Probiotics are live microorganisms which, when administered in adequate amounts, confer health benefits on the host . Indigenous fermented food products possess the potentials to meet the increasing demand for clean-label and health-beneficial foods by incorporating probiotic strains. Probiotics strains are typically selected from species of lactic acid bacteria and bifidobacteria . However, the prospects of broader health benefits and delivery in unconventional food systems, including cereals, plant juices, and legumes have driven efforts toward exploring the larger microbial communities, including yeasts for microbial strains expressing interesting functionalities .
Several authors have reported the probiotic potentials of yeast strains from several indigenous fermented foods and beverages: burukutu, cheese, fura, gowe, kunu-zaki, mawe, nunu, kefir, ogi, olives, and wines [4,5,6,7,8,9,10,11]. Most of these yeasts are non-Saccharomyces species, including strains of Debaryomyces hansenii, Issatchenkia orientalis, Galactomyces geotrichum, Kluyveromyces marxianus, K. lactis, Pichia farinosa, P. anomala, P. kudriavzevii, and Yarrowia lipolytica. Their robust sizes (approx. 5 × 10 μm), stress tolerance, antibiotic resistance that is not due to mobile genetic materials, non-pathogenic, non-toxigenic and non-allergenic nature, versatile enzyme profile, and production of several bioactive compounds contribute to the selection of yeasts as probiotics.
Technological suitability, including contribution to appealing flavor and improvement of nutritional value, are desirable for the selection of probiotic strains to be incorporated in non-dairy food systems, especially cereal models . Volatile organic compounds (VOCs) are flavor-active metabolic products of organic compounds in living cells, especially yeasts through specific pathways such as Ehrlich, β-oxidation, and glycolytic pathways [13, 14]. Recently, non-Saccharomyces yeasts are gaining attention as excellent producers of flavor compounds. They include some species of Candida, Galactomyces, Geotrichum, Hanseniaspora, Pichia, Saccharomycopsis, Saprochaete, Starmera, and Wickerhamomyces [13,14,15]. VOCs, including organic acids, esters, and higher alcohols determine the distinctive bouquet of the fermented product, contributing fruity, flowery, spicy, coffee to meaty nuance [14,15,16,17,18].
Phytate (Inositol hexaphosphate, IP6), the main form of phosphorous and a complex with dietary minerals (calcium, iron, magnesium, and zinc) in cereals, legumes, and nuts, is indigestible in the monogastric gastrointestinal tract [19, 20]. Phytate is considered to be the most important anti-nutritional factor for the bioavailability of dietary minerals to consumers with diets exclusively based on cereals . It is implicated in the global burden of iron deficiency and the attending complications particularly among women and children in low-income countries. Bioavailability of dietary minerals may be improved by using phytase, an enzyme that catalyzes the sequential hydrolysis of phytate [22, 23].
Phytase-active probiotic strains have the potential to improve the in situ and in vivo bioavailability of the divalent minerals, during food fermentation and in the gastrointestinal tracts respectively [20, 24]. Several authors have reported high phytase production by yeasts from various food sources, including Arxula adeninivorans, Hanseniaspora guilliermondii, I. orientalis, P. anomala, P. kudriavzevii, Saccharomyces cerevisiae, and S. pastorianus [20, 25,26,27,28]. However, the application of yeast phytases is dependent on the stability of the enzyme to evolving conditions during food fermentation and gastrointestinal transit. Therefore, broad pH and thermal stability are important properties for the enzyme.
In a previous study, we determined the probiotic potentials of yeasts isolated from some cereal-based Nigerian traditional fermented food product . These yeast strains were evaluated as platform strains for the production of volatile compounds and phytase. In addition, the activity and stability of extracellular phytases from selected strains were determined for possible application during food fermentation and gastrointestinal transit.