“In contrast with other lactic acid bacteria, the probiotic status of S. thermophilus remains still questioned,” the researchers wrote in their study.
For a microorganism to be considered a probiotic, it must survive in the human gastrointestinal tract and exert health benefits on the host.
This current study, published in the October edition of the Journal of Functional Foods, is an update of the human trials, in vivo assays in animal models, and in vitro experiments which investigate the bacterial strain’s survivability and potential positive health effects.
A key ingredient in the dairy industry, surviving human digestion
S. thermophilus is the only Streptococcus species to have a ‘Generally Recognized as Safe’ (GRAS) no-objections letter from the Food and Drug Administration (FDA).
But “they have not been considered as probiotics during a long time by most scientists as they were not found to survive in the GI tract,” according to the researchers.
From the human clinical trials conducted on the bacteria’s survivability that the researchers reviewed, three of them found no viable S. thermophilus detected in the fecal samples, while five identified some bacteria to survive the gastrointestinal tract.
However, the scope of human clinical trials was still limited—most study participants ingested the bacteria from yogurt or a probiotic mix, and mostly fecal samples were used, meaning that there is not yet enough data to understand if the bacteria survives in other parts of the digestive system.
Potential health benefits
There have been enough studies that suggest S. thermophilus may alleviate lactose intolerance, though most of the clear evidence came from animal studies.
Nevertheless, 14 human intervention studies on consuming yogurt with this live culture was enough for the European Food Safety Authority (EFSA) to allow yogurt companies to make the health claim that “live yogurt cultures in yogurt improve digestion of lactose in yogurt in individuals with lactose maldigestion.”
“Even if the beneficial effect of yogurt on alleviation of lactose intolerance is well established by clinical studies, there are strong proofs in animals but yet no solid evidence in humans that this effect can be specifically attributed to S. thermophilus,” the researchers wrote.
Additionally, there is building science backing the species’ potential to prevent chronic gastritis, with evidence mostly from animal studies, as well as preventing diarrhea.
‘S. thermophilus as a new promising probiotic candidate’
According to the researchers, the combination of data collected from human, animal, and in vitro studies, which were published from 1989 to 2016, offers enough data to “show the potential of S. thermophilus as a new promising probiotic candidate.”
“Even if most of S. thermophilus strains appeared to be sensitive to acid pH and bile salts, human studies have established their ability to survive passage through the GI tract and transiently colonize while ingested,” they wrote.
“In addition, some strains of S. thermophilus have the ability to adhere to intestinal epithelial cells, which is an important criterion for probiotic strain selection.”
This provides a positive implication for the food industry, the researchers argued. “The resistance of S. thermophilus to industrial process is already well established, mainly in dairy products. This represents a strong advantage for designing new probiotic dairy food, especially fermented milks, using the appropriate strains.
“Indeed, fermented milks and yogurts benefits from favorable public opinion and are highly consumed (about 2 kg of yogurt per person worldwide), which should facilitate the commercialization of new products of this type.”
Source: Journal of Functional Foods
Published online ahead of print, https://doi.org/10.1016/j.jff.2017.07.038
Streptococcus thermophilus: From yogurt starter to a new promising probiotic candidate?
Authors: Ophelie Uriot