5. Yeast “New” Strains as Probiotics: Myth or Reality?
While research into probiotic yeasts is ongoing, there are not any definitively established "new" probiotic yeast strains yet [
3]. However, the exciting part is that researchers are looking beyond
S. boulardii. They are investigating the potential of various yeast genera like
Debaryomyces,
Kluyveromyces,
Yarrowia,
Pichia, and
Torulaspora, isolated from fermented foods, traditional beverage, human microbiota, and natural sources [
3,
42,
43,
44].
These “new” probiotic yeast strains might offer a wider range of functionalities compared to existing probiotic options. They could potentially target specific gut health concerns or work synergistically with bacteria to enhance overall gut health [
3].
Isolated from a variety of fermented foods and natural sources, strains of
Debaryomyces yeast have been shown to have potential benefits, including tolerance to bile and stomach acid, which enables them to enter the intestines, and the generation of compounds that support gut microbiota [
3]. Though intriguing,
Debaryomyces as a validated probiotic is still in its early stages because it has not been as well researched as more well-known probiotics like
S. boulardii.
To validate its particular health benefits in humans, more research is required [
3]. So, what is real and what is myth? As of right moment, neither. Probiotics like
Debaryomyces strains have potential, but further study is required to make that potential a reality. Furthermore, distinct
Debaryomyces strains may have differing probiotic capabilities, similar to bacteria. Finding the most effective strains is therefore essential [
3].
Ochangco
et al. [
45] investigated the potential probiotic benefits of various
D. hansenii strains that were isolated from cheese and fish gut. The results indicated that the various traits of each strain might result in a range of probiotic effects. Although none of the strains exhibited the same level of stress resistance as
S. boulardii strains, one strain survived well in the hostile gastric environment. Compared to
S. boulardii, two strains produced a stronger anti-inflammatory response in immune cells, but one strain distinguished out as the most promising probiotic candidate because of its ability to adhere to gut cells, survive in hostile conditions, and produce anti-inflammatory effects [
45].
Kluyveromyces, Yarrowia, and Torulaspora are all exciting possibilities in the realm of new probiotic yeasts, but like Debaryomyces, they are still in the early stages of exploration.
Strains of
Kluyveromyces, in particular
K. marxianus, have been isolated from fermented foods, including kefir grain, fermented traditional dairy products, sewage from sugar businesses, and natural environments, such as plants and sisal leaves, showing promise for probiotic applications [
3,
46]. Early research suggests that
K. marxianus produces a broad range of distinct metabolites that may be useful to the food and biotechnology sectors and that this yeast might be tolerant to stomach acid and bile, allowing it to survive the digestive tract and reach the intestines. [
3,
46].
Similar to
Debaryomyces,
Kluyveromyces strains have not been extensively studied in humans. However, early research suggested that
K. marxianus has potential benefits for gut health and immune function [
47]. Recently, Nag
et al. [
48] observed in vitro that this yeast improved insulin sensitivity and reduced fat storage in fat cells, suggesting benefits for type 2 diabetes and obesity. Furthermore, this yeast showed cytotoxicity against colon cancer cells, suggesting anti-tumoral activity. Hence, these authors suggested that
K. marxianus could have therapeutic potential. However, more research is needed to confirm their specific health benefits and identify the most effective strains [
3,
47,
48].
Yarrowia is a relatively new genus being explored for potential probiotic properties [
49]. Research for probiotic applications is even more limited compared to
Kluyveromyces. Extensive investigation is needed to understand their safety and efficacy in humans [
3]. For the past 20 years, the yeast
Y. lipolytica has been used in industry to produce docosahexaenoic acid and eicosapentaenoic acid while adhering to good manufacturing procedures [
50]. It has drawn notice recently for innovative biotechnological uses, like as animal feed addition with functional properties. The productive and immunological characteristics of the animals given
Y. lipolytica were improved, and their microbioma, fatty acid content, and biochemical profiles were also enhanced [
51]. Some strains might possess characteristics like adhesion to gut lining and antimicrobial activity against harmful gut pathogens [
49,
52]. Research has shown that this yeast is probiotic and beneficial to fish, birds, mammals, crabs, and mollusks. It is also harmless [
51,
53,
54,
55].
Pichia sp. This genus has a probiotic potential among non-
Saccharomyces yeasts [
56,
57].
Pichia probiotics are mostly obtained from food fermentation and have been shown to be able to thrive in gastrointestinal tracts. In addition to its probiotic functions as an antioxidant, the species
P. kudriavzevii lowers cholesterol, has biological effects on the binding capacities of heavy metals, and improves the nutritional value of food [
52,
58,
59].
Early research suggests
Torulaspora strains, particularly the species
T. delbrueckii, has potential as a probiotic showing benefits like improving gut barrier function and modulating the immune system [
3]. Studies suggest
T. delbrueckii may promote the growth of beneficial bacteria and inhibit harmful ones, leading to better digestion, reduced inflammation, and a stronger immune system [
60]. Even if very little is known about its specific effects on gut health in humans, some
Torulaspora strains exhibit an additional benefit, such as antibacterial and antifungal activity against like
Candida albicans,
Escherichia coli,
Staphylococcus aureus, and
Salmonella enterica [
3,
61].
