Exopolysaccharides produced by lactic acid bacteria are widely used to improve the sensory properties of yogurt. The relation between the physical properties of the microbial exopolysaccharides and the structural and rheological properties of the yogurt are incompletely understood to date. To address this knowledge gap, we studied how two distinct exopolysaccharides influence the microstructure, rheological properties, and syneresis of yogurt. The effect of a negatively charged, capsular exopolysaccharide produced by Streptococcus thermophilus and a neutral, non-capsular exopolysaccharide produced by Lactococcus lactis were investigated. Using quantitative microstructural analysis, we examined yogurt samples prepared with either the capsular or the non-capsular exopolysaccharide, and with mixtures of the two. Confocal laser scanning microscopy and stimulated emission depletion microscopy were employed to visualize the microstructures, revealing differences in pore size distribution, protein domain size, and casein interconnectivity that were not apparent through visual inspection alone. Additionally, variations in rheological properties were observed among the different yogurt types. In the yogurt fermented with both bacterial strains, we observed a combined impact of the two exopolysaccharide types on relevant microstructural and rheological properties. The negatively charged capsular exopolysaccharide enhanced casein interconnectivity and gel stiffness, while the neutral non-capsular exopolysaccharide led to thicker protein domains, an abundance of small pores, and a lower loss tangent. These factors collectively hindered syneresis, resulting in improved structural integrity. Our study not only provides valuable insights into the influence of different exopolysaccharides on yogurt properties, but also presents the first demonstration and quantification of the effect of multiple types of exopolysaccharides on casein interconnectivity. These findings offer guidance for the production of yogurts with customized microstructure, rheological properties, and resistance to syneresis.

In the present study, the influence of topographic and mechanical cues on neuronal growth cones (NGCs) and network directionality in 3D-engineered cell culture models is explored. Two-photon polymerization (2PP) is employed to fabricate nanopillar arrays featuring tunable effective shear modulus. Large variations in mechanical properties are obtained by altering the aspect ratio of the nanostructures. The nanopillar arrays are seeded with different neuronal cell lines, including neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (iPSCs), I³Neurons, and primary hippocampal neurons. All cell types exhibit preferential orientations according to the nanopillar topology, as shown by neurites creating a high number of oriented orthogonal networks. Furthermore, the differentiation and maturation of NPCs are affected by the topographic and mechanical properties of the nanopillars, as shown by the expression of the mature neuronal marker Synapsin I. Lastly, NGCs are influenced by effective shear modulus in terms of spreading area, and stochastic optical reconstruction microscopy (STORM) is employed to assess the cytoskeleton organization at nanometric resolution. The developed approach, involving laser-assisted 3D microfabrication, neuro-mechanobiology, and super-resolution microscopy, paves the way for prospective comparative studies on the evolution of neuronal networks and NGCs in healthy and diseased (e.g., neurodegenerative) conditions.