Dairy Systems

Studying stirred yogurt microstructure and its correlation to physical properties: A review

“…Milk gelation is defined as the physical transition during which the milk changes from a low viscosity Newtonian fluid to a semi-solid or to a solid state (Foegeding, Vardhanabhuti, & Yang, 2011). In yoghurts and fermented milks, it is achieved through a slow acidification by lactic acid bacteria.…”

“…Rheological and textural measurements are considered as the response at the macroscopic level of the properties at the microscopic level of food (Rao, M. A., 2007); and rheological properties of a yogurt gel network depend on interactions between the building blocks forming strands and between strands as well as on the concentration of strands forming a continuous network (Lucey, 2016;Rao, M. A., 2007). For stirred yogurt, three types of rheological experiments are generally used (Foegeding et al, 2011;Mortazavian et al, 2009): flow experiments using a rotational rheometer to characterize viscosity (apparent viscosity at a given shear rate, flow modelization, …) ; small deformation oscillatory experiments using a rheometer to characterize the viscoelastic properties of the stirred gel (complex viscosity, storage modulus, loss modulus, …), penetration or texture profile analysis (TPA) test using a texturometer to measure yogurt firmness. Recently, large amplitude oscillatory shear (LAOS) was used to probe gel network inner-interaction.…”

Changes in Milk Protein Functionality at Low Temperatures and Rennet Concentrations

“…These protein changes tend to increase milk's storage modulus (G ′ ), suggesting a more structured or solidified state. Simultaneously, the loss modulus (G ′′ ) also changes and typically increases as the milk transitions from a predominantly liquid to a more gel-like state [62]. Rennet treatment also influences milk viscosity since the rennet enzymatic activity promotes protein aggregation and makes gel, increasing the milk's viscosity.…”

“…These protein changes tend to increase milk's storage modulus (G′), suggesting a more structured or solidified state. Simultaneously, the loss modulus (G″) also changes and typically increases as the milk transitions from a predominantly liquid to a more gel-like state [62].…”

Characterization of syneresis phenomena in stirred acid milk gel using low frequency nuclear magnetic resonance on hydrogen and image analyses

“…Milk gelation is responsible of the rheological transformation of milk from a Newtonian fluid to a semi-solid or solid product (Foegeding, Vardhanabhuti, & Yang, 2011). It is achieved through an enzymatic action, acidification or a combination of both.…”