Bioavailability for rats of thiamin in whole wheat and thiamin-restored white bread.

The relative biological value of thiamin in leavened bread (whole wheat and thiamin-restored white) and thiamin mononitrate was examined by using thiamin-deficient rats as the test model. Erythrocyte transketolase (ETK) activities and liver thiamin content responded positively to graded but suboptimal levels of dietary thiamin in these rats. Biological values were calculated (slope ratio assay) by using these response parameters, which may depict the body's thiamin status, at least in the deficient rats. Compared to thiamin in thiamin mononitrate (100%), the biological value of thiamin in breads measured 88% (white bread) and 91% (whole wheat bread) based on ETK activity and 68% (white bread) and 75% (whole wheat bread) based on liver thiamin response. Thus, diets high in fermented cereal foods (thiamin enriched or not) may require a generous allowance of thiamin to compensate for reduced biological value.