Hunting for Probiotic Microorganisms: Is There an Easy Road to Success?

By definition probiotic foods must contain live microorganisms in adequate amounts so as to be beneficial for the consumer's health. There are numerous probiotic products marketed today and many probiotic strains are commercially available. However, the question that arises is how to determine the real probiotic potential of microorganisms. This is becoming increasingly important, as even a superficial search of the relevant literature reveals that the number of proclaimed probiotics is growing fast. Potential probiotics are selected after in vitro or in vivo assays by evaluating simple traits such as resistance to the acidic conditions of the stomach or bile resistance, or by assessing their impact on complicated host functions such as immune development, metabolic function or gut-brain interaction. Human clinical trials are considered mandatory for communicating health benefits but only few strains with positive studies have been able to convince legal authorities with these health claims. Here an overview of the most common assays employed in screening for probiotics will be presented, highlighting the potential strengths and limitations of these approaches.