Rapid assessment of ordered molecular structure in a semi-crystalline polymer, starch, directly from solid state NMR spectra

1. Materials and Methods1.1 Materials1.2 13 C CP/MAS NMR spectroscopy1.3 Wide Angle X-Ray Diffractometry1.4 DSC1.5 Data analysi

Extrusion induced low-order starch matrices: enzymic hydrolysis and structure

Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing

Extracellular depolymerisation triggers fermentation of tamarind xyloglucan and wheat arabinoxylan by a porcine faecal inoculum

Arabinoxylan (AX) and xyloglucan (XG) are important components of primary cell walls of cereal grains and vegetables/fruits, respectively. Despite the established health benefits of these non-starch polysaccharides, the mechanisms of their utilisation by the gut microbiota are poorly understood. In this study, the mechanisms of solubilised wheat AX and tamarind XG degradation were investigated under in vitro fermentation conditions using a porcine faecal inoculum. Through structural analysis of the polymers, we demonstrate that depolymerisation by microbial surface accessible endo-degrading enzymes occurs prior to active fermentation of AX or XG. Breakdown products are released into the medium and potentially utilised cooperatively by other microbes. Acetate and propionate are the main fermentation products and are produced concurrently with polysaccharide depletion. Butyrate, however, is produced more slowly consistent with it being a secondary metabolite

Characteristics of starch-based films with different amylose contents plasticised by 1-ethyl-3-methylimidazolium acetate

Starch-based films plasticised by an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), were prepared by a simple compression moulding process, facilitated by the strong plasticisation effect of [Emim][OAc]. The effects of amylose content of starch (regular vs. high-amylose maize) and relative humidity (RH) during ageing of the samples on a range of structural and material characteristics were investigated. Surprisingly, plasticisation by [Emim][OAc] made the effect of amylose content insignificant, contrary to most previous studies when other plasticisers were used. In other words, [Emim][OAc] changed the underlying mechanism responsible for mechanical properties from the entanglement of starch macromolecules (mainly amylose), which has been reported as a main responsible factor previously. The crystallinity of the plasticised starch samples was low and thus was unlikely to have a major contribution to the material characteristics, although the amylose content impacted on the crystalline structure and the mobility of amorphous parts in the samples to some extent. Therefore, RH conditioning and thus the sample water content was the major factor influencing the mechanical properties, glass transition temperature, and electrical conductivity of the starch films. This suggests the potential application of ionic liquid-plasticised starch materials in areas where the control of properties by environmental RH is desired

Investigation of the micro- and nano-scale architecture of cellulose hydrogels with plant cell wall polysaccharides: a combined USANS/SANS study

The structure of protiated, deuterated and composite cellulose hydrogels with plant cell wall (PCW) polysaccharides has been investigated by combined USANS/SANS experiments, complemented with spectroscopy and microscopy. The broad size range covered by the USANS/SANS experiments enabled the identification of cellulose architectural features in the cross-sectional and longitudinal directions. In the cross-sectional direction, cellulose ribbons are modelled as core-shell structures. Xyloglucan and mixed linkage glucans interfere with the cellulose crystallisation process, reducing the crystallinity and establishing cross-bridges between ribbons. However, only xyloglucan is able to establish strong interactions with the cellulose microfibrils, affecting the properties of the ribbons' core. Longitudinally, the ribbons are hypothesised to present a ca. 1.4-1.5 μm periodic twist with a crystallite length of ca. 140-180 nm for the individual microfibrils. These results highlight the potential of USANS/SANS techniques to investigate the multi-scale architecture of cellulose hydrogels as well as the interaction mechanism between cellulose and PCW polysaccharides

Impact of down-regulation of starch branching enzyme IIb in rice by artificial microRNA- and hairpin RNA-mediated RNA silencing

