Pectin was isolated by aqueous extraction at pH 6.0 or 2.0 from okra (Abelmoschus esculentus L.) pods. An isolation protocol was designed to extract pectin and to study the influence of the ...extraction pH on their composition and physicochemical properties. The extracted pectin was assessed using sugar compositional analysis (neutral sugars, galacturonic acid, acetyl and methyl contents). FT-IR and NMR spectroscopy, size exclusion chromatography (SEC) and dilute solution viscometry were also used to determine the macromolecular characteristics of isolated pectin. The extraction protocols resulted in the isolation of pectin of high purity as evidenced by their high total carbohydrate (70.0–81.8%) and low protein (4.3–6.3%) contents. Samples contained between 46 and 56% galacturonic acid, had broad molecular weight distributions, a low degree of methylation (40.0 and 24.6%) and high degree of acetylation (52.2 and 37.6%). Neutral sugar analysis showed that the pectin extracted at pH 6.0 contained more neutral sugars, particularly, galactose (21.7–25.7 mol%), rhamnose (10.1–13.2 mol%) and arabinose (7.1–7.3 mol%) than that extracted at pH 2.0 indicating variations in fine structure. In addition, molecular parameters of the isolated pectins, such as intrinsic viscosity (2.8–4.4 dL g−1), critical concentration (0.15–0.45 dL g−1) and coil overlap parameter (0.66–1.51), showed that extraction conditions resulted in pectin with different chain morphology. The yield and physico-chemical characteristics of the extracted pectin from okra pods were influenced by the extraction conditions.
Display omitted
•Isolation protocol was design to extract pectins from okra.•Low methoxyl, highly acetylated pectins were extracted.•Complete chemical and physicochemical characterization was performed.
Polysaccharides from okra pods (Abelmoschus esculentus) were extracted using a sequential extraction protocol and compared with a simple extraction at pH 6. Rheological properties of three okra ...extracts were then investigated by means of molecular weight determination, dilute solution rheology, steady shear and oscillatory rheological measurements. The extraction protocols resulted in extracts of relatively high purity and multimodal molecular weight distribution. Furthermore, molecular parameters of the isolated biopolymers such as intrinsic viscosity, Huggins constant, critical concentration and coil overlap parameter were calculated from dilute solution viscometry. Investigation of the generalized flow behaviour using a modified Cross equation and Cox–Merz plots showed evidence that as concentration increases specific interactions start taking place among the polymeric chains that modify the rheological behaviour of the extracts. The change in the rheological behaviour could not only be explained by differences in the molecular weight of the samples but also should be attributed to the fine structure of the chains that are obtained under the different extraction protocols. Present investigation shows that further optimization of such protocols may result in polysaccharide fractions with specific rheological properties.
Deviations from rheological master curves is indicative of chain interactions. Display omitted
Extracts rich in pectins were isolated by aqueous extraction at pH4.0 (OE4) and 6.0 (OE6) from okra (Abelmoschus esculentus) pods. They were examined in terms of their composition and emulsion ...stabilizing capacity in model acidic emulsions (hexadecane-in-water at pH3.0). Extracted polysaccharides were assessed using size exclusion chromatography (SEC) and FTIR spectroscopy. The properties and stability of the resulting emulsions were examined by means of droplet size distribution and ζ-potential measurements, viscometry, fluorescence microscopy and protein interface concentration. As emulsifiers, both extracts produce emulsions of initially monomodal size distribution and of similar average droplet size, while ζ-potential was negative for both. The emulsions prepared using OE6 are relatively stable in terms of droplet size distribution and average droplet size after 30days of storage, while emulsions prepared with OE4 increase in droplet size, in part attributable to Ostwald ripening. Determination of the protein interface coverage Γ suggests that the increased stability of the OE6 emulsions should be attributed to the higher protein load of the interfaces prepared using this extract, resulting to increased rigidity of the interface. Viscosity of emulsions containing OE6 was two times greater than OE4 while aging increases the viscosity of both emulsions. The present work suggests that okra extracts can be strong candidates for emulsification in acidic environments.
•Okra extracts showed good emulsification capacity under acidic conditions.•Emulsions with extracts isolated at pH 6 are more stable than those at pH 4.•Ostwald ripening is one of the major coarsening mechanisms for both emulsions.•Aging increases the viscosity of both emulsions.
