Application of Carbon Stable Isotope Ratio Mass Spectrometry in Authenticity of “Zero-Added-Glutamate” Soy Sauces

The zero-added exogenous monosodium glutamate (MSG) soy sauce market is developing rapidly, but its authenticity remains a challenge for the industry. In this study, carbon stable isotope ratio mass spectrometry was utilized to determine 13C/12C ratio (δ13C value) of a variety of commercially available natural plain fermented soy sauces, and the main amino acid distribution and glutamic acid content were analyzed. δ13C value of glutamic acid in soy sauce showed strong positive correlation with the amount of exogenous glutamic acid/glutamate added; increment in exogenous glutamic acid/glutamate concentration resulted an increased δ13C value. δ13C value of a variety of authentic natural plain fermented soy sauces with zero added glutamate accounted for less than −24.45‰ with glutamic acid content lower than 12.89 mg/mL. On the other hand, high monosodium glutamate soy sauce added with MSG, δ13C values are greater than −15.51‰ while glutamic acid content exceeded 35.12 mg/mL. δ13C values of glutamic acid in soy sauce suspected to adulterate with exogenous glutamic acid/glutamate ranging between −17.91‰ and −17.30‰ and its glutamic acid content ranging from 30.42 to 37.82 mg/mL. The method specified in Association Standard accurately discriminated a variety of real “zero-added-glutamate” soy sauces currently available on the market accurately.