**4. Conclusions**

The antioxidant activities, TPC, and TFC of 23 fruit vinegars were studied. The FRAP values of the fruit vinegars were in the range of 0.15–23.52 μmol Fe(II)/mL, and the TEAC values ranged from 0.03 to 7.30 μmol Trolox/mL. The TPC and TFC values ranged from 29.64 to 3216.60 mg GAE/L and from 2.22 to 753.19 mg QE/L, respectively. Balsamic vinegar of Modena (Galletti), Aceto Balsamico di Modena (Monari Federzoni), red wine vinegar (Kühne), and red wine vinegar (Galletti) exhibited the highest antioxidant activities among 23 fruit vinegars tested. The high correlation of FRAP and TEAC with TPC values indicated that the abilities of fruit vinegars to reduce oxidants and to scavenge free radicals were mainly attributed to polyphenols. Several phenolic compounds, including, gallic acid, protocatechuic acid, chlorogenic acid, caffeic acid, and *p*-coumaric acid, and organic acids including tartaric acid, malic acid, lactic acid, citric acid, and succinic acid, were mainly detected in fruit vinegars. Some of the phenolic compounds (such as gallic acid and *p*-coumaric acid) might be responsible for the high antioxidant content and strong antioxidant activities of fruit vinegars and need to be further explored. The polyphenols and organic acids of fruit vinegars might contribute to their antioxidant activities, flavors, and health effects. Overall, fruit vinegars can be good natural sources of dietary antioxidant polyphenols and organic acids, which should be of interest to food scientists, nutritionists, the public, and food producers.

**Author Contributions:** Conceptualization, Q.L., R.-Y.G and H.-B.L.; Formal analysis, Q.L. and G.-Y.T.; Funding acquisition, R.-Y.G.; Investigation, Q.L., G.-Y.T. and C.-N.Z.; Project administration, H.-B.L.; Resources, C.-N.Z.; Software, Q.L.; Supervision, R.-Y.G. and H.-B.L.; Validation, Q.L. and H.-B.L.; Writing – original draft, Q.L.; Writing – review & editing, R.-Y.G. and H.-B.L.

**Funding:** This study was funded by the Shanghai Basic and Key Program (18JC1410800), Shanghai Pujiang Talent Plan (No. 18PJ1404600), the Agri-X Interdisciplinary Fund of Shanghai Jiao Tong University (No. Agri-X2017004), and the Shanghai Agricultural Science and Technology Key Program (18391900600).

**Conflicts of Interest:** The authors declare no conflict of interest.
