Identification Of Coffea Arabica By Infrared And Raman Spectra

Coffea arabica market value is high,the flavor is unique,coffee market often appear the situation of quality confusion which damaged to the interests of consumers,therefore,coffea arabica identification research is of great significance for high-quality coffea arabica agricultural production and market quality control.In this paper,Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy,second derivative spectroscopy and two-dimensional correlation infrared spectroscopy(2D-IR)combined with curve fitting and multivariate statistical analysis,including principal component analysis(PCA)and hierarchical cluster analysis(HCA),were used to study coffea arabica at different altitudes,aging coffee and multi-substance adulteration.The results are as follows:1.The results showed that lipid,protein,polysaccharide and chlorogenic acid were the most important substances in coffea arabica.According to compere the peak strength ratio and peak area ratio of curve fitting and two-dimensional correlation infrared spectra of coffea arabica,produced the result that the relative content or structure of polysaccharide,caffeine,protein,chlorogenic acid,may change with the increase of altitude.Through the second derivative spectra of different altitude coffea arabica show that there is a big difference between altitude of 750 m samples with other three categories.The infrared spectra of coffea arabica of principal component analysis and hierarchical cluster analysis to distinguish coffea arabica samples at different altitude.2.According to the peak intensities of IR and Raman spectra,the characteristic peak intensity of lipids,carbohydrates,proteins and chlorogenic acid changed with aging time.The second derivative infrared spectra and Raman spectra showed that the peak number were different of coffea arabica seeds with different artificial aging time decreased with the increase of aging time.There are differences in the location and area percentage of curve fitting sub-peaks and the relative contents of corresponding peaks of lipid and caffeine in artificially aged coffea arabica seeds increased first and then decreased.The relative content of corresponding peaks of protein decreased first and then increased,while that of corresponding peaks of polysaccharide increased first and then decreased and then increased.Multivariate statistical analysis showed that both principal component analysis and hierarchical cluster analysis could effectively distinguish coffea arabica seeds with different degrees of aging,and hierarchical cluster analysis was better than principal component analysis.3.Six different types of adulterated coffea arabica powder were analyzed by Fourier transform infrared spectroscopy combined with multivariate statistical analysis.The results showed that the IR spectra of coffea arabica and coffea canephora(Vietnam and Uganda)were similar,while the IR spectra of coffee shells and other grain samples were quite different.By comparing the characteristic peak intensity ratio of the adulterated samples,it can be concluded that the content of lipid and polysaccharide of coffea canephora in Vietnam is lower than that of coffea arabica,and the content of protein of coffea canephora in Uganda is higher than that of coffea arabica.The contents of lipid,protein and polysaccharide in coffee shell are much higher than those in coffea arabica.The lipid content of barley,corn and rice is lower than that of roasted coffea arabica,while the polysaccharide content is higher than that of coffee.The protein content of corn and rice is lower than that of coffee.With the continuous increase of adulteration ratio,the peak ratio of lipid in barley,corn and rice decreases,while the peak ratio of polysaccharide increases.Principal component analysis and hierarchical cluster analysis could effectively detect the pure coffea arabica and adulterated samples.The work of this dissertation shows that both infrared spectroscopy and Raman spectroscopy can quickly and effectively study coffea arabica,and infrared spectroscopy combined with multivariate statistics can realize qualitative analysis of coffea arabica at different altitudes,different aging degrees and different types of adulteration,which can provide reference for the future development of coffea arabica.