| Abstract: | Lysine content and availability were determined in a set of milk samples which had sustained increasing heat treatments. Lysine content was measured after acid hydrolysis of the sample (TLV or x-value), lysine availability by an enzymic digestion procedure (ALV-e or y-value) and by two modifications of the fluorodinitrobenzene method: the direct method (ALV-f I or z-value) and Carpenter's corrected straight acid procedure (ALV-f II or v-value). The four procedures gave strongly correlated, but numerically quite different results. The enzymic procedure and Carpenter's chemical method produced very similar results for lysine availability. In all heated samples, lysine content was much higher than lysine availability. The direct fluorodinitrobenzene method yielded values intermediate between those for lysine content and ‘true’ lysine availability. A nomograph is presented which accounts for the different conditions of lysine in heated milk and allows the interconversion of the x, y, z and v-values. |
