Amino acid determination in pure proteins, foods, and feeds using two different acid hydrolysis methods

Abstract

To compare the rapid acid hydrolysis (proposed by Gehrke) to the classic acid hydrolysis method, the amino acid content in 15 samples of animal and vegetable nature, with variable quantities of protein and other nonproteic components, were determined following the two methods of acid hydrolysis using 6 n HCl at 110°C for 24 h and at 145°C for 4 h. Because the high-temperature, short-time hydrolysis (HTST) method has been used only in pure proteins, the purpose of the present work was to confirm that it could be applied to any material, especially foods and feeds. Three groups of samples were tested: pure proteins, protein concentrates, and vegetable samples with a high carbohydrate content. The acid hydrolysis by the two methods was performed in duplicate. The statistical analyses (Student's t test) of the total amino acids and the total essential amino acids indicated no differences between the two methods in any of the three groups of samples. In the group of protein concentrates there appeared differences in only three amino acids: in valine (higher values by the HTST method) and in aspartic acid and serine (lower values by the HTST method). These results indicate that the HTST hydrolysis method is equivalent to the classic method and can be used for any type of material. The use of this method can also save considerable time in the determination of amino acids, especially in food analysis.