基于CFD方法的稀释水新型添加装置

针对造纸工业中流浆箱使用的稀释水圆管添加装置中浆料与稀释水混合不均匀的问题,本课题设计了一种基于流体动力学(CFD)方法的稀释水新型添加装置,并对这两种稀释水添加装置中浆料与稀释水的混合流动状态进行了数值模拟分析。结果表明,与稀释水圆管添加装置相比,稀释水新型添加装置使浆料与稀释水混合及出口速度更均匀,有更好的稀释调节效果。     

基于CFD方法的稀释水添加装置结构优化设计

针对稀释水流浆箱两种不同结构的稀释水添加装置,采用计算流体动力学方法,对浆料与稀释水的混合流动状态进行数值模拟。结果表明稀释水环形添加装置比稀释水圆管添加装置有更好的稀释调节效果。     

5类食品中叶酸的检测及稀释倍数估算

目的 解决GB 5009.211—2014《食品安全国家标准 食品中叶酸的测定》检测食品中叶酸时, 试样稀释液浓度偏离的问题。方法 实测5类常见食品的叶酸含量, 归纳试样稀释方法, 推导稀释倍数估算公式, 验证理论稀释倍数f在实测中的应用。结果 测得植物产品中叶酸的质量分数在5.03~287.3 μg/100 g之间, 含量差异较大, 试样稀释5~50倍; 肉类食品中叶酸在11.1~65.4 μg/100 g之间, 稀释5~20倍; 婴幼儿辅食营养包中叶酸在653.2~1024.4 μg/100 g之间, 可以按100倍稀释; 婴幼儿配方乳粉中叶酸为91.8~143.5 μg/100 g, 稀释10~25倍; 维生素片中叶酸含量很高, 定容后需要稀释8000~20000倍。结论 试样的稀释可以通过稀释倍数估算公式进行估算, 结合稀释梯度, 可大幅提高有效检测的概率, 其中植物产品需要设置0.5f、1f、2f三个稀释梯度。稀释倍数估算和稀释梯度设置可以减少反复实验, 提高检测效率。     

稀释倍数对食品包装纸中高锰酸钾消耗量的影响

目的研究稀释倍数对食品包装纸中高锰酸钾消耗量测定结果的影响。方法样品经浸泡前处理后,采用滴定法对多个试样不同稀释倍数下的高锰酸钾消耗量进行测定,进而确定不同滴定体积试样的稀释范围。结果滴定体积大于10 mL的试样,需要稀释5倍以上;滴定体积在9～10 mL之间的试样,需要稀释2～5倍;滴定体积7～9 mL之间的试样稀释需要1～2倍。滴定体积在约9 mL的试样稀释不得超过5倍,滴定体积约10 mL的试样稀释不得超过10倍,滴定体积在7～9 mL之间的试样稀释不得超过4倍。结论煮沸时出现褪色现象的试样需要稀释后测定,稀释倍数对高锰酸钾消耗量影响很大,要选择合适的稀释倍数才能测得准确的结果。     

同位素稀释质谱法在食品分析中的应用研究进展

同位素稀释质谱法是一种快速、灵敏、准确的定量分析方法,已广泛应用于食品分析领域。本文介绍了同位素稀释质谱法的基本原理及特点,综述了近年来同位素稀释质谱法在国内食品分析中的应用现状,指出了同位素稀释质谱法在分析检测研究中的局限性,并对其未来发展趋势进行展望。     

五日生化需氧量测定过程中稀释倍数的确定

五日生化需氧量测定是进行水质检测和采取污水处理的一种重要工作,但是在实际测定中,影响测定结果精确性的因素有多种,例如环境温度、水样pH值以及稀释倍数等。文章首先介绍了地表水、工业废水的样品稀释倍数确定方法,随后通过试验,介绍了一种利用公式进行稀释倍数计算的方法,并分别从前期准备、试验步骤、测定结果等,对这种稀释倍数确定方法进行了简要概述。     

