Extrusion Encapsulation of Probiotics: Key Geometric and Operational Parameters

The encapsulation of probiotic cultures is a promising method to enhance their survival during the production and storage of fermented dairy products. This study investigates the influence of design and operational parameters of an extrusion encapsulation setup on capsule size, mechanical strength, process productivity, and probiotic viability. The effect of the inner diameter of the injector (0.16–0.82 mm) on capsule diameter and spinneret reliability was quantified. The dependencies of the gel-forming mixture’s viscosity on temperature (20–50 °C) and peristaltic pump rotation speed (0.333–1.333 s−1), as well as their influence on productivity, were established. The mechanical properties of the obtained capsules were evaluated using a custom-built device based on a penetrometer principle, and an apparent stiffness coefficient (K_app) was defined. Probiotic viability remained above 108 CFU/g under all tested conditions. It was shown that the mixture’s temperature decisively influences the perceived hardness of the capsules (via K_app), while their diameter shows only a minor change (maximum difference 0.06 mm, ~2%). Based on a comprehensive data analysis, a rational operating mode is proposed for obtaining capsules with favourable strength and organoleptic characteristics while maintaining high viability. The findings contribute to the systematic engineering of extrusion-based encapsulation processes for probiotic delivery in food applications.