In this study, we developed a method to simultaneously measure the stable carbon isotope ratio for acetic acid (δ 13 C acetic acid ) and acetoin (δ 13 C acetoin ) in rice vinegar by gas chromatography-combustion-isotope ratio mass spectrometry. The method showed good precision and accuracy. With this method, data from 16 brewed rice vinegars and 10 acetic acid samples were used to evaluate the feasibility of adulteration detection. On the basis that all δ 13 C acetoin values of brewed rice vinegars are nearly constant, a characteristic pattern of the stable carbon isotope in rice vinegar was built with the 95% confidence intervals for δ 13 C acetic acid (−26.97 to −25.38‰), δ 13 C acetoin (−28.14 to −27.09‰), and Δδ 13 C (0.61 to 2.27‰). An adulteration detection curve of Δδ 13 C was proposed based on the results of vinegar and acetic acid samples and confirmed by vinegar spiked with different amounts of acetic acid. This method could be useful in estimating the blending ratio of adulterated rice vinegar products. Products containing more than 10% of synthetic acetic acid could be possibly identified.

Rice vinegar plays an important role in daily life. However, some unscrupulous manufacturers may deliberately add synthetic acetic acid in vinegar products to reduce fermentation time and save production costs. To protect the rights and health of consumers, vinegar authenticity must be controlled. The rice vinegar protein was used as an intrinsic reference and its stable carbon isotope ratio (δ 13 C protein ) was analyzed by elemental analyzer-isotope ratio mass spectrometry. The stable carbon isotope ratio difference between the acetic acid and the rice vinegar protein (Δδ 13 C acetic acid-protein ) was calculated to evaluate vinegar authenticity. Sixteen rice vinegar samples were analyzed and a stable carbon isotopic pattern of rice vinegar was established by the 95% confidence interval for Δδ 13 C acetic acid-protein (0.27‰–2.10‰). An acetic acid adulteration curve of Δδ 13 C acetic acid-protein was also assumed according to the data from rice vinegar samples, and its validity was confirmed by rice vinegar deliberately blended with acetic acid at different ratios (25, 50, and 75%). The Δδ 13 C acetic acid-protein values of the adulterated vinegars decreased with increasing amounts blended acetic acid, but the δ 13 C protein values did not, showing that rice vinegar protein could be used as an intrinsic reference for identifying the adulterated rice vinegar. The rice vinegar adulterated with acetic acid at higher than approximately 10% could be detected.