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Subject: search.filters.subject.Milk protein concentrates

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    Formation of by high power ultrasound aggregated emulsions stabilised with milk protein concentrate (MPC70)
    (Elsevier BV, 2021-12-03) Zhang R; Luo L; Yang Z; Ashokkumar M; Hemar Y
    In this work, oil-in-water emulsions stabilised by milk protein concentrate (MPC70) were investigated. The MPC70 concentration was kept constant at 5% (close to the protein content found in skim milk) and the oil volume fraction was varied from 20 to 65%. Sonication was performed at 20 kHz and at a constant power of 14.4 W for a total emulsion volume of 10 mL. Under certain oil concentration (≥35%) and sonication times (≥3s) the emulsion aggregated and formed high-viscosity pseudo plastic materials. However, the viscosity behaviour of the emulsion made with 35% oil reverted to that of a liquid if sonicated for longer times (≥15 s). Confocal laser scanning microscopy showed clearly that the oil droplets are aggregated under the sonication conditions and oil concentrations indicated above. An attempt to explain this behaviour through a simple model based on the bridging of oil droplets by the MPC70 particles and, taking into account the oil droplet and MPC70 particle sizes as well as the oil volume fraction, was made. The model fails to describe in details the aggregation behaviour of these emulsions, likely due to the inhomogeneous protein layer, where both free caseins and casein micelles are adsorbed, and to the packing of the oil droplets at concentrations ≤55%. Nonetheless, this work demonstrates the potential of ultrasound processing for the formation of dairy emulsions with tailored textures.
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    The functional properties of milk protein concentrates : a thesis presented for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 1999) Carr, Alistair James
    The aim of this thesis was to explore aspects of the functional properties of MPC85 (milk protein concentrate, 85% protein). A rheological study of milk protein concentrate (52°C) prior to spray drying showed a slight age-thinning behaviour which lasted about one hour, after which the apparent viscosity of the concentrate remained constant. This result is the opposite of skim milk concentrate which age-thickens at evaporator temperatures. The flow behaviour of the concentrate was adequately described by a Power Law rheological model. The rheological properties of reconstituted commercial MPC85 were studied at various temperatures and concentrations. At low concentrations (<10% w/w total solids) MPC85 solutions were Bingham Plastics. The yield stress was found to increase with temperature and concentration. At high concentrations (>15% w/w total solids) the logarithm of apparent viscosity was found to increase linearly with protein concentration. These solutions were also found to be Bingham Plastics. At lower temperatures (<35°C), however, these MPC85 solutions (>15% w/w total solids) were pseudoplastic and did not possess a yield stress. The solubility of commercial MPC85 was found to be dependent on the temperature at which the solution was prepared, increasing from ≈59% at 20°C to 100% at 50°C Homogenisation was shown to improve the solubility of MPC85 at 20°C. The rheological properties of MPC85 were profoundly influenced by the presence of any insoluble solids. The effect of preheat treatments during the pilot-scale manufacture of MPC85 on functionality was investigated. Heat treatment had no effect on heat stability of reconstituted MPC85 solutions for whey protein denaturation (WDN) values up to 86%. Heat treatments resulting in ≥90% WDN produced a dramatic loss in heat stability. The variations in rheology and rennet coagulation properties among the pilot plant powders were found to be correlated with the apparent diameter of the casein micelles. In reconstituted solutions the apparent diameter of the casein micelles increased gradually with heat treatments up to 86% WDN and dramatically at higher WDN levels. The main effect of preheat treatments during manufacture on the rheology of MPC85 solutions was the linear increase in apparent viscosity with apparent diameter of casein micelles. The variation in apparent viscosity with apparent diameter of casein micelles was found to be greater at low shear rates. A schematic model was proposed to account for these observations. A factorial design experiment was used to identify the components and interactions of components which play a significant part in determining the functionality of MPC85. This work demonstrated techniques for modelling heat stability - pH profiles and thereby allowing the quantitative comparison of the entire profiles of different solutions rather than comparisons at just single pH values or qualitative comparisons regarding the shape of the profile. The addition of divalent cations in the absence of added phosphate resulted in solutions that were completely unstable at 120°C. Overall this work has provided a detailed characterisation of commercial MPC85, both of the rheology of the concentrate prior to spray drying and of the functional properties of the powder. The research presented here has implications for both processing and product formulation.
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    Physicochemical changes in a model protein bar during storage
    (Elsevier, 2009) Loveday, SM; Hindmarsh, Jason; Creamer, Lawrence K; Singh, Harjinder
    High-protein snack bars (protein bars) contain high-quality protein, sugars and other low molecular weight polyhydroxy compounds (PHCs), high-energy confectionary fats, and a minimum of water (water activity ≤ 0.65). The consequence of the intimate mixing of these components in protein bars is that they can react together, creating sensory characteristics that are unacceptable to consumers. This study examined the changes occurring in a model protein bar during storage for 50 days at 20 °C. Over this time, fracture stress increased from 20.1 +/- 1.8 Pa to 201 +/- 75 Pa at a rate that decreased slightly over time. 1H nuclear magnetic resonance (NMR) showed that the molecular mobility of PHCs decreased dramatically over the first 5 days as the batter set into a solid bar. Over the first 17 hours after manufacturing, protein particles became more clustered, and soluble protein appeared to precipitate, as shown by confocal microscopy. Reactive lysine fell 38% in the first 10 days of storage and was approximately constant thereafter. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed little change in protein molecular weights. Following the initial ‘setting’ phase of 5-10 days, fracture stress continued to increase and the molecular mobility of PHCs decreased. Changes in PHC molecular mobility were consistent with glucose crystallisation. Chemical changes were minimal during this phase, which suggests that chemical reactions play little part in the hardening of protein bars and that changes in molecular mobility and changes in microstructure driven by moisture migration may be more important.