Importance of biofilm age and growth medium on the viability of probiotic capsules containing Lactobacillus rhamnosus GG biofilm

Health benefits conferred by probiotic organism Lactobacillus rhamnosus GG taken as food supplements to its human hosts have been well established clinically. Probiotic capsules containing biofilm form of L. rhamnosus GG was shown very recently to exhibit greater freeze drying and thermal tolerance than their planktonic cell counterparts. Herein we examine the impacts of biofilm age (1, 3, and 5 days) and growth medium (Lactobacilli broth de Man, Rogosa and Sharpe (MRS) or Lactobacilli broth according to the Association of Official Analytical Chemists (AOAC)) on the biofilm capsules' tolerance towards stresses typically encountered in food product lifecycle, i.e. freeze drying, two-week storage at 4 °C, heating at 100 °C, and simulated gastrointestinal juice exposure. While freeze drying and thermal tolerance are minimally affected, storage and gastrointestinal viabilities are highly dependent on biofilm age and growth medium. Capsules prepared in AOAC exhibit higher cell viabilities than those prepared in MRS attributed to higher extracellular polymeric substance (EPS) in the former. Mature biofilm capsules (>1 day) survive storage better, however, their gastrointestinal juice viability is compromised, particularly for MRS capsules. The best overall viability is obtained from 5-day-old biofilm capsules in AOAC.