食品包装材料中油墨成分的迁移及溶出

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1、河北大学2012届本科生毕业论文（设计）食品包装材料中油墨成分的迁移及溶出摘要采用食品模拟物进行迁移实验，结合固相微萃取-气相色谱质谱联用技术（SPME/GC-MS），建立了食品包装材料印刷油墨中两种光引发剂溶出量的测定方法。研究了迁移温度和时间对光引发剂迁移的影响，以纯水和10%乙醇-水为食品模拟物，在4和45下迁移120min。模拟液用固相微萃取（SPME）技术进行萃取，对萃取头、萃取温度和时间进行了优化。利用GC-MS对目标物进行定量分析。结果表明，二苯甲酮和4-甲基二苯甲酮在0.03g/L1.0g/L的范围内线性关系均良好（r20.99），检测限分别为0.0012g/L、0.0040g

2、/L。两种目标物在三个添加水平下，平均回收率为75.1%95.6%，相对标准偏差均小于11.5%。本方法简单、快速、准确，能够满足食品包装的日常检验需要。关键词：食品包装材料；食品模拟物；气相色谱质谱法；光引发剂；迁移实验Migration and dissolution of components in printing ink of food packing materialsABSTRACTFood stimulant and solid phase microextractiongas chromatography-mass spectrometry (SPME/GC-MS) were

3、 used in the abstraction experiment. A method for the determination of two kind of photoinitiators migrated from the printing ink on the surface of food packaging material has been developed. Photoinitiators in the food packaging samples were abstracted with food stimulant at the condition of 4、45、1

4、20min. The influence of temperature and time were for photoinitiators abstraction was studyed. Abstract was extracted by a solid phase microextraction （SPME）technology. Extraction-fiber, temperature and time were optimized. The target was analysised by GC-MS. The results showed that, the limit of de

5、tection for benzophenone and 4-methyl benzophenone was 0.0012g/L and 0.0040g/L with a good linear correlation (r20.99) in the range of 0.03g/L1.0g/L.The average recoveries of the two compounds at three spiked level of were 75.1%95.6%, with the relative standard deviation were less than 11.5%. The me

6、thod was simple, rapid, accurate and can satisfy the daily inspection of food packaging.Keywords:Food packaging material；Food stimulant ；Gas chromatography-mass spectrometry；Photoinitiator；Abstraction experiment目录1前言11.1食品安全问题11.2油墨中的光引发剂11.3食品模拟物11.4国内外对光引发剂迁移的研究21.5本实验研究内容及意义32实验部分42.1仪器与试剂42.2实验样

7、品42.3标准溶液42.4实验方法42.4.1样品前处理42.4.2实验条件43结果与讨论63.1光引发剂萃取条件的确定63.1.1萃取头的选择63.1.2萃取温度和时间的选择63.2光引发剂迁移实验73.2.1迁移温度的选择73.2.2不同食品模拟物的迁移83.3方法评价83.4实际样品的测定94结论11参考文献12致谢13附录14河北大学2012届本科生毕业论文1前言1.1食品安全问题食品安全关系着人们身体健康和生命安全、经济健康发展、社会发展与稳定。包装材料能保护食品免于各种外来因素的损害，对食品质量产生直接或间接的影响。目前，紫外（UV）固化油墨更是凭借其自身的优异性被广泛用于食品包装

8、印刷。虽然它不存在溶剂挥发问题，但是所用的低分子量光引发剂具有一定毒性，对皮肤有一定的刺激性，而且容易挥发和迁移，给食品带来难闻气味，甚至毒性，对人体健康是一种威胁1。2005年发生在意大利、法国、西班牙和葡萄牙的雀巢婴儿配方奶召回事件表明光固化油墨并非没有安全隐患。2011年，德国召回从比利时进口的冷冻细面条，主要是因为二苯甲酮迁移量超标2。1.2油墨中的光引发剂光引发剂能在紫外光区(250420nm)或可见光区(400800nm)吸收一定波长的能量，产生自由基、阳离子、阴离子等，从而引发单体聚合交联固化的化合物，因此，常用于食品包装材料的印刷中。光引发剂按光解机理分为自由基聚合光引发剂和阳

