Browsing by Author "Bisht A"

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    Does harvesting age matter? Changes in structure and rheology of a shear-thickening polysaccharide from Cyathea medullaris as a function of age
    (Elsevier Ltd, 2024-04-01) Bisht A; Goh KKT; Sims IM; Edwards PJB; Matia-Merino L
    A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of −4)-β-D-GlcpA-(1 → 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.
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    Process-structure-function relationship for mamaku suspension: Effect of drying methods on powder functionality
    (Elsevier Ltd., 2023-12-30) Bisht A; Goh KKT; Matia-Merino L
    The pith from mamaku tree fern entraps a unique shear-thickening biomacromolecule called mamaku polysaccharide (MP) that may alter the rheological profile in the gut. Here we examined the potential of using the whole pith—natural entrapment of MP in the tissue of pith—to develop a food ingredient with shear-thickening behaviour as an alternative to MP extract. In this study, fresh mamaku pith was collected and dried using an oven-dryer or freeze-dryer, and ground into a powder (ODP: oven-dried powder; FDP: freeze-dried powder). Both the ODP and FDP were characterised for their physical properties (colour, densities, surface morphology), rehydration in water, rheological behaviour and in vitro starch digestion. Freeze-drying resulted in a porous structure, while after oven-drying, the structure collapsed and an increase in density was observed. Upon rehydration with water, both FDP and ODP absorbed water, causing the powder particles to swell and release the water-soluble compounds into the continuous phase. The ability of FDP to release water-soluble MP into the continuous phase resulted in a rheological behaviour of a suspension similar to MP extract solution (shear-thickening behaviour). No shear-thickening was observed in ODP suspension because not enough MP was available in the continuous phase to form polymer-polymer interactions. In-vitro digestion of wheat biscuits mixed with rehydrated FDP suspension reduced starch digestion by ∼35% after 10 min, but starch digestion was unaffected by ODP suspension. This was due to the changes in the rheological behaviour resulting from the alteration in structural characteristics of the powder samples by the different drying methods.
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    Shear and temperature sensitivity of a shear-thickening biopolymer from the New Zealand black tree fern
    (Elsevier Ltd, 2023-12-01) Bisht A; Goh KKT; Sims IM; Edwards PJB; Matia-Merino L
    Mamaku polysaccharide (MP) is a water-soluble shear-thickening biopolymer that has shown potential to be used in the design of novel food products targeting satiety management and weight loss. During the processing of MP at industrial scale, the polymer may be exposed to high temperature and shear, which could affect its rheological behaviour. Thus, herein we subjected extracted MP to high shear (between 1000–8000 rpm at various times, using a lab-scale high-shear mixer) and temperature treatment (between 65 and 115 °C, for 30 min) and investigated the changes in molecular structure and rheological properties. The temperature treatment disintegrated the backbone of MP into smaller fragments (molecular weight-Mw, reduced from ∼3.9 × 106 Da with no heat, to ∼0.6 × 106 Da at 115 °C), which caused a reduction in viscosity and in the extent of shear-thickening as well as an increase in the damping factor (Gʹʹ/Gʹ). Similar rheological trends were observed post-shear treatment, however, there was no evidence of depolymerisation, with the Mw, constituent sugar composition and NMR spectra (1H and 13C) being unaffected. It is suggested that the changes in rheological behaviour after shear treatment could be due to changes in the re-arrangement of MP molecules, which led to a compact and folded structure due to increased intra-molecular interactions. The results, therefore, indicate that modification of MP molecules during the industrial process such as shearing and heating should be considered as it may adversely affect the rheological properties of the product where MP is incorporated and the expected physiological benefits in the gastrointestinal tract.