Natural stabilizer Levan enhances the casein network, rheological properties and sensory quality of yogurt

Levan is a macromolecular fructan with demonstrated prebiotic potential. Here, the effect of levan concentration (0-1 %, w/v) on the gel's physical stability, molecular interactions and casein secondary structure was investigated in this work. In addition, this study identified the optimal levan concentration for gel-based dairy products. The optimal concentration was applied to stirred and set yogurt, and the effect of levan on the storage stability and flavor characteristics were evaluated using rheological, microstructural, and sensory analyses. The results showed that the casein gel system with the addition of 0.3 % levan in gel system exhibited optimal stability, with an average particle size of 7325 ± 498 nm, a Zeta potential of -23.1 ± 0.44 mV, and an increase in protein β-sheet structure content. Moreover, 0.3 % levan effectively improved the stability of both types of yogurt during the 21-day refrigeration period. Rheological analysis confirmed that levan enhanced the shear resistance of yogurt, with the system exhibiting typical shear thinning behavior. In particular, the addition of 0.3 % levan significantly improved the texture properties (firmness, chewiness, gel strength) of stirred yogurt. Fluorescence microscopy revealed that the addition of levan contributed to a more stable fat-protein network structure. Sensory evaluation indicated that the addition of 0.3 % levan did not adversely impact the basic flavors (sour, sweet, umami, bitter, salty) of the yogurt. Furthermore, as storage time increased, the gel network structure of stirred yogurt approached that of set yogurt. In conclusion, levan might be used as an effective natural stabilizer for yogurt products.