Journal Articles
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Item 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 LThe 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.Item Emulsification Properties of Garlic Aqueous Extract: Effect of Heat Treatment and pH Modification(MDPI, Basel, Switzerland, 2023-10-10) Bravo-Núñez Á; Golding M; Gómez M; Matia-Merino L; Dai HDespite the broad research available in the literature dealing with garlic health benefits, little information is found regarding the functional properties of garlic components. The aim of this study was to evaluate the emulsification properties of garlic water-soluble compounds (GWSC), encompassing proteins, saponins, and carbohydrates, after heat treatment (10 min at 95 °C) or pH adjustments (2.5, 3.5, and 7.8). After the various treatments, the extracts were used as such or filtrated (0.45 µm), and 10% soybean oil-in-water emulsions were prepared using low (0.48%) or high (6.55% wt/wt) extract concentrations. Results showed that whereas at low GWSC concentrations, both heating and acidifying resulted in the formation of bigger oil droplet sizes (i.e., from d32 = 0.36 µm using unmodified extract to d32 = 7-22 µm at pH 2.5 with or without extract filtration), the effects were opposite at the highest GWSC concentration. In the latter, heat treatment clearly reduced the droplet size as observed from the micrographs as well as the degree of creaming, though the occurrence of depletion and/or bridging flocculation was still strong. The acidification of the extract at this high GWSC concentration significantly reduced the droplet size, as observed from the micrographs; however, a strong flocculation was observed. Removal of protein aggregates, and possibly also saponin micelles, from the extract resulted in an obvious increase in emulsion droplet size. This research brings valuable insights on this study and utilisation of novel natural food emulsifiers from plant sources.Item The Role of Gastric Lipase and Pepsin in Lipid Digestion of a Powder Infant Formula Using a Simulated Neonatal Gastric System(Springer Nature, 2024-02-08) Deng L; Golding M; Lentle R; MacGibbon A; Matia-Merino LThis study has sought to determine the impact of interfacial dynamics on the in vitro lipid digestion of a commercial infant formula; in particular, the specific role of interfacial proteolysis on the subsequent rates of reaction of droplet lipolysis. A powder infant formula was used as the as a protein-stabilised emulsion substrate during simulated infant gastric digestion at different pH level 3.5, 4.5 and 5.5. The digestate was treated with a fungal lipase and porcine pepsin (used to analogue human gastric lipase and pepsin) respectively and in a combined action. The study found that for fungal lipase treated digestate, the rate and extent of lipolysis were observed to be maxim at pH 5.5, in accordance with the optimal pH activity of the lipase. Findings also indicated that the proteinaceous interface did not appear to act as a barrier to lipolysis, since treatment with lipase and pepsin did not result in any significant increase in extent of lipolysis. However, it was observed that surface proteolysis did lead to alteration of the structural fate of the enzyme during digestion when compared to when the emulsion was digested solely by lipase. Findings suggest that lipolysis under these conditions may be independent of the structural dynamics of the emulsion during digestion, as observed within the context of this study design.Item 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 LA 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.Item 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 LMamaku 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.Item Glycaemic potency reduction by coarse grain structure in breads is largely eliminated during normal ingestion(Cambridge University Press on behalf of The Nutrition Society, 2022-05-28) Srv A; Mishra S; Hardacre A; Matia-Merino L; Goh K; Warren FJ; Monro JAThe hypothesis that coarse grain particles in breads reduce glycaemic response only if the particles remain intact during ingestion was tested. Three breads were formulated: (1) White bread (WB - reference), (2) 75 % of kibbled purple wheat in 25 % white bread matrix (PB) and (3) a 1:1 mixture of 37·5 % kibbled soya beans and 37·5 % of kibble purple wheat in 25 % white bread matrix (SPB). Each bread was ingested in three forms: unchewed (U), as customarily consumed (C) and homogenised (H). Twelve participants ingested 40 g available carbohydrate portions of each bread in each form, with post-prandial blood glucose measured over 120 min. Glycaemic responses to WB were the same regardless of its form when ingested. Unchewed PB had significantly less glycaemic effect than WB, whereas the C and H forms were similar to WB. Based on a glycaemic index (GI) of 70 for WB, the GI values for the C, U and H breads, respectively, were WB: 70·0, 70 and 70, PB: 75, 42 and 