The inactivation of starch branching IIb (SBEIIb) in rice is traditionally associated with elevated apparent amylose content, increased peak gelatinization temperature, and a decreased proportion of short amylopectin branches. To elucidate further the structural and functional role of this enzyme, the phenotypic effects of down-regulating SBEIIb expression in rice endosperm were characterized by artificial microRNA (amiRNA) and hairpin RNA (hp-RNA) gene silencing. The results showed that RNA silencing of SBEIIb expression in rice grains did not affect the expression of other major isoforms of starch branching enzymes or starch synthases. Structural analyses of debranched starch showed that the doubling of apparent amylose content was not due to an increase in the relative proportion of amylose chains but instead was due to significantly elevated levels of long amylopectin and intermediate chains. Rices altered by the amiRNA technique produced a more extreme starch phenotype than those modified using the hp-RNA technique, with a greater increase in the proportion of long amylopectin and intermediate chains. The more pronounced starch structural modifications produced in the amiRNA lines led to more severe alterations in starch granule morphology and crystallinity as well as digestibility of freshly cooked grains. The potential role of attenuating SBEIIb expression in generating starch with elevated levels of resistant starch and lower glycaemic index is discussed

Molecular interactions between cereal soluble dietary fibre polymers and a model bile salt deduced from 13C NMR titration

Soluble dietary fibres (SDF) such as (1,3:1,4)-beta-D-glucan (beta G) and arabinoxylan (AX) have been reported to lower plasma cholesterol levels in the human body, at least in part by preventing bile salts (BS) from being reabsorbed into the enterohepatic circulation. The mechanism(s) by which SDF interact with BS in the digestive tract is not known. This report describes investigations of molecular interactions between a model bile salt (taurochenodeoxycholate - TCDC) micelle with each of beta G and AX using C-13 NMR. In the presence of beta G, chemical shift changes were observed for many bile salt resonances, but not beta G resonances, without any apparent change in line widths. In contrast, in the presence of AX, no consistent chemical shift changes were observed for either TCDC or AX resonances, but TCDC signal intensities were reduced. This was not due to simple viscosity effects as the viscosity of the beta G used was greater than that of the AX. The results suggest two different mechanisms of interaction between cereal non-starch polysaccharides and TCDC micelles: beta G interacts directly on a molecular length scale with the micelles, whilst AX changes the local environment, resulting in reduced micellar mobility without direct molecular interaction. (C) 2010 Elsevier Ltd. All rights reserved

Infrared spectroscopy as a tool to characterise starch ordered structure - A joint FTIR-ATR, NMR, XRD and DSC study

Starch has a heterogeneous, semi-crystalline granular structure and the degree of ordered structure can affect its behaviour in foods and bioplastics. A range of methodologies are employed to study starch structure; differential scanning calorimetry, C-13 nuclear magnetic resonance, X-ray diffraction and Fourier transform infrared spectroscopy (FUR). Despite the appeal of FTIR as a rapid, non-destructive methodology, there is currently no systematically defined quantitative relationship between FTIR spectral features and other starch structural measures. Here, we subject 61 starch samples to structural analysis, and systematically correlate FTIR spectra with other measures of starch structure. A hydration dependent peak position shift in the FTIR spectra of starch is observed, resulting from increased molecular order, but with complex, non-linear behaviour. We demonstrate that FTIR is a tool that can quantitatively probe short range interactions in starch structure. However, the assumptions of linear relationships between starch ordered structure and peak ratios are overly simplistic. (C) 2015 Elsevier Ltd. All rights reserved

Rapid quantification of starch molecular order through multivariate modelling of ¹³C CP/MAS NMR spectra

A partial least squares model has been generated enabling the rapid assessment of ordered molecular structure in a semi-crystalline polymer, starch, directly from solid state NMR spectra. Solid state NMR spectroscopy offers many advantages over conventional analysis tools being non-destructive and functional in complex mixtures

“Dietary fibre”: moving beyond the “soluble/insoluble” classification for monogastric nutrition, with an emphasis on humans and pigs

This review describes dietary fibres originating from a range of foods, particularly in relation to their plant cell walls. It explores the categorization of dietary fibres into "soluble" or "insoluble". It also emphasizes dietary fibre fermentability, in terms of describing how the gastro-intestinal tract (GIT) microbiota respond to a selection of fibres from these categories. Food is categorized into cereals, legumes, fruits and vegetables. Mention is also made of example whole foods and why differences in physico-chemical characteristics between "purified" and "non-purified" food components are important in terms of health. Lastly, recommendations are made as to how dietary fibre could be classified differently, in relation to its functionality in terms of fermentability, rather than only its solubility