Determination of bioavailability of some long-chain N-substituted derivatives of L-methionine and L-lysine

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Abstract
The bioavailability of N-acyl-L-methionine derivatives was determined using microbiological assay with Tetrahymena pyriformis. Palmitoyl- and stearoyl-L-methionine, stearoyl-L-methionine ethyl ester, and stearoyl-L-methionine sodium salt were partially utilized (14-38%) for growth of the microorganism. These compounds partially inhibited utilization of free methionine added to the media. The shorter derivatives, acetyl-, hexanoyl-, lauroyl- and myristoyl-L-methionine completely inhibited T. pyriformis growth. This effect was not reversed when DL-methionine was added to the media. N6-fatty acyl L-lysine derivatives gave low availability values (3-18%) in microbiological assessment with T. pyriformis. N2-Acetyl-and N6-acetyl-lysine did not inhibit the utilization of the added parent amino acid. Nutritional evaluation of L-methionine derivatives by the rat growth method using net protein ratio (NPR) as the performance index indicated complete availability of stearoyl-L-methionine, stearoyl-L-methionine sodium salt and partial availability of stearoyl-L-methionine ethyl ester (52%), stearoyl-L-methionylglycine (32%) and lauroyl-L-methionine (75%).

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