# Flavour Volatiles of Fermented Vegetable and Fruit Substrates: A Review
## 3 Results
### Alcohols
acidophilus_ monoculture, the ethanol concentration increased from 44 to 57.4 ug/g [46]; (4) in unfermented apple juice, the ethanol concentration was 188.4 ng/mL, compared to 83.4-123.5 ng/mL after fermentation with various LAB strains [19]; (5) in non-pH-adjusted (2.7) sea buckthorn juice, the ethanol concentration was 170.7 ng/mL, which reduced after fermentation for 36 and 72 h by _L. plantarum_ to 165.4 and 152 ng/mL, respectively. However, if the pH of the juice was adjusted to pH 3.5, the initial ethanol concentration of 166.3 ng/mL increased after _L. plantarum_ fermentation for 36 and 72 h to 194.6 and 206.5 ng/mL, respectively [42]; and (6) in tomato juice, the ethanol concentration after fermentation with either _L. plantarum_ or _L. casei_ was 2.7 and 1.2 times lower, respectively, compared to its concentration in the unfermented juice [32]. 1-Octanol is a fatty alcohol produced by micro-organisms utilizing glucose as a substrate through a fatty acid synthesis pathway using various enzymes [53]. The 1-octanol concentration was generally reported to increase after LAB fermentation in the 5 studies reviewed: (1) In Chinese wolfberry juice fermented by either _L. plantarum_, _L. casei_, _Lacticas-eibacillus paracasei_ (_L. paracasei_), _L. acidophilus_, _L. helevticus_, or _Bifidobacterium Lactis_ (_B. lactis_), the 1-octanol concentration was 172.9, 119.1, 137.2, 209.3, 131.4, and 142.4 ug/mL, where it was not detected in the unfermented juice [50]; (2) the 1-octanol concentration in a distillate prepared using vacuum distillation from orange pomace fermented by _L. rhamnus_ was 1.5 ug/mL, compared to 0.1 ug/mL in the distillate from unfermented pomace; in distillates prepared using a simple distillation method, the 1-octanol concentration in the fermented orange pomace distillate was 2.1 ug/mL, compared to 1.8 ug/mL in the unfermented pomace distillate. Interestingly in the same study, using the simple distillation method, the 1-octanol concentration in the fermented melon by-product distillate was 21.5 ug/mL, compared to 7.1 ug/mL in the unfermented by-product distillate, whereas in extracts prepared by vacuum distillation, the 1-octanol concentration in the distillate from melon by-product fermented by _L. rhamnus_ was 1.1 ug/mL, compared to 0.2 ug/mL in the unfermented by-product distillate [44]; (3) in kiwifruit juice (Xuxiang and Hongyang cultivars), the 1-octanol concentration was 285.5 and 325.5 ng/mL in Xuxiang cultivar juice fermented by either _L. helevticus_ or _L. plantarum_, respectively, compared to 146.4 ng/mL in the unfermented juice, where it was not detected in Xuxiang cultivar juice fermented by _L. acidophilus_. Interestingly, with the Hongyang cultivar juice, 1-octanol was not detected in the unfermented juice or in any of the LAB fermented juices. [49]; (4) in cherry juice fermented by either _L. plantarum, L. rhamnus, or L. paracasei_, the 1-octanol concentration was 4.5-7.8, 8.4, and 5.2 ng/mL, respectively, compared to 3.4-3.6 ng/mL in the unfermented juice [29]; and (5) in apple juice fermented by either _L. acidophilus, L. rhamnus, L. casei_ or _L. plantarum,_ the 1-octanol concentration was 4.2, 3.5, 3.8, and 4.0 ng/g, respectively, compared to 1.0 ng/g in the unfermented juice [21]. However, in okara fermented by LAB monoculture of either _L. rhamnus, P. acidilactic_ or co-culture (_L. acidophilus, L. rhamnus, and _P. acidilactic_), the 1-octanol concentration was 11.7, 17.8, and 1.7 ug/g, respectively, compared to 30.0 ug/g in the unfermented okara, whereas okara fermented with _L. acidophilus_ had an 1-octanol concentration of 34.7 ug/g [46]. 1-Hexanol is produced from the enzymatic oxidation of the fatty acid linoleic acid [54]. In 11 experiments, the 1-hexanol concentration increased after fermentation: (1) In Chinese wolfberry juice fermented by either _L.