61, SPB: 57, 48 and 55 (%) (Least significant difference = 17·43, P < 0·05, bold numbers significantly different from WB). The similar glycaemic response to the H and C forms of the breads, and their difference from the U form, showed that the glycaemia-moderating effect of grain structure on starch digestion was lost during customary ingestion of bread. We conclude that the kibbled-grain structure may not effectively retard starch digestion in breads as normally consumed because it is largely eliminated by ingestive processes including chewing.Item Evaluation of formulation design on the physical and structural properties of commercial cream cheeses(John Wiley and Sons Ltd on behalf of Institute of Food, Science and Technology (IFSTTF)., 2022-10) Kim J; Watkinson P; Matia-Merino L; Smith JR; Golding MThis study investigated how the compositional properties and formulation design of commercial cream cheese products model cheese influenced physical and structural properties as compared to a model cheese composition. Of the seven products evaluated, three were block format (B), two were spreadable (S) and two were spreadable light (SL), with fat contents ranging from 13.7 to 35.7%. The majority of cream cheese products indicated the inclusion of starter culture, and all formulations contained one or more stabilisers. Protein/moisture (p/m) ratio, i.e. the effective protein concentration in the non-fat substance, was seen to most strongly correlate with material properties, with a positive slope for fracture stress (R2 = 0.808) and modulus of deformability (R2 = 0.721). In terms of outliers, the datapoint for SL2 on this modulus versus p/m graph was lower than its regression line, and one rationale is that lower fat content (13.7%) gave a lower modulus from the milkfat component at 10°C test temperature. B1, with the highest p/m of 0.17, had a more dense distribution of larger fat globules coated with proteins than B2 and B3. Fracture stress and modulus of deformability were noted to be higher for full-fat than for lower fat cheese. In all products, elastic characteristics dominated viscous flow as expected. Findings have demonstrated that significant variance exists across the material properties of commerical cream cheeses, and which shows specific dependencies on their formulation.Item Effect of Process and Formulation Variables on the Structural and Physical Properties in Cream Cheese using GDL Acidulant(Springer Science+Business Media, LLC, 2022-06) Kim J; Watkinson P; Lad M; Matia-Merino L; Smith JR; Golding MWe report on the properties of analogue cream cheeses prepared using glucono delta-lactone (GDL) acidulant, notably the impact of particular processing and formulation variables, (homogenisation pressure, coagulation pH and temperature, and stabiliser level) on cream cheese physical, material and microstructural properties. Protein–protein and protein-fat interactions were seen to be the primary structural contributors to the physical properties of cream cheese. Cream cheese microstructure and its properties demonstrated well-defined correlations to specific and controllable processing elements within the manufacturing process, showing significance in interactions between parameters in multivariable linear regression analysis (P < 0.05). Summarising the effect of processing variables on key cheese properties, we observed that a progressive reduction in fat particle size of cheese milk arising from increasing homogenisation pressures was seen to increase the total surface area of fat that could be incorporated into the curd during coagulation. The greater extent of fat-fat and fat-proteins interactions during coagulation provided a reinforcing effect on the microstructure of the final cream cheese, with a corresponding increase in compressive fracture stress, shear storage modulus (G′) and shear loss modulus (G″). In terms of other processing variables, cream cheese firmness was also observed to progressively increase through lowering of coagulation pH from 5.13 to 4.33. Increasing coagulation temperature from 58 °C to 78 °C similarly caused an increase in cheese firmness. Finally, increasing the levels of added stabiliser were shown to correlate with increasing cheese firmness. Similar correlations could be observed in relation to physical properties, notably forced expressible serum separation. This model cream cheese preparation method has provided a useful model system for relating food structure to material and functional properties. In addition, it has the advantage of being able to rapidly screen many formulation and process variables because it is faster than the traditional cheesemaking. This study showed that the adjustment of process and formulation variables, either in isolation or in combination, in the manufacture of cream cheese can significantly influence the final material and textural properties of the product, thereby enabling controllable functional attributes capable of meeting different customer needs.
