Effect of Dietary Soy Protein Isolate Level on the Ratio of N¹-Methyl-2-pyridone-S-carboxamide plus N¹-Methyl-4-pyridone-3-carboxamide to N¹-Methylnicotinamide Excretion in Rats

Abstract

A 10%, 20% or 40% soy protein isolate (SPI) diet containing sufficient niacin was fed to rats for 9 days and urine was collected for the last 2 days. The ratio of N¹-methyl-2-pyridone-5-carboxamide (2-py) plus N¹-methyM-pyridone-S-carboxamide (4-py) to N¹-methylnicotinamide (MNA) excretion increased with increasing in the dietary SPI level; this ratio in the groups with the 10%, 20% and 40% SPI diets was 0.56±0.08, 1.04±0.34 and 10.33±1.60, respectively. The great increase in the ratio of 2-py plus 4-py to MNA excretion on changing the 20% SPI diet to the 40% SPI diet was attributed to the great decrease in MNA excretion in the group with the 40% SPI diet compared with the group with the 20% SPI diet. From these results and our previous results [Agric. Biol. Chern., 52, 1765 (1988)], it is suggested that the 2-py + 4-py/MNA excretion ratio can be used for assessment of the protein nutrition.