## 2 Results and Discussion  
### Volatile Compounds in Fermented Rice Samples  
The volatile compounds in the fermented rice samples inoculated by LAB are listed in Table 1. The 45 identified volatile compounds were comprised of three acids, five aldehydes, four esters, four furan derivatives, four ketones, 13 alcohols, 10 benzene and benzene derivatives, one hydrocarbon, and one terpene. Esters, which have floral and fruity odor notes, are formed by esterification between alcohols and acids during LAB metabolism [23]. The present study detected four esters (butyl acetate, ethyl acetate, hexyl acetate, and methyl butanoate) in the fermented rice samples, although they were present at only low levels. In particular, ethyl acetate and methyl butanoate were found in all of the samples studied. These compounds, which were formed from pyruvate metabolism, were previously identified as key aroma compounds in fermentation products by _Lactobacillus_[13]. On the other hand, butyl acetate was detected in only five samples (KR7, KR10, JKA1-6, JFK2-2, and RTCL9), whereas hexyl acetate was observed only in samples KR7 and KR10; both of these LABs are _Lactobacillus brevis_ strains. Esters were generally most abundant in JKA1-6, with the largest amounts in samples fermented by obligatorily heterofermatative LAB except for sample RTCL16. It was considered that heterofermatative LABs produce more ethanol and acetic acid [19], which can be better used for esterification compared to facultatively hetero-/homo- ones. Various alcohols and acids are produced via the pentose phosphate pathway and the TCA cycle of LAB [24]. Ethanol was the predominant alcohol in most of the fermented rice samples in the present study, and is mainly formed from alcoholic fermentation. In homofermentative LAB, ethanol is derived from pyruvate via acetyl-CoA, whereas it is derived from the pentose phosphate pathway of glucose in heterofermentative LAB [24]. The level of ethanol was much higher in samples KR10 and KR7, which are _Lac. brevis_ strains. [PERSON] et al. reported that _Lac. brevis_ produced more ethanol than other LABs [25]. In addition, the level of ethanol differed significantly between obligatorily heterofermentative and facultatively heterofermentative/obligatorily homofermentative LAB samples in the present study. 1-Octen-3-ol, which can be produced from unsaturated fatty acids with some microbial involvement via an enzymatic reaction [26], was found in samples RTCL16, JFK2-2, JKA1-6, and RTCL9. [PERSON] et al. reported that 1-octen-3-ol could be formed from 10-hydroperoxide of linoleic acid [26]. Linoleic acid would be hydroperoxided by lipoxygenase, producing 10-hydroperoxylineic acid, and then hydroperoxide lyase would decompose 10-hydroperoxylinoleic acid into 1-octen-3-ol and 10-oxo-trans-8-decenoic acid [26; 27]. (_E_)-Hept-2-en-1-ol and heptan-2-ol were observed in only obligatorily heterofermentative LAB and not in facultatively heterofermentative or obligatorily homofermentative LAB. 3-Methylbutan-l-ol can be formed by the reduction of 3-methylbutanal produced by the Strecker degradation of leucine, and RTCL16 contained the most 3-methylbutan-l-ol. [PERSON] et al. reported that _Lactobacillus sanfrancisensis_, which is classified as heterofermentative, reduced aldehydes to the corresponding unsaturated alcohols, whereas _Lactobacillus sakei_, which is facultatively heterofermentative, did not metabolize the unsaturated aldehydes at all [28]. In heterofermentative LAB, the reduction of aldehydes is related to the oxidation of NADH to NAD+, which enables this heterofermentative LAB to produce additional ATP from glucose [28]. However, LAB, which metabolize glucose via the Embden-Meyerhof pathway, were not affected from NADH recycling during growth in sourdough [28]. 2-Pentyfuran, which has a beamy odor note, has been reported as one of the odor-active compounds in various rice cultivars [29] and is mainly derived from the specific oxidation of 9-hydroperoxides by lipoxygenase.