Changes in Free Amino Acids During Heating Bouillon Prepared at Different Temperatures

Abstract

The changes in the concentration and amounts of free amino acids were analyzed while heating bouillon at three different temperatures; 80℃ (low-temperature heating, LH), 95℃ (gentle boiling, GB) and 98℃ (regular boiling, RB). The concentration and total amount of free amino acids, except for glutamine (Gln), gradually increased during heating because of their extraction and heat-triggered water evaporation in the bouillon. The extraction reached respective peaks after 2hr and 4hr with RB and GB, while the amino acids were not completely extracted even after 5hr with LH. Irrespective of the heating temperature, the major free amino acids in the bouillon were glutamate (Glu), alanine (Ala) and arginine (Arg). Although Gln was initially the most concentrated free amino acid in the bouillon at 0 hr, its concentration gradually decreased during heating. It has been suggested that Gln becomes 2-pyrrolidone-5-carboxylic acid (PCA) at a temperature higher than 70℃ in an aqueous solution.