Hoa K. Chau

Characterization of pectin, flash-extracted from orange albedo by microwave heating, under pressure.

Pectin was acid extracted from orange albedo by microwave heating under pressure. Extraction times ranged from 2.5 to 8 min. Solubilized pectin was characterized for molar mass (M), rms radius of gyration (Rg) and intrinsic viscosity [eta] by HPSEC with online light scattering and viscosity detection. M, Rg and [eta] all decreased with increasing extraction time. Nevertheless, at heating times of 2.5 and 3.0 min, M, Rg and [eta] were significantly higher than a commercial citrus pectin when the albedo:solvent ratio was 1:25 (w/v). At the heating time of 2.5 min Mw was 3.6 x 10(5), Rgz was 38 nm and [eta]w was 10.8 dL/g. Chromatography revealed that solubilized pectin distributions were bimodal in nature and that the low-molar-mass fraction increased at the expense of the high-molar-mass fraction with increasing extraction time. Scaling law exponents revealed that the high-molar-mass fraction was extremely compact in shape, whereas the low-molar-mass fraction was more asymmetric in shape. Possibly these results indicated that at short extraction times, pectin was solubilized as compact aggregated network structures that were broken down to their more asymmetric components with increased heating times.

An Improved Process for Isolation of Corn Fiber Gum

ABSTRACT Sequential alkaline extraction and alkaline hydrogen peroxide (AHP) bleaching have been used to prepare corn fiber gum in yields ranging from 21 to 40%, depending on the pH of the extraction medium. The pH was adjusted by using different ratios of NaOH and Ca(OH)2 The whitest product was obtained after AHP bleaching of the extract obtained using the lowest pH value. In order for the product gum to give its characteristic clear and low viscosity solutions, it was necessary to remove starch from the corn fiber substrate using α-amylase. The water-insoluble hemicellulose A fraction, a minor component, was removed by neutralizing AHP-treated extracts before ethanol precipitation of the useful hemicellulose B (corn fiber gum) fraction. At ambient temperature, AHP bleaching was near optimal after ≈2 hr under the processing conditions used. High ratios of arabinose (39%) to xylose (50%) were present in the corn fiber gum extracted under various alkaline conditions, and the H2O2 processing step did not s...

Global Structure of Microwave-Assisted Flash-Extracted Sugar Beet Pectin

The global structure of microwave-assisted flash-extracted pectins isolated from fresh sugar beet pulp has been studied. The objective was to minimize the disassembly and possibly the degradation of pectin molecules during extraction. These pectins have been characterized by high-performance size exclusion chromatography with light scattering, viscometric detection, and atomic force microscopy (AFM). Analysis of molecular parameters was performed on 15 and 8 microm size column packings. Samples analyzed with 15 microm packing gave weight-average molar masses that ranged from 532,000 to 1.2 million Da, radii of gyration from about 35 to 51 nm, polydispersities from 1.78 to 2.58, intrinsic viscosities from about 3.00 to 4.30 dL/g, and recoveries from 8.40 to 14.81% of dry weight. Chromatography revealed that a bimodal distribution of high molar mass spherical particles and lower molar mass coils was obtained. AFM images of pectin corroborated this conclusion and further revealed that these strands and spherical particles were integrated into networks. It is demonstrated that microwave-assisted extraction of sugar beet pulp under moderate pressure and at relatively low temperature could extract under acid conditions high molar mass, moderate-viscosity pectin in minutes rather than hours as required by conventional heating.

Macromolecular characterisation of three barley β-glucan standards by size-exclusion chromatography combined with light scattering and viscometry: an inter-laboratory study

Abstract Six (1→3)(1→4)-β- d -glucan standards (A–F) isolated from barley were analysed by size-exclusion chromatography (SEC) in five different laboratories with varying columns, solvent conditions and detector systems (low- and multi-angle light scattering and viscometry). Static (batch) measurements by capillary viscometry and laser light scattering were included. Fairly consistent results were obtained for the weight average molecular weights (Mw), radii of gyration (RG) and intrinsic viscosities [η], demonstrating that the β-glucans may serve as useful standards or reference materials in the study of cereal β-glucans. Average values for Mw were: A,E: 114,000 (±11%); B,C: 374,000 (±9%), D,F: 228,000 (±13%). Some inconsistencies regarding the polydispersity (Mw/Mn) could be ascribed to the influence of peak broadening in certain column/solvent systems. The study further demonstrated that individual researchers tended to use different processing parameters, especially refractive index increments (dn/dc), due to ambiguities in the literature or to differing experimental values. The need for consistent parameters and processing methods is clearly demonstrated.

Molecular Characteristics of Corn Fiber Gum and Their Influence on CFG Emulsifying Properties

ABSTRACT The molecular characteristics of two purified arabinoxylan fractions derived from corn kernels, corn fiber gum-1 and -2 (CFG-1 and -2), have been studied and correlated with emulsifying properties. CFG-1 and -2 fractions were isolated from different corn fiber sources by 1) a sequential alkaline extraction and H2O2 bleaching to produce CFG-1; and 2) additional H2O2 treatment of the alkali-extracted residue at pH 11.5, yielding CFG-2. Multiangle laser light-scattering and online viscosity were used to measure the molar mass, polydispersity, structure compactness, and intrinsic viscosity of the generated CFG fractions. Emulsification properties in an oil-in-water emulsion system with 10:1 oil-to-gum ratio was investigated by measuring turbidity of an aliquot from the bottom of the diluted emulsion over 10 days. The isolated CFG-2 from each fiber source was higher in weight-average molar mass (Mw) polydispersity) (Mw/Mn) and structure compactness, and also lower in solution weight-average intrinsic ...