7. Commercial Formulas with Yeast Probiotics
As it is known probiotics are live microorganisms that offer health benefits when consumed. They work by promoting the growth of good bacteria in the gut and inhibiting the growth of harmful bacteria. The applications of yeasts in human foods and animal feeds as well as in agriculture and other sectors are increasing and market demand is providing motivation to continue or even increase research and development in this field [
66]. Probiotics are widely used by healthy people and in clinical settings, but there can be side effects. With new strains and uses in vulnerable groups, clear instructions are needed for safe and effective use. An international group met to discuss potential risks, including those for vulnerable people, and the importance of high-quality probiotics for these groups. They also stressed the need for reporting side effects and using whole genome sequencing to check probiotic safety. This will help scientists and physicians determine how safe probiotics really are [
67].
While D. hansenii has potential as a probiotic, it is not yet widely used in commercial formulas, especially for humans. Torulaspora, similar to D.hansenii, it is not yet a common ingredient in commercially available formulas. This is mainly due to:
a)
Limited research in humans. Most research on
D. hansenii as a probiotic has been conducted on animals. While promising, human trials are needed to confirm its effectiveness and safety [
68,
69].
b) Focus on established strains. Commercially available probiotic formulas often include well-studied strains like Lactobacillus and Bifidobacterium with a longer track record of safety and efficacy in humans.
c)
Formulation challenges.
D. hansenii might require specific processing or formulation techniques to ensure viability and delivery of its potential benefits. This yeast is sensitive to various environmental factors like drying, high temperatures, and low pH. These factors can damage the cells and reduce their viability during processing and storage [
70].
Things can be different in the future.
D. hansenii may show up more frequently in commercial probiotic formulations as research continues. Alternative scenarios should be taken into consideration. These include combination formulas, where
D. hansenii may be combined with established probiotic strains for a wider range of benefits, and/or specialized formulas, where
D. hansenii may be included for specific gut health needs once research validates its benefits in those areas [
70].
While
Torulaspora, and especially
T. delbrueckii, exhibits probiotic potential comparable to that of
D. hansenii, it is not yet frequently found as an ingredient in commercially available formulations. Improved intestinal health is one possible advantage [
71].
9. The Future
“New” probiotic yeasts could be incorporated into fermented foods or probiotic supplements, offering interesting possibilities for expanding the range of health benefits we can achieve through our diet and gut health [
29,
42]. Traditionally, probiotics have been associated with fermented dairy products like yogurt. Probiotic yeasts could be introduced into a wider range of fermented foods, like kimchi, kombucha, or even sourdough bread [
74]. This would create an increased variety of fermented foods and more options for people with lactose intolerance or those who simply prefer different flavors. Further possibilities are represented by developing specific fermentation processes using various probiotic yeast strains. This could lead to fermented foods designed to target certain health concerns, like gut inflammation or immune function [
75,
76,
77]. Moreover, probiotic yeasts might offer advantages when it comes to delivering beneficial microbes to the gut. Some yeast strains may be more resilient to stomach acid and bile, allowing them to reach the intestines in higher numbers. Hence, a wider range of health benefits could be achieved. For example, a) Probiotic strains can improve gut health, helping to maintain a healthy balance of gut microbiota and potentially reducing digestive issues like diarrhea or constipation. b) Some yeasts might stimulate the immune system, potentially reducing susceptibility to infections. c) Probiotic yeasts could target specific health concerns, like allergies, skin conditions, or even mental health, developing more targeted benefits.
To achieve these goals, the approach that uses probiotics for human health, to treat gut imbalances, is changing. Next-generation yeast probiotics are emerging as a powerful new approach in the field of live biotherapeutics [
78,
79]. These modified yeast strains go beyond the fundamental idea of probiotics. By using genetic engineering, scientists are able to give these tools specialized capabilities. Compared to conventional probiotics, this enables them to more effectively target particular health issues. For the time being,
S. boulardii is one of the most promising next-generation yeast probiotics. Although this strain is currently utilized as a conventional probiotic to treat diarrhea, scientists are working to engineer it for additional uses [
8,
9,
79]. Yeasts can be engineered to produce specific molecules that benefit the gut environment. For instance, they can be programmed to synthesize short-chain fatty acids that promote gut health or modifications can be made to allow the yeasts to reach specific areas of the gut where they can exert their desired effects. The hostile environment of the gut can be challenging for probiotics; hoewever, scientists are engineering yeast strains that are better able to pass them through the digestive system and establish themselves in the gut. Probiotics derived from next-generation yeast may revolutionize the way gastrointestinal disorders are treated and perhaps even other medical conditions. Though the field is still in its early stages, ongoing research and clinical trials are paving the way for the development of more effective and targeted treatments.