Research On Detection Method Of Food Volatile Compounds Based On Infrared And Laser Spectroscopy

Volatile organic compounds are produced in various stages of food growth,maturation,storage,preservation and deterioration,and have been widely used in food quality and safety monitoring.In recent years,the author's team has carried out the application research of extractive Fourier transform infrared spectroscopy to detect food volatiles,and has made many results.However,in order to improve the detection sensitivity,the extracted Fourier transform infrared spectrum is easy to impact by the absorption of water and carbon dioxide,and is not suitable for the rapid detection of large-area food volatiles.Open optical path infrared and laser spectroscopy can measure gas from a few meters to several kilometers,and even observe the spatial distribution of gas,which is very suitable for large-scale detection of food volatiles.In view of the above situation,this paper carried out infrared and laser spectroscopy to detect food volatiles,the main research contents and conclusions are as follows:(1)The extractive Fourier transform infrared spectroscopy was used to detect the volatiles during ripening of mango.The method for reducing the absorption interference of water and carbon dioxide under 20 m optical path was studied.The results show that molecular sieve can better inhibit the absorption interference of water and carbon dioxide.PCA analysis of infrared absorption spectroscopy successfully divided the mangoes into green-maturity,semi-ripe and full-ripe.(2)The open-path Fourier transform infrared spectroscopy was used to detect the volatiles of spirit,vinegar and grapes.The feasibility study of active and passive pattern for detecting food volatiles was carried out under the 5 m optical path.The infrared absorption peak of alcohol or esters in spirit volatiles were detected at 3050-2800,1430-1330,1300-1200,1100-1000,910-850 cm-1,and infrared absorption peak of acetic acid or ester in vinegar volatiles at 1340-1240,1100-1040,1040-940 cm-1 were detected,and infrared absorption peak of ethanol or ethyl acetate in grape volatiles at 3050-2800,1300-1200,1100-1000 cm-1 were detected,which verify the feasibility of optical path Fourier transform infrared spectroscopy for remote measurement of food volatiles.Based on the feasibility verification,combined with chemometric and spectral pretreatment method,feasibility study on the identification of food types and metamorphic degree was carried out.The 1178 cm-1 differential characteristic peak of Guizhou and Fenjiu spirit volatiles,and identified fresh,mild and severely degraded grapes.According to the characteristics of absorption peak intensity and area variation with time in infrared spectrum,the dynamic volatilization characteristics of volatiles in the optical path were analyzed,which laid a foundation for two-dimensional correlation spectrum analysis.(3)Based on 1512 nm and 1578 nm DFB lasers,we developed a tunable laser diode absorption spectroscopy system for detecting ammonia and hydrogen sulfide and verified the feasibility of tunable laser diode absorption spectroscopy for remote sensing food volatiles under different absorption signals.Taking beef and eggs as research objects,the feasibility study of tunable laser diode absorption spectrum telemetry food volatiles under different absorption signals was carried out.The ammonia in the volatiles of spoiled beef was successfully detected based on direct absorption mode at a light range of 2 m.Addition,hydrogen sulfide in metamorphic egg volatiles was successfully detected based on the second harmonic absorption signal under 1.5 m optical path.Simultaneously,the intensity of the absorption peak increased with the aggravation of the deterioration degree.It is confirmed that the tunable laser diode absorption spectrum can be used to detect volatiles in deteriorating foods.(4)According to the dynamic characteristics of the infrared absorption spectrum of vinegar and grape volatiles,the spectral absorption characteristics were deeply explored based on the two-dimensional correlation spectrum analysis method with time as the disturbance.The synchronization and autocorrelation coefficient spectra showed that for the Longmen vinegar,the 1070 cm-1 absorption peak submerged in the background noise was successfully extracted,and for the 3rd day grape,1250 and 1050 cm-1 absorption peak submerged in the background noise were successfully extracted.Two-dimensional correlation analysis improves spectral detection sensitivity.