No abstract

The uptake and accumulation of the B-group vitamins thiamine, riboflavin, nicotinamide, pantothenic acid and pyridoxine in Saccharomyces cerevisiae was studied by gradually increasing the specific dosage of vitamins in an ethanol-stat fed-batch culture. Thiamine, nicotinamide, pantothenic acid, and pyridoxine were almost completely taken up at low vitamin dosages. Thiamine was determined to be the major accumulating form of vitamin B1 while most of the assimilated nicotinamide and pantothenic acid accumulated in cofactor forms. Despite the obvious uptake of pyridoxine, accumulation of B6 vitamers was not observed. In contrast with the other vitamins studied, riboflavin began accumulating in the culture medium immediately after vitamin addition was initiated. By the end of the experiment, the apparent uptake of all vitamins exceeded their accumulation in the cells. Variations in the growth rate of yeast at different vitamin dosages demonstrate the importance of balancing the vitamins in the media during cultivation.

The application of LC/MS-TOF method combined with stable isotope dilution assay was studied for determination of thiamine, riboflavin, nicotinamide, nicotinic acid, pantothenic acid, pyridoxal, and pyridoxine in food. Nutritional yeast powder was used as a model food matrix. Acid extraction was compared with various enzymatic treatments in ammonium formate buffer to find a suitable method for the conversion of more complex vitamers into the same forms as the used isotope-labeled internal standards. The enzyme preparations α-amylase, takadiastase, β-glucosidase, and acid phosphatase were all able to liberate thiamine and riboflavin. The diastatic enzyme preparations α-amylase and takadiastase also expressed proteolytic side activities resulting in the formation of small peptides which interfered with the mass spectra of thiamine and riboflavin. Liberation of nicotinamide and pantothenic acid from NAD(+) and CoA, respectively, could not be achieved with any of the studied enzyme preparations. Hydrochloric acid extraction at 121 °C for 30 min was found to be destructive to pantothenic acid, but increased the liberation of pyridoxal.