Browsing by Author "Loveday SM"
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- ItemDigestive diversity and kinetic intrigue among heated and unheated β-lactoglobulin species.(ROYAL SOC CHEMISTRY, 2014-11) Loveday SM; Peram MR; Singh H; Ye A; Jameson GBFood processing often alters the structure of proteins, and proteins are deliberately denatured and aggregated to improve technological functionality in many cases. However, the digestive consequences of processing-induced alterations to protein structure have only recently been studied. Here we explored the process-structure-digestibility relationship in the context of heat-processing effects on the structure and gastric digestibility of the bovine whey protein β-lactoglobulin (β-lg). Heating β-lg produces an array of non-native monomers, dimers and aggregates, and we have characterised these with reverse-phase high performance liquid chromatography (RP-HPLC) as a complement to our earlier work using polyacrylamide gel electrophoresis (PAGE) techniques. Using a combination of SDS-PAGE and RP-HPLC we have identified pepsin-resistant dimers and peptides that appear early in digestion. In an unexpected finding, native β-lg underwent complete hydrolysis during prolonged incubation (48 h) with pepsin. Two phases of hydrolysis were identified, and the transition between phases appears to result from alterations to the secondary structure of β-lg at 3-4 h, as measured with circular dichroism spectroscopy, and/or the binding and release of a pepsin inhibitor peptide. This work has unpacked some of the complexities of the processing-structure-digestibility relationship in a highly simplified system; further work is needed to explore the implications of these findings for food processors, regulatory authorities and consumers.
- ItemHeat-induced colloidal interactions of whey proteins, sodium caseinate and gum arabic in binary and ternary mixtures(Elsevier Ltd, 2013-11) Loveday SM; Ye A; Anema SG; Singh HMany food-grade proteins and polysaccharides will aggregate together when acidified or heated, due to electrostatic and hydrophobic interactions. At low concentrations, aggregates are soluble and colloidally stable, and they have potential applications as Pickering emulsifiers and nutrient carriers. Sodium caseinate (SC) and gum arabic (GA) at pH. 7 will form colloidal aggregates when heated, but aggregation is largely reversed on cooling. Whey proteins (in the form of whey protein isolate, WPI) will aggregate irreversibly with GA when they are heated together, but aggregation is often so rapid and extensive that aggregates precipitate. Here we sought to overcome those limitations, and to develop an in situ method for quantifying heat-induced aggregation. Aggregation was measured using temperature-controlled dynamic light scattering equipment and transmission electron microscopy. Combinations of SC, WPI and GA were heated at either pH. 7 or 3.5, and the weight ratio of protein to polysaccharide was held at 1:5 for simplicity. Heat-induced colloidally stable aggregates of SC. +. WPI. +. GA did not dissociate on cooling. Aggregation was measured in situ, both in temperature ramps and with isothermal experiments. In situ measurement allowed us to avoid potential artefacts stemming from the temperature changes and measurement delays associated with ex situ measurements. This work demonstrated how the size and heat-stability of colloidal protein-polysaccharide aggregates can be tailored by judicious selection of proteins, pH and heat treatment.
- ItemModelling Lactation Curves for Dairy Sheep in a New Zealand Flock(MDPI (Basel, Switzerland), 2023-01-19) Marshall AC; Lopez-Villalobos N; Loveday SM; Ellis A; McNabb WLactation curves were modelled for dairy sheep in a New Zealand flock, providing information on the lactation yields of milk, fat, protein, and lactose, corrected for 130 days of milking. From 169 ewes, a total of 622 test-day records were obtained during the milk production season of 2021-2022 (from October to January). The flock produced an average of 86.1 kg of milk, 5.1 kg of fat, 4.5 kg of protein, and 4.1 kg of lactose, and moderate to large coefficients of variation were observed (27-31%) for these traits. The lactation persistency of milk, fat, protein, and lactose yields ranged from 52.3 to 72.7%. Analyses of variance for total yield and persistency were performed with an animal model that included the fixed effects of age (parity number), litter size, coat colour, and milking frequency (days in twice-a-day milking) and random residuals. Age and milking frequency were the only factors that significantly affected the yields of milk, fat, protein, and lactose. Age significantly affected the lactation persistency of milk and lactose yields, whereas litter size affected the persistency of protein, and milking frequency affected the persistency of fat. This study on this single flock provides valuable experience for a larger-scale animal breeding programme in New Zealand.
