Every country in the world is concerned with the nutritional status of
its population and in utilizing its natural food resources in the most
effective way possible. Surveys based on food intakes and food
compositional data are being conducted with the object of establishing
recommended intakes of vitamins. These recommendations are constantly
being changed as new knowledge comes to light. Analytical techniques
using physicochemical and microbiological methods have been largely
developed to determine the total vitamin content of a food commodity or
diet using the most rigorous extraction method commensurate with the
stability of the vitamin. The extraction procedures frequently involve
prolonged heating of suitably prepared food samples at extremes of pH to
liberate vitamins from chemically bound forms in the food matrix or to
remove a preponderance of fat from fatty foods. For several vitamins the
data obtained by these means grossly overestimate the nutritional value
of the food because the human digestive system fails to liberate bound
vitamin forms for subsequent absorption by the intestine. This statement
is borne out by reports of vitamin deficiency in situations where the
dietary supply of vitamin is adequate on the basis of conventional
analysis. Various research labora- tories are directing their effort
toward the estimation of bioavailable vitamin, i. e. the proportion of
vitamin in the food which is available for utilization by the body. So
far, few data have been published and there are many gaps in the
knowledge required to interpret experimental results.
