Sally L Gras

University of Melbourne, Melbourne, Victoria, Australia

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Publications (53)223.1 Total impact

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    ABSTRACT: The curcuminoid-carrying potential of oat fiber was examined as a potential route to overcome the low aqueous solubility of curcuminoids. Aqueous dispersions of oat fiber were mixed with curcuminoids solubilized in ethanol to obtain curcuminoid - oat fiber (1% w/w) dispersions in aqueous ethanol (2% v/v). Centrifugation of the curcuminoids - oat fiber dispersions resulted in a supernatant (95.3% w/w, 0.11% w/w protein, 0.17% w/w β-glucan) and precipitate (4.74% w/w, 0.18% w/w protein, 0.11% w/w β-glucan), with the curcuminoids being almost equally partitioned into the both fractions. Curcuminoids solubility in the supernatant was markedly greater than that in aqueous ethanol and water. The curcuminoids were in the amorphous state in the precipitate fraction and was more stable to degradation than the curcuminoids in the supernatant. These studies show that potential of oat fiber as a carrier for curcuminoids into functional foods.
    Journal of Agricultural and Food Chemistry 12/2014; · 3.11 Impact Factor
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    ABSTRACT: Milk fat globules and their surrounding biological membrane (the MFGM) are not well understood despite the importance of these milk components in human nutrition and the role of fat globules in determining the properties of dairy products. The objectives of this study were to investigate these unique colloidal assemblies and the microstructure of the MFGM in buffalo milk, which is the second largest global source of dairy products. In-situ structural investigations were performed at room temperature using confocal microscopy with multiple fluorescent probes (Nile Red, Rh-DOPE, the lectin WGA-488). Microscopic observations showed cytoplasmic crescents around fat globules and the heterogeneous distribution of glycosylated molecules and polar lipids with the occurrence of lipid domains. The lipid domains in the buffalo MFGM appear to form by the segregation of lipids with a high phase transition temperature (e.g. sphingomyelin and saturated phosphatidylcholine molecular species) and cholesterol resulting in a gel phase or a Lo phase forming circular domains. The structure of the buffalo MFGM results from a non-random mixing of components, consistent with observations for other species. Structural heterogeneities of the MFGM could affect the processability of buffalo fat globules and the bioavailability of milk lipids.
    Food Research International 11/2014; · 3.05 Impact Factor
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    ABSTRACT: Colonic bacteria may mediate the transformation of curcuminoids but studies of this metabolism are limited. Here, the metabolism of curcuminoids by Escherichia fergusonii (ATCC 35469) and two Escherichia coli strains (ATCC 8739 and DH10B) was examined in modified medium for colon bacteria (mMCB) with or without pig cecal fluid. LC-MS analysis showed that 16-40% of curcumin, 6-20% of demethoxycurcumin (DMC) and 7-15% of bis-demethoxycurcumin (Bis-DMC) were converted following 36 h of fermentation, with the amount of curcuminoids degraded varying depending on the bacterial strain and medium used. Three metabolites (dihydrocurcumin (DHC), tetrahydrocurcumin (THC), ferulic acid (FA)) were found in fermentation cultures with all strains used. In addition, a compound with m/z [M-H]- 470 was found and identified to be a curcumin adduct (curcumin-L-cysteine), using accurate mass FT-ICR-MS. This study provides insights into the bacterial metabolism of curcuminoids.
    Journal of Agricultural and Food Chemistry 10/2014; · 3.11 Impact Factor
  • Food Hydrocolloids 10/2014; 40:16–21. · 4.28 Impact Factor
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    ABSTRACT: Tissue engineering is a complex and dynamic process that requires varied biomolecular cues to promote optimal tissue growth. Consequently, the development of delivery systems capable of sequestering more than one biomolecule with controllable release profiles is a key step in the advancement of this field. This study develops multilayered polyelectrolyte films incorporating alpha-melanocyte stimulating hormone (α-MSH), an anti-inflammatory molecule, and basic fibroblast growth factor (bFGF). The layers were successfully formed on macroporous poly lactic-co-glycolic acid microspheres produced using a combined inkjet and thermally induced phase separation technique. Release profiles could be varied by altering layer properties including the number of layers and concentrations of layering molecules. α-MSH and bFGF were released in a sustained manner and the bioactivity of α-MSH was shown to be preserved using an activated macrophage cell assay in vitro. The system performance was also tested in vivo subcutaneously in rats. The multilayered microspheres reduced the inflammatory response induced by a carrageenan stimulus six weeks after implantation compared to the non-layered microspheres without the anti-inflammatory and growth factors, demonstrating the potential of such multilayered constructs for the controlled delivery of bioactive molecules.
