在线光电离质谱研究茉莉花烘干过程香气成分的变化

Monitoring the Changes of Aroma Components in Jasmine Flowers During Roasting Process by On-line Photoionization Mass Spectrometry

使用自制低压光电离飞行时间质谱装置(VUV-PI-TOF MS)对茉莉鲜花烘焙过程中产生的香气成分进行实时、在线研究,获得了不同温度下的烘焙产物质谱图。实验还研究了茉莉鲜花在40~170℃升温烘焙过程中释放的香气成分的变化情况,获得了90、120、150℃下茉莉鲜花主要烘焙香气成分随时间的变化趋势。结果表明,过高和过低的温度均不利于茉莉花的烘焙品质。该研究结果可以将依赖于人的感官评审数据化、标准化和可视化,为茉莉花的工业生产提供指导。

Due to the high specificity and high speed of mass spectrometer,on-line monitoring of the roasting process by mass spectrometry has attracted increasing attention at present.In this work,fresh jasmine flowers were roasted in a home-made tube furnace,and the vaporized aroma components were monitored by an on-line low pressure vacuum ultraviolet photoionization time of flight mass spectrometry(VUV-PI-TOF MS)in real time.The jasmine flowers were roasted at four different temperatures(90,120,150and200℃),and the mass spectra of the roasting products were quickly obtained.Since PI produces little or no fragments,nearly all the mass peaks can be attributed to molecular ions.Products identification was fulfilled according to the previous GC/MS results.The contents of these substances had been reported to be positively correlated with the quality of jasmine flowers.The relationship between the roasting temperature and various releasing aroma components was studied by the temperature programmed mode with a heating rate of5℃/min.Water is abundant in jasmine flowers,whose signal strength first increased slowly,then kept stable and finally decreased slowly with the rise of roasting temperature from40to170℃.During this process,the signal strength of most vaporized aroma compositions kept increasing and increased quickly at a temperature higher than140℃.The increasing rates of compounds such as acetone,butanone,ethyl acetate,phenylethyl alcohol,benzoate-cis-3-hexenyl and benzyl alcohol were higher than that of indole and benzyl alcohol.The time-evolved profiles of water and four main vaporized aroma compounds in jasmine flowers over1700s were also investigated at90,120and150℃,respectively.With the elapse of time,all substances except butanone had the same trend at90,120and150℃.They rose quickly within a short period of time,then maintained at a lower concentration for a long time.However,when the roasting temperature was150℃,the signal of butanone appeared again at1500s.The results showed that more aroma ingredients were lost at a higher temperature,which was bad for the preservation of jasmine flowers’quality.However,too low temperature was not favorable for the vaporization of water and the taste of toasted jasmine flowers would be bad.Therefore,90℃is a highly-recommended roasting temperature.VUV-PI-TOF MS can be used for the evaluation of the roasting process of jasmine flowers,and offer guide for the industrial production.