Real time quantitative PCR detection of histamine-producing lactic acid bacteria in cheese: Relation with histamine content

Biogenic amines (BAs) are low molecular weight organic bases with biological activity, mainly formed by the microbial decarboxylation of amino acids. The consumption of food containing large amounts of some BAs can have toxicological consequences. Histamine is the most active BA and the most frequently involved in food-borne intoxications. This article reports the concentrations of histamine found in 80 cheeses made from different types of milk and subjected to different ripening periods. Histamine was detected in 41.25% of the samples, with values ranging from 20 to over 1000 mg per Kg of cheese. The highest histamine concentrations were recorded in long ripening cheeses made from raw milk. The presence and quantification of histamine-producing lactic acid bacteria was determined by RT-qPCR, and a good association was obtained between the C_t values and histamine concentrations determined by HPLC.     

Sulfite determination using sulfite oxidase biosensor based glassy carbon electrode coated with thin mercury film

The preparation of sulfite biosensor by immobilization of sulfite oxidase on a glassy carbon electrode coated with mercury thin film is described. Dissolved oxygen can be readily reduced at the glassy carbon electrode coated with mercury thin film. The working principle of the biosensor was based on monitoring decrease in the peak current due to the depletion in dissolved oxygen concentration according to the reaction of sulfite oxidase.     

银-氨基磺酸膜电极对食品中维生素C的测定

利用电化学方法制成了银和氨基磺酸聚合物膜修饰电极,研究了Vc在此电极上的电化学行为,建立了循环伏安法测定Vc的新方法。银和氨基磺酸复合膜修饰电极对Vc的电化学氧化具有明显的催化作用。在pH5.0磷酸盐缓冲溶液中,Vc在修饰电极上氧化,氧化峰电流与其浓度在2.68×10-6～3.1×10-3mol/L内呈良好的线性关系,检出限为3.80×10-7mol/L。修饰电极具有良好的灵敏度、选择性和稳定性,用于食品中Vc的测定,结果满意。     

直接测汞仪测定食品中总汞

目的建立直接测汞仪测定食品中总汞的方法。方法采用直接测汞仪测定食品中的总汞,并对FAPAS 07322大豆粉样品采用直接测汞仪法、原子荧光光谱法、电感耦合等离子质谱法测定进行方法比对,结合FAPAS 07322能力验证报告对直接测汞仪法进行评价。结果直接测汞法在低浓度范围(0～20 ng)和高浓度范围(20～300ng)的相关系数均能达到0.999,方法检出限为0.07μg/kg,精密度小于8.0%,回收率范围为90.0%～103.5%。FAPAS 07322测定结果为323μg/kg, Z值为0.0,接近实验室比对中位值。结论直接测汞仪测定食品中的总汞,操作简便快捷,结果准确,适用于食品中总汞的分析。     

测汞仪测定稻谷及其制品中总汞含量研究

建立了采用测汞仪直接测定稻谷及其制品中总汞含量的方法,对20份稻谷及其制品中总汞含量进行了测定和分析。结果表明,方法在0~400 ng范围内呈良好线性关系,最低检出限为0.1μg/kg,定量下限为1μg/kg,相对标准偏差(RSD)均在2.0%以内。测定国家标准参考物质辽宁大米和湖南大米,测定值均在标示值范围内,与国标方法比较结果无显著差异。所测稻谷及其制成的糙米和大米的总汞含量均在国标限量值以下,稻谷中总汞主要分布在大米中,其次是糙米表皮部分,稻壳部分中含量相对较低。     

Determination of lead, arsenic and mercury in cosmetic formulations at modified electrodes

Lead, arsenic and mercury in cosmetic formulations digested with HNO₃+ HF (10:3) or HNO₃+ H₂SO₄ (5:1) in a microwave oven were determined, respectively, by the thin mercury film electrode, gold electrode and thin gold film electrode in sodium acetate buffer, in 6 m HNO₃ and 0.1 m HCIO₄ solution. Comparison with results obtained from atomic absorption spectrophotometric analysis (AAS) showed good agreement. The detection limits were 0.38 ppb (μgl^-1), 0.66ppb and 0.04ppb for lead, arsenic and mercury, respectively, using square wave anodic stripping voltammetry. The detection limits for lead, arsenic and mercury were 0.53 ppb, 1.24ppb and 0.40ppb, respectively, using AAS. The two methods proposed were applicable to the determination of concentrations at ppb levels of commercial cosmetic formulations.     

