The Pure Probiotic Initiative: Sourcing probiotics: Selecting strains that survive

By Kelly C. Heim, Ph.D.

Pure Encapsulations’ probiotic strains are selected based on evidence of stability, durability and function.  To help expand on these critical points and provide a sequential overview of each step in the process, from sourcing and manufacturing to finished product testing and shipping, we have created an online series entitled, Probiotic Quality: A series on Sourcing, Manufacturing and Testing.  An inside look into each aspect will illuminate key areas of innovation and comprehensive quality assurance essential to The Pure Probiotic Initiative that are unmatched in the industry.

The diversity within the body’s microbial ecosystems stems from a wide range of disparate bacterial species. Within each species are an array of functionally unique strains. A familiar analogy of this diversity is the physically and behaviorally distinctive breeds within an animal species such as Canis spp. (the dog). The Human Microbiome Project, a federally funded research endeavor similar to the Human Genome Project, has recently documented up to 1,000 different strains of beneficial bacteria that naturally inhabit the body.1 Strain-specific biochemical attributes include (1) storage stability, (2) survival in the upper digestive tract, and (3) adhesion to the intestinal lining.2 Thus, selecting the proper strains is the first and most important step in evidence-based probiotic product development.

Storage stability

The storage durability of a bacterial strain through its expiration date is a fundamental determinant of clinical efficacy. To qualify as a Pure Encapsulations probiotic source, suppliers must meet a comprehensive series of testing and quality criteria. Among the most basic requirements is definitive storage stability data proving 100% survival through the date of expiration at the specified storage temperature. Finished products are also evaluated for stability over the 1-year shelf life.

Survival in the upper digestive tract

Surviving storage is only one of several challenges a probiotic must negotiate in order to reach its site of action in the intestinal tract. When the prototypical vegetable capsule is swallowed, it enters the stomach, where it dissolves, releasing the organisms into the acidic, pepsin-rich gastric fluid. Subsequently, the probiotic organisms are propelled into the small intestine, where they encounter bile and pancreatic enzymes. Different strains exhibit varying degrees of hardiness in these environments. For example, in simulated gastric fluid at pH 2, the Bl-04 strain of Bifidobacterium lactis remains 90-100% viable, while the PANDA strain of this species remains 80-89% viable.3 Through careful evaluation of in vitro research data on specific strains, Pure Encapsulations selects strains that exhibit natural tolerance to the conditions of the digestive tract.

Adhesion to the intestinal lining

Successful application of most probiotics is contingent upon their arrival at their functional destination, the intestinal lining.4 Colonization is a requisite for proliferation and production of beneficial metabolites that mediate local and systemic health benefits. As with storage and digestive stability, adhesion is strain-specific.2,3 Only the strains that exhibit a natural ability to adhere to intestinal cells are selected as raw ingredients.

Selection of naturally robust strains that perform under a variety of adverse physiological conditions is just one of many aspects of Pure Encapsulations’ commitment to probiotic excellence. Each product is formulated and manufactured according to the highest standards of purity, potency and efficacy. This dedication to quality ensures maximum clinical reliability in every finished product.




  1. Aagaard K, Petrosino J, Keitel W, et al. The Human Microbiome Project strategy for comprehensive sampling of the human microbiome and why it matters. FASEB J. 2012 Nov 19.
  2. Jensen H, Grimmer S, Naterstad K, Axelsson L. In vitro testing of commercial and potential probiotic lactic acid bacteria. Int J Food Microbiol. 2012 Feb 1;153(1-2):216-22.
  3. Unpublished manufacturer research of simulated gastric and intestinal conditions at physiological pH.
  4. González-Rodríguez I, Ruiz L, Gueimonde M, et al. Factors involved in the colonization and survival of Bifidobacteria in the gastrointestinal tract. FEMS Microbiol Lett. 2012 Nov 26.