Determination of available lysine in foods

• 1.1. Methods for the determination of available lysine in foodstuffs all based on reaction with fluorodinitrobenzene are discussed with special reference to the problem of analyzing carbohydrate-rich products.
• 2.2. A recording and very sensitive method, based on chromatographic separation and polarographic detection of the eluents, has been developed for the determination of available lysine. The results are compared with those obtained with a photometric method.
• 3.3. Experiments were carried out to prove an expected effect of sample weight on the results found in the determination of available lysine with the above method. It was shown that with the usual methods an extrapolation procedure (to zero sample weight) is necessary to overcome interferences by other sample components.
• 4.4. Experimental evidence was obtained to show that interferences in the determination of available lysine can be largely diminished by adding dinitrophenol before hydrolysis of the fluorodinitrobenzene-treated sample.
• 5.5. A comparison is made between available lysine and the difference between total lysine and blocked lysine for a variety of samples. The latter figures were, with one exception, systematically higher.
• 6.6. A standard method for the determination of available lysine is described.