Analysis of seven purines and pyrimidines in pork meat products by ultra high performance liquid chromatography–tandem mass spectrometry

An ultra high performance liquid chromatography–tandem mass spectrometry method (UPLC–MS/MS) is proposed for the simultaneous quantification of inosine, adenosine, guanosine, uridine, hypoxanthine, xanthine and uric acid in pork meat, dry-cured and cooked ham. Samples were added with ¹⁵N₂-xanthine (internal standard) and extracted with boiling water for 30 min. Supernatants were washed with hexane, added with formic acid 10% in water, methanol:acetone (1:1, v/v), evaporated to dryness under N₂, and finally re-dissolved in water prior to injection. Chromatographic separation was carried out with a HSS T3 column with a total time of analysis of 15 min. Two specific transitions for each compound were used for identification and quantification (with matrix matched calibration curves). Linearity, limit of detection, repeatability and accuracy were evaluated. The method was used to quantify the seven purines and pyrimidines in 15 commercial samples.     

HPLC法测定鳗鱼、猪肉和对虾中的痢特灵残留

在传统法的基础上，常量分析与微量分析技术有效地相结合，研究了测定动物性食品中痢特灵残留的快速ＨＰＬＣ法，用二氯甲烷提取样品中的痢特灵，浓缩提取液至干，８０％乙腈水溶液溶解残渣，在５ｍＬ离心管中用正已烷萃取、分离杂质，清液供ＨＰＬＣ分析用，方法回收率大于８０％，相对标准编差（ｎ＝６）小于８％。     

胶束毛细管电泳在线推扫技术分离检测猪肉组织中痕量喹诺酮类药物

利用胶束毛细管电泳法结合在线推扫富集技术对组织中残留的痕量环丙沙星、氧氟沙星和恩诺沙星进行了检测, 弥补了毛细管电泳检测灵敏度低的缺点, 大大减化了操作过程, 为动物食品组织中残留的痕量药物检测提供了一种新的简便可靠的方法.     

表面增强拉曼光谱法快速检测猪肉中左旋咪唑残留

左旋咪唑是一种广谱抗虫药,被广泛应用于抗猪、牛等牲畜体内的线虫。同时左旋咪唑具有特殊的免疫调节作用,在动物养殖中常用于抗菌消炎、抗病毒、促生长等方面。当其被不合理使用时容易在禽畜肉中产生残留,目前常见的左旋咪唑检测方法为液相色谱法与气相色谱法,该类方法具有操作复杂、耗时长、成本高等缺点。表面增强拉曼光谱法具有分析速度快、检测灵敏度高和特异性好等优点,近年来被广泛应用于农残、兽残等物质的快速检测。为实现猪肉中左旋咪唑残留的快速检测,建立了一种猪肉中左旋咪唑残留的表面增强拉曼光谱快速检测方法。通过单因素实验,确定了金胶与样品溶液最佳体积比和最适积分时间分别为2∶1与20 s。通过比较不同萃取方法与萃取溶剂对猪肉中左旋咪唑盐酸盐残留量的提取效果,确定了正己烷液液萃取后离心、取上清液氮吹复溶的操作简单、耗时短的提取条件。通过密度泛函理论中B3LYP/6-311+G(d)基组对左旋咪唑盐酸盐理论光谱进行计算,在优化分子结构后进行频率与拉曼光谱计算,所得理论计算光谱与固体光谱、溶液光谱出峰情况具有较好的一致性。根据理论计算光谱、固体光谱与溶液光谱确定左旋咪唑盐酸盐的SERS特征峰并进行振动归属,得到469,627和969 cm-1处特征峰作为左旋咪唑盐酸盐的定量特征峰,其中469 cm-1为C—S键伸缩振动,627 cm-1为苯环C—C弯曲变形振动,969 cm-1为咪唑环面内弯曲和侧链骨架振动。在最佳实验条件下,建立了左旋咪唑盐酸盐标准溶液特征峰SERS信号与浓度的标准曲线,线性方程R2值均在0.9以上。对不同加标浓度的实际样品进行检测,得到平均回收率为80.39%~95.94%,RSD值为3.08%~6.20%。该法操作简便、稳定性好,无需对样品进行复杂的预处理即可实现对猪肉中左旋咪唑残留的快速准确测定。     

