Determining the Dehydroalanine and Amide Contents of Wool as a Means of Estimating Damage Caused by Alkaline Treatments

Abstract

Two analytical methods for determining the extent of alkaline damage to wool are described. In the first method, the dehydroalanine residues formed by alkali were first converted to pyruvic acid by acid hydrolysis. The enzyme-catalyzed reduction of pyruvic acid to lactic acid by reduced nicotinamide-adenine dinucleotide (NADH) was then used to determine quantitatively the pyruvic acid content of the hydrolysate. Reproducible results were obtained provided they were extrapolated to zero time of hydrolysis and the conditions of reduction with NADH were closely controlled. In the second method, amide contents were determined by estimating the ammonia produced when the wool samples were hydrolyzed with 6 N sulfuric acid at 110°C for 8 hours. Quantitative results were obtained without the need to extrapolate to zero time of hydrolysis. The methods were used to analyze wool samples that had been treated with sodium carbonate and sodium hydroxide solutions at temperatures up to 40°C. A linear correlation was found between the decreases in cystine and amide contents and the increase in dehydroalanine content.