    Journal of Biomedical Materials Research Part A 09/2014; · 2.83 Impact Factor
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    ABSTRACT: Porous microspheres capable of delivering high payloads of biomolecules with suitable biodegradability and biocompatibility would be valuable in delivery systems to aid tissue regeneration. This study describes a facile, scalable technique to produce biodegradable porous microspheres by combining continuous ink-jetting through a piezoelectric nozzle with thermally induced phase separation (TIPS). A selection of biomaterials is investigated to suit delivery in tissue engineering, the synthetic polyesters poly(lactic-co-glycolic acid) (PLGA), and poly caprolactone (PCL) and a natural polymer, gelatin. The parameters governing the microsphere production are determined experimentally and compared to theoretical predictions derived from the fluid mechanics and heat transfer during the ink-jetting process. The microspheres produced have open interconnected pores with mean particle diameters of 80–200 μm and no significant skin region. The physical properties, such as the mean particle diameter, pore size, and surface area could be controlled by varying production parameters including the ink-jetting pressure, nozzle height, and the size and oscillation frequency of the nozzle. The technique is demonstrated to successfully encapsulate a model hydrophobic molecule during microsphere production with uniform distribution. Porous PLGA microspheres are also used to achieve much higher adsorption capacities of a short peptide than non-porous microspheres of the same material.
    Particle and Particle Systems Characterization 06/2014; · 0.54 Impact Factor
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    ABSTRACT: Amyloid fibrils are ordered, insoluble protein aggregates that are associated with neurodegenerative conditions such as Alzheimer's disease. The fibrils have a common rod-like core structure, formed from an elongated stack of β-strands, and have a rigidity similar to that of silk (Young's modulus of 0.2-14 GPa). They also exhibit high thermal and chemical stability and can be assembled in vitro from short synthetic non-disease-related peptides. As a result, they are of significant interest in the development of self-assembled materials for bionanotechnology applications. Synthetic DNA molecules have previously been used to form intricate structures and organize other materials such as metal nanoparticles and could in principle be used to nucleate and organize amyloid fibrils. Here, we show that DNA origami nanotubes can sheathe amyloid fibrils formed within them. The fibrils are built by modifying the synthetic peptide fragment corresponding to residues 105-115 of the amyloidogenic protein transthyretin and a DNA origami construct is used to form 20-helix DNA nanotubes with sufficient space for the fibrils inside. Once formed, the fibril-filled nanotubes can be organized onto predefined two-dimensional platforms via DNA-DNA hybridization interactions.
    Nature Nanotechnology 06/2014; · 31.17 Impact Factor
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    ABSTRACT: Nanotechnology promises to affect many aspects of our lives with its development being greeted with both excitement and fear. The debate concerning nanotechnology has echoed that of genetically engineered organisms and their introduction into the environment and the food chain. Nanotechnology offers many potential advantages in the processing and manufacture of foods: enhanced bioavailability, colour and flavour; novel food textures; new delivery mechanisms; and access to biosensors to enhance food safety. In fact, many of the foods we have been consuming for centuries already contain nanostructures, leading many to assume that they are safe. The extent to which novel nanostructures may afford new risks has not been adequately resolved, however, leading to concern within some consumer groups. In this article, we use proteins as a case study to explore our current understanding of nanostructures in foods and the extent to which novel nanostructures may introduce new properties. It is well recognised that some protein nanostructures are toxic and are associated with disease, so there is legitimate concern as to whether such species should be deliberately introduced into our foods. This review highlights current literature on protein nanostructures in food and possible risks associated with their use. We aim to provide a balanced assessment to inform future decision-making regarding the utilisation of nanostructures in food.