Mesoscopic structure of pectin in solution Alba, K.; Bingham, R. J.; Kontogiorgos, V.
Biopolymers,
June 2017, 2017-Jun, 20170601, Letnik:
107, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Mesoscopic structure of pectin with different molecular characteristics was investigated by means of small angle X‐ray scattering (SAXS), electrokinetic measurements and data modelling. The influence ...of a broad range of pH (2–7) on chain conformation in the dilute and semi‐diluted regime was investigated. Scattering data and concomitant analysis revealed two length scales at all environmental conditions studied. pH showed greater influence at acidic values (pH 2.0) enhancing the globular component of the structure due to association of galacturonic acid residues. Double logarithmic scattering intensity plots revealed fractal dimensions of 1.9 ± 0.2 in the low‐q regime and 1.5 ± 0.2 in the high q‐region, irrespectively of the specific environment. Increase in branching of RG‐I regions of the polysaccharide chains enhanced the compact conformation irrespectively of the pH or concentration. The present work shows that radical changes in pectin conformation can be induced only under strongly acidic conditions a finding that has important consequences in tailoring the technological performance of these biopolymers.
Pectin Conformation in Solution Alba, K; Bingham, R J; Gunning, P A ...
The journal of physical chemistry. B,
07/2018, Letnik:
122, Številka:
29
Journal Article
Recenzirano
Odprti dostop
The interplay of degree of methylesterification (DM), pH, temperature, and concentration on the macromolecular interactions of pectin in solution has been explored. Small-angle X-ray scattering ...complemented by atomic force microscopy and molecular dynamics was employed to probe chain dimensions and solution structure. Two length scales have been observed with the first level of structure characterising chain clusters with sizes ranging between 100-200 nm. The second level of structure arises from single biopolymer chains with a radius of gyration between ∼6 and 42 nm. The development of a range of macromolecular dimensions in vitro and in silico shows that the chain flexibility increases with DM and at acidic pH, whereas hydrogen bonding is the responsible thermodynamic driving force for cluster formation. High methyl pectins create structures of lower fractal dimension with less efficient packing. This work unveils pectin conformations covering most of its industrially and biologically relevant environments, enabling rational design of advanced biomaterials based on pectin.
Display omitted
•Stable emulsions were fabricated using pectin at low pH environments.•Pectin extracted at pH 6 is better emulsifier than pectin extracted at pH 2.0.•Protein is not the predominant ...factor for emulsion formation and stabilization.
Pectins with distinct molecular design were isolated by aqueous extraction at pH 2.0 or 6.0 and were examined in terms of their formation and stabilisation capacity of model n-alkane–in–water emulsions at acidic pH (pH 2.0). The properties and stability of the resulting emulsions were examined by means of droplet size distribution analysis, Lifshitz-Slyozov-Wagner modelling, bulk rheology, interfacial composition analysis, large-amplitude oscillatory surface dilatational rheology, electrokinetic analysis and fluorescence microscopy. Both pectin preparations were able to emulsify alkanes in water but exhibited distinct ageing characteristics. Emulsions prepared using pectin isolated at pH 6.0 were remarkably stable with respect to droplet growth after thirty days of ageing, while those prepared with pectin isolated at pH 2.0 destabilised rapidly. Examination of chemical composition of interfacial layers indicated multi-layered adsorption of pectins at the oil-water interface. The higher long-term stability of emulsions prepared with pectin isolated at high pH is attributed to mechanically stronger interfaces, the highly branched nature and the low hydrodynamic volume of the chains that result in effective steric stabilisation whereas acetyl and methyl contents do not contribute to the long-term stability. The present work shows that it is possible by tailoring the fine structure of pectin to engineer emulsions that operate in acidic environments.
The present review examines how macromolecular structure and functional groups of pectin affect its functionality with particular focus on its interfacial activity. We venture into a description of ...the particularly complex pectin structure and describe the major building blocks and their properties. In the following section, the role of each structural parameter is discussed with particular attention to protein, degree of acetylation and methylation, molecular weight, and branching. Finally, we discuss how modification of the extraction conditions could be tailored to obtain pectin with the desired emulsification properties. It is proposed that pectin with protein content in the range of 3%, with degree of acetylation greater than 10%, molecular weight between 100 and 200 × 103 g mol−1 and enriched in RG-I segments is more likely to perform well as an emulsifier. To tailor such a structure, an aqueous extraction protocol with low pH values (between 2.5 and 3.5) with a strong monoprotic acid (e.g., HCl) and one-step solvent precipitation should be selected. The proposed set of extraction conditions could be used as a first step towards rational design of pectin with desirable interfacial functionality.