未稀释粘胶中三硫代碳酸钠和总硫代碳酸钠的测定

粘胶中的副产物(即总硫代碳酸钠)通常是将粘胶稀释500—5000倍后用分光光度法测定。但是,高倍稀释会导致主反应和副反应平衡的移动。本文所介绍的方法能够测定未稀释或稍加稀释的粘胶中三硫代碳酸钠(TTC)及总 TTC 和过硫代碳酸钠(PTC)     

生乳中亚硝盐回收率检测分析研究

目的 改进国标中因生乳本底对回收率结果的影响。方法 依据GB 5009.33-2016《食品中亚硝酸盐与硝酸盐的测定》中第二法分光光度法, 在加标回收实验中将生乳本底进行不同倍数稀释, 确定回收率最佳时的稀释倍数。结果 对生乳本底进行稀释后, 确定10倍稀释后加标回收率全部符合要求, 最大相对标准偏差为9.118%。检测实际样品时, 本方法与国标检测结果经无显著性差异(P=0.10)。结论 改进后的方法操作简单, 回收率高、准确性高, 可用于牛乳中亚硝酸盐的检测。     

快速提取肉类基因组DNA的裂解液的研究

目的配制一种快速提取肉类DNA且满足重组酶聚合酶扩增技术(recombinase polymerase amplification,RPA)要求的裂解液。方法分别配制3种裂解液:Na OH裂解液、Chelex裂解液与PBS裂解液,取200μL裂解液与20 mg肉类样品进行混合,振荡5 s,取上清液稀释10倍直接作为扩增模板。结果 3种裂解液中Na OH裂解液提取DNA在稀释与未稀释条件下均有较好的扩增,Chelex裂解液提取DNA在稀释与未稀释下均无扩增,PBS裂解液提取DNA在稀释作用下有较好的扩增,在未稀释作用下无扩增。裂解液提取法和试剂盒方法提取的纯度、产物的大小几乎一致,所扩增的为同一产物,裂解液所需成本与试剂盒方法相比较低。结论 Na OH裂解液可以在5 min内提取肉类中的DNA,浓度与纯度均较高,所需时间短,成本低,且满足分子检测要求。     

稀释啤酒初探

稀释啤酒技术是在国际上发展较快的啤酒生产技术之一,在我国,由于存在技术、设备以及人们的心理承受能力等多方面因素的影响,使该技术一直未得到较快的发展。自1990年以来,为增加啤酒产量,我厂在稀释啤酒方面开展了一些研究工作,并用此方法生产稀释啤酒近5000吨,质量全部达到了国家一级啤酒标准。根据我厂生产情况,就稀释啤酒的工艺和特征谈几点体会,不妥之处,望专家指正。一稀释用水的要求及其处理 1.对稀释用水的要求稀释用水质量是影响稀释啤酒质量的最重要因素,它必须达到下列要求:①无任何     

Isotope ratio and isotope dilution analysis of lead in wine by inductively coupled plasma-mass spectrometry

The lead content of 12 wine samples was measured by inductively coupled plasma-mass spectrometry using the methods of standard addition and isotopic dilution analysis. An additional wine sample was analysed by external calibration, standard addition and isotopic dilution analysis. The lead content of the wine samples was in the range 30-150 ng ml-1 and good agreement between the different techniques was observed. Analysis of lead isotope ratios revealed significant differences between Australian and European wines, reflecting the different isotopic composition of Australian lead.     

Application of advanced instrumental methods for yogurt analysis

Compared to the classical methods of analysis, advanced instrumental methods have received increasing attention due to their highly precise analysis of food micro-/macro-structure. Due to its widespread popularity, yogurt has been the subject of numerous studies. This article discusses major advanced instrumental methods applied to the analysis of set/stirred yogurt reported in the literature. Discussed analytical methods have been categorized into two parts, namely chemical analysis methods (including flavor analysis of yogurt, analysis of milk constituents, and assays of indexes), and structural analysis methods (including textural and rheological analysis as well as microstructural analysis).     

