pH Stability

Summary
Individual, pure culture samples of probiotic microorganisms contained in Protexin human health formulations were tested for stability under acidic conditions to mimic the extreme fasting pH of the human stomach.

Introduction
In order to produce beneficial effects within the gastrointestinal tract (GIT), probiotic microorganisms must have the capacity to survive and metabolise in the gut. They must therefore be resistant to GIT levels of acid.

Probiotic formulations also need to contain large numbers of viable organisms (highly concentrated) which, on ingestion, survive the rigorous onslaught of the mammalian upper gut in order to deliver their bacterial content to the small intestine. One of the primary barriers to the passage of bacteria is the acidity of the stomach. The pH of the stomach varies throughout the day under the influence of the buffering action which food or liquid may have on the stomach. However, the fasting pH of the human gut is around pH 3.0.

The amount of time food takes to pass through the stomach also varies greatly, from a few minutes to an hour or more. The food itself will have some neutralising effect on the pH of the stomach; hence a pH of 3.0 is probably the lowest to which the bacteria will be subjected. In addition, the food may also have a physically protective role to play.

Our laboratory tests will therefore probably be the most vigorous conditions the bacteria will be subjected to, i.e. a pH 2.0 for 2 hours, and the results obtained will need to be analysed accordingly. It should also be noted that the laboratory conditions designed for these tests (in vitro), whilst attempting to mimic the conditions within the stomach, are only a simplistic view of what is in fact a very complex situation.

Viability of Probiotic Microorganisms within the Gastrointestinal Tract
When held at a pH of 2.0 for a two-hour period, there is no significant loss in viability/concentration of any of the bacterial strains. The contact time is extreme – a two-hour contact time period without any buffering effect of, for example, food or water before plating out.

Conclusions
Total viable bacterial counts do not reduce in viability/concentration after contact with acid of pH 2.0 for 2 hours. This means that a high concentration of microorganisms survive, which could reach the small intestine and establish themselves as part of the normal microflora. Laboratory tests are not necessarily a reflection of in vivo conditions, although the experiments were designed to mimic the situation as closely as possible.