Display omitted
•Review of the influence of pectin functional components on emulsion formation.•Review of experimental techniques that can be used to obtain tailored structures.•3% protein and >10% degree of acetylation is required for optimum performance.•Pectin should have Mw ∼200 × 103 gmol−1 and be rich in RG-I and ferulic acid.•Extraction at pH ∼3.0 with a strong acid and one step alcohol precipitation.
•High pH values result in extended chain conformation and early vitrification.•WLF modeling confirmed the early vitrification at high pH values.•Spectral analysis reveals one relaxation regime ...regardless pH of systems.•Biopolymer conformation plays determinant role on vitrification.
The influence of pH on the mechanical relaxation of LM-pectin in the presence of co-solute has been investigated by means of differential scanning calorimetry, ζ-potential measurements and small deformation dynamic oscillation in shear. pH was found to affect the conformational properties of the polyelectrolyte altering its structural behavior. Cooling scans in the vicinity of the glass transition region revealed a remarkable change in the viscoelastic functions as the polyelectrolyte rearranges from extended (neutral pH) to compact conformations (acidic pH). This conformational rearrangement was experimentally observed to result in early vitrification at neutral pH values where dissociation of galacturonic acid residues takes place. Time–temperature superposition of the mechanical shift factors and theoretical modeling utilizing WLF kinetics confirmed the accelerated kinetics of glass transition in the extended pectin conformation at neutral pH. Determination of the relaxation spectra of the samples using spectral analysis of the master curves revealed that the relaxation of macromolecules occurs within ∼0.1s regardless of the solvent pH.
The emulsifying characteristics of pectins isolated from six different okra genotypes were investigated and their structure-function relationships have been evaluated. Emulsion formation and ...stabilization of acidic oil-in-water emulsions (pH 2.0,
φ
= 0.1) were studied by means of droplet size distribution,
ζ
-potential measurements, viscometry, interfacial composition analysis and fluorescence microscopy. Fresh and aged emulsions differed in terms of droplet size distribution, interfacial protein and pectin concentrations (Γ) depending on the molecular properties of pectin that was used. Specifically, pectins with intermediate length of RG-I branching with molar ratio of (Ara + Gal)/Rha between 2 and 3 exhibit the optimum emulsification capacity whereas samples with the molar ratio outside this range do not favour emulsification. Additionally, low amounts of RG-I segments (HG/RG-
I
> 2) improve long term stability of emulsions as opposed to the samples that contain high amounts of RG-I (HG/RG-
I
< 2) which lead to long term instability. Protein was not found to be the controlling factor for the stability of the dispersions. The present results show that rational design of pectin should be sought before application as functional ingredient in food and/or pharmaceutical systems.
•The gum extracted from the leaves of Sesamum radiatum is a branched glucuronomannan.•Has a backbone of →4)-β-d-GlcpA-(1→2)-α-d-Manp-(1→ with side-chains of Gal and Xyl.•Sesamum gum has independent ...viscoelastic properties with no thermal hysteresis.•Physical behaviour was consistent with an entangled biopolymer solution.
A polysaccharide from the leaves of Sesamum radiatum was extracted by maceration in deionized water followed by ethanol precipitation then chemically and physically characterised. Monosaccharide composition and linkages were determined by high performance anion exchange chromatography (HPAEC), gas chromatography–mass spectrometry (GC–MS) and nuclear magnetic resonance (NMR) spectroscopy respectively. Sesamum gum was composed of glucuronic acid, mannose, galactose, and xylose with trace quantities of glucose, rhamnose and arabinose. Proton and 13C NMR spectroscopy, and linkage analysis revealed a glucuronomannan based structure comprising a backbone of →4)-β-d-GlcpA-(1→2)-α-d-Manp-(1→ with side-chains of galactose and xylose. Hydrated sesamum gum displayed temperature independent viscoelastic properties with no thermal hysteresis. Intrinsic viscosity was determined to be 3.31 and 4.40dLg−1 in 0.1M NaCl and deionised water respectively, while the critical concentration was determined to be 0.1% w/v. The characterisation performed in this study will help direct potential applications of this material in foods and pharmaceuticals.
PDF
