The Availability of Vitamins from Yeasts

Abstract

Thiamine in an unfortified fresh bakers' yeast ingested by human subjects was unavailable for absorption. Yeasts high in thiamine content, either from propagation or from fortification yielded only a small proportion of their thiamine for absorption; in the case of the highly fortified yeast a much larger proportion of thiamine was released in vitro in comparison. The ingestion of a fresh unfortified bakers' yeast as a supplement to a weighed basal diet lowered the urinary output of thiamine and therefore apparently interfered with the absorption of food thiamine, this effect being greater on the larger yeast dose of 150 gm per day. The duration of the period of ingestion of fresh yeast affected the speed with which the previous level of urinary output of thiamine was again attained when yeast was removed from the diet, indicating a progressive depletion of body stores from ingestion of fresh yeast. The drying of bakers' yeast did not of itself influence significantly the effect of the yeast on thiamine absorption; live dried yeast suitable for leavening also withheld its thiamine from absorption and interfered with the absorption of food thiamine judged by decreases in urinary output. On the other hand, bakers' yeast killed by commercial drying processes or by treatment in boiling water released its thiamine for absorption and offered no interference to absorption of food thiamine. It is believed that live yeast cells in the digestive tract compete with the host for thiamine that is present.