9、离子聚合光引发剂两大类，又以自由基型光引发剂最为广泛。按结构特点光引发剂可分为以下几类：苯偶姻及衍生物、苯偶酰类、烷基苯酮类、酰基磷氧化物、二苯甲酮类、硫杂蒽酮类。 图1.BP结构式 图2.4-MBP结构式二苯甲酮（BP）别名：苯酮、苯酰苯，化学式：C13H10O，结构式如图1所示。其不溶于水，能溶于乙醇、醚和氯仿，白色片状结晶，有微玫瑰香味。BP是自由基光引发剂，主要用于自由基紫外光固化清漆体系，如UV木器漆、UV纸张上光油、UV涂料、UV油墨等，同时也用于有机颜料、医药、香料、杀虫剂的中间体。4-甲基二苯甲酮（4-MBP）化学式：C14H12O，结构式如图2所示。白色或类白色结晶体，熔点5

10、6-57。用于UV固化型涂料和油墨，也用作紫外线吸收剂、医药中间体。毒理学实验表明ITX和EHDAB具有高度亲脂性，细胞长时间低含量接触会导致细胞破裂，甚至某些功能的丧失，并可能具有遗传毒性；BP和4-MBP具有致癌作用，还有生殖毒性和皮肤接触毒性3。1.3食品模拟物根据实际情况考虑，在进行迁移实验时应直接分析哪些成分进入食品，然而由于食品本身和食品包装系统分的复杂性，直接分析食品中的迁移物是十分困难的，因此引进食品模拟物的概念。食品的组成、结构特性直接影响迁移结果，由此美国FDA和欧盟EC都根据食品的的食用特性对食品进行了分类，见表14。表1.FDA、EC推荐的食品模拟物1.4国内外对光引发

11、剂迁移的研究当塑料、纸、金属、橡胶等包装材料与一定类型的食品接触时都会释放少量的化学物成分，这种化学物质向食品中的释放在学术上被认为是迁移。迁移从理想角度的理论上讲就是一个扩散和平衡的过程，是低分子量化学物从包装材料中向所接触食品的传质过程。早在20世纪60年代美国就已经开始关注并研究包装材料迁移问题。针对这一问题欧盟委员会(EU)和美国食品药品管理局(Food and Drug Administration，FDA)制定了一系列相关的法令法规和框架指令：根据食品的实际使用条件，给出了加速迁移试验适合的温度和时间，建立了相关化学物在不同塑料材料、不同温度条件下的扩散系数数据库。目前，印刷油墨中

12、光引发剂的检测方法主要有气相色谱法5和液相色谱法6。2008年，Sanches-Sliva等对包装液体奶的纸盒中的5种PIs建立了LC-PDA和LC/MS检测法，根据迁移结果，得出了不同PIs在包装纸盒中的扩散速率以及PIs在纸盒与液体奶之间的分配系数7。德国联邦风险评估中心（BFR）建议食品接触材料用印刷油墨中ITX和EHDAB的安全迁移量为0.5mg/kg8。欧盟食物链和动物健康常务委员会于2009年规定印刷油墨食品包装材料中BP和4-MBP的总迁移量不得高于0.6mg/kg9。目前，我国对食品包装的监管依旧不完善，对食品包装中的的BP和4-MBP等有害物质没有卫生标准及相应的检测方法标准

13、。1.5本实验研究内容及意义本课题对几种塑料包装材料中光引发剂的迁移进行了研究，建立了固相微萃取（SPME）和气相色谱质谱联用（GC/MS）的检测方法10-12。采用食品模拟物13进行迁移实验，考察了温度和时间对光引发剂迁移效率的影响，并对萃取条件进行了优化。所得模拟液用SPME萃取后在GC/MS上进行分析。对食品包装材料上油墨成分的分析监测及其向食品的迁移行为的研究具有重要的意义。实验成果能为企业及研究者提供实例；为质检部门对包装材料中光引发剂成分的迁移安全性做出可靠的鉴定提供参考；为政府在油墨使用方面（如油墨使用成分许可列表的建立）、印刷安全方面（如印刷面积与所包食品体积或质量的比例规定）

14、和迁移方面（如针对某种油墨成分迁移而选用合适的的食品模拟液和迁移条件）制定相关的标准提供科学的理论和实例参考。282实验部分2.1 仪器与试剂仪器：Agilent 7890A-5975C 气相色谱-质谱联用仪（美国安捷伦公司）；固相微萃取装置（萃取台和手柄），萃取头：涂层为100m聚二甲基硅氧烷（PDMS）；85m聚丙烯酸酯(PA)；65m聚二甲基硅氧烷/二乙烯基苯（PDMS/DVB）（美国Supelco公司）；电子加热磁力搅拌器（美国Corning公司）；DHG-9053A型电热恒温鼓风干燥箱（上海飞越实验仪器公司）；塑料薄膜封口机（温州兴业机械设备有限公司，SF-300型）；40mL顶空进