Pork fat peroxidation by gamma-irradiation

In this paper, pork fat peroxidation by γ-irradiation and the possible effects of oxygen, UV-irradiation and storage after the γ-irradiation have been investigated. It has been found that the level of peroxides in irradiated pork increases linearly with the increasing absorbed dose. The chemical yield of peroxides formed in the irradiated fat is about 4.2 and independent on the sample temperature or absorbed dose rate, but dependent on storage time of sample before γ-irradiation. The irradiated pork exhibits some unusual features as following: 1) the peroxide content in irradiated pork is higher than that in unirradiated one; 2) the peroxide content in irradiated pork increases gradually on storage and is essentially constant in unirradiated one, which is very useful for the detection of irradiated pork; 3) the further peroxidation in irradiated pork is much more susceptible to UV radiation than that in unirradiated pork.     

Novel molecularly imprinted stir bar sorptive extraction based on an 8-electrode array for preconcentration of trace exogenous estrogens in meat

A novel 8-electrode array as stir bar was designed for selective extraction of trace level exogenous estrogens from food samples, followed by liquid desorption and HPLC-photodiode array detection. The array consisted of 8 screen-printed electrodes and each electrode was modified with Fe₃O₄@meso-/macroporous TiO₂ microspheres and molecularly imprinted film (m-TiMIF). The fabrication of the imprinted film coating was very simple without organic solvents and chemical grafting. Both bisphenol A (BPA) and diethylstilbestrol (DES) were employed as templates in m-TiMIF fabrication in order to enrich both targets simultaneously. Interestingly, the imprinted stir bar array showed higher extraction capacity and selectivity for BPA and DES than the non-imprinted counterpart. Meanwhile, it exhibited fast adsorption and desorption kinetics due to increased mass transport in the ultra-thin film. Importantly, the m-TiMIF coating was robust enough for at least 20 uses without obvious alteration in extraction performance. The main parameters affecting the extraction efficiency, including stir speeding, sample pH, ionic strength, extraction time, desorption solvent and time, were optimized. Under optimal experimental conditions, the limits of detection (S/N = 3) of the developed method were 0.28 and 0.47 μg L⁻¹ for BPA and DES respectively, with enrichment factors of 32.6 and 52.8-fold. The linear ranges were 3.0–1500 μg L⁻¹ and 4.0–1500 μg L⁻¹ for BPA and DES, respectively. The m-TiMIF-coating conferred better recovery and selectivity, compared with the commercial stir bar coating. The new method was successfully applied to assess BPA and DES in pork and chicken samples with satisfactory recovery.     

液相色谱串联质谱法测定猪肉和猪肝中9种磺胺类药物的残留

建立了高效液相色谱-串联质谱法(HPLC/MS/MS)同时测定猪肉及猪肝中9种磺胺类药物残留的检测方法.样品经10％的Na2SO4溶液和乙腈-氯仿(10:1)提取,乙腈饱和正己烷去脂,使用乙二胺-N-丙基硅烷(PSA)和十八烷基键合相硅胶(ODS C18-N)两种基质分散净化剂净化,采用LC-MS/MS多反应监测(MRM)正离子模式测定,内标法定量.9种磺胺检出限为0.1 ～0.8 μg/kg,在5,10,20μg/kg 3个浓度添加水平,回收率为74.1％ ～ 115.8％,相对标准偏差均小于6.2％(n=6).     

Development of a single-chain variable fragment-alkaline phosphatase fusion protein and a sensitive direct competitive chemiluminescent enzyme immunoassay for detection of ractopamine in pork

A rapid, sensitive chemiluminescent enzyme immunoassay (CLEIA) for ractopamine (RAC) based on a single-chain variable fragment (scFv)-alkaline phosphatase (AP) fusion protein was developed. The scFv gene was prepared by cloning the heavy- and light-chain variable region genes (V_H and V_L) from hybridoma cell line AC2, which secretes antibodies against RAC, and assembling V_H and V_L genes with a linker by means of splicing overlap extension polymerase chain reaction. The resulting scFv gene was inserted into the expression vector pLIP6/GN containing AP to produce the fusion protein in Escherichia coli strain BL21. The purified scFv-AP fusion protein was used to develop a direct competitive CLEIA (dcCLEIA) protocol for detection of RAC. The average concentration required for 50% inhibition of binding and the limit of detection of the assay were 0.25 ± 0.03 and 0.02 ± 0.004 ng mL⁻¹, respectively, and the linear response range extended from 0.05 to 1.45 ng mL⁻¹. The assay was 10 times as sensitive as the corresponding enzyme-linked immunosorbent assay based on the same fusion protein. Cross-reactivity studies showed that the fusion protein did not cross react with RAC analogs. DcCLEIA was used to analyze RAC spiked pork samples, and the validation was confirmed by high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS). The results showed a good correlation between the data of dc-CLEIA and HPLC–MS (R² > 0.99), indicating that the assay was an efficient analytical method for monitoring food safety.     

样品物理方法前处理提高猪肉中Pb元素的LIBS分析精度研究

农产品基体复杂,为了减弱水分和有机质对其痕量重金属元素LIBS检测能力的影响,以期提高目标元素LIBS分析灵敏度和预测精度。以实验室含Pb溶液污染处理的新鲜猪肉样品为例,对猪肉样品进行烘干、粉碎、压片处理,比较样品简单的物理方法前处理提高目标元素LIBS探测效果的可行性。通过采集猪肉鲜样和干样的LIBS谱线信息发现,鲜样受水分、有机质成分影响致使其谱线信息背景和噪声信号干扰较大;对于10个浓度梯度的样品,目标元素特征谱线Pb Ⅰ 405.78的LIBS强度信息在鲜样中无明显的差异性,而在干样样品中差异明显并表现出一定的梯度关系。说明LIBS缺乏对鲜样样品低浓度Pb污染的探测能力,干燥处理削弱了水分的影响、浓缩了样品浓度范围,提高了LIBS的检测灵敏度。通过目标元素Pb的真实浓度与其特征谱线LIBS强度线性定量模型分析,干样样品的线性相关系数远大于鲜样样品,此时猪肉干样样品检测限为5.13 mg·kg-1,说明干样样品具有一定的预测精度。整个工作证明猪肉等农产品在经过合适的、简单的物理方法前处理后,有望在LIBS分析灵敏度和检测精度方面发挥应有的潜力,且该物理方法前处理同样适用于其他肉类的LIBS检测分析。     

New methods for acceleration of meat sample preparation prior to determination of the metal content by atomic absorption spectrometry

Focused microwave-assisted digestion and ultrasound leaching have been applied for the extraction of Pb, Cd, Cr, Cu, Fe, Zn, Ca, and Mg from raw meat. Semimembranous muscle (SM) of raw pig ham was used for optimizing both the digestion and extraction steps by multivariate approaches. The detection and quantification limits were 0.5 and 0.9 g kg^–1 for Pb, 0.06 and 0.1 g kg^–1 for Cd, 0.2 and 1.2 g kg^–1 for Cr, 0.4 and 3 g kg^–1 for Cu, 0.04 and 0.1 mg kg^–1 for Fe, 0.012 and 0.017 mg kg^–1 for Zn, 0.3 and 0.4 mg kg^–1 for Ca, and 0.01 and 0.03 mg kg^–1 for Mg. The precision, expressed as relative standard deviation (RSD), ranged between 2.5 and 9.6% for focused microwave-assisted digestion and between 3.5 and 10.6% for ultrasound leaching. The methods were then compared with a reference method and applied to a certified reference material (bovine muscle 184, from the BCR). The t-test, applied to the results obtained from focused microwave-assisted digestion, revealed that they are in agreement (p>0.01) with the certified and estimated values in the case of Pb, Cd, Cr, Cu, Fe, Ca, Mg, and Zn but not in that of Fe. In the case of ultrasound leaching, only the extraction of Pb, Cu, and Ca was quantitative. The method based on microwave digestion provides more accurate and precise results than ultrasound leaching. These new procedures have many advantages with regards to conventional methods, namely, reduction of the extraction time, simplification of the process, avoidance of chemical emissions to the atmosphere, and no losses of metals by volatilization.