Authentication Of Cabernet Sauvignon Wine And Walnut Oil Using GC-IRMS And Other Instrumental Analysis Techniques

In recent years,adulteration of wine and walnut oil has become a well-known problem which has seriously disrupted the market order and damaged the rights and interests of consumers.As the current official methods are not sufficient to solve this problem,it is critical to establish suitable analytical approaches with high speed,effectiveness and accuracy to determine the authenticity of them.In this paper,multiple instrumental analysis techniques were studied,including mid-infrared spectroscopy（MIR）,near-infrared spectroscopy（NIR）,electronic tongue（E-tongue）,gas chromatography（GC）,gas chromatography-mass spectrometry（GC-MS）,gas chromatography-isotope ratio mass spectrometry（GC-IRMS）and elemental analyzer-isotope ratio mass spectrometry（EA-IRMS）.The aim of this study was to evaluate the capability of multiple techniques to identify the authenticity of a popular imported Cabernet Sauvignon wine,and to differentiate the walnut oils from different cultivated origins.The main results are listed as follow:Firstly,it was found that MIR and NIR spectra were not sufficient to discriminate the Cabernet Sauvignon wine samples,whereas they were shown to be applicable for discrimination when combined with grey relational analysis（GRA）.E-tongue analysis assisted by principal component analysis（PCA）or hierarchical cluster analysis（HCA）was able to differentiate the wine samples.HS-SPME-GC-MS showed detailed information about the volatile compounds and more clearly differentiated wine samples when combined with PCA.The above four techniques allowed unanimous differentiation of the wines.This study provides reliable evidence to determine the authenticity of the typical Cabernet Sauvignon wine and may be useful for other wine authentication as references.Secondly,an analytical method using GC-IRMS was developed to measure theδ¹³C values of six typical volatiles commonly occurring in wine（isoamyl acetate,2-octanone,limonene,2-phenylethanol,ethyl octanoate and ethyl decanoate）for the first time.Solid phase micro-extraction（SPME）selectedwithacarbon molecular/divinylbenzene/polydimethylsiloxane（CAR/DVB/PDMS）fiber was combined with the GC-IRMS for pretreatment optimization.The optimized SPME parameters of extraction time,extraction temperature and salt concentration were 40 min,40°C and 10%,respectively.Theδ¹³C values measured by HS-SPME-GC-IRMS were in good agreement with those measured via EA-IRMS and GC-IRMS.The differences ranged from0.02 to 0.44‰with EA-IRMS and from 0 to 0.28‰with GC-IRMS.This newly established method was proved with good precision,accuracy and repeatability and was successfully validated to differentiate typical real wine samples.This study provides an innovative,convenient and effective analysis method for wine authentication and tracing.Finally,fourteen walnut oils from six different areas（Xinjiang,Shaanxi,Sichuan,Tianjin,Shandong and Yunnan）were studied in this paper.GC was applied to determine the fatty acid composition and IRMS was used to differentiate the walnut oils from different cultivated origins.The walnut oil was composed of linoleic acid（52.28-68.87%）,oleic acid（13.84-35.08%）,linolenic acid（5.04-12.54%）,palmitic acid（4.61-7.91%）and stearic acid（1.42-3.73%）.Significant differences were observed among walnut oils from different cultivated regions in terms of the fatty acid composition.Theδ¹³C values of walnut oil ranged from-25.82‰to-28.84‰.Theδ¹³C values of fatty acid were basically consistent with the following order,namely oleic acid(C_18:1)>palmitic acid(C_16:0)>linoleic acid(C_18:2)>stearic acid(C_18:0)>linolenic acid(C_18:3).Significant differences were also observed among walnut oils from different cultivated origins in terms of theδ¹³C values of bulk oil andδ¹³C values of fatty acids.Walnut oils from different cultivated origins could be effectively differentiated based on theδ¹³C values when combining with PCA.This study can be useful for differentiation of walnut oils from different geographical origins by isotope mass spectrometry as references.