The identification of antioxidants in dark soy sauce

Soy sauce is a traditional fermented seasoning in Asian countries, that has high antioxidant activity in vitro and some antioxidant activity in vivo. We attempted to identify the major antioxidants present, using the 2,2'-azinobis( 3-ethylbenzothiazoline-6-sulfonic acid) ( ABTS) assay as a guide. 3-Hydroxy-2-methyl-4H-pyran-4-one ( maltol) was one of several active compounds found in an ethyl acetate extract of dark soy sauce ( DSS) and was present at millimolar concentrations in DSS. However, most of the antioxidant activity was present in colored fractions, two of which ( CP1 and CP2) were obtained by gel filtration chromatography. Their structural characteristics based on nuclear magnetic resonance ( NMR) and electrospray-ionization time-of-flight mass spectrometry ( ESI-TOF-MS) analysis suggest that carbohydrate-containing pigments such as melanoidins are the major contributors to the high antioxidant capacity of DSS.