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Page 16 of 22 D’Aimmo et al. Microbiome Res Rep 2024;3:11 https://dx.doi.org/10.20517/mrr.2023.59

For example, the folate content in the traditional Tanzanian cereal-based food/beverage, togwa, was
increased 20-fold (from 3.4 μg/100 g to 69 μg/100 g of dry matter) using selected strains in model
[15]
fermentations . In another example, everyday wheat bread was fortified with folate by employing a specific
yeast strain and bioprocessing. This resulted in four times higher folate levels than bread made with a
commercial baker’s yeast strain (from 35 μg/100 g to 137 μg/100 g of dry matter) . Kefir-strains of yeast are
[12]
[14]
also promising in increasing folate content . Additionally, oat bran can be fermented to improve its folate
content, as shown by Korhola et al. .
[98]
Other studies focussed on a traditional African cereal-based fermented food called ben-saalga, a pearl-
millet-based fermented porridge consumed in Burkina Faso . The microbiota in ben-saalga has the genetic
[99]
potential for folate production . The total amount of folate in the soaked and fermented grains was
[100]
significantly higher (circa 30% more) than in the original pearl-millet grains.

Some studies investigated the ability of bifidobacteria to increase folate content directly in fermented milk,
indicating their potential use in obtaining fermented dairy products [77,101,102] . Thirty-two Bifidobacterium
isolates (B. lactis spp., B. animalis spp., B. infantis spp., B. breve spp.) were examined for folate production
while fermenting skim milk. Of these strains, Bifidobacterium breve 5181 resulted in the most significant
increase in folate levels. The B. animalis (CSCC 1941) and B. lactis (CSCC 5123, CSCC 5127, Lafti B94)
[101]
isolates roughly doubled the folate concentration in the skim milk . However, in a different study,
Bifidobacterium bifidum was found to deplete 5-methylTHF in milk by approximately 0.15 µg/100 g after
[103]
12 h of fermentation . However, some strains reduce 5-methyl-THF in milk, suggesting the importance of
strain selection . This microbial-based approach in food fermentations is an attractive alternative to
[103]
synthetic folic acid fortification, especially considering that the active form of folate in microorganisms
(THF) is identical to that in humans.

To fulfill human vitamin B needs, utilizing a co-culture of different bacterial strains and yeasts, alongside
9
the selection of strains with high folate production capabilities, could be more effective than using single
cultures. For example, in reconstituted skim milk, a co-culture of two B. animalis subsp. lactis and
L. acidophilus strains produced at least 30% more folate than the single cultures .
[101]
A few studies have also registered the use of metabolically engineered industrial microorganisms, such as
Escherichia coli, Bacillus subtilis, LAB (Lactic Acid Bacteria), and the fungus Ashbya gossypii capable of
overproducing folate. Consumption of food fermented with overproducing LAB strains improved the folate
status in deficient rats . The use of genetically modified microorganisms may be limited by ethical and
[64]
regulatory considerations. However, such studies are important to demonstrate the possibility of this
biotechnological approach for industrial folate production .
[104]
In the near future, the nutritional analysis may combine the most suitable associations of probiotics
(microbiome data) and precise dietary information to target people’s needs so that folate deficiency can be
prevented (“personalized medicine”).

As research for folate-producing starter strains in food fermentation is still nascent, there is a substantial
potential to enhance the natural folate content in fermented foods. It has been shown that growth rate,
physiological state, and medium composition strongly affect the specific folate content in yeasts. A
manyfold higher folate content was obtained in fermenting fast-growing yeasts compared with respiring
slow-growing yeast . Similar variations have also been observed in bifidobacteria . It is of high
[105]
[74]
importance to not only optimize strain but also the process.