Wettability of Probiotic Powders: Fundamentals, Methodologies, and Applications

Wettability is a macroscopic consequence of microscopic phenomena occurring at
the fluid-solid interfaces. This functional property is crucial for the formulation of
wettable powders in food and non-food sectors. Basically, powder wettability is
mostly assessed through the contact angle measurements of solid particles reacting
with dispersing media, by either the sessile drop method or the capillary rise technique. Among the most popular bioactive agents nowadays are probiotics and their
metabolites, which are receiving a growing interest for their beneficial effects on our
ecosystem health. As live functional ingredients, probiotics are mainly available in a
powder form that is sensitive to the environmental stress factors during processing
and storage steps. It is therefore crucial to understand and control their wettability,
regarding their performance, dispersibility, and stability when probiotic particles
come into contact with dispersing media and body fluids. The proposal chapter aims
to review: (1) the theoretical aspects of powder wettability by considering compact
and porous materials; (2) the analytical tools and methodologies of measurement,
including sessile drop and capillary rise methods using models Lucas-Washburn
equation and Darcy's law; and (3) the applications to probiotic powders as functional
ingredients in food and agricultural sectors.