Niacin contents of cereal-milling products in food-composition databases need to be updated

Abstract

The niacin content of cereal raw materials reported in food-composition databases often differs considerably. One major reason for this discrepancy is the analytical method used for its measurement is that a significant part of the niacin in cereals exists in bound form. In this study, we compared the niacin content of some representative cereal raw materials analysed with a sensitive and validated ultra-high performance liquid chromatography-fluorescence method against the values found in five national food-composition databases. We used established extraction methods that are assumed to liberate niacin available for absorption (acid hydrolysis mimicking human digestion) or total niacin (strong acid-alkaline hydrolysis). The niacin content (mg/100 g dry weight) obtained with acid hydrolysis ranged from a low level in corn flour (0.26), white wheat flour (0.45) and oat flakes (0.48), to a higher level in wholegrain flours (rye: 0.79, barley: 0.99, wheat: 0.88), wheat bran (2.7) and wheat germ (2.7). The niacin content with the acid-alkaline hydrolysis, however, was 1.9-11-fold the value measured after extraction with acid hydrolysis. In general, the niacin content found in the databases is closer to the results obtained after the acid-alkaline extraction, suggesting that the niacin values reported in the databases may not reflect actual bioaccessible niacin but total niacin.