## 3 Results and Discussion
### Effect of Fermentation on Volatile Components  
The volatile components of oat fermented by different LAB strains for 48 h are shown in Table 2. The volatile components included 10 alcohols, 10 aldehydes, 7 acids, 15 ketones, 7 esters, 11 furan derivatives, 8 hydrocarbons, and 1 terpene. Oat is prone to oxidative rancidity and deterioration during processing, storage, and circulation, which is related to the high fat content of oat, especially the high percentage of unsaturated fatty acids and the large amount of lipase with high activity in the endosperm. The oxidative cleavage of oleic or linoleic acid during the contact between unsaturated fatty acids and lipase in oat crushing or milling produces hexanal and nonanal. Nonanal production may be caused by the loss of a hydrogen from the 10 th carbon of the oleic acid chain, followed by the absorption of a hydrogen peroxyfree group (OOH) and subsequent fracture. The cleavage of the 13-hydroperoxide after the oxygenation of linoleic acid chain may lead to the formation of hexaldehyde. The fatty oxygenase-specific oxidation of 9-hydroperoxides can form 2-pentylfurans, which have greeny, beamy, and buttery aromas, whereas 1-octen-3-ol may arise from the 10-hydroperoxide of linoleic acid. This finding was confirmed by the fact that 1-octene-3-ol, hexanal, and nonanal had high concentrations in the unfermented samples as presented in Table 2, revealing that partial oxidation occurred before fermentation. At the same time, we observed that 2-pentylfuran, as one of the important volatile compounds, was detected in each fermented sample, and was significantly higher than that in the fermented sample (\(p<0.05\)). This indicates that oxidation also occurred during fermentation. No pentanal, hexanal and heptanal were detected in O-Lc and O-La. This result was very similar to the conclusion of [PERSON] et al. [40], who fermented oats with _L. paracasei_ and found that hexanal content decreased considerably within the first 2 h and was completely undetectable at 24 h. This outcome was due to the fact that microbial action can convert aldehydes into alcohols and acids. In our experiment we observed the fact that 1-pentanol, 1-hexanol, 1-heptanol, acetic acid and hexanoic acid increased correspondingly. Overall, after LAB fermentation, the contents of aldehydes in the sample decreased, and the contents of alcohols, acids, and ketones increased. However, there were distinct differences in flavor components among fermented samples with different strains. As can be seen from Table 2, the contents of alcohols and acids in O-Lp, O-Lc and O-La were higher than those in O-St and O-Lb by up to 5.86 and 2.55 times (O-La compared to O-Lb). In contrast, the contents of aldehydes and esters in O-St and O-Lb were higher than those of O-Lp, O-Lc and O-La, up to 2.85 and 9.61 times (O- St compared to O-La).This difference may be closely related to carbohydrate and amino acid metabolism. The taste characteristics of amino acids and their catabolic by-products during LAB fermentation make an important contribution to the flavor of cereal-based foods [41]. O-St and O-Lb contained lesser 1-hexanol, benzyl alcohol (fruity and slightly floral), phenylethanol (floral and slightly rose), acetic acid, hexanoic acid (sweaty and cheesy), valeric acid, and nonanoic acid and more abundant hexanal (grassy, tallow, fatty), heptanal octanal (fatty, greeny), nonanal (fatty, citrus, greeny), and esters (floral and fruit flavor). Alcohols were predominant in O-Lp, O-Lc, and O-La, 2,3-Butanedione and 3-hydroxy-2-butanone were only present in O-Lc and O-La, which showed a buttery odor. Limonene, which has a citrus-like aroma, was detected in all samples but at low concentrations. Fermented oats contain volatile components, such as 1-hexanol, hexanal, nonanal, acetic acid and 2-pentylfuran. These components are also considered the key flavor compounds in Lactobacillus-fermented foods and influence the organoleptic properties of fermented products.