15、样瓶（附带聚四氟乙烯密封垫）。试剂：二苯甲酮（Benzophenone，BP，99.0%， JK公司）、4-甲基二苯甲酮（4-Methylbenzophenone，4-MBP，95.0%，TCI公司）、甲醇为进口色谱纯(HPLC)，一次去离子水、二次去离子水（实验室用水），纯净水、3%乙酸-水、10%乙醇-水（实验用水）。2.2实验样品样品选用日常生活中常见塑料食品包装材料。2.3标准溶液光引发剂标准储备液的配制：分别称取2种光引发剂标准品各2.50mg，用甲醇溶解并定容至2支25 mL容量瓶中，配成100 mg/L的标准储备溶液并于4冷藏。光引发剂标准溶液的配制：从光引发剂标准储备液中分别移

16、取0.05 mL于一支10 mL容量瓶中并用甲醇定容，配成浓度为500 g/L的2种光引发剂混合标准溶液。逐级稀释，分别配制成浓度为300.0、240.0、150.0、60.0、30.0、9.0 g/L的系列标准溶液，现用现配。2.4 实验方法2.4.1样品前处理样品前处理选取纯净水、10%乙醇-水二种食品模拟液进行迁移研究。待测食品包装袋用洗涤剂、自来水、一次去离子水、二次去离子水洗净后，自然晾干。按1mL/cm2计算装入食品模拟物，用塑封机封口。对于包装低温冷藏食品的的包装，在4下进行迁移实验120min；对于包装常温储存食品的包装，则在45下进行迁移实验120min。经完成迁移后的模拟液

17、量取30mL于40mL顶空瓶中并加入磁转子密封，选用PDMS-DVB萃取头，在40恒温水浴下萃取40min。萃取结束后，直接将其送入气相色谱汽化室解吸3min。2.4.2实验条件GC-MS条件：HP-5MS毛细管色谱柱（30m0.25mm0.25m），升温程序：初始温度80，以25/min的升温速率升到170保持1min，然后以5/min的升温速率升到220保持1min；最后再以20/min的升温速率升到270保持5min，整个走样程序历时23.1min。进样口温度：260；载气：高纯氦气（99.999%），流量：1mL/min；不分流进样，吹扫流量：50mL/min。离子源：EI，源能量70

18、eV，温度230，四级杆温度为150，辅助通道加热温度为280。选择离子模式（SIM），无溶剂延迟。电子轰击电离源(EI)，电子能量70 eV。3结果与讨论3.1光引发剂萃取条件的确定3.1.1萃取头的选择本实验考察了PDMS、PA、PDMS/DVB三种萃取头对BP和4-MBP的萃取效率，实验结果见图3。结果表明，在其它实验条件相同的情况下，三种萃取头对4-MBP的萃取效率均高于BP，而PDMS/DVB萃取头对BP和4-MBP的萃取效率明显高于其他两种萃取头。因此，选择PDMS/DVB作为本实验的萃取头。图3.不同萃取头对BP和4-MBP萃取效率的影响3.1.2萃取温度和时间的选择图4.温度对

19、PIs萃取效率的影响 图5.时间对PIs萃取效率的影响本实验在其它实验条件相同的情况下，分别考察了不同温度、时间条件下BP和4-MBP的萃取效率。实验结果如图4、图5所示，在其它实验条件相同的情况下，随着萃取温度的升高，BP和4-MBP的萃取效率先增大后减小，在40时萃取效率达到最大；随着萃取时间的增加，BP和4-MBP的萃取效率增大，40min时萃取效率达到最大，之后随萃取时间增加萃取效率降低。因此，选择40min、40水浴温度作为萃取条件。3.2光引发剂迁移实验3.2.1迁移温度的选择图6.BP迁移量与迁移温度和迁移时间的关系图（纯水）本实验选择中性食品模拟物（纯净水）和酒精类食品模拟物（

