Influence of fat substitution by inulin on fermentation process and physical properties of set yoghurt evaluated by an optical sensor

Inulin is a natural product with beneficial effects for human health commonly used as a source of dietary fiber, bulking agent and fat substitute in products like cheese and yoghurt. There are some confusing or contradictory results in the literature about the water holding capacity of inulin and its effect on syneresis, coagulation kinetics, rheology and texture of yoghurt, so in this study those effects were evaluated. Yoghurt fermentation tests were conducted with three fat concentrations (0.4, 1.6 and 3.6%) and three inulin levels (0, 1.6 and 3.2%). The coagulation process was monitored for the first time using simultaneously an inline light backscatter sensor, inline potentiometry and a rheometer. The increase in milk fat concentration from 0 to 3.6% delayed the start of coagulation and increased time to pH = 4.8 in 11 min. 3.2% of inulin addition increased yoghurt acidification rate, reduced 12 min the time to pH = 4.8, and increased final storage modulus and gel firmness. It was also determined that 3.2% of inulin addition increased 32% the spontaneous syneresis and had no effect on the water holding capacity of set yoghurt.