J. Gen. Appl. Microbiol., 51, 221–227 (2005)

Probiotics are microorganisms that when ingested in high enough numbers beneficially affect the host’s health. To reach these beneficial results, it is necessary to maintain good viability of the probiotic strains during processing, storage and consumption. Stress conditions that usually affect viability of probiotics during production are the following: large concentration of fermentation by-products (e.g., lactic acid in the culture medium), harvesting (centrifugation, ultrafiltration), freezing, and drying (during the freeze-drying process). In addition, the strains encounter the following stress conditions in the gastrointestinal tract: re-hydration in an acidic environment, long exposure time to stomach acidity, sometimes in the presence of antimicrobial compounds (in certain foods) and thereafter the exposure to bile acids (Siuta Cruce and Goulet, 2001). Probiotics are usually added to animal feed as freeze-dried cultures which sometimes are mixed with Survival of Lactobacillus plantarum 44a after spraying and drying in feed and during exposure to gastrointestinal tract fluids in vitro