Deamination of lysine in soy sauce by reaction with active carbonyl compounds produced by Maillard reaction

Abstract

The development of a brown colour during the thermal treatment of many foods, such as coffee, roasted beef, soysauce or evaporated milk, mainly originates from interaction between reducing carbohydrates and amino acids, known as the Maillard reaction. It is commonly known at present that one of the causes of changes in colour, aroma, flavor and nutritional value of food products. The Maillard reaction involves condensation, dehydration and polymerization. As a result of this complex reaction, a variety of by products, intermediates and brown pigment. An amino-carbonyl reaction in soysauce yielded a rapid brown coloration. An apparent decrease in the free amino group, determined by the TNBS method, was observed to be associated in parallel with the brown pigment formation by UV-Vis spectrum, amino acids by HPLC, Protein content by Lowry method, pH and reducing sugar. “Moromi”, moromi with heating and soysauce were examined to effect Maillard reaction. The positive effect of sugar on browning suggested that lysine content decreased from 1.18% to 0.69%, free amino group decreased from 3.16 mg/ml to 2.27 mg/ml and their UV-Vis spectrum in range 400 nm. These results indicate that e-amino group of lysine in protein could easily be determined by the amino-carbonyl reaction Key words : Maillard reaction, soysauce, brown pigment, lysine