# Flavour Volatiles of Fermented Vegetable and Fruit Substrates: A Review
## 3 Results
### Fermented Flavours of Vegetables and Fruits  
Twenty-three of the thirty-five papers described VOCs originating from the fermentation of fruit juices (with 2 of the 23 on goji/wolfberry juice, 2 on jujube juice/pulp, 3 on cashew apple juice, and 3 on apple juice). Nine of the papers described VOCs originating from the fermentation of vegetable substrates (with 2 of the 9 on okara (soybean pulp)), with one investigating tomato and red pepper pomace. Three articles investigated the VOCs generated from a mixture of vegetables and mixtures of vegetables and fruits, with carrot juice being a component in all three studies and apple juice in two. A wide range of micro-organisms were reported as being used, encompassing bacteria, LAB, fungi, and yeast. Thirty-three papers described the use of LAB, with twenty-nine studies only referring to LAB strains, one paper referring to LAB combined with other bacteria, and three papers referring to LAB and yeasts. In the remaining two studies, one study referred to the use of fungi, while the other referred to fungi in combination with yeast. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  
The most commonly mentioned LAB was _Lactiplantibacillus plantarum_ (_L. plantarum_) (28 papers), followed by _Lactiaseibacillus casei_ (_L. casei_) (12 papers), _Lactobacillus acidophilus_ (_L. acidophilus_) (9 papers), _Lactiaseibacillus rhamnus_ (_L. rhamnus_) (9 papers), _Lactbacillus helveticus_ (_L. helevticus_) (4 papers), and _Streptococcus thermophilus_ (_S. thermophilus_) (4 papers). Only four of the papers investigated the use of yeast in combination with LAB and fungi. The most common fermentation temperature and time combination was 37 \({}^{\circ}\)C for 48 h (10 papers), as shown in Table 2. As additional examples, 9 papers described studies carried out at 37 \({}^{\circ}\)C with fermentation times (excluding 48 h) ranging from 20 to 120 h. Six papers described studies carried out at 30 \({}^{\circ}\)C with fermentation times ranging from 24 to 120 h. In 4 papers where multiple LAB strains were investigated, fermentation temperatures of 37 \({}^{\circ}\)C and 30 \({}^{\circ}\)C were used at different times. Thirty-three of the papers isolated VOCs using headspace solid-phase microextraction (HS-SPME), and one study using a purge and trap method, while other one using a static headspace technique. HS-SPME is a simple, rapid, solvent-free method that can extract a diverse mixture of VOCs using a fibre coated with an adsorbent resin. The fibre most frequently stated as being used was 50/30 \(\upmu\)m DVB/CAR/PDMS (Divinylbenzene-Carboxen/polydimethylsiloxane) (17 papers), followed by 75 \(\upmu\)m CAR/PDMS (6 papers), 75 \(\upmu\)m DVB/CAR/PDMS (1 paper), and 50/30 \(\upmu\)m DVB/CAR (2 papers). For SPME, the most frequently reported adsorption time was 30 min (19 papers) for temperatures ranging from 35 to 85 \({}^{\circ}\)C, with 9 papers using 30 min at 40 \({}^{\circ}\)C. The remaining papers reported the use of a wide range of time and temperature combinations, ranging from 7 to 60 min at 40 to 80 \({}^{\circ}\)C. Gas chromatography-mass spectrometry (GC-MS) was used in 34 papers to detect the extracted VOCs, and the remaining paper reporting using gas chromatography-ion mobility spectrometry (GC-IMS). In the papers reviewed, the main VOCs detected due to fermentation were alcohols, esters, aldehydes, ketones, acids, terpenes and norisoprenoids, sulphur compounds, phenols, furans, alkanes, alkenes, and benzene derivatives (Table 2 and Table S1). The flavour notes of the major VOCs from each of the above classes are listed in Table 3. Additional  
Figure 2: The journals in which the papers were published and the number of papers in each journal. details about these different classes of compounds are presented in the following sections.