Yamada K, Yamada Y, Fukuda M, Yamada S
Department of Liberal Arts and Sciences, School of Health Sciences, Sapporo Medical University, Japan.
Int J Vitam Nutr Res. 1999 Nov;69(6):412-8. doi: 10.1024/0300-9831.69.6.412.
We have already reported that raw nori (Porphyra tenera) contains cobalamin (Cbl) but not Cbl analogues (J. Nutr. Sci. Vitaminol., 42, 497, 1996). It seems, therefore, that it is an excellent natural vegetable source of Cbl. On the other hand, it has been reported that the Cbl nutritional status of vegetarian children deteriorated as estimated by the hematological index, mean corpuscular volume (MCV), after they had dried nori as a source of Cbl. Such a discrepancy between raw and dried nori as a source of Cbl led us to investigate whether Cbl in dried nori had different properties from that in raw nori. We found that contents of Cbl homologues determined by a bioassay method in both raw and dried nori were similar. The urinary methylmalonic acid excretion increased when human female volunteers were given 40 g of dried nori daily during the test period. On the other hand, the urinary methylmalonic acid excretion did not change when volunteers were daily given 320 g of raw nori, which was equivalent to 40 g of the dried one on the basis of dehydrated weight, during the test period. By paper chromatography, 65% of the Cbl homologues were found to be comprised of Cbl analogues in dried nori, while 73% of the Cbl homologues in the raw nori were genuine Cbl. These results were confirmed by the finding that the bioassay method gave higher values for Cbl homologues than those obtained by a competitive binding assay method using an intrinsic factor as a Cbl-binding protein. Our present data demonstrated that Cbl in raw nori can be changed into harmful Cbl analogues by the drying process.
我们已经报道过，新鲜紫菜（条斑紫菜）含有钴胺素（Cbl），但不含有Cbl类似物（《营养科学与维生素学杂志》，42卷，497页，1996年）。因此，它似乎是Cbl的一种优质天然蔬菜来源。另一方面，有报道称，素食儿童将干紫菜作为Cbl来源后，根据血液学指标平均红细胞体积（MCV）估计，其Cbl营养状况恶化。作为Cbl来源，新鲜紫菜和干紫菜之间存在这样的差异，这促使我们研究干紫菜中的Cbl是否具有与新鲜紫菜中不同的特性。我们发现，通过生物测定法测定的新鲜紫菜和干紫菜中Cbl同系物的含量相似。在测试期间，当人类女性志愿者每天食用40克干紫菜时，尿甲基丙二酸排泄量增加。另一方面，在测试期间，当志愿者每天食用320克新鲜紫菜（按脱水重量相当于40克干紫菜）时，尿甲基丙二酸排泄量没有变化。通过纸色谱法发现，干紫菜中65%的Cbl同系物由Cbl类似物组成，而新鲜紫菜中73%的Cbl同系物是真正的Cbl。生物测定法得出的Cbl同系物值高于使用内因子作为Cbl结合蛋白的竞争性结合测定法得出的值，这一发现证实了上述结果。我们目前的数据表明，新鲜紫菜中的Cbl在干燥过程中可转变为有害的Cbl类似物。
