# Flavour Volatiles of Fermented Vegetable and Fruit Substrates: A Review
## 3 Results
### Acids
Hexanoic acid was detected after fermentation in 4 studies: (1) In jujube juice fermented by a mixture of _L. plantarum_, _L. rhamnus_, and _S. thermophilus_, the hexanoic acid concentration was 15.1 ug/g, compared to 7.1 ug/g in the unfermented juice [47]; (2) in non-pH-adjusted (2.65) bog bilberry juice fermented by two strains of _L. plantarum_, the hexanoic acid concentration was 266 and 272.1 ng/mL, compared to 147 ng/mL in the unfermented juice. However, if the pH of the juice was adjusted to pH 3.5, the initial hexanoic acid concentration of 132.6 ng/mL was slightly changed after fermented by two strains of _L. plantarum_ to 136.9 and 123.2 ng/mL [34]; (3) in grape juice fermented by LAB, the hexanoic acid concentration was 14.2 ng/mL, where it was not detected in the unfermented juice [43]; and (4) in mango slurry fermented by different LAB, the hexanoic acid concentration was 1.4-1.7 times higher than the concentration in the unfermented slurry. However, in yeast fermentation, the hexanoic acid concentration was 1.2-1.6 times lower compared to the concentration in the unfermented juice [41]. According to [PERSON] et al. [20], in Muzao varietal jujube juice, the initial hexanoic acid concentration of 69 ug/mL was reduced after fermentation by different LAB to between 9.2 and 54.5 ug/mL, with the highest reduction being reported for _L. acidophilus_ fermented juice. In the same study, in Hetain varietal jujube juice, the initial hexanoic acid concentration was 19.0 ug/mL, which increased after fermentation by different LAB to 31.2-75.9 ug/mL, with the highest concentration being obtained in _L. acidophilus_ fermented juice. Octanoic acid, which is synthesised from sugars (glucose) through the fatty acid biosynthesis pathway [74], was detected in 6 studies after the fermentation of juices: (1) In non-pH-adjusted (2.65) bog bilberry juice fermented by two strains of _L. plantarum_, the octanoic acid concentration was 3921.6 and 4013.2 ng/mL, compared to 1538.2 ng/mL in the unfermented juice. However, if the pH of the juice was adjusted to pH 3.5, the initial octanoic acid concentration of 1156.5 ng/mL was reduced after fermentation by two strains of _L. plantarum_ to 655.3 and 722.9 ng/mL [34]. (2) in goji juice fermented by a bacterial mixture, the octanoic acid concentration ranged from 251.8 to 321.5 ng/g, and it was not detected in the unfermented juice [25]; (3) in grape juice fermented by LAB, the octanoic acid concentration was 5.7 ng/mL, and it was not detected in the unfermented juice [43]; (4) in yam juice fermented by LAB, the octanoic acid concentration was 2 times higher compared to the concentration in the unfermented juice [33]; (5) in durian pulp fermented by _L. casei_, the octanoic acid concentration was 2.3 times higher compared to the concentration in the unfermented pulp, and when the pulp was fermented by _L. casei_ combined with yeast _W. saturus_, the octanoic acid concentration was 2 times lower compared to the concentration in the unfermented pulp [30]; and (6) in mango slurry, the octanoic acid was detected after fermentation by the yeast _S. cerevisiae_, but it was not detected after LAB fermentation [41]. [PERSON] et al. [33] reported that _L. plantarum_ alone or in combination with _S. thermophilus_ increased acetic, nonanoic, and decanoic acids in fermented yam juice, reducing the astrin-gent odour of the fermented juice. Overall, volatile acids after LAB fermentation made contributions to the flavour of fruit and vegetable juices, where acetic acid (15 papers) was the most commonly detectedvolatile acid present in fermented juices, followed by octanoic acid (6 papers), hexanoic acid (4 papers), 3-methyl-1-butanoic acid (3 papers), and butanoic acid (3 papers).