**5. Conclusions**

An enzymatic method on an automated spectrophotometric system was used for the quantification of acetic acid in vinegar. The enzymatic method met many validation requirements (linearity, sensitivity, and uncertainties) but not accuracy. However, the method can be considered applicable as the precision and uncertainty are lower than those of the Community method (deviations are around 10%). The validation of instrumental analytical methods not yet used as conventional methods should find more space in the scientific literature. By transferring knowledge on operating methods, the repetition of long and laborious validation processes that involve high costs and waste of time will be avoided.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2304-8158/9/6/761/s1, Figure S1: Standard calibration curve, Figure S2: Normal residual probability, Figure S3: Shapiro-Wilk test (5% significance levels), Figure S4: Balsamic wine vinegar accuracy statistical analyses, Figure S5: Red wine vinegar accuracy statistical analyses, Figure S6: White wine vinegar accuracy statistical analyses, Table S1: Data considering calculating type A uncertainty, Table S2: Type B: Systematic uncertainty estimates, Table S3: Red wine vinegar data, Table S4: Withe wine vinegar data, Table S5: Balsamic wine vinegar data, Table S6: Upper and lower limit of repeatability.

**Author Contributions:** I.D., data curation and writing—review and editing; R.D.L., investigation; A.S., investigation; D.C., investigation.; S.L., investigation. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

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

#### **References**


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