Occurrence of Pyridoxine
The best natural sources of pyridoxine are those foods containing other members of the B complex. Yeast, rice polishings, the germ of various grains and seeds and egg yolk are outstanding sources. The vitamin is widely distributed in other foods of both aplant and animal nature. In many of its sources pyridoxine is chemically bound to protein and is present in liver, for example, mainly as pyridoxal and pyridoxamine protein complexes.
Determination of Pyridoxine
Both rats and chicks have been used in the biological methods. The rat growth method is used more than other biological methods. It consists of a depletion period on a specific ration and then a comparison of weight gain of groups fed this ration, supplemented with various levels of pure pyridoxine, and other groups fed the basal ration, plus at least two levels of material under test. Microbiological methods are rapid and accurate. Cheslock reported 100 per cent recovery of pyridoxine added to blood nitrates in her modification of the method of Parrish and co-workers.
Some microorganisms do not respond equally to the different forms of Bs, and in some cases they show no response to one or two of the forms; thus methods for the different molecules are available. An enzymatic procedure for pyridoxal phosphate capable of estimating as little as 0.03 /lg was developed by Wada and others. Pyridoxal, pyridoxamine, and pyridoxine are not active in the test. A sensitive fluorometric method has been used for pyridoxic acid, the main excretory product of pyridoxine.
