conclusions: The results revealed dependencies between AGPs, arabinan and homogalacturonan distribution in apple fruit, which are correlated with changes in microstructure during senescence. We propose that AGPs are involved in establishment of the cell wall - plasma membrane continuum.

Structural network of arabinogalactan proteins (AGPs) and pectins in apple fruit during ripening and senescence processes.

The cell wall is an essential framework determining the overall form of the plant cell. Our study was focused on the distribution of arabinogalactan proteins (AGPs), arabinan, and homogalacturonan in fruit cells during ripening and storage with emphasis on quantitative analysis of their presence in particular regions of the cell wall - plasma membrane. The localization of the examined compounds was determined with immunohistochemistry techniques and immunogold labelling. Spatio-temporal colocalization between AGPs epitopes - [ßGlcA(1→3)-αGalA(1→2)Rha] recognized by JIM13 and MAC207 antibodies, and arabinan labelled by the LM16 antibody was detected in the inner cell wall layer, in association with the plasma membrane. The specific arrangement of AGP and arabinan epitopes differentiated them from homogalacturonan epitopes, consisting of GalA residues recognized by LM19 and LM20 antibodies in all the examined fruit maturity stages. The disruption of cell wall - plasma membrane continuum, observed during ripening-associated softening process, was associated with both the substantial decrease of AGPs, pectins content and with remodeling of their arrangement. The results indicate that the textural properties of fruit during growth and postharvest storage, an attribute of fruit quality becoming selection criteria for consumers, depend on the existence of dynamic network organizing polysaccharides and glycoproteins in the extracellular matrix.

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.