Effect of sterlilzation of milk on vitamin B-6 composition and bioavailability

To assess the effect of heat sterilization of milk on vitamin B-6 composition and bioavailability, rats were orally administered [3H]pyridoxine (PN), [3H]-4-pyridoxic acid (4-PA) or [3H]pyridoxal (PL) in water, or [3H]PL in fresh milk with or without subsequent sterilization at 120 degrees C for 20 min. [3H]PL in sterilized milk underwent partial conversion to pyridoxamine (PM) and 4-PA, as well as irreversible binding to protein. [3H]PL in water and unheated milk was well absorbed and similar to [3H]PL. The intestinal absorption of 3H from sterilized milk and [3H]4-PA was significantly reduced compared to [3H]PN or [3H]PL. The results of this study indicate that heat sterilization of milk reduces vitamin B-6 activity by irreversible binding to protein, as well as by partial formation of 4-PA, a nonbiologically active form of vitamin B-6.