20、10%乙醇-水）进行迁移实验。考虑食品的实际存储情况，迁移条件按最苛刻的情况进行，即对于低温冷藏食品，其包装的迁移温度为4；对于常温储存食品，其食品的迁移温度为45，两种温度下迁移时间均为120min。图7.4-MBP迁移量与迁移温度和迁移时间的关系图（纯水）迁移温度和迁移时间对BP和4-MBP迁移量的影响如图6、图7所示(由于这两种食品模拟物的实验结果无显著差异, 因此只列出其中一种)。由图可知，BP和4-MBP在45条件下的迁移速率约是4下的3倍；并且45下的其实迁移速率较快，4条件下的迁移速率较缓慢。3.2.2不同食品模拟物的迁移实验同时还考察了纯净水、3%乙酸-水、10%乙醇-水三种食

21、品模拟物在45、120min条件下光引发剂的溶出情况。结果如图8所示，可知迁移到10%乙醇-水食品模拟物中的BP和4-MBP的量相对较多。图8.不同食品模拟物对BP和4-MBP迁移的影响3.3方法评价GC-MS/SPME对2种光引发剂的检测线性范围、线性方程、相关系数、仪器的检出限见表2，其标准曲线见图9。BP和4-MBP这两种物质在浓度为0.03g/L1.0g/L的范围内线性良好，r20.99,在3倍信噪比（S/N）下的检测限分别为0.0012g/L和0.0040g/L。表2.BP和4-MBP的线性范围、线性方程、相关系数、检出限化合物线性范围（g/L）线性回归方程相关系数(r2)检出限(g

22、/L)BP0.031.0y=3828.6x+442920.99400.00124-MBP0.031.0y=1700.5x-799000.99110.0040在空白食品模拟物中添加不同浓度的标准溶液，按照本文所述实验条件进行测定，每个添加浓度平行做3次，计算回收率。结果如表3所示，在3个添加水平下，二苯甲酮（BP）回收率在76.2%95.6%之间；4-甲基二苯甲酮（4-MBP）回收率在75.1%81.3%之间。图9.BP和4-MBP标准溶液的曲线图表3.BP和4-MBP不同添加水平下的回收率和精密度目标化合物添加水平0.10g/L0.50g/L0.80g/L平均回收率/%RSD/%平均回收率/%

23、RSD/%平均回收率/%RSD/%BP95.69.176.28.182.310.24-MBP81.34.875.59.675.111.53.4实际样品的测定按照本文所述方法，分别以纯水、10%乙醇-水作为食品模拟液对10种食品包装样品中光引发剂的迁移情况进行了研究，结果见表4、表5。在10种样品中均检出BP，6种样品中检测到4-MBP，纯水做食品模拟液时样品中BP和4-MBP的总迁移量在0.05g/L0.36g/L之间，10%乙醇-水做食品模拟液时BP和4-MBP的总迁移量在0.09g/L0.54g/L之间，均未超出欧盟标准。表4.10种食品包装样品中PIs的溶出量（单位: g/L）（纯水）样

24、品编号1#2#3#4#5#6#7#8#9#10#BP0.150.090.190.030.060.060.060.070.050.054-MBP0.090.190.170.060.12NDNDNDND0.14总量0.240.280.360.090.180.060.060.070.050.19注：ND表示未检测出表5. 10种食品包装样品中PIs的溶出量（单位: g/L）（10%乙醇-水）样品编号1#2#3#4#5#6#7#8#9#10#BP0.270.150.30.10.20.170.110.220.090.164-MBP0.180.330.240.210.27NDNDNDND0.28总量0.4

25、50.480.540.310.470.170.110.220.090.44注：ND表示未检测出4结论实验结果表明，食品常温储存与低温储存相比，常温时其包装材料中的光引发剂溶出量较多，食品储存时间越长，光引发剂溶出量越多；通过比较三种食品模拟物对PIs迁移的影响，发现迁移到酒精类食品模拟物中PIs的量比中性食品模拟物中的多。利用所建立的方法，测定了10种食品包装材料分别在两种不同食品模拟物中BP和4-MBP的溶出量。结果表明，所检测的这10种食品包装样品中，除4种无4-MBP迁移外，其它样品中的BP和4-MBP均存在不同程度的迁移，但其最大迁移量未超过欧盟对BP和4-MBP总迁移量的规定；同时发