测汞仪原子吸收光谱法测定野生食用菌中的总汞

目的建立应用测汞仪直接测定野生食用菌中总汞含量的测定方法。方法样品经均质器粉碎,称量后,直接进样。样品在催化管内加热分解,在氧气的作用下,汞在齐化管内与金粉反应被捕集下来,形成金汞齐,再经高温使金汞齐分解成汞原子蒸气经载气带入吸收池,在253.7 nm处进行吸收测定。结果测汞仪检测方法线性范围:0.0~1000 ng/L,检出限为0.005 ng/m L,相关系数(R2)优于0.999,相对标准偏差(RSD)小于1.5%,回收率大于99%。结论用此仪器检测的方法无需进行样品前处理、进样量少、方法灵敏度高、精密度好、结果准确可靠、操作简单快速、没有试剂污染、检测速度快和运行成本不高,适用于野生食用菌中总汞的测定。     

直接进样测汞法测定生鲜乳中汞含量

目的 建立直接进样测汞法测定生鲜乳中汞的分析方法.方法 分别以测汞仪的分解温度、分解时间以及进样量为变量考察其对检测信号的影响,在最优测试条件下,测试并计算该方法的线性关系、检出限、精密度及加标回收率.结果 确定最优的仪器测试参数为:分解温度750℃、分解时间2 min、进样量0.10 g.在0～40 ng范围内呈良好...     

聚吡咯修饰铂电极快速测定植物油中维生素E的研究

采用恒电位聚合的方法,在0.9V（vs.Ag/AgC l）电位下,修饰铂电极使其表面形成对苯磺酸掺杂聚吡咯薄膜。通过循环伏安法扫描发现,在0.696V处维生素E在该修饰电极表面形成一个明显的氧化峰。利用微分脉冲伏安技术作为检测方法,在最佳实验条件下,维生素E的氧化峰电流与其浓度在6×10-6～3×10-3mol/L范围内呈良好的线性关系,相关系数为0.9963,最低检出限为2×10-6mol/L（S/N=3）。应用该电极可以简便、准确、快速测定植物油中维生素E含量。      

工艺计算及辅助设计系统

以Visual Basic 6．0为开发工具，开发了薄膜蒸发器辅助设计系统。该系统包括设计计算、参数化绘图、结果输出及管理系统四大部分。通过对薄膜蒸发器内各料液进行CFD分析，针对高粘度物料提出了一种物料膜厚计算方法。以此为基础。综合考虑CFD数值模拟得出的最佳进料量要求，实现薄膜蒸发器的工艺计算。，薄膜蒸发器辅助设计系统的开发，结束了长期以来工艺计算采用手工计算或工程放大估算的现状，有效地缩短设计周期，加快设备的推广和应用，进一步提高其研究水平。     

原子荧光光谱法测定大米中的汞

通过对硼氢化钠浓度、酸介质浓度、线性范围和回收率的探讨,优化了原子荧光光谱法测定大米中汞含量的测定条件.     

Voltammetric method using a lead film electrode for the determination of caffeic acid in a plant material

This paper deals with development of an adsorptive stripping voltammetric method for determination of caffeic acid (CA) at a lead film electrode (PbFE). The working electrode was prepared in situ on a glassy carbon substrate as a “mercury-free” electrochemical sensor. The method is based on the accumulation by adsorption of caffeic acid on PbFE and then the oxidation of CA during the stripping step. In a acetate buffer based supporting medium the oxidation signal for caffeic acid was found to be proportional to the CA concentration in the range from 1 × 10⁻⁸ to 5 × 10⁻⁷ mol/L with the limit of detection equal to 4 × 10⁻⁹ mol/L (with preconcentration for 30 s). The method, operated in the square-wave voltammetric mode, was successfully applied to the determination of CA in a plant material (herbs of Plantago lanceolata). The content of caffeic acid received by the proposed method was in close agreement with that obtained by high performance thin-layer chromatography (HPTLC) combined with densitometry. This appears to be the first application of a lead film electrode to the determination of an organic compound in such complicated matrix.     

Characterization of a traditional semi-hard Italian cheese produced by soaking in wine

A traditional type of semi-hard cheese which, after a ripening period in the warehouse, is soaked in wine or fermented must, was studied. In particular, the effect of the soaking phase on the characteristics of the cheese and on the profiles of the volatile compounds was investigated. The study proved that it is the alcohols and the short-chain ethyl esters which chiefly contribute to the distinctive aromatic fraction of the product. These compounds migrate from the wine into the cheese as a result of the different concentrations existing between the two systems.     

Effects of ripening conditions on the texture of Gouda cheese

Summary The effects of ripening temperature, type of packaging film and storage period before packaging were related to the degree of proteolysis and the texture of Gouda cheese, so as to determine the optimum ripening conditions. Gouda cheeses from a local plant were subjected to different ripening conditions. A factorial design of 2³× 5 was used, where the three factors selected in two levels were: (1) time of storage before packaging, 4 and 10 days, (2) ripening temperature, 10 and 20 °C and (3) plastic film, BK1 and BK5 (Grace, Quilmes, Argentina). Ripening time was a fourth factor analyzed; sampling times were 15, 25, 35, 49 and 70 days after production. Cheeses traditionally ripened (without packaging) were also analyzed. Water content and pH were determined. Nonprotein nitrogen (soluble in 12% trichloracetic acid (TCA)) was quantified by the Kjeldhal method. Cheese texture was analyzed by compression and relaxation tests which were done by using an Instron Universal Testing Machine (Instron Corp., Canton, MA, USA). The pH and water content of cheeses which ripened at 20 °C were lower than the corresponding ones ripened at 10 °C. Only ripening time and temperature had a significant effect on water content, nonprotein nitrogen concentration and rheological parameters. Results show that texture properties of Gouda cheese ripened in plastic films with low gaseous permeability are similar to those of traditionally ripened Gouda. Texture development was accelerated by increasing the storage temperature.     

