Effects of food composition on the bioavailability of vitamin B-6 in the rat.

The effects of food composition and thermal processing on the relative bioavailability of vitamin B-6 in beef, spinach, potato, and cornmeal were assessed by a series of rat bioassays. The protein content of the basal diets was varied from 5 to 50%. Within each protein subgroup, graded levels of pyridoxine (PN) were added to basal diets to obtain standard PN dose-response curves. Poor correlation was observed between bioavailability values calculated from plasma pyridoxal 5'-phosphate (PLP) and the less specific bioassay criteria (growth and feed efficiency). Plasma PLP values indicated that: 1) the bioavailability of vitamin B-6 in beef was greater than that in cornmeal, spinach and potato; and 2) thermal processing of the tested foods or increasing dietary protein levels did not adversely affect, and often increased, the bioavailability of the vitamin. The results also showed that diet composition and food processing must be considered in evaluating the bioavailability of vitamin B-6.