Abstract: Solid phase extraction combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to separate and identify the acidic components of soy sauces fermented at different pH values and their taste characteristics were evaluated. The results showed that a total of 14 flavor peptides were identified from the soy sauce from moromi with pH adjustment, and 12 flavor peptides without pH adjustment. Eight flavor peptides were common to both. The first soy sauce sample contained many small peptides greatly contributing to the taste, among which ED, EE, EF, ESAY and AELY had rich umami and sour tastes with the lowest threshold value at a concentration of 500 mg/L. FLET and SV had kokumi taste at 500 mg/L. In the second soy sauce sample, SV, LLVVQ and ALVLL exhibited a strong kokumi taste, and SV had the lowest threshold value, 500 mg/L. QLLN, LLVVQ, ESAY, AELY, FLET, FLTW, ALVLL, QVELF and SV were synthesized and added to soy sauce at 0.03 g/100 mL each. ESAY was identified to significantly reduce the salty taste and to enhance the kokumi taste of soy sauce. QLLN significantly enhanced the umami taste, while LLVVQ, AELY and FLET did so only slightly, and SV had distinct kokumi-enhancing effect. This study showed that the flavor peptides in the soy sauce fermented by adjusting pH had good flavor characteristics, and imparted rich and well-balanced umami and kokumi tastes to the soy sauce.

Key words: soy sauce; flavor peptides; solid phase extraction; taste characteristics