A comparison of the dye-binding and fluorodinitrobenzene methods for determining reactive lysine in leaf-protein concentrates.

1. Twenty-eight leaf-protein concentrate (LPC) samples, subjected to different thermal treatments, were produced from five curd batches. For these samples, the fluorodinitrobenzene (FDNB)-reactive lysine values gave closer agreement with dye-binding lysine (DBL) than with the dye-binding capacity (DBC). 2. No relationship was established between the dye-bound-after-propionylation (DBAP) and the histidine + arginine value. 3. Comparison of dye-bound-protein values with those for tungstic-acid-precipitated nitrogen x 6.25 for the LPC samples showed the heat-damaged samples to lie below the regression line for the other samples. 4. Reactive-lysine values by dye-binding and by FDNB methods correlated well with total lysine, but the slopes of the regression line indicated closer agreement for values for samples not damaged by heat. 5. The correlation coefficients between DBC and total basic amino acids, DBC and histidine + arginine + DBL, and DBC and histidine + arginine + FDNB-reactive lysine were similar. 6. There was no correlation between the lightness of colour of the LPC samples and the availability of lysine.