- ItemSoy Protein Pressed Gels: Gelation Mechanism Affects the In Vitro Proteolysis and Bioaccessibility of Added Phenolic Acids(MDPI (Basel, Switzerland), 2021-01-13) Marinea M; Ellis A; Golding M; Loveday SMIn this study, a model system of firm tofu (pressed gel) was prepared to study how the coagulation mechanism-acidification with glucono δ-lactone (GDL) or coagulation with magnesium sulphate (MgSO4)-affected the physical properties of the gels along with their in vitro proteolysis (or extent of proteolysis). The two types of gels were also fortified with 3.5 mM protocatechuic (PCA) and coumaric acid (CMA) to test whether they can be used as bioactive delivery systems. Texture analysis showed that all MgSO4-induced gels (fortified and control) had a higher hydration capacity and a weaker texture than the GDL-induced gels (p < 0.05). MgSO4 gels had almost double proteolysis percentages throughout the in vitro digestion and showed a significantly higher amino acid bioaccessibility than the GDL gels (essential amino acid bioaccessibility of 56% versus 31%; p < 0.05). Lastly, both gel matrices showed a similar phenolic acid release profile, on a percentage basis (~80% for PCA and ~100% for CMA). However, GDL gels delivered significantly higher masses of bioactives under simulated intestinal conditions because they could retain more of the bioactives in the gel after pressing. It was concluded that the coagulation mechanism affects both the macro- and microstructure of the soy protein pressed gels and as a result their protein digestibility. Both pressed gel matrices are promising delivery systems for bioactive phenolic acids.
- ItemThe use of confocal Raman microscopy and microfluidic channels to monitor the location and mobility of β-carotene incorporated in droplet-stabilized oil-in-water emulsions(Elsevier B V, 2023-05-17) Okubanjo SS; Brooke SJ; Ward R; Mostert N; Loveday SM; Ye A; Wilde PJ; Singh H; Waterland MThis study sought to explore the combined use of confocal Raman microscopy and microfluidic channels to probe the location and mobility of hydrophobic antioxidant (β-carotene) incorporated at the interface of food-grade droplet-stabilized emulsions (DSEs). Microfluidic channels were used to isolate emulsion droplets for efficient investigation of antioxidant mobility. This approach proved more conclusive than fixing the sample in agarose, because a single layer of droplets could be obtained. Results also indicated that the migration of β-carotene incorporated in shell droplets of olive oil and trimyristin DSEs to core droplets was minimal and beta-carotene remained mostly localised at the interface even after 3 days of production. This work demonstrates that microfluidic isolation of emulsion droplets combined with confocal Raman microscopy can give new insights into the spatial variation of chemical composition within emulsions. This study revealed that the migration of β-carotene between shell and core was minimal and hence it may be possible to concurrently deliver two incompatible compounds by spatially segregating them between shell and core compartments of DSEs.
- Itemβ-Lactoglobulin nanofibrils: Effect of temperature on fibril formation kinetics, fibril morphology and the rheological properties of fibril dispersions(Elsevier Ltd, 2012-05) Loveday SM; Wang XL; Rao MA; Anema SG; Singh HAlmost all published studies of heat-induced b-lactoglobulin self-assembly into amyloid-like fibrils at low pH and low ionic strength have involved heating at 80 C, and the effect of heating temperature on self-assembly has received little attention. Here we heated b-lactoglobulin at pH 2 and 75 C, 80 C, 90 C, 100 C, 110 C or 120 C and investigated the kinetics of self-assembly (using Thioflavin T fluorescence), the morphology of fibrils, and the rheological properties of fibril dispersions. Self-assembly occurred at all temperatures tested. Thioflavin T fluorescence increased sigmoidally at all temperatures, however it decreased sharply with >3.3 h heating at 110 C and with >5 h heating at 120 C. The sharp decreases were attributed partly to local gelation, but destruction of fibrils may have occurred at 120 C. Thioflavin T fluorescence results indicated that maximal rates of fibril formation increased with increasing temperature, especially above 100 C, but fibril yield (maximum Thioflavin T fluorescence) was not affected by temperature. At 100 C and 110 C, fibrils were slightly shorter than at 80 C, but otherwise they looked very similar. Fibrils made by heating at 120 C for 1 h were also similar, but heating at 120 C for 8 h gave predominantly short fibrils, apparently the products of larger fibrils fragmenting. Heating at 100 C gave consistently higher viscosity than at 80 C, and heating for >2 h at 120 C decreased viscosity, which may have been linked with fibril fragmentation seen in micrographs.