中文摘要：

猪肉是我国人民的主要肉食之一,监督原料肉的新鲜度具有重要的现实意义。采用自行研制的表面解吸常压化学电离质谱（DAPCI-MS）,在无需样品预处理的条件下,对放置1~8天的猪肉进行正离子模式检测,获得其化学指纹图谱。通过分析谱图中各分解产物的信号峰,可将冷藏保存的猪肉新鲜度划分为3个等级：第1等级为保存1~3天,是新鲜度变化的初期,谱图中主要以丝氨酸、甘氨酸的微弱信号峰为特征,表明新鲜猪肉样品中的蛋白质正在发生微弱的降解;第2等级为保存4~6天,是猪肉向腐败变化的过渡时期,谱图中主要以吲哚、2,3-丁二醇的信号峰为特征;第3等级为保存7~8天,是猪肉完全变质的时期,谱图中以三甲胺的信号峰为主要特征。丝氨酸、甘氨酸、吲哚、2,3-丁二醇、三甲胺,这些主要分解产物的信号峰强弱可作为评价猪肉新鲜度的关键依据。根据指纹图谱之间的差异,结合主成分分析（PCA）和聚类分析（CA）法,实现了对不同新鲜级别猪肉的分类识别及对本方法的重现性验证。该方法无需样品预处理、灵敏度高、分析速度快、无污染,有望应用于市场上猪肉新鲜度的快速鉴别,也可为高粘性复杂基体样品的分析提供方法参考。

英文摘要：

China is the largest producer and consumer of pork meat in the world, and the quality as well as safety of pork meat has been an issue of public concern. However,freshness of pork meat is a rather complex concept, which includes different microbio- logical, physicochemical and biochemical attribute. Therefore, it has important signifi- cance to monitor the quality of freshness for pork meat due to the positive position in our life. At present, quality control in the meat industry is mostly tested by two methods. One is the measurement of viable bacterial counts, the other is a sensory test by experts. The former is a very objective method, but it takes 2-5 days and more days to obtain results. This means that the method cannot simultaneously evaluate meat fresh- ness when the meat is sold. The latter is a very rapid method. However, it is very diffi- cult to evaluate slight differences in the meat freshness before the initial stage of putre- faction. Therefore, it would be important to develop novel methodologies for the rapid monitor the quality of pork meat. A contemporary revolution, ambient mass spectrometry was raised by the Cooks et al, which enabled the ionization of samples in their native environment without sample pretreatment or minimal sample pre-treatment was developed. After the emergence of the pioneered technique, desorption electrospray ionization, more than 20 direct-ioniza- tion techniques have been developed. Among these techniques, several ionization meth- ods including direct analysis in real time （DART）, desorption atmospheric pressure chemical ionization （DAPCI）, dielectric barrier discharge ionization （DBDI）, plasma- assisted desorption ionization（PADI） et al, were based on the atmospheric plasmas. In particular, DAPCI-MS has been well demonstrated as a noninvasive analytical method of high sensitivity, good chemical selectivity and fast analysis speed. To date, DAPCI-MS has been successfully applied for trace analysis in food safety forensic science, environ- mental scie