To clarify the bioavailability of vitamin B-12 in lyophylized purple laver
(nori; Porphyra yezoensis), total vitamin B-12 and vitamin B-12 analogue co
ntents in the laver were determined, and the effects of feeding the laver t
o vitamin B-12-deficient rats were investigated. The amount of total vitami
n B-12 in the dried purple laver was estimated to be 54.5 and 58.6 (se 5.3
and 7.5 respectively) mug/100 g dry weight by Lactobacillus bioassay and ch
emiluminescent assay with hog intrinsic factor respectively. The purple lav
er contained five types of biologically active vitamin B-12 compounds (cyan
o-, hydroxo-, sulfito-, adenosyl- and methylcobalamin), in which the vitami
n B-12 coezymes (adenosyl- and methylcobalamin) comprised about 60 % of the
total vitamin B-12. When 9-week-old vitamin B-12-deficient rats, which exc
reted substantial amounts of methylmalonic acid (71.7(se 20.2) mu mol/d) in
urine, were fed the diet supplemented with dried purple laver (10 mug/kg d
iet) for 20 d, urinary methylmalonic acid excretion (as an index of vitamin
B-12 deficiency) became undetectable and hepatic vitamin B-12 (especially
adenosylcobalamin) levels were significantly increased. These results indic
ate that vitamin B-12 in dried purple laver is bioavailable to rats.