    Trends in Food Science & Technology 05/2014; · 4.65 Impact Factor
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    ABSTRACT: The physicochemical and rheological properties of yoghurt made from unstandardised unhomogenised buffalo milk were investigated during fermentation and 28 days of storage and compared to the properties of yoghurt made from homogenised fortified bovine milk. A number of differences observed in the gel network can be linked to differences in milk composition. The microstructure of buffalo yoghurt, as assessed by confocal laser scanning microscopy (CLSM) and cryo scanning electron microscopy (cryo-SEM), was interrupted by large fat globules and featured more serum pores. These fat globules have a lower surface area and bind less protein than the homogenised fat globules in bovine milk. These microstructural differences likely lead to the higher syneresis observed for buffalo yoghurt with an increase from 17.4 % (w/w) to 19.7 % (w/w) in the weight of whey generated at days 1 and 28 of the storage. The higher concentration of total calcium in buffalo milk resulted in the release of more ionic calcium during fermentation. Gelation was also slower but the strength of the two gels was similar due to similar protein and total solids concentrations. Buffalo yoghurt was more viscous, less able to recover from deformation and less Newtonian than bovine yoghurt with a thixotropy of 3,035 Pa.s−1 measured for buffalo yoghurt at the end of the storage, at least four times higher than the thixotropy of bovine yoghurt. While the titratable acidity, lactose consumption and changes in organic acid concentrations were similar, differences were recorded in the viability of probiotic bacteria with a lower viability of Lactobacillus acidophilus of 5.17 log (CFU/g) recorded for buffalo yoghurt at day 28 of the storage. Our results show that factors other than the total solids content and protein concentration of milk affect the structural properties of yoghurt. They also illustrate the physicochemical reasons why buffalo and bovine yoghurt are reported to have different sensory properties and provide insight into how compositional changes can be used to alter the microstructure and properties of dairy products.
    Food and Bioprocess Technology 04/2014; · 3.13 Impact Factor
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    ABSTRACT: The amyloid fibril-forming ability of two closely related antifungal and antimicrobial peptides derived from plant defensin proteins has been investigated. As assessed by sequence analysis, thioflavin T binding, transmission electron microscopy, atomic force microscopy and X-ray fibre diffraction, a 19 amino acid fragment from the C-terminal region of Raphanus sativus antifungal protein, known as RsAFP-19, is highly amyloidogenic. Further, its fibrillar morphology can be altered by externally controlled conditions. Freezing and thawing led to amyloid fibril formation which was accompanied by loss of RsAFP-19 antifungal activity. A second, closely related antifungal peptide displayed no fibril-forming capacity. It is concluded that while fibril formation is not associated with the antifungal properties of these peptides, the peptide RsAFP-19 is of potential use as a controllable, highly amyloidogenic small peptide for investigating the structure of amyloid fibrils and their mechanism of formation.
    Biochimica et Biophysica Acta 05/2013; · 4.66 Impact Factor
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    ABSTRACT: Non-core residues can affect the formation and protofilament packing of fibrils assembled from short peptide sequences. These residues are of interest in understanding amyloid diseases and in the design of self-assembling peptide materials with a cross-β core, where the assembly process should be reproducible and functional groups accessible on the fibril surface. In this study, the well characterised TTR1 peptide, also known as TTR105–115, was functionalised with glycine and lysine residues forming the peptide TTR1-GGK, with the aim of producing a self-assembling fibril scaffold that can be functionalised following assembly. A second aim was to develop a sequence capable of fibril assembly under a wide range of solution conditions. The lysine residue was found accessible on the surface of TTR1-GGK fibrils and the C-terminal residues influenced the mature fibril width and rate of fibril assembly, as observed for other TTR1-based fibrils. The assembly of TTR1-GGK fibrils was examined for conditions of varying ionic strength (NaCl, 0–0.5 M), solution pH or in the presence of anions (NaCl, NaI, NaNO3 and NaSO4) or cations (NaCl, CaCl2, MgCl2, LiCl and KCl). The addition of salt increased the rate of TTR1-GGK fibril nucleation but decreased the rate of elongation at high salt concentrations. A combination of electrostatic and hydrophobic interactions was found to promote initial contacts between peptides. Specific ion effects were seen with chaotropic anions, which promoted fibril nucleation. The cross-β core structure, secondary structure and morphology of TTR1-GGK fibrils were largely unaltered by the presence of salt or a range of solution pH. The length of fibrils was also maintained at the high ionic strengths tested, indicating that these fibrils may make suitable scaffolds for fibril functionalisation under a range of conditions.
