Degradation of phytate by Pichia kudriavzevii TY13 and Hanseniaspora guilliermondii TY14 in Tanzanian togwa.

The fermented cereal-based gruel togwa is used as weaning food for children in Tanzania. Togwa is rich in minerals but these are often not available for uptake in the human intestine due to natural inhibitors, such as phytate (IP(6)). The yeasts Pichia kudriavzevii TY13, Hanseniaspora guilliermondii TY14 and TY20, isolated from Tanzanian togwa, and selected for high phytase activity in complex yeast medium YPD, were now studied regarding their ability to degrade IP(6) in maize-based model togwa. A modified constitutively high-phytase producing Saccharomyces cerevisiae BY80 and commercial Aspergillus ficuum phytase were included for comparison. In addition, a strain of Lactobacillus plantarum was included in the model-togwa set-up. All yeasts in the study grew and reached final cell density 1.5-2 log units higher than the start value. S. cerevisiae BY80 degraded 85% of the IP(6) in 48 h; the same degradation level as with A. ficuum phytase (89%). Of the togwa-isolated yeasts, P. kudriavzevii TY13 and H. guilliermondii TY14 showed strong phytate degradation in the model-togwa; 95% or more of the initial IP(6) was degraded after 48 h. This corresponds to a remaining level of 0.4 and 0.3µmol IP(6)/g dw. Co-inoculation with L. plantarum did not increase IP(6) degradation. Moreover, fermentation with P. kudriavzevii TY13 yielded a successive increase in inorganic phosphate (P(i)), from 0.7 to 5.4 mM, suggesting a phytase production in TY13 which is fairly insensitive to P(i) repression. The study shows that phytate in a model togwa is available for yeast phytase enzymes, and addresses the importance of strain selection for effectively degrading the phytate. Certain yeasts originating from togwa seem to have developed a natural high phytase production, and P. kudriavzevii TY13 and H. guilliermondii TY14 seem particularly well adapted to phytate degradation in togwa, and is our choice for further studies and strain improvement.

Biodiversity and phytase capacity of yeasts isolated from Tanzanian togwa.

The focus of the present investigation was on the Tanzanian fermented food togwa as a source for dietary iron and zinc, and the potential for mineral availability improvements using selected yeasts. To establish the content of target minerals and main inhibitor for intestinal uptake, iron and zinc as well as the mineral chelating phytic acid, (IP(6) or phytate) were determined in naturally fermented togwa. Yeasts were isolated from sorghum, maize and cassava based togwa, and identified by sequencing the D1/D2 region of the LSU rRNA gene. The isolated yeasts were subsequently screened for phytase activity. The total iron content in sorghum, maize and cassava based togwa were 41.5 (+/-7.2), 85.4 (+/-31.9) and 28.6 (+/-3.8) microg/g dw (dry weight) respectively. The zinc content was 12.3 (+/-3.1), 11.0 (+/-1.1) and 6.4 (+/-4.5) microg/g dw in sorghum, maize and cassava based togwa, and the phytate content in the three varieties were 2.6+/-1.2, 4.7+/-0.8 and 0.4+/-0.4 micromol/g dw respectively. The phytate levels in the sorghum and maize based togwa are expected to substantially reduce the availability of iron. The molar ratio phytate to iron for these two varieties were estimated to be 3.5:1 and 3.1:1 respectively. In general, a phytate to iron molar ratio below 1 is needed to increase the availability of iron. Among 26 isolates, 9 different species could be distinguished: Issatchenkia orientalis, Pichia anomala, Pichia norvegensis, Pichia burtonii, Pichia guilliermondii, Kluyveromyces marxianus, Saccharomyces cerevisiae, Hanseniaspora guilliermondii and Candida glabrata. The strains were screened for phytase activity in YPD supplemented with 0.5 mM IP(6). Of 26 screened strains, the phytase activity was most prominent in strains of I. orientalis and H. guilliermondii. The strains and data constitute a basis for further improvements of iron and zinc bioavailability in togwa.

Production of folates by yeasts in Tanzanian fermented togwa.

We have investigated the impact of different yeasts and fermentation time on folate content and composition in a fermented maize-based porridge, called togwa, consumed in rural areas in Tanzania. The yeasts studied, originally isolated from indigenous togwa, belong to Issatchenkia orientalis, Pichia anomala, Saccharomyces cerevisiae, Klyveromyces marxianus and Candida glabrata. The main folate forms found, detected and quantified by HPLC during the fermentations were 5-methyl-tetrahydrofolate (5-CH(3)-H(4)folate) and tetrahydrofolate (H(4)folate). The content of H(4)folate, per unit togwa, remained fairly stable at a low level throughout the experiment for all strains, whereas the 5-CH(3)-H(4)folate concentration was highly dependent on yeast strain as well as on fermentation time. The highest folate concentration was found after 46 h of fermentation with C. glabrata (TY26) (6.91+/-0.14 microg 100 mL(-1)), corresponding to a 23-fold increase compared with unfermented togwa. The cell concentration per se could not predict the togwa folate level, as shown by the much higher specific folate content (g folate CFU(-1)) in the S. cerevisiae strain (TY08) compared with the other species tested. This study provides useful data when trying to maximize folate content in togwa as well as in other yeast-fermented products.