Good practices for effective probiotics into final marketed products

Probiotics are live micro-organisms such as bacteria that, when administered in adequate quantities, confer a health benefit on the host (1). Probiotic end products can have many different benefits, ranging from improving aspects of gut function to boosting the immune system. However, to be an effective health tool, careful selection of the probiotic strain, a thorough knowledge of its stability, and a relevant dose are required.

Strain: Live micro-organisms may be present in many fermented foods such as kimchi, kefir or kombucha, but only products containing characterised strains with a scientifically proven effect on health should be called probiotic products. In addition, micro-organisms must be identified at the taxonomic level of strains and not just at species level. Indeed, there is considerable variability within species, and many species contain both beneficial strains and other pathogens (a classic example is the E. coli species). The identification of strains by sequencing universal marker genes such as the 16S rRNA gene should be avoided as this technique remains limited in resolution for intra-species analysis (2).

Stability: The definition of probiotics requires the micro-organisms to be consumed alive, yet micro-organisms are highly sensitive to environmental stress. Temperature, pH, water activity and the oxygen level of the carrier matrix will have an impact on the viability of microbial cells over time (3). Viability refers to the ability of a cell to grow and subsequently generate a colony of cells and is expressed in colony-forming units (CFU). While some species are known to be more stable than others (such as Bacillus species), it is important to study the impact of these parameters over time for each strain. Stability data will help probiotic product formulators to choose the most suitable strain, considering the downstream processing and the manufacturing of the final product.

Relevant dose: The definition of a probiotic requires the administration of an “adequate quantity” to obtain a health benefit, but there is no consensus as to what this quantity should be (3). The dose must correspond to the dose documented in clinical trials, where these exist, or, at the very least, meet the requirements of local regulations. For example, the Canadian and Italian authorities require a minimum of 10⁹ CFU per dose, while the French authority has set the threshold at 10⁷ CFU.

The dose must also consider the natural loss of viability of the product matrix until the end of the shelf life. Indeed, it is the responsibility of suppliers of finished products to ensure that the dose indicated on the packaging is delivered throughout the shelf life. To ensure that the product contains enough viable probiotic cells at the end of its shelf life, an excess is often necessary. Common overages typically range from 10% to 50%, although some formulations may use higher or lower overages depending on the results of stability studies of the strain, packaging and storage conditions. Each batch may be counted and checked by an independent laboratory accredited according to ISO methods.

Formulating probiotic products requires a great deal of skill and experience. Each criterion needs to be carefully considered at strain level, as strains of the same species can exhibit different behaviours and health benefits. It is also essential that the strain supplier carries out stability testing so that the probiotic product formulator can determine the appropriate surplus and ensure the viability of the probiotic cells throughout the product’s shelf life.

Ultimately, it is essential to guide consumers towards more conscientious choices. Achieving this goal requires effective dissemination of knowledge among universities, consumers, manufacturers and stakeholders to avoid misinterpretation of scientific findings about the beneficial effects of probiotics.