    Soft Matter 01/2013; · 4.15 Impact Factor
  • Elizabeth B Sawyer, Sally L Gras
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    ABSTRACT: Amyloid fibrils are attractive targets for applications in biotechnology. These thin, nanoscale protein fibers are highly ordered structures that self-assemble from their component proteins or peptides. This chapter describes the use of several biophysical techniques to monitor the formation of amyloid fibrils including a common dye-binding assay, turbidity assay, and small-angle X-ray scattering. These techniques provide information about the assembly mechanism, the rate and reproducibility of assembly, as well as the size of species along the assembly pathway.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 996:77-101. · 1.29 Impact Factor
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    ABSTRACT: Large bowel luminal short chain fatty acids (SCFA) are protective against gut diseases such as colorectal cancer, Crohn’s disease and ulcerative colitis. High amylose maize starches acylated with acetic, propionic or butyric were previously shown to deliver SCFA to the gut and increase gut SCFA. This study examines the ability of five Bifidobacterium spp. (B. longum, B. breve, B. infantis, B. adolescentis and B. bifidum), Ruminococcus bromii and Faecalibacterium prausnitzii to degrade starches acylated with SCFA. Release of SCFA from modified starches was not observed, suggesting no preferential hydrolysis of the SCFA ester bond over the glycosidic bond. Acetylated and propionated starches are more readily degraded than either the base or butyrated starches in tested cultures. These observed differences may depend on modification to the starch structure. These structural differences alter the kinetics of starch digestion, irrespective of bacterial type, which may impact current approaches of prebiotic selection.
    Journal of Functional Foods 01/2013; · 4.48 Impact Factor
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    Zhenyu Shi, Anthony G Wedd, Sally L Gras
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    ABSTRACT: The development of synthetic biology requires rapid batch construction of large gene networks from combinations of smaller units. Despite the availability of computational predictions for well-characterized enzymes, the optimization of most synthetic biology projects requires combinational constructions and tests. A new building-brick-style parallel DNA assembly framework for simple and flexible batch construction is presented here. It is based on robust recombination steps and allows a variety of DNA assembly techniques to be organized for complex constructions (with or without scars). The assembly of five DNA fragments into a host genome was performed as an experimental demonstration.
    PLoS ONE 01/2013; 8(2):e56854. · 3.53 Impact Factor
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    ABSTRACT: A novel combination of site-specific isotope labelling, polarised infrared spectroscopy and molecular combing reveals local orientational ordering in the fibril-forming peptide YTIAALLSPYSGGRADS. Use of (13)C-(18)O labelled alanine residues demonstrates that the N-terminal end of the peptide is incorporated into the cross-beta structure, while the C-terminal end shows orientational disorder.
    Chemical Communications 09/2012; · 6.38 Impact Factor
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    ABSTRACT: The effect of milk pH at renneting on the microstructure, composition and texture of Cheddar cheese was investigated. Four different Cheddar cheeses were made by the addition of rennet to milk pre-acidified to pH 6.7, pH 6.5, pH 6.3 or pH 6.1. The gel renneted at pH 6.1 showed a dense protein network when observed using confocal laser scanning microscopy and cryo scanning electron microscopy. This structure became more compact after cooking, forming an irregular and coarse matrix with lower porosity than in other treatments. There was less fat lost to the whey during the draining of curd after cooking and higher fat lost to the whey during pressing in samples made from milk renneted at a lower pH. The texture of the Cheddar cheese made using milk renneted at pH 6.1 was altered, with lower chewiness, gumminess, cohesiveness and springiness when compared to cheese made using milk renneted at pH 6.7 or pH 6.5. The yield in dry matter of cheese renneted at pH 6.1 or pH 6.3 was 11–13% higher than for cheese renneted at pH 6.7. These results indicate that the pH of milk at renneting is a process variable that can be used to increased yield and alter the texture of Cheddar cheese.
    Food Research International 08/2012; 48(1):119–130. · 3.05 Impact Factor
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    ABSTRACT: Many bacteria produce protein fibrils that are structurally analogous to those associated with protein misfolding diseases such as Alzheimer's disease. However, unlike fibrils associated with disease, bacterial amyloids have beneficial functions including conferring stability to biofilms, regulating development or imparting virulence. In the present review, we consider what makes amyloid fibrils so suitable for these roles and discuss recent developments in the study of bacterial amyloids, in particular the chaplins from Streptomyces coelicolor. We also consider the broader impact of the study of bacterial amyloids on our understanding of infection and disease and on developments in nanotechnology.
