| Baijiu is known as the national liquor of China,which has a long history and is deeply loved by domestic consumers.Because of its unique fermentation technology and complex raw materials,compared with other distilled spirits,Baijiu contains more kinds of trace components and the concentrations varies greatly.And the aroma quality and healthcare function of Baijiu are determined by these trace components.Therefore,it is of great significance to scientifically improve the aroma quality and healthcare function of liquor,promote the modern production of Baijiu,meet the diverse needs of consumers,advocate healthy and scientific drinking,and promote Baijiu to the world by exploring the trace components and their functions under the direction of flavor and health dual guidance.However,currently,the research on aroma compounds and their functions in Baijiu is not systematic and deep enough.In the thesis,we chose Gujinggong Baijiu(one of the Luzhou-aroma type of Baijiu)as the main research object,different extraction and analysis methods were applied to systematically analyze the aroma compounds in Gujinggong Baijiu,and to explore the contribution of aroma compounds to the flavor formation of Gujinggong Baijiu.At the same time,we focused on the phenolic aroma compounds in Gujinggong Baijiu,and different methods were adopted to explore the antioxidant activity and anti-inflammatory activity of phenolic compounds in Gujinggong Baijiu,and to clarify the intracellular mechanism of phenolic compounds.The main research contents and results of this paper are as follows:(1)Qualitative analysis and aroma contribution evaluation of the aroma compounds in Gujinggong Baijiu were carried out by liquid-liquid extraction(LLE)and aroma extract dilution analysis(AEDA)combined with gas chromatograph-mass spectrometry(GC-MS)and gas chromatograph-olfactometry(GC-O).The qualitative analysis results showed that a total of 60 aroma compounds were identified in Gujinggong Baijiu,including 21 esters,12 acids,8 alcohols,7 phenols,3 lactones,3 acetal,2 pyrazines,2 aldehydes and ketones,and 2 furans.The results of AEDA showed that the flavor dilution(FD)values of ester compounds and acid compounds were higher than other kinds of aroma compounds,which indicated that ester compounds and acid compounds had stronger aroma expression intensity and made a greater contribution to the flavor formation of Gujinggong Baijiu.Specifically,the FD values of ethyl hexanoate,hexanoic acid and ethyl 3-phenylpropanoate were among the top three,which had great influence on the aroma of Gujinggong Baijiu and were important aroma compounds in Gujinggong Baijiu.(2)The direct injection(DI)combined with gas chromatography-flame ionization detector(GC-FID)and LLE combined with GC-MS were applied to quantify the concentrations of aroma compounds in Gujinggong Baijiu,and the odor activity values(OAVs)of aroma compounds were calculated as well.On this basis,aroma reconstitution and omission experiments combined with partial least squares regression(PLSR)method were conducted on the selected aroma compounds in order to investigate the contribution of aroma compounds to the flavor formation of Gujinggong Baijiu and the relationship between the aroma compounds and the aroma profile of Gujinggong Baijiu.The results of quantitative analysis showed that esters,acids and alcohols were the skeleton aroma compounds of Gujinggong Baijiu,and their concentrations in Gujinggong Baijiu were significantly higher than other kinds of aroma compounds.The result of OAV showed that a total of 35 aroma compounds were simultaneously confirmed with their OAVs ? 1 in all five Gujinggong Baijiu samples,including 12 esters,10 acids,6 alcohols,4 phenols,2 aldehydes and ketones,and 1 lactone,which were identified as important aroma compounds of Gujinggong Baijiu.Furthermore,the relationship between the aroma compounds and the aroma profile of Gujinggong Baijiu was confirmed by aroma reconstitution experiment,aroma omission experiment and PLSR analysis.The results showed that ethyl 3-phenylpropanoate,ethyl butanoate,and ?