## 4 Conclusions  
In summary, a total of 88 aroma-active compounds were identified by LLE combined with GC-O-MS analysis in four different grades of FJ. Among them, six aroma compounds were identified as active aroma components in LFB for the first time, although they may make fewer contributions to the overall aroma because of their low some values. GC-O analysis showed that high-grade FJ had more aroma compounds and higher aroma intensities. Seventy aroma compounds were quantified by three different methodologies. The contents of most aroma compounds in high-grade FJ were higher than those in low-grade FJ. There were 28 aroma compounds with OAVs >1 simultaneously in four samples, which indicated that these odorants might contribute to the characteristic aroma of FJ. TDS well characterized the aroma quality differences of four different grades of FJ during consumption and suggested that high-grade FJ had a rich, pleasant and lasting retronasal aroma perception. The QDA results showed that low-grade FJ mainly presented the aroma of grain and acidic, while high-grade FJ mainly exhibited the pleasant aroma of floral, fruity, sweet and grassy. The combination of TDS and QDA could more comprehensively characterize the sensory quality of LFB. PLSR analysis effectively distinguished 4 kinds of FJ and revealed the associations between the orthonasal aroma attributes and the aroma compounds with OAVs > 1. 3-Methylbutyl acetate, 1-butanol, ethyl hexanoate, ethyl butanoate, ethyl octanoate, acetic acid, 3-methylbutanol, hexanoic acid, 1-octen-3-ol, phenylacetaldehyde, ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, 3-methylbutanoate acid, ethyl 3-methylbutanoate, and 2-methylpropanol with their VIP values > 1 were considered as the odorants causing aroma differences among the four different grades of FJ. However, a large number of samples and omission tests were still needed to identify the quality markers which cause the different quality grades of FJ. A better understanding of the different grades of LFB will help improve the flavor quality and processing technology and increase the yield of high-grade Baijiu products. This study paid attention to the aroma quality of different grades of LFB during consumption for the first time. During the consumption of alcoholic beverages, retronasal aroma perception plays a crucial role in determining the final aroma characteristics and significantly affects consumer preferences. In addition, future research should be focused on the dynamic analysis of the retronasal aroma compounds and the exploration of the relationship between retronasal aroma perception and release. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods12061238/s1](https://www.mdpi.com/article/10.3390/foods12061238/s1)]([https://www.mdpi.com/article/10.3390/foods12061238/s1](https://www.mdpi.com/article/10.3390/foods12061238/s1)), Table S1: Definition and reference of the retronasal aroma attributes; Figure S1: The evaluation procedure of TDS; Table S2: Definition and reference of the orthonasal aroma attributes; Table S3: QDA scoring standard; Table S4: Quantitative methodological parameters of aroma compounds in four different grades of FJ; Figure S2: Concentrations of aroma-active compounds with OAVs > 1 in four different grades of FJ. Conceptualization, H.L. and K.T. ; methodology, H.L. and K.T. ; software, H.L. ; validation, X.Z., X.G. and X.S. ; formal analysis, H.L. ; investigation, H.L. ; resources, X.Z., X.G. and X.S. ; data curation, H.L. ; writing--original draft preparation, H.L. ; writing--review and editing, K.T., S.C. and Y.X. ; visualization, H.L. ; supervision, K.T. and Y.X. ; project administration, K.T., S.C. and Y.X. ; funding acquisition, X.Z., X.G. and X.S. All authors have read and agreed to the published version of the manuscript. The grant of Chinese Baijiu Industrial Technology Innovation Strategic Alliance (2021-09). The data presented in this study are available on request from the corresponding author.