We analyzed the effect of Cornelian cherry varieties differing in fruit color ('Yantaryi'-yellow fruits, 'Koralovyi'-coral fruits, 'Podolski'-red fruits) and the production method on the physicochemical and antioxidative properties of Cornelian cherry vinegars, and on their content of iridoids and polyphenols. Acetic fermentation was conducted by two methods: I) single-stage (spontaneous) acetic fermentation, without inoculation with microorganisms, and II) two-stage fermentation in which the first stage involved the use of Saccharomyces bayanus-Safspirit fruit yeast for alcoholic fermentation, and the second one included spontaneous acetic fermentation. Acetic acid, glycerol, individual iridoids, phenolic acids, flavonols, and anthocyanins were quantified by a high-performance liquid chromatography (HPLC) method. The antioxidative activity was determined based on the following tests: 2,2-Diphenyl-2-picryl-hydrazyl (DPPH•), 2,2'-Azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid (ABTS•+), and ferric reducing antioxidant power (FRAP), while the total polyphenols content was determined using the Folin-Ciocialteu (F-C) reagent test. Both the Cornelian cherry variety and vinegar production method affected the antioxidative properties as well as concentrations of iridoids and polyphenols in the finished product. The concentration of total polyphenols (F-C) in vinegars ranged from 326.60 to 757.27 mg gallic acids equivalents (GAE)/100 mL vinegar, whereas the antioxidative activity assayed with the DPPH• and FRAP methods was the highest in the vinegars produced from the coral and red varieties of Cornelian cherry with the two-stage method. Loganic acid predominated among the identified iridoids, reaching a concentration of 185.07 mg loganic acid (LA)/100 mL in the vinegar produced in the two-stage fermentation from the coral-fruit variety. Caffeoylquinic acid derivatives were the main representatives among the identified phenolic compounds. The results of this study demonstrate Cornelian cherry vinegars to be rich sources of biologically-active iridoids and phenolic compounds with antioxidative properties.
Keywords: Cornelian cherry vinegar; antioxidative activity; fermentation; iridoids; polyphenols.