Influence of Stabilizers, Milk Proteins, and Heat Treatment on the Tribology and Rheology of Drinking Yogurt

This study investigated the effects of protein substitution, stabilizer addition, and heat treatment conditions on the physicochemical properties of drinking yogurt. Milk proteins (sodium caseinate [NaCas], milk protein concentrate [MPC], and whey protein isolate [WPI]) were used to replace the protein in skim milk powder (SMP) at ratios of 10%, 20%, and 40% (w/w). Stabilizers (pectin, gelatin, and soluble soybeanpolysaccharide [SSPS]) were added post‐fermentation, and their concentrations in the final yogurt were 0.2%, 0.4%, and 0.4% (w/w), respectively. Milk was heated under different conditions (75°C/20 min [75‐Y], 85°C/15 min [85‐Y], and 95°C/5 min [95‐Y]). Replacing SMP WPI, especially at 40%, yielded smaller particle sizes and higher water‐holding capacity (WHC), whereas MPC or NaCas increased particle size. All stabilizers enlarged particles, with pectin exhibiting the most pronounced effect due to bridging flocculation. Heat treatment at 85°C produced the smallest particle size and highest WHC, whereas 95°C and 75°C treatments resulted in larger particles and reduced WHC. Higher protein substitution levels generally reduced viscosity, with 40% WPI significantly reducing viscosity. Conversely, pectin addition generated the highest viscosity, and SSPS the least. The high viscosity of 75‐Y corresponded to its larger particles and lower WHC. Tribological analysis indicated that increasing the proportion of protein substitutes reduced the coefficient of friction, and notably, a 40% WPI substitution significantly improved lubrication properties associated with the creaminess sensation. Pectin also induced a rapid friction drop, consistent with its high viscosity. Although friction curves were similar across heat treatment, the friction coefficients of 75‐Y and 95‐Y were lower than that of 85‐Y at medium sliding speeds.