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.

Development of a simplified method for the determination of folates in baker's yeast by HPLC with ultraviolet and fluorescence detection.

A simplified HPLC method for rapid determination of folates in yeast with ultraviolet and fluorescence detection without sample purification has been developed. By use of the column Aquasil C(18), specially designed for polar analytes, and gradient elution, it was possible to separate and determine five folate derivatives: tetrahydrofolate, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate with fluorescence detection, and 10-formylfolic acid and folic acid with ultraviolet detection. The sample preparation required only a small amount of dry yeast (25-50 mg) and included an extraction of folates by heat treatment and deconjugation of folate polyglutamates to monoglutamates with the use of rat serum conjugase. Validation involved investigation of matrix effects, determination of recovery by standard addition method, repeatability, and stability tests. The dominating folate forms in commercial dry baker's yeast were found to be tetrahydrafolate and 5-methyltetrahydrofolate with a total folate content of 2890 microg/100 g (63.4 nmol/g). The simplicity of the method makes it suitable for folate screening studies of different yeast strains.