基于E-NOSE与SPME-GC/MS技术分析温湿度动态变化过程中稻谷的挥发性成分

The Volatile Compositions from Rice Stored with Dynamic Temperature and Humidity Based on SPME-GC/MS and Electronic Nose(e-nose)Technics

【目的】明确稻谷在温湿度动态变化过程中挥发性物质的组成和差异,找出与稻谷品质密切相关的特征性挥发物,为更好地安全运输稻谷提供参考。【方法】根据粮食实际运输条件对稻谷进行实验室动态温湿度模拟试验,稻谷样品以14%、16%、18%、20%、22%五种不同梯度的初始水分含量进行为期2个月的动态低温、中温和高温(分别是10℃左右波动、20℃左右波动和30℃左右波动,湿度均在80%左右波动)模拟试验,应用顶空固相微萃取-气质联用分析(SPME-GC/MS)和电子鼻技术(E-NOSE)对温湿度动态条件下不同初始水分含量和时间的稻谷每15 d进行挥发性成分检测,结合主成分分析法(PCA)对其检测结果进行分析。【结果】在不同试验温度条件下,不同水分含量稻谷在不同时间的特性雷达图均有不同变化,在15 d时,同一水分不同温度稻谷的响应值差异最大,而随着模拟试验时间的延长,14%—18%水分稻谷样品在不同温度条件下差异减小;电子鼻主成分分析能明显区别不同水分含量、不同温度、不同时间的稻谷样品。在低温、中温和高温试验条件下,稻谷的挥发性物质(含烃类、苯环类、醛类、酮类、醇醚类、酸酯类和杂环类等化合物)分别检测出275种、262种、215种,而原样品中仅有46种,其中烷烃类物质在低温条件下差异较大,中温、高温次之;烯炔烃类、苯环类、醇醚类、杂环类挥发性物质随温度上升而差异越大;醛类、酮类、酸酯类挥发性物质在中温时差异最大,低温低水分稻谷中烷烃类特征性挥发物质随时间延长由直链烷烃转变为环烷烃;试验后期烯炔烃特征物质主要为含氧或环状物质;苯环类物质2,6-二叔丁基对甲酚、辛基酚、肉桂腈是新鲜稻谷中的特征性挥发性物质,随着稻谷品质劣变,苯环类特征物质多为含甲氧基或者萘环物质;醇醚类、醛类、酮类特征性物质多为2-甲基-1-十六醇、苄醇、癸醛、胡椒酮等具有果香味或者刺激性特殊气味的物质;在低温或试验早期的稻谷酸酯类挥发性物质多为氨茴酸甲酯、水杨酸甲酯、二氢猕猴桃内酯等具有香甜味物质,试验后期酸酯类特征物质出现肉豆蔻酸、癸酸等无味或有刺激性气味的物质;杂环类特征性物质多为呋喃、喹啉等具有特殊味道的物质。【结论】电子鼻能快速、有效地对不同水分含量、温度的样品进行区分,各类挥发性物质种类和含量受水分含量、温度等条件影响较大。低水分含量(14%—16%)稻谷样品在30 d以内有利于控制挥发性成分变化,高水分含量(20%—22%)加快稻谷中挥发性成分变化。

[Objective] Through laboratory simulation of dynamic temperature and humidity conditions, the volatile compositions of rice were studied to find out some characteristic volatiles closely related to the rice quality. The objective of this paper is to provide reference for the construction of dynamic storage and transportation of rice. [ Method ] According to the actual transportation conditions of rice, rice was stored by simulating dynamic temperature and humidity of storage and transportation. Rice samples with 5 moisture contents （14%, 16%, 18%, 20% and 22%） were stored and transported for two months, respectively, at low temperature, middle temperature and high temperature （respectively fluctuates around 10℃, 20℃, and 30℃, humidity fluctuates around 80%）. All rice samples were tested by SPME-GC/MS and electronic nose （e-nose） in this study. Principal component analysis （PCA） was used to analyze the data. [Result] Under different temperature conditions, the radar graphs of different moisture contents and time of rice all were different. The response values of the same moisture content rice had obvious differences under the different temperature conditions at 15 day. With the time, the differences of 14%-18% moisture contents rice samples reduced. Principal component analysis of e-nose could significantly distinguish all rice samples during storage. There were 275, 262 and 215 kinds of volatile compositions of rice samples including alkanes, olefin or alkyne, aromatic compounds, glycol ether, aldehydes, ketones, acid esters, and heterocyclic were detected, respectively, under low, medium and high temperature conditions, but only 46 kinds of which were detected in the original samples. Alkanes showed a bigger difference under low temperature conditions, and followed by medium temperature, high temperature. Olefin or alkyne, aromatic compounds, glycol ether and heterocyclic showed greater difference with temperature rising, and aldehydes, ketones, acid esters showed the largest difference under medium temperature conditions. With the time, characteristic alkane transformed from straight-chain into cycloalkane under low temperature or moisture content conditions. Haracteristic olefin or alkyne were mainly oxygen-containing or ring-shaped material at the late stage of storage. The 2,6-Di-tert-butyl-4-methylphenol, octyl phenol, and cinnamonitrile were aromatic compounds of fresh rice. With the deterioration of rice quality, methoxy or naphthalene ring materials were main characteristic aromatic compounds in rice. The 2-methyl-l-hexadecanol, benzyl alcohol, decanal, and piperitone were main characteristic glycol ether, aldehydes or ketones and had special fruity or irritating smell. Methyl-2-aminobenzoate, methyl salicylate, dihydroactinidiolide were main characteristic acid esters and had a sweet taste at early stage or under low temperature conditions, and myristic acid, decanoic acid were found at later stage and were tasteless or offensive. Furan, quinolone were characteristic heterocyclic substances with special flavor. [ Conclusion] E-nose could quickly and effectively distinguish rice samples under different moisture contents and temperatures conditions. The types and content of volatile compositions are affected by moisture content and temperature conditions of rice. Low moisture contents of rice （14%-16%） and short-term storage （30 days） are conducive to control the change of volatile compositions, and high moisture contents （20%-22%） could speed up the change of volatile compositions in rice.