Rapid recognition of irradiated dry-cured ham by on-line coupling of reversed-phase liquid chromatography with gas chromatography and mass spectrometry

The use of on-line coupling of reversed-phase liquid chromatography and gas chromatography (RPLC-GC) with the through oven transfer adsorption desorption (TOTAD) interface and mass spectrometry (MS) was proposed for testing different types of commercial Spanish dry-cured ham for irradiation treatment at various doses (0, 1.5, 2, and 4 kGy). The qualitative analysis of radiation-specific compounds (e.g., n-pentadecane, 1-hexadecene, 1,7-hexadecadiene, n-heptadecane, 8-heptadecene, and 2-dodecylcyclobutanone) can be simultaneously established in a single run with samples that have or have not been irradiated. The overall analysis, which takes less than 100 min, includes a rapid extraction step using a small amount of dichloromethane-methanol (1:1, vol/vol) and anhydrous sodium sulfate, the subsequent fractionation of the sample in the first dimension of the system (RPLC), the transfer of the target fraction to the second dimension, the GC separation, and the MS detection. The calculated limits of detection in ham were lower than 22 ng/g. Repeatability studies provided relative standard deviation values of 0.8 to 13.5%.     

Viability and antigenicity of anisakis simplex after conventional and microwave heating at fixed temperatures

Inactivation of parasites in food by microwave treatment may vary due to differences in the characteristics of microwave ovens and food properties. Microwave treatment in standard domestic ovens results in hot and cold spots, and the microwaves do not penetrate all areas of the samples depending on the thickness, which makes it difficult to compare microwave with conventional heat treatments. The viability of Anisakis simplex (isolated larvae and infected fish muscle) heated in a microwave oven with precise temperature control was compared with that of larvae heated in a water bath to investigate any additional effect of the microwaves. At a given temperature, less time was required to kill the larvae by microwaves than by heated water. Microwave treatment killed A. simplex larvae faster than did conventional cooking when the microwaves fully penetrated the samples and resulted in fewer changes in the fish muscle. However, the heat-stable allergen Ani s 4 was detected by immunohistochemistry in the fish muscle after both heat treatments, even at 70°C, suggesting that Ani s 4 allergens were released from the larvae into the surrounding tissue and that the tissues retained their allergenicity even after the larvae were killed by both heat treatments. Thus, microwave cooking will not render fish safe for individuals already sensitized to A. simplex heat-resistant allergens.     

Assessment of commercial lamb meat quality by British and Spanish taste panels

Trained sensory panels in Britain and Spain assessed loin meat from commercial lambs purchased in Spain, which included Welsh lamb (imported from Britain) and two Spanish breeds (Merino and Rasa Aragonesa). The British panel also assessed British lamb purchased in local butcher shops and supermarkets. Sensory panels, in each country, received meat from the same lambs and used their local methods of cooking and assessment. Spanish panels used unstructured line scales to measure lamb odour intensity, tenderness, juiciness, lamb flavour intensity and two hedonic scales of flavour liking and overall liking. The British panel used 8 point category scales with the same attributes. Results from both panels in objective parameters were in agreement, hence showing that different trained sensory panels may arrive at the same conclusion. However, when panellists were allowed to make hedonic judgements (preference), the British panel preferred British lamb and the Spanish panel preferred Spanish lamb. This finding has important consequences for lamb producers who export their lambs and demonstrates that the underlying reasons for different preferences should be investigated. Production variables are discussed in relation to their influence on lamb eating quality and as a way to tailor lamb eating quality attributes familiar to consumers in the importing country.     

Arcobacter spp. enumeration in poultry meat using a combined PCR-ELISA assay

A rapid assay for enumeration of Arcobacter spp. in chicken meat was developed by using the polymerase chain reaction (PCR) coupled to an enzyme-linked immunosorbent assay (ELISA). Following a short selective enrichment of poultry samples, bacterial DNA was extracted and amplified using digoxigenin-labelled primers specific for 16S rRNA sequences of Arcobacter spp. Amplified fragments were heat denatured before being quantified by an ELISA. In this technique, a biotinylated probe immobilized onto streptavidin-coated microplates was used to capture the digoxigenin-PCR products. A peroxidase antidigoxigenin conjugate was added to the plate and, in the presence of substrate, PCR products were quantitated based on an optical density reading. Distinct absorbance differences were obtained when assaying poultry samples containing Arcobacter spp. in the range 10-10(4) CFU/g.     

