Valorization of Organic Third-Category Fruits Through Vinegar Fermentation: A Laboratory-Scale Evaluation of Apples, Peaches, and Clementines

This study aimed to evaluate the feasibility of producing vinegar from organic third-category apples, peaches, and clementines on a laboratory scale. Two-step fermentation with <i>Saccharomyces cerevisiae</i> and <i>Gluconobacter oxydans</i> was applied, monitoring production of ethanol and acetic acid and microbial dynamics. Fruit vinegars were subjected to analyses of sensory traits, color, volatile organic compounds (VOCs), and antioxidant activity. Comparable ethanol yields across substrates were obtained, ensuring consistent acetous fermentation and achieving acetic acid concentrations of 5.0-5.6%. Dynamics of yeasts and acetic acid bacteria reflected the production of and subsequent decrease in ethanol. Overall, fermentation proceeded a bit faster in peach juice. Overall, the fruit vinegars, particularly those from peaches and clementines, exhibited darker and more saturated tones. The values of colorimetric indexes fell within the range reported for vinegars. Sensory analysis highlighted large differences among the vinegars. Notwithstanding the highest scores of color, aroma intensity, and floral aroma received by the peach vinegar (PV), it received the lowest acceptability. Clementine vinegar (CV) was especially appreciated. Multivariate analysis based on the VOC profile showed that apple vinegar (AV) was quite similar to the commercial one, whereas PV and CV were well distinguished from it. CV showed the highest antioxidant activity followed by PV.