26、现，在酒精类食品模拟物中这两种物质的检出量均高于中性食品模拟物。SPME法集采样、萃取、进样于一体，操作简单、方便，不需要消耗有机溶剂，并具有较高的回收率和富集倍数，检测方法灵敏度高、重现性好。适合于市面上常见的复合食品包装袋中BP和4-MBP的检测。参考文献1于艳军，李宁涛，韩伟等食品接触材料表面印刷油墨中光引发剂的高效液相色谱-串联质谱法检测和提取研究J分析化学研究报告，2011，39(9)：138713932赖毅东，彭喜春GC-NPD法测定复合食品包装袋中2,4-二氨基甲苯J现代食品科技，2009，25(1)：95973莫佳琳，缪璐，干宁军超高效液相色谱-串联质谱法测定食品包装材料中全氟

27、辛酸及其盐类物质J现代食品科技，2011，27(4)：4734764吕刚，王利兵，刘军等包装材料中的酚类环境雌激素的测定-固相微萃取/气相色谱质谱法J分析实验室，2008，27(9)：73755丁力，吕昌银，曾栋等复合食品包装袋中二氨基甲苯的GC-MS测定方法研究J中国卫生检验杂志，2007，17(9)：154015766Modock G，Schwack WDetermination of isopropylthioxanthone (ITX) in milk，yoghurt and fat by HPTLC-FLD，HPTLCESIMS and HPTLC-DARTMSJAnalytical

28、 And Bioanalytical Chemistry，2006，385(3)：5865957王红松，陈明，汤礼军等高效液相色谱法同时测定食品包装水性模拟液中二苯甲酮和4-甲基二苯甲酮J中国卫生检验杂志，2011，21(2)：2722768Constituents of Printing Inks in Beverages from Cartons. BFR Expert Opinion No.044/2005, 25 November 20059Conclusions of the Meeting of 06 March 2009,Standing Committee on the Foo

29、d Chain and Animal Health, Section Toxicological Safety. European Commission Health and Consumers Directorate-General, Brussels, 06 March 200910王敏，郭德华，丁卓平食品中杂环胺检测的分析方法J现代科学仪器，2010，（6）：14515311邓晓军,郭德华,李波等气相色谱2质谱法测定乳制品中光引发剂异丙基硫杂蒽酮的残留量J2007，25(1)：394212李中皓，唐纲岭，王庆华等超高效液相色谱法测定卷烟包装纸中的二苯甲酮和4-甲基二苯甲酮J现代食品科技，

30、2011，27(10)：1276128013罗辉甲,曹国荣,许文才食品包装材料中双酚A检测与分析方法的研究进展J包装工程，2010，31(17)：4751致谢我首先要感谢我的导师刘芃岩教授。在近一学期的课题研究、论文写作阶段，刘芃岩老师给予了我极大的关心和帮助。刘老师治学严谨、知识渊博、诲人不倦，在学术和为人上都为我做出了榜样。在刘老师的帮助下，我的课题研究进展顺利，并取得了一定的成果。在此，谨向给予我悉心培养和不倦教诲的导师致以最衷心的感谢！本实验是在黄恩洁师姐的倾力帮助下完成的，她为本实验研究进行了大量细致的准备工作。在实验和论文写作期间，给予了我极大的帮助。在此，向她表示衷心的感谢！同时

31、也要感谢化学与环境科学学院各位领导和老师。每位老师鲜明的授课风格与独特的个性都给我留下了深刻难忘的印象，不仅对我的学习，更对我看待世界的方式方法大有裨益。再次致以深深的谢意！附录VOLATILE PROFILES OF SICILIAN PRICKLY PEAR (OPUNTIA FICUS INDICA) BY SPME-GC/MS ANALYSISABSTRACTThe aroma compounds present in the headspace of homogenized slur ries of fresh prickly pears (Opuntia cus indica) f

32、rom Sicilian cultivars were determined. Solid Phase Microextraction (SPME) followed by Gas-chromatography/Mass Spectrometry (GC/MS) analysis was used to characterize the volatile compounds. The volatile avor proles of the three cultivars investigated (red, white and yellow) showed signicant differen

33、ces. The aromatic prole of pealed prickly pears stored for one day was different from that of the fresh samples, mainly due to the occurrence of some oxidative and hydrolytic reactions.Key words: Gas-chromatography/Mass Spectrometry (GC/MS)；Opuntia cus indica, Prickly Pear；Solid Phase Microextractio

34、n (SPME)；Volatile Flavor ProlesINTRODUCTIONPrickly pear (Opuntia cus indica (L.) Mill. Cactaceae) is a bushy, treelike cactus, native to Mexico and widespread throughout Sicily and the whole Mediterranean area, South Africa and Central and South America (BARBERA and INGLESE, 1993; MUOZ DE CHVEZ et a

35、l., 1995). In Sicily the principal areas of cultivation are located in three zones: Etnea (eastern Sicily), the district of San Cono (east-central Sicily) and the western area of the Belice Valley (Santa Margherita-AG). The owers and fruits form on the margin of the succulent leaf (cladodes). The fr

36、uit, usually eaten raw after peeling, is sweet and juicy, with the esh enclosing many small edible seeds.The different parts of the plant have a wide range of applications. The fruits and cladodes are used for human and animal consumption (BARBERA et al.,1988), the cladodes are also used in traditio

37、nal medicine to reduce serum cholesterol levels, regulate blood pressure and treat several pathologies such as ulcers, fatigue, dyspnea glaucoma, capillary fragility, liver conditions, rheumatic pain and wounds (MUOZ DE CHVEZ et al., 1995; BARBERA et al., 1988). Further, prickly pear may be used for

38、 the treatment of gastritis, hyperglycemia, ar- teriosclerosis, diabetes and prostate hypertrophy (HEGWOOD, 1990; FRATI et al.,1990; PALEVITCH et al., 1993). A ower infusion is used in traditional medicine in Sicily as a diuretic (BARBERA et al.,1988). Other recent studies have shown antioxidant act

39、ivities of Sicilian prickly pear (BUTERA et al., 2002; TESORIERE et al., 2003).The pulp of the Sicilian cultivars is characterized by three different colors: yellow, purple red and pale green (white). The red and yellow pigments have been identied as betacyanins and betaxanthines, respectively (PIAT

40、TELLI and MINALE, 1964; PIATTELLI et al., 1964; FORNI et al., 1992). These water soluble pigments can be used as natural food colorants (BARBERA and INGLESE, 1993; BARBERA et al., 1988). A comparison of the chemical and biochemical parameters (total acidity determination, sugar analysis and vitamin

41、C contents, transition metal ions and pectin methylesterase activity) of different Sicilian cultivars was reported by GURRIERI et al. (2000).In this study the volatile avor proles of different cultivars of Sicilian prickly pear from western Sicily were compared, particularly the yellow, so-called “S

42、urfarina” (the color of sulphur), the white “Muscaredda” (sweet like muscatel) and red “Sanguigna” (bloody) cultivars. In addition, tests were conducted to detect if there was any variation in the aromatic prole when peeled fruit was stored before selling. The results were compared with those of oth

43、er researchers on fruits from eastern Sicily (ARENA et al., 2001).Headspace Solid Phase Micro-Extraction (HS-SPME) was used followed by Gas-Chrom-atographic/Mass Spectrometry (GC/MS) analysis. These techniques offer several advantages with respect to other established methods. In fact, SPME GC/MS (V

44、AS and VKEY, 2004) does not require the use of solvents, complex sample handing or complicated apparatus (FLATH and TAKAHASHI, 1978); it is fast and ensures excellent sensitivity and reproducibi-lity. It has been used recently for the analysis of the volatile components responsible for the aroma in

45、various fruit (AUGUSTO et al., 2000; WAN et al., 1999).MATERIALS AND METHODSAll the fruit used in this study came from the Belice Valley. The plants were subjected to a forcing technique: summer owers were removed, and fruits formed from a late blossoming were picked from September to December.Five

46、fruits of each cultivar were peeled and gently squeezed. The fresh juice of each fruit (4 g) was placed in 15 mL vials with pierceable silicone rubber septa coated with PTFE film. The vials were stirred with a magnetic device in a thermostated water bath which gave temperature control within, at lea

47、st 360.5C.Sampling was carried out by using a SPME (Supelco, Bellafonte, PA) ber coated with a 100 m lm of polydimethylsiloxane (PDMS) in the headspace; a 85m carboxen/PDMS ber was also tested but the aromatic prole obtained was not as rich. After several tests at increasing times, it was determined

48、 that 15 min was suitable to obtain equilibrium and to reproduce the extraction procedure. Desorption time in the chromatograph injector at 250C was xed at 5 min in the splitless mode.The analyses were run on a GC/ MS Varian Saturn 3-Ion Trap System, equipped with a 30 m x 0.25 mm i.d. fused-silica

49、capillary column Supelcowax-10 (Supelco, Bellafonte, PA) coated with Polyethylene glycol with a lm thickness of 0.25 m. The carrier gas (helium) pressure was xed at 12 psi at the head of the column. The transfer line and ion trap temperature was 180C. The GC temperature program started at 35C (5 min

50、 hold), rst step 5C/min to 130C(10 min hold), second step 10C/min to 220C (5 min hold). The ion trap mass spectrometer parameters were: electron ionization mode (EI) 70 eV, mass range 40-400 Da and the scan frequency was 3 scans-second. The collected data were processed with the data system of the i

51、nstrument and the chromatographic and spectrometric results showed excellent reproducibility. Each determination was carried out three times. The variation in the peak area did not exceed 5%.The standard compounds, 1-hexanol, 3-hexen-1-ol, and 2-hexen-1-ol, were purchased from Fluka (Buchs, Switzerl

52、and) and octanoic acid methyl ester and 1-octanol were obtained from Carlo Erba (Milano, Italy).The volatile constituents of fresh and one-day stored prickly pears of the yellow, white and red cultivars were extracted by SPME in headspace and analyzed by GC/MS. The compounds were identied by linear

53、retention indexes (RI) calculated using the Van Den Dool and Kratzs equation (VAN DEN DOOL and KRATZ, 1963) and by mass spectra through a critical and reasoned comparison with the NIST 2002 registry of mass spectral data; 1-hexanol, 3-hexen-1-ol,2-hexen-1-ol, octanoic acid methyl es- ter, 1-octanol

54、were also conrmed us- ing standard compounds.RESULTS AND DISCUSSIONThe percentage of reconstructed total ion current (RIC) and the retention index of each compound for fresh peeled and one-day stored fruits are reported in Tables1 and 2, respectively. The use of RIC % in a quantitative approach has

55、severe limitations, as is evident in the peak areas that do not reflect the real amounts of the different compounds, but, such semi- quantitative data is very useful as a tool for comparison.Gas chromatograms of the fresh peeled fruit are showed in Fig. 1; where the most abundant compounds are indic

56、ated. The most abundant compound in the yellow and white cultivars is 2-hexen-1-ol followed by 2-nonen-1-ol; this order is reversed in the red cultivar. In red and white cultivars 1-hexanol is quite abundant.Similar qualitative results have been reported (ARENA et al., 2001) for prickly pears cultiv

57、ated in eastern Sicily (in a volcanic area), with the same three alcohols being the prevalent compounds. However there were remarkable differences in the quantitative ratio of these compounds compared with our results; this could be attributable to the differences in the soil composition, but also t

58、o the ripening and to the different extraction procedures used.Esters are also present with the most abundant one being 4-decenoic acid methyl ester, followed by 2-hexen-1-ol acetate and acetic acid hexyl ester; remarkable amounts of butanoic Terpenes were always present in small amounts and traces

59、of aldheydes were only found in the white fruit.For an overall view of the aromatic proles of just-peeled fruit, the histograms of the compounds arranged on the basis of chemical families (alcohols, esters, terpenes, etc.) are reported in Fig. 2a.The three cultivars show different aromatic proles; t

60、he esters predomin-ate in the yellow-type, whereas alcohols predominate in both the white and red fruit. This could account for the fact that the intensity of fruit aroma follows the same scale as the ester components, yellow red white.Differences were determined between the aromas of fresh, just pi

61、cked and peeled fruit (Table 1) and those of fruit stored for 24 h after peeling (Table 2). The histograms of the volatile components (alcohols, esters, terpenes, and aldhehydes) present 24 h after peeling are shown in Fig. 2b.The most important variation in the aromatic prole in the fruits stored f

62、or 24 h after peeling (Table 2) was the increase of two alcohols (2-nonen-1-ol and 2,6 nonadien-1-ol) and the corresponding aldhehydic derivatives (Table 1). These results suggest that hydrolysis and some oxidation have occurred in the presence of atmospheric oxygen (DI CESARE et al.,1993; GROSCH an

63、d SCHWARZ, 1971;HATANAKA et al., 1975).Moreover there was a marked decrease in the amount of esters, probably due to hydroly-sis, and/or their high volatility, before the analysis was run. However, the appreciable, rapid change in the aromatic prole shows that the practice of some vendors and consumers of storin