Identification of lactic acid bacteria from spontaneous fermentation of 'Almagro' eggplants by SDS-PAGE whole cell protein fingerprinting

In order to complete the previously performed phenotypic identification [Sánchez et al., 2000. Int. J. Food Microbiol. 59 (2000) 9], whole cell protein patterns obtained using Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE) of 149 lactic acid bacteria (LAB) strains, isolated from 'Almagro' eggplants spontaneous fermentation, were analysed. Phenotypic identification of those strains had revealed the presence of the species Lactobacillus (Lb) plantarum, Lb. pentosus, Lb. brevis biotype 2, Lb. brevis biotype 3, Lb. fermentum, Lactobacillus spp. and Aerococcus viridans. The SDS-PAGE technique generated complex and stable patterns that were easy to interpret and compare with those of the 17 reference strains used in this study. After numerical analysis of the resulting electrophoretic protein patterns, six well-delineated clusters were discriminated that, with some exceptions, correlated well with the different groups phenotypically found. Only two strains showed unique protein patterns without meaningful homology to any of the reference strains used for this study and remained unidentified.     

基于数值模拟的海浪水轮机变角度导流装置参数优选

为保护叶轮在高海浪流速情况下不超载工作,提出一种新型变角度导流罩装置,即在流速较小时流体在导流罩内加速,提高波能利用率降低叶轮启动速度;随着流速增加,变角度导流口收缩,有效减少受冲击叶轮面积保护叶轮。并采用RNG湍流模型对变角度装置长短轴比值、导流罩形状、角度三个参数进行数值分析和性能选择。结果表明,在高流速情况下加装变角度导流罩对叶轮保护作用明显,选取长短轴比值3∶1、采用Y型导流罩、初始角度值45°时波能利用率最高;模拟结果与试验结果吻合较好,验证了模拟结果的可靠性。     

基于HBV模型的实际蒸散发估算模型评估

为了更准确地评估三种基于蒸发互补相关原理的实际蒸散发计算模型(AA模型、GG模型、CRAE模型)对实际蒸散发的估算能力,首先根据北江流域1964~1987年间的逐日气象资料和同期径流量数据,采用HBV模型模拟得到逐日实际蒸散发量,再利用三种模型分别估算该流域的逐日实际蒸散发量,并对计算结果进行初步分析比较,而后以HBV模型计算结果为标准进行原始参数的率定,最后在不同的时间尺度上对三种模型的实际蒸散发计算结果进行对比评价。结果表明,三种模型利用原始参数进行模拟的计算结果误差较大;模型参数经率定后,各模型的模拟精度在年、月尺度上均得到提高:以HBV模型模拟得到的实际蒸散发量为标准,计算所得年极差的变化情况分别为AA模型由274mm减至-0.1mm;GG模型由-84.5mm减至0.3mm;CRAE模型由-91.1mm减至0.3mm;AA模型与GG模型的模拟结果相似,在冬季均呈现出模拟结果偏大的现象。通过分析年、月尺度上的结果可知,在北江流域,三种模型中AA模型对实际蒸散发量的估算能力最佳。     

基于系统动态耦合模型的河湖水系连通与城市化系统协调度分析

当前河湖水系连通已成为解决人水矛盾、实现可持续发展的战略选择。为有效促进河湖水系连通的工程实践,探究工程实施后河湖水系连通系统与城市化系统的相互作用机制,基于系统工程理论,综合考虑复合系统静态和动态层面,建立了系统动态耦合模型。在模型框架内,用综合发展度、耦合度和系统协调度定量表示复合系统的耦合协调状况,并以桂林市两江四湖工程为例,在时间尺度上定量分析了复合系统的演变规律。结果表明,工程实施后桂林市河湖水系连通系统与城市化系统的系统协调度等级接近良好耦合发展,今后应加强非工程措施建设,与工程措施互补,实现复合系统长期协调发展。     

基于灰色关联分析的GA-BP网络需水预测模型研究

针对城市需水预测涉及因素众多、不同地区影响因子不尽相同且多寡不一及影响因子的选择直接决定需水量预测的结果与实际是否相符等问题,提出了灰色关联分析法、遗传算法和BP神经网络相结合的需水预测模型,并以南京市为例,通过灰色关联分析法筛选出主要影响因素,采用遗传算法优化BP神经网络,构建基于灰色关联分析的GA-BP神经网络需水预测模型。实例应用结果表明,该模型用于需水预测能够比较全面地考虑需水量影响因子,与传统BP网络相比,GA-BP网络预测精度更高,训练速度更快,可作为资料时间序列较短情况下一种较好的需水预测方法。     

模糊综合评价法在梯级库群系统安全评价中的应用

为克服现有大坝安全评价方法尚未考虑上下游工程之间水力联系的缺陷,针对梯级库群系统规模大、系统内各水库工程标准不一、关系复杂、不易确定等特点,将模糊层次分析法(FAHP)与模糊数学理论引入到梯级库群系统安全评价中,建立了梯级库群系统安全层次结构,并确定了不同层次因素的权重和模糊评价矩阵,通过模糊运算得到评价综合结果。工程实例运用结果表明,该方法为梯级库群的设计和安全风险分析提供了新思路。