    Biochemical Society Transactions 08/2012; 40(4):728-34. · 2.59 Impact Factor
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    ABSTRACT: Protein nanofibers are emerging as useful biological nanomaterials for a number of applications, but to realize these applications requires a cheap and readily available source of fibril-forming protein material. We have identified fish lens crystallins as a feedstock for the production of protein nanofibers and report optimized methods for their production. Altering the conditions of formation leads to individual protein nanofibers assembling into much larger structures. The ability to control the morphology and form higher order structures is a crucial step in bottom up assembly of bionanomaterials. Cell toxicity assays suggest no adverse impact of these structures on mammalian cell proliferation. There are many possible applications for protein nanofibers; here we illustrate their potential as templates for nanowire formation, with a simple gold plating process.
    Biopolymers 08/2012; 97(8):595-606. · 2.29 Impact Factor
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    ABSTRACT: The milk fat globule membrane (MFGM) is a complex soft matter system that encapsulates the milk fat globule (MFG). It is important for the successful delivery of nutrients for newborns and it is also increasingly studied for its potential pharmaceutical benefits. Yet, the persistence and integrity of the MFGM through many steps common in the processing of milk for consumption and cheese manufacture is not completely understood and is an area of ongoing interest. In this study, atomic force microscopy (AFM) was used to characterize the MFGM membrane interface to demonstrate the effects of mechanical force and shear encountered during milk processing. The results showed that significant differences can be observed and such a soft biological system with complex constituents can be quantitatively characterized using AFM. Major differences were observed in the surface morphology and the roughness of the MFGM in raw milk, raw ultra filtrate (UF) retentate, homogenized milk, cheese milk and cream samples. The MFGM of the homogenized fat globules showed the greatest difference in appearance when compared to the native raw MFGM from damage largely due to the homogenization process. In addition, AFM elasticity and thickness measurements of the MFGM showed quantitative differences between the five different samples with an increase in the stiffness of the MFGM of milk samples that have undergone more processing steps. The quantitative results of the physical nature of the MFGM from the AFM study, combined with the qualitative results on the chemical nature of the MFGM, demonstrate that AFM can aid in the understanding of the interfacial behaviour of complex soft matter systems where access to detailed chemical composition is limited.
    RSC Advances 02/2012; 2(6):2384-2394. · 3.71 Impact Factor
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    ABSTRACT: The incorporation of low molecular weight drugs and therapeutic peptides into multilayer films assembled via the layer-by-layer technique can potentially provide means to deliver small molecules to target sites and to tune their release. This study describes the use of both hydrophobic and electrostatic interactions to incorporate a tridecapeptide antiinflammatory hormone, α-melanocyte stimulating hormone (α-MSH), as a building block at the base of a multilayer assembly of hyaluronic acid (HA) and chitosan (CS) on poly(lactic-co-glycolic acid) (PLGA) surfaces. A range of switching layers, including a neutral lipid, dioleylphosphatidylcholine (DOPC), a negatively charged lipid mixture DOPC/dioleylphosphatidylserine (DOPS) and a negatively charged polysaccharide, HA, were investigated for their ability to support subsequent HA and CS layers. Molecular dynamics simulations were performed to examine the structure and surface chemistry of α-MSH in solution and on surfaces to provide insights into the conditions most likely to support multilayer assembly. The multilayer assembly was stable at physiological pH and was successfully applied to particulate systems.
    The Journal of Physical Chemistry B 12/2011; 116(3):1120-33. · 3.38 Impact Factor

Publication Stats

475 Citations
223.10 Total Impact Points

Institutions

  • 2006–2014
    • University of Melbourne
      • • Department of Chemical and Biomolecular Engineering
      • • School of Chemistry
      • • Bio21 Molecular Science and Biotechnology Institute
      Melbourne, Victoria, Australia
  • 2009–2013
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
  • 2011
    • University of Reading
      • Department of Chemistry
      Reading, ENG, United Kingdom
  • 2006–2011
    • University of Cambridge
      • • Department of Chemistry
      • • Department of Physics: Cavendish Laboratory
      Cambridge, ENG, United Kingdom