Rhamnogalacturonan I containing homogalacturonan inhibits colon cancer cell proliferation by decreasing ICAM1 expression

Pectin modified with pH, heat or enzymes, has previously been shown to exhibit anti-cancer activity. However, the structural requirements for modified pectin bioactivity have rarely been addressed. In this study several pectin extracts representing different structural components of pectin were assessed for effects against colon cancer cells. Rhamnogalacturonan I (RGI) extracts reduced proliferation of DLD1 and HCT116 colon cancer cells in a dose- and time-dependent manner. RGI reduced ICAM1 gene expression and siRNA-mediated knockdown of ICAM1 expression decreased cell proliferation providing a potential novel mechanism for the anti-cancer activity of pectin. Structural analysis of bioactive and non-bioactive RGIs suggested that a homogalacturonan component is maybe essential for the anti-proliferative activity, furthering the understanding of the structural requirements for pectin bioactivity.

Screening the physical properties of novel Pseudomonas exopolysaccharides by HPSEC with multi-angle light scattering and viscosity detection

The physical properties of three novel acidic exopolysaccharides obtained from P. marginalis types A, B and C, one from P. ‘gingen’, one from P. andropogenis and one from P. fluorescens have been partially characterized. These EPSs were chromatographed on three serially placed SE Shodex OH pak columns covering a molar mass range for pullulans from about 4 × 107 to 1 × 103. The mobile phase was 0.05 M NaNO3. Physical measurements were performed on about 30 mg of sample for each EPS. The weight average molar mass of these EPSs ranged from about 0.71 to 2.85 × 106, the weight average intrinsic viscosity from 7.15 to 35.3 dl/ g and the radius of gyration from 62 to 123nm. The polydispersities of these EPSs ranged from 1.01 to 1.37. The large molar mass, size and viscosities of these EPSs may indicate that they have potential for use as thickeners, stabilizers, emulsifiers, and gelling agents in the food and non-food industries.

Investigation of molecular interactions between β-lactoglobulin and sugar beet pectin by multi-detection HPSEC.

Molecular interactions between β-lactoglobulin (β-LG) and sugar beet pectin (SBP) were studied using online multi-detection high performance size exclusion chromatography (HPSEC) at neutral pH and 50mM ionic strength. The hydrodynamic properties of various interacting polymer fractions were characterized in detail and compared with those of β-LG and SBP. Results showed that ∼6.5% (w/w) of native dimeric β-LG molecules formed complexes with over 35% SBP molecules of varying sizes, 800, 110 and 75 kDa. Although the β-LG molecules bind to SBP molecules of all sizes and shapes, they tend to favor the intermediate (110 kDa) and small sized (75 kDa) SBP molecules. All resulting complexes possess altered shapes and hydrodynamic properties when compared to unbound SBP and β-LG. About half of the interacting β-LG (∼3.5%) molecules were thought to bind to a small amount of non-covalently bound feruloyl groups, possibly present in SBP. When pre-heat treated β-LG and SBP were combined, more than 16% of β-LG formed complexes with at least 45% of SBP molecules of varying sizes, Mw∼750-800, 110, and 55-80 kDa. The complexes formed between β-LG aggregates and/or oligomers and the large SBP molecules (750-800 kDa) adopt the shape of β-LG aggregates, random coil. Both groups of complexes formed between β-LG intermediate (110 kDa) and small sized (55-80 kDa) SBP take on the shape of rigid rod. It was speculated that half of the interacting heat-treated β-LG molecules (∼8%) are complexed with non-covalently bound feruloyl groups in SBP.

Characterization of Hemicellulose B from Corn Fiber by High-Performance Size Exclusion Chromatography with On-Line Molar Mass and Viscometric Detection

Abstract Hemicellulose B (arabinoxylan, corn fiber gum, CFG) was prepared from corn fiber (CF) by alkaline extraction with 2 meq/g of CF using either NaOH, Ca(OH)2 or an equimolar mixture of the two. Prior to CFG extraction, oil was removed from CF by extraction with hexane and starch was removed from CF by treatment with α-amylase. The solutions of alkali-extracted CFG were then bleached with alkaline H2O2. The effect of extractant composition on the weight-average molar mass M w, weight-average intrinsic viscosity [η]w, and z-average root-mean-square radius of gyration R gz on CFG was determined. Depending on extractant composition and method of calculation, M w ranged from 2.7–6.96 × 105, [η]w from 1.87 to 2.00 dL/g and R gz from about 31 to 50 nm. Substituting Ca(OH)2 for NaOH reduced M w and R gz but had little or no effect on [η]w. Chromatographic analysis in conjunction with molar mass detection revealed that molar mass distributions were bimodal. M w for the high-molar-mass component ranged from about 8.4–16.1 × 105, whereas M w ranged from about 1.1–2.1 × 105 for the low-molar-mass component. The high-molar-mass component comprised about 15–43% by weight of CFG and was much more compact in shape than the low-molar-mass component.

Modified sugar beet pectin induces apoptosis of colon cancer cells via an interaction with the neutral sugar side-chains.

Pectins extracted from a variety of sources and modified with heat and/or pH have previously been shown to exhibit activity towards several cancer cell lines. However, the structural basis for the anti-cancer activity of modified pectin requires clarification. Sugar beet and citrus pectin extracts have been compared. Pectin extracted from sugar beet pulp only weakly affected the viability of colon cancer cells. Alkali treatment increased the anti-cancer effect of sugar beet pectin via an induction of apoptosis. Alkali treatment decreased the degree of esterification (DE) and increased the ratio of rhamnogalacturonan I (RGI) to homogalacturonan. Low DE per se did not play a significant role in the anti-cancer activity. However, the enzymatic removal of galactose and, to a lesser extent, arabinose from the pectin decreased the effect on cancer cells indicating that the neutral sugar-containing RGI regions are important for pectin bioactivity.