Study On Fluorescence Characteristics And Age Detection Of Luzhou-flavor Aged Baijiu

Luzhou-flavor Baijiu has occupied the most part of Baijiu market shares in China for its characteristics of strong pit aroma,soft and sweet taste.Thus,it is of great significance to develop the physical and chemical detection technology on Luzhou-flavor Baijiu.In this work,the fluorescence characteristics of Luzhou-flavor Baijiu were studied by three-dimensional fluorescence spectra.Properties of acetic acid,one of the main trace components,were studied under Baijiu solvent environment using quantum chemical calculations.Finally,the classification of Baijiu flavor and the year prediction of Luzhou-flavor aged Baijiu were accomplished by time-resolved fluorescence spectra.In this work,the fluorescence characteristics of Luzhou-flavor Baijiu in different brands and different productive years were studied using three-dimensional fluorescence spectra,while the similarities,differences and rules between them were analyzed as well.Meanwhile,the spectral characteristics of the main trace components in Luzhou-flavor Baijiu and their effects on the fluorescence characteristics of Baijiu were discussed.The fluorescence characteristics of Baijiu samples in other flavors were studied,while the similarities and differences between their fluorescence characteristics and those of Luzhou-flavor Baijiu were analyzed.Through the study of fluorescence characteristics,the limitation of steady-state fluorescence spectra in the study on monomer characteristics in complex systems was pointed out.The steady-state spectra can’t meet the requirements of detecting and identifying the substances when the steadystate spectra of several substances are similar or the spectra overlap seriously.Thus,new methods for the study of trace component monomer’s properties in Baijiu by theoretical chemical calculations and the detection of Baijiu based on time-resolved spectra were introduced.Through quantum chemical calculations and spectral analyses,the acetic acid monomer,dimer and cluster in water and ethanol solvent were studied,while the spectral characteristics of acetic acid,the main trace component in Luzhou-flavor liquor,were investigated in this paper.Acetic acid is normally existed as dimeric structure in gas,vapor and liquid phase.It is predicted that sufficient ethanol molecules can dissociate this dimeric structure,while stable clusters can be formed.To investigate this process,optimized structures,geometry parameters,interaction energy values and theoretical Raman spectra of acetic acid dimers and clusters are investigated.The geometry and energy parameters provide the minimum number of solvent molecules to destroy the structure of acetic acid dimer.The energy decomposition analysis of the interaction energy investigates the influence of hydrogen bond on the interaction in the cluster.Reduced density gradient function analysis investigates the position and strength of H-bond interaction.The effect of H-bond interaction on the dissociation of acetic acid dimer was investigated by the shift of O-H stretching vibration peaks in the theoretical spectra of acetic acid cluster.The results of this study provide reliable information and useful insights on the structures and properties of acetic acid clusters in different solvents as well as the theoretical guidance for the further determination and investigation of the spectral characteristics of acetic acid clusters in Baijiu.Based on the measurements and analyses of steady-state fluorescence spectra and timeresolved fluorescence spectra,a method of flavor classification and year prediction of Baijiu through time-resolved fluorescence spectra was proposed.42 Baijiu samples of 6 brands with3 flavors are prepared and their steady-state and time-resolved fluorescence spectra are measured and analyzed.Through the analysis of fluorescence spectra on trace components in Baijiu,hexanoic acid and ethyl butyrate were found to have great impact on Baijiu fluorescence characteristics.The variation of fluorescence lifetimes with storage time of Baijiu in different flavors was studied.The parameters related to fluorescence lifetimes were used as the original indexes of the principal component analysis and the flavor classification of Baijiu samples was carried out.The mechanism of the variation on lifetimes of Luzhou-flavor Baijiu with productive years was studied by quantum chemical calculations.Finally,the relationship between fluorescence lifetimes and storage time of Luzhou-flavor Baijiu were obtained.This result led to a reliable and efficient method to establish the year forecast model of Luzhouflavor Baijiu with a mean error of 2.79 months.It also provides an important reference of the utility of time resolved fluorescence for quantitative research of multi-component system.