同位素稀释质谱在食品与环境分析中的应用

介绍了同位素稀释质谱的测量过程、分类及其联用技术,阐述了该技术在食品与环境分析中的应用进展。     

Identification and analysis of 2-chloro-6-methylphenol, 2,6-dichlorophenol and indole: causes of taints and off-flavours in wines

Background and Aims: The aim of this study was to determine the cause of taints and off-flavours in a number of commercial wines and to develop methods for quantitative analysis of the compounds responsible. Methods and Results: Three compounds, 2-chloro-6-methylphenol (i.e. 6-chloro-ortho-cresol), 2,6-dichlorophenol and indole, were identified by gas chromatography (GC)/mass spectrometry (MS)/olfactometry as causes of taints or off-flavours in the wines. New methods for quantitative analysis of these three compounds, as well as some other chloro- and bromophenols were developed. The methods employed GC/MS and stable isotope dilution analysis, and confirmed the presence of 2-chloro-6-methylphenol, 2,6-dichlorophenol and indole in some wines at concentrations well above their odour and taste detection thresholds. Conclusions: 2-Chloro-6-methylphenol, 2,6-dichlorophenol and indole were confirmed as causes of taints and off-flavours in commercial wines. Significance of the Study: The development of new analytical methods will make it possible to determine whether chlorophenol (and perhaps also bromophenol) taint in wine is more widespread than previously recognised. Similarly, the simple, rapid and accurate method for quantifying indole in wine will allow large numbers of wine and ferment samples to be studied to determine those factors that can result in unacceptably high concentrations in commercial wines.     

Stable isotope dilution analysis of the Fusarium mycotoxins deoxynivalenol and 3-acetyldeoxynivalenol

Trichothecenes are secondary metabolites produced by several fungi of the Fusarium genus during their growth period. They inhibit protein biosynthesis in eukaryotic cells resulting in numerous toxic effects such as diarrhea, vomiting, and gastro-intestinal inflammation. Considering its occurrence in food and feedstuff, deoxynivalenol (DON) is one of the most important trichothecenes. We report the synthesis of stable isotope labeled 15-d(1)-deoxynivalenol (15-d(1)-DON) from its natural precursor 3-acetyldeoxynivalenol (3-AcDON) as starting material. Furthermore, a method for the analysis of DON and 3-AcDON using HPLC-MS/MS with stable isotope labeled 15-d(1)-DON and 3-d(3)-AcDON as internal standards has been developed. In total, 18 cereal product samples were analyzed with contamination levels ranging from 10-301 microg/kg for DON and 5-14 microg/kg for 3-AcDON. This is the first report of an isotope dilution MS method for the analysis of type B-trichothecenes.     

初烤烟叶辣感关键成分的感官导向分析

为探索烟叶中的辣感关键成分,利用凝胶渗透色谱(GPC)对一种浓香型初烤烟叶的提取物进行了感官导向分离,根据滋味特征评价结果合并辣感流份,得到了辣感特征组分;采用气相色谱质谱联用技术(GC/MS)对所定位辣感特征组分进行定性分析,鉴定出4种化合物,依据定性结果用4个标样物质进行了感官评价;对辣感特征组分中烟碱进行了定量分析,依据定量分析结果复配烟碱溶液,并分别对辣感特征组分溶液和复配溶液进行了滋味分析实验(TDA);通过空白卷烟加香考察了烟碱在卷烟中的感官作用效果。结果表明:(1)4种物质中只有烟碱表现出辣感特征;(2)辣感特征组分溶液和烟碱复配溶液具有类似的辣感强度并表现出一致的稀释倍数,说明烟碱是特征组分中辣感的主要来源,是烟叶中辣感关键成分;(3)烟碱与卷烟刺激性有紧密的关联,其在显著提升烟气劲头的同时,也使口腔、喉部和鼻腔的刺激明显增强。     

Evaluation of potent odorants in heated egg yolk by aroma extract dilution analysis

Egg yolk was extracted using the method of Likens-Nickerson (simultaneous distillation/extraction). The resulting aroma extract, which smelled characteristic of heated egg yolk was analysed by aroma extract dilution analysis and gas chromatography–mass spectrometry. Of 41 odorants that were detected, 19 could be identified. Compounds with high flavour dilution factors were methional, phenyl acetaldehyde, 2-acetyl-1-pyrroline, heptanal, 1-octen-3-