-nonalactone were positively correlated with the sweet aroma of Gujinggong Baijiu;ethyl hexanoate,ethyl butanoate,ethyl octanoate,ethyl pentanoate,and 3-methyl-1-butanol were positively correlated with the fruity aroma of Gujinggong Baijiu;phenylacetaldehyde and ethyl phenylacetate were positively correlated with the floral aroma of Gujinggong Baijiu;4-methylphenol,4-ethylphenol,and 4-ethylguaiacol were positively correlated with the phenolic/smoky aroma of Gujinggong Baijiu;acetic acid was positively correlated with the acidic aroma of Gujinggong Baijiu;hexanoic acid and butanoic acid were positively correlated with the cellar/cheese aroma of Gujinggong Baijiu;1-butanol was positively correlated with the alcoholic aroma of Gujinggong Baijiu;1-butanol and 2-methylpropanol were positively correlated with the grain aroma of Gujinggong Baijiu.Finally,9 aroma compounds were identified as the key aroma-impact compounds of Gujinggong Baijiu,including ethyl hexanoate,ethyl octanoate,ethyl butanoate,ethyl pentanoate,hexanoic acid,butanoic acid,?-nonalactone,4-methylphenol,and ethyl 3-phenylpropanoate.(3)Vanillin,4-methylguaiacol,and 4-ethylguaiacol,three important phenolic aroma compounds of Gujinggong Baijiu,were evaluated in terms of their possible antioxidant activities and structural similarity by DPPH,ABTS,ORAC,reducing power,metal chelation assays.In addition,DI-GC-MS was applied to determine the concentrations of vanillin,4-methylguaiacol,and 4-ethylguaiacol in Baijiu samples.On this basis,PLSR was conducted to investigate the contribution of vanillin,4-methylguaiacol,and 4-ethylguaiacol to the antioxidant activity of Baijiu and the relationship between vanillin,4-methylguaiacol,4-ethylguaiacol and the antioxidant activity of Baijiu.The results showed that vanillin,4-methylguaiacol,and 4-ethylguaiacol exhibited stronger antioxidant activities than Trolox in ABTS,ORAC,and reducing power assays.The quantitative results showed that 4-methylguaiacol and 4-ethylguaiacol were detected in all 103 Baijiu samples,and their concentrations ranged from 4.45±0.02 ~ 1575.41±9.70 ?g/L and 3.76±0.13 ~ 2180.2±20.42 ?g/L,respectively.However,vanillin was only detected in 94 Baijiu samples,and its concentration ranged from 0.54±0.02 ~ 279.18±5.19 ?g/L.PLSR result showed that the concentrations of 4-methylguaiacol and 4-ethylguaiacol were correlated with DPPH and ABTS scavenging activities of Baijiu,especially with ABTS scavenging activity.In general,the antioxidant activity of Baijiu was positively correlated with the concentrations of vanillin,4-methylguaiacol,and 4-ethylguaiacol in Baijiu.(4)AAPH-induced HepG2 cell was used as the cell model to investigate the antioxidant effect and mechanism of vanillin,4-methylguaiacol,and 4-ethylguaiacol in cells.The results showed that vanillin,4-methylguaiacol,and 4-ethylguaiacol could improve the antioxidant defense systems in HepG2 cell,relieve the oxidative stress induced by AAPH,and maintain the cell homeostasis by activating Keap1–Nrf2 signaling pathway,inducing the expression levels of SOD,CAT and GPx;enhancing the enzyme activity of SOD,CAT and GSH-Px;promoting the generation of GSH and increasing the ratio of GSH/GSSG;relieving ROS induced by AAPH;inhibiting the generation of MDA and GSSG.(5)LPS-induced THP-1 cell was used as the cell model to assess the anti-inflammatory effect and to explore the anti-inflammatory mechanism of 4-ethylguaiacol(an important phenolic aroma compounds of Gujinggong Baijiu)in cells.The results showed that low(10 ?M),medium(100 ?M)and high(500 ?M)level treatment doses of 4-ethylguaiacol could alleviate the inflammatory response induced by LPS to some extent,which indicated that 4-ethylguaiacol possess potent anti-inflammatory effect in THP-1 cells.The expression results of target genes and target proteins showed that 4-ethylguaiacol could significantly mitigated LPS-induced inflammation in THP-1 cells via activating the Nrf2/HO-1 and AMPK/SIRT1 pathways and inhibiting the activation of TLR4-MAPKs-NF-?B/I?B?/AP-1 pathway,thereby markedly inhibiting the activation of inflammasome and down-regulating the secretion of inflammatory cytokines. |
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