The effect of Sodium Caseinates (SCN) and Whey Proteins Concentrates (WPC) addition, as well as the starter culture type (kefir grains and commercial starter culture) on the viscoelastic properties of kefir samples was evaluated. The kefir samples were prepared from homogenized and pasteurized full fat bovine milk with or without the addition of SCN or WPC at 2% (w/w) concentration. According to the results, SCN increased the fermentation time of kefir samples when compared to control samples (samples without SCN or WPC addition), while WPC decreased it. The elasticity of the protein matrix was increased with SCN or WPC addition, however, the effect of SCN was more pronounced to than that of WPC. SCN contributed to the elasticity of the samples by the formation of strong as well as weak chemical bonds, while WPC participated to protein interactions that were characterized as weak ones. The commercial starter culture resulted in lower fermentation time and increased viscoelastic properties of the kefir samples when compared to kefir grains.