Effect of whey protein isolate microparticle addition on some physical and chemical properties of kefir

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. Graphical abstract High-protein kefir production outcomes