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    Effect of whey protein isolate microparticle addition on some physical and chemical properties of kefir
    (Springer Int Publ Ag, 2022) Ince-Coskun, Alev Emine; Ozdestan-Ocak, Ozgul
    Protein intake is important for some people, such as the elderly and patients, who can consume mostly liquid foods. For this purpose, we designed a functional high-protein kefir product containing whey protein isolate microparticles and investigated their physicochemical and textural properties during 14 days. We have used soft and dense particles produced at pH 6.8 and pH 5.5, respectively. The highest protein amount was obtained from the kefir sample containing dense particles (8.31%). On the other hand, the lowest serum separation was obtained from samples containing soft particles. The titration acidity of all samples increased during storage, but the soft particles increased the acidity higher values due to their lower buffering effect than the dense particles did. Total free amino acid contents were increased from 0.083 to 0.173% with increasing volume fraction of particles and during storage. The viscosity of samples was not affected by the presence of particles. The average total biogenic amine content was 16.17 mg/kg, and tyramine was the most abundant one with an average concentration of 11.1 mg/kg. The total biogenic amine content of all samples was lower than the values considered unsafe for consumption. This study demonstrated that a functional kefir product could be produced with twice the protein content without altering its texture, and therefore this could be a good alternative drink for elderly and obese people for a high protein intake. [GRAPHICS] .
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    Effects of salt ions and heating on the behaviour of whey protein particle dispersions
    (Elsevier Sci Ltd, 2020) Ince-Coskun, Alev Emine; Ozdestan-Ocak, Ozgul
    We investigated the aggregation stability of whey protein isolate (WPI) particles in the presence of different salts (NaCl2, MgCl2, and AlCl3) and the heat stability of dispersions in the presence of protein (native WPI) and polysaccharides (dextran and gum Arabic, GA). WPI particles coagulated either at pH values close to the isoelectric point of proteins or at high salt concentrations. Critical coagulation concentration (CCC) for different salts decreased with increasing valence of ions. CCC values for colloidal WPI particle dispersions closely followed the Schulze-Hardy rule, which is derived from the DLVO theory; however, deviations from the theory, particularly in the case of multivalent ions, showed that the specific ion adsorption also played a role. To investigate the heat stability of WPI particles, particle size and viscosities of dispersions containing different biopolymers were measured. Using dynamic viscosity of dilute dispersions, with the assumption of no particle aggregation after heating, swelling ratio (SR) of particles was estimated. Increasing concentrations of biopolymers decreased the SR of particles, and the presence of GA totally inhibited the swelling. Shear viscosity of concentrated dispersions showed an increase and shear-thickening behaviour after heating, when native WPI or dextran was present, whereas viscosity did not change when GA was present in the continuous phase. At low volume fractions, swelling was more likely to occur; whereas at high volume fractions, possibly both swelling and aggregation occurred. in addition, concentration and type of biopolymer were found to be important for the heat stability of dispersions.