纺织品中可萃取痕量汞的测定

建立采用氢化物发生电感耦合等离子发射光谱（HGdCP-AES），测定纺织品中可萃取痕量汞的方法。通过对ICP—AES工作参数进行优化和选择，方法的检出限为0．11μg／L，最小检出量为0．0022mg／kg；汞含量为20．0μG/L时，相对标准偏差为4．9％；汞含量为5．5μg／L时，相对标准偏差为6.3％（n=8）；回收率为93．3％-102．7％。该方法可满足Oeko-Tex标准100对纺织品中可萃取痕量汞的检测要求。     

Evaluation of a chitosan-based edible film as carrier of natamycin to improve the storability of Saloio cheese

The purpose of this study was to evaluate the effects of the application of chitosan coating containing natamycin on the physicochemical and microbial properties of semi-hard cheese. Three cheese groups were prepared: samples without coating, samples coated with chitosan and with chitosan containing 0.50 mg mL⁻¹ of natamycin, whose minimum inhibitory concentration was previously determinated on cheese surface. Microbiological analyses showed that natamycin coated samples presented a decrease on moulds/yeasts of 1.1 log (CFU g⁻¹) compared to control after 27 days of storage. Addition of natamycin also affected O₂ and CO₂ permeability, increasing from 7.12 to 7.68 × 10⁻¹⁵ g·(Pa s m)⁻¹, and from 10.69 to 64.58 × 10⁻¹⁴ g·(Pa s m)⁻¹, respectively. The diffusion coefficient values of natamycin from the film to phosphate buffered saline solution and to the cheese were 3.60 × 10⁻¹⁰ and 1.29 × 10⁻¹² cm² s⁻¹, respectively. This study demonstrated that chitosan-based coating/films can be used as release system containing natamycin to create an additional hurdle for moulds/yeasts in cheese thus contributing to extend its shelf-life.     

铜离子选择电极测定蔗糖中铜的含量

采用离子选择电极法测定蔗糖中的铜的含量。方法简便快速、准确。标准曲线线性范围1．O×1O－6～1.0×10－4mol／l，平均回收率101．5％，RSD=2．4％（N=4）     

锑膜修饰电极差分脉冲溶出伏安法测定食品中痕量铅、镉

目的 考察并优化同位镀锑膜电极差分脉冲溶出伏安法测定铅、镉的条件.方法 采用差分脉冲溶出伏安法,以锑膜修饰金电极作为工作电极测定食品中痕量铅、镉离子.结果 铅、镉在锑膜电极上可得到灵敏的溶出峰,铅、镉的溶出电位分别为0.58 V(Epb)和0.81 V(Ecd).当电沉积时间为180 s时,铅、镉的检出限分别为1.95和2.10 μg/L,RSD分别为1.14％和0.95％,铅、镉溶出峰电流同0～100μg/L铅、镉离子呈良好的线性关系(r≥0.997).结论 利用本方法测定了食品样品中铅、镉的含量,并与石墨炉原子吸收分光光度法做了对比,结果令人满意,同时使用锑膜修饰电极可避免使用汞膜电极带来的环境污染.     

微波消解-原子荧光光谱法测定苹果中的汞

建立了微波消解-原子荧光光谱法测定苹果中汞的方法,采用密闭微波消解苹果样品,优化了微波消解条件和仪器测定条件。方法的检测限为0.00043ng/mL,RSD为2.01%,回收率在98%～104%之间,方法简便、快速、准确,结果令人满意。     

同位镀铋方波溶出伏安法检测蜂蜜中的痕量铅

目的 采用同位镀铋方波溶出伏安法检测蜂蜜中的痕量铅。 方法 采用铋膜电极替代传统的汞膜电极,并结合方波溶出伏安法和电极同位镀铋膜法,实现对蜂蜜中痕量铅的快速检测。结果 优化了底液, pH, 铋浓度, 沉积电位和沉积时间五项最佳实验条件参数。铅在铋膜电极上可得到灵敏的溶出峰, 其溶出电位为0.580 V。在优化的实验条件下, 该方法检测铅的线性范围为5~100 μg/L(r=0.9965), 检测限低达0.630 μg/L。实验结果与石墨炉原子吸收法结果相比无显著性差异。结论 该研究为蜂蜜等食品中铅的快速、高灵敏检测提供了新的手段。