A study has been made of the volatile organic compounds (VOCs) released into the contained headspace of packaged lamb's lettuce (Valerianella locusta) plants, cut at the roots, and of separated rocket (Eruca sativa) and baby spinach (Spinacia oleracea) leaves. Direct real‐time analyses of the headspace were carried out on each of five consecutive days using selected‐ion flow‐tube mass spectrometry (SIFT‐MS) and secondary electrospray ionization mass spectrometry (SESI‐MS), together with concomitant off‐line analyses using solid‐phase microextraction (SPME) and gas chromatography mass spectrometry (GC‐MS). It was observed that the concentrations of organosulphur compounds, especially dimethyl sulphide (DMS) and dimethyl disulphide (DMDS) were relatively low in the headspace of fresh samples, but increased exponentially over the 5 days for rocket, increased to a lesser extent for spinach, and increased to an even lesser extent for lamb's lettuce. Methanol was detected in the headspace of even fresh samples of lamb's lettuce, and its concentration increased for the subsequent 2–3 days before decreasing. This trend was mirrored in the isoprenoids analysed, which are characteristic of plant tissues. These results show that direct real‐time VOC analyses by SIFT‐MS can be usefully exploited to monitor fresh leaf salad spoilage, and that SESI‐MS spectra show patterns that are characteristic of salad type and storage time.

中文翻译：

---

包装的叶沙拉中与腐败相关的挥发性有机化合物的表征

已经研究了挥发性有机化合物（VOC）释放到包装的羔羊生菜（Valerianella locusta）植物的根部空间，在根部切开的情况以及分离的火箭（Eruca sativa）和小菠菜（Spinacia oleracea）） 树叶。使用选择离子流质谱（SIFT-MS）和二次电喷雾电离质谱（SESI-MS）以及连续的离线分析，在连续五天中的每一天都进行了顶空的直接实时分析。使用固相微萃取（SPME）和气相色谱质谱（GC-MS）。据观察，新鲜样品的顶空中有机硫化合物的浓度，尤其是二甲基硫醚（DMS）和二甲基二硫化物（DMDS）的浓度相对较低，但是对于火箭而言，在5天之内呈指数级增长，对于菠菜则有所下降，羊肉生菜的增长幅度甚至更低。即使在新鲜的羔羊生菜样品的顶部空间也检测到了甲醇，并且其浓度在接下来的2至3天内增加，然后降低。这种趋势反映在所分析的类异戊二烯中，该类异戊二烯是植物组织的特征。这些结果表明，通过SIFT-MS进行的直接实时VOC分析可用于监测新鲜的叶沙拉变质，并且SESI-MS光谱显示出具有沙拉类型和保存时间特征的模式。