Bio21 - Research Publications
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ItemCharacterising the influence of milk fat towards an application for extrusion-based 3D-printing of casein-whey protein suspensions via the pH-temperature-route(ELSEVIER SCI LTD, 2021-09)This study presents the design and characterisation of casein−whey protein suspensions (8.0/10.0% (w/w) casein and 2.0/2.5% (w/w) whey protein) mixed with dairy fat (1.0, 2.5 and 5.0% (w/w) total fat) processed via the pH−temperature-route in preparation for 3D-printing. Mechanical treatment was applied to significantly decrease the particle size of the milk fat globules and increase surface area, creating small fat globules (<1 μm) covered with proteins, which could act as pseudo protein particles during gelation. Different proteins covered the fat globule surface after mechanical treatment, as a result of differences in the pH adjusted just prior to heating (6.55, 6.9 or 7.1). The protein-fat suspensions appeared similar by transmission electron cryogenic microscopy and the zeta-potential of all particles was unchanged by the heating pH, with a similar charge to the solution (~−20 mV) occurring after acidification (pH 4.8/5.0) at low temperatures (2 °C). A low heating pH (6.55) resulted in increased sol−gel transition temperatures (G՛ = 1 Pa) and a decreased rate of aggregation for protein−fat suspensions. A higher heating pH (6.9 and 7.1) caused an increased rate of aggregation (aggregation rate ≥ 250 Pa/10 K), resulting in materials more promising for application in extrusion-based printing. 3D-printing of formulations into small rectangles, inclusive of a sol−gel transition in a heated nozzle, was conducted to relate the aggregation rate towards printability.
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ItemTailoring the structure of casein micelles through a multifactorial approach to manipulate rennet coagulation properties(Elsevier Inc., 2020-04-01)The properties of casein micelles are known to be affected by modifications to the environment, such as variations in pH or the addition of salts, yet the scientific literature typically considers the effects of one factor at a time, while in industrial processes, several modifications are performed simultaneously. The aim of this study was to assess the impact of multifactorial environmental modifications on the colloidal, structural and rennet coagulation properties of casein micelles in a simplified model system. A key finding was that dense regions (~20 nm in size) could be released from the casein micelle. The addition of NaCl and CaCl2 had opposing effects, i.e. enhancing or limiting this micellar disruption, respectively. A decrease in pH had the strongest impact on the mineral balance, causing the colloidal CaP to solubilize and the micelle to swell. The rennet clotting time was impacted by variations in pH and NaCl content. Interestingly, a consideration of all three levels of casein micelle structure and their interactions was needed to explain variations in the firmness of rennet gels. This study illustrates the complex interplay of factors affecting micellar structure and improves our understanding of how micelles can be manipulated to control their properties.