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Formation and rheological properties of mixed protein-polysaccharide gels (composites) was studied. The composites consisted of whey proteins gelling separately, which were surrounded by polysaccharide gel. The polysaccharide gels were obtained from κ-carrageenan and κ-carrageenan-galactomannan (guar gum and locust bean gum) mixtures. The texture of gels obtained was examined by their compression and bending test. The composite gels obtained from 14% WPI solution and the 1.5% mixture of κ-carrageenan with locust bean gum in a 1:1 ratio exhibited a higher shear stress value at fracture in comparison to WPI gels, but they were less resistant to fracture in the bending test. The texture of gels was highly influenced by pH.

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This study measured the flow behaviour of whey protein isolate mixtures with cinnamic or ferulic acids. Samples were heated in a vacuum (80 °C, –0.9 atm, 280 r.p.m., 0.5 h). The flow curves of all samples showed a non- Newtonian shear thinning flow and the viscoelastic properties were typical for weak gel systems. At pH 6.0, 6.7, and 8.0, the highest shear stress values were obtained with 20, 40, and 40 mg of cinnamic acid g–1 protein, respectively. At pH 6.0, the use of ferulic acid (20 mg g–1 protein) resulted in the elevation of shear stress values, but at pH 8.0, ferulic acid caused a decrease in shear stress values in comparison to cinnamic acid. The thixotropic area (AT) was increased in mixtures containing 20–40 mg cinnamic acid g–1 protein (at pH 6.7) and 20 mg of cinnamic acid g–1 protein (at pH 6.0). Similarly, the addition of ferulic acid (40 and 20 mg g–1 protein at pH 6.7 and 6.0, respectively) caused a significant increase in AT. At pH 8.0, no significant differences in AT values were observed between samples. Such systems can be applied with reference to health promoting foods such as WPI-based desserts.

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The objective of this work was to assess the impact of various NaCl concentrations on Lactobacillus rhamnosus OXY viability after freeze-drying. Osmotic stress was applied during the exponential growth phase of bacterial culture. At salt concentrations between 0.2–0.5 M, a high biomass concentration and a significant increase in cell viability after lyophilisation was observed. An analysis of two-dimensional protein gels indicated the presence of shock proteins, for example, GroEL, ClpB, DnaK, TF, which provide resistance during freeze-drying and subsequent storage. On the basis of these results, it is recommended that lactic acid bacteria cultures be sub-lethally treated with 0.5 M NaCl before freeze-drying.

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Acta Alimentaria
Authors: M. Tomczyńska-Mleko, W. Gustaw, T. Piersiak, K. Terpiłowski, B. Sołowiej, M. Wesołowska-Trojanowska, and S. Mleko

The objective of the research was to obtain aerated gels by magnesium and iron(II) ion induced gelation of preheated whey protein isolate dispersions. Preliminary research allowed finding conditions of the pH, protein, and ion concentrations to produce aerated gels capable of holding air bubbles. A novel method applying gelation and aeration process simultaneously was used. Aeration using a laboratory mixer at 2000 r.p.m. produced stronger aerated gels than using a homogenizer at 8000 r.p.m. The gelation process was monitored using an ultrasound viscometer and a constant increase of dynamic viscosity was noted. A different aerated gel microstructure was observed for magnesium and iron(II) induced gels, which probably resulted in differences in the texture and viscosity, as well. The aeration process decreased hardness. In some cases texture parameters correlated with the viscosity measured using an ultrasound viscometer. Aerated whey protein gels could be applied as matrices for food applications or to controlled release of active ingredients.

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