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Industrially, the sensitivity of acetic acid bacteria (AAB) to the high temperatures and the high ethanol concentrations is the major concerns for manufacturers. This study was conceived and designed to isolate and identify new thermo- and ethanol-tolerant AAB from Opuntia ficus-indica L. fruits. As a result, among 140 isolated bacterial strains, five selected strains (CR1, CR5, CR23, CZ2, and CZ15) exhibited important acetic acid production until 40 °C. The use of 16S rDNA gene analysis was insufficient to identify selected bacteria. Indeed, except CR5 that presented 100% similarity to A. cerevisiae, the other strains presented similar homology rates simultaneously to the 16S rDNA sequences of A. cerevisiae and A. malorum. The reidentification by 16S-23S rDNA gene sequencing showed that CR1, CR23, and CZ15 were A. malorum, which were shown tolerance to the highest concentration of ethanol (12%) and produced elevated amount (40 g/L) of acetic acid at 37 °C. In summary, we showed the thermotolerance and ethanol tolerant character of new A. malorum strains, which can be used as a starter for vinegar production. Furthermore, during the molecular characterization of the isolated strains, we concluded that 16S-23S rDNA internal transcribed spacer sequence is of great importance for discriminating between AAB species as a complement to the identification by 16S rDNA sequencing., (© 2020 International Union of Biochemistry and Molecular Biology, Inc.)

BACKGROUND: In several countries, the cactus plant (Opuntia ficus‐indica (L). Mill.) has received renewed attention because of its ecological, socio‐economic and environmental role. In this study, prickly pear vinegar was produced employing two types of acetification processes: surface and submerged culture. Both acetification processes were performed at different temperatures (30, 37, 40 °C) by using two different species of thermotolerant acetic acid bacteria (Acetobacter malorum and Gluconobacter oxydans). Polyphenols and volatile compounds analyzed by ultra‐performance liquid chromatography with diode array detection and stir bar sorptive extraction–gas chromatography–mass spectrometry, respectively, were considered as the main variables to determine the effect of the acetification process on the quality of the vinegar. RESULTS: As a result, 15 polyphenols and 70 volatile compounds were identified and quantified in the vinegar samples produced by both acetification processes. The results showed that the surface acetification method led to an increase in the concentration of phenolic components, which was higher than that in the submerged process. However, a significant increase in volatile compounds predominated by esters and acids was observed when submerged culture acetification was employed, whereas alcohols were predominant in surface culture vinegars. Moreover, multivariate statistical analysis showed that the components that mostly contributed to the differentiation between all vinegar samples were the volatile compounds. CONCLUSION: It has been proved that prickly pear vinegar could be successfully produced at higher temperatures than usual, by employing thermotolerant bacteria, and that the type of acetification method significantly affects the final quality of the vinegar produced. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This work intends to determine the effect on the aroma profile, phenolic content and antioxidant activity of prickly pear vinegars produced by the surface culture at two different fermentation temperatures and using different acetic acid bacteria (AAB) inocula. Prickly pear wine was fermented at two temperature levels (30 and 37 °C) by using bacteria inocula containing Acetobacter, Gluconobacter or a mixture of bacteria isolated from Sherry vinegars. Eighty-five individual volatile compounds from different families and sixteen polyphenolic compounds have been identified. It was confirmed that the highest temperature tested (37 °C) resulted in a lower concentration of volatile compounds, while no significant effect on the vinegars' volatile composition could be associated with the AAB inoculum used. Contrariwise, the highest content of polyphenolic compounds was detected in those vinegars produced at 37 °C and their concentration was also affected by the type of AAB inoculum used. Prickly pear wine displayed greater antioxidant activity than juices or vinegars, while the vinegars obtained through the mixture of AAB from Sherry vinegar showed higher antiradical activity than those obtained through either of the two AAB genera used in this study. It can be therefore concluded that, although the volatile content of vinegars decreased when fermented at a higher temperature, vinegars with a higher content in polyphenols could be obtained by means of partial fermentations at 37 °C, as long as thermotolerant bacteria were employed. [ABSTRACT FROM AUTHOR]

Prickly pear (Opuntia ficus-indica (L). Mill.) vinegar has been produced by submerged culture using scale laboratory fermenters at three acetification temperatures (30 °C, 37 °C, and 40 °C). Pure thermotolerant Acetic Acid Bacteria (AAB) which had been previously submitted to molecular identification by PCR–RFLP of the 16S–23S rDNA regions and 16S–23S ITS rDNA sequencing, were used. The AAB used were identified as Acetobacter malorum and Gluconobacter oxydans. The acetic fermentation achieved by A. malorum at 30 °C and 37 °C was more efficient, in terms of acidity, than that accomplished by G. oxydans. The chemical analysis revealed the presence of 85 individual volatile compounds and 17 polyphenolic compounds. The concentration of approximately half the volatile compounds was significantly affected by fermentation temperature, with clearly lower concentrations as temperature increased, whereas few significant differences were observed when comparing the vinegars produced by the two AAB species. Regarding phenolic compounds, significant increases were registered when temperature changed from 30 °C to 40 °C. Furthermore, the vinegars produced by A. malorum presented a greater concentration of phenolic compounds than those produced by G. oxydans. • Submerged culture for prickly pear vinegar was studied at three temperatures. • Two thermotolerant acetic acid bacteria were identified by molecular identification. • Higher temperatures decreased volatile composition and increased phenolic content. • Acetobacter malorum produced vinegars with a greater concentration of polyphenols. [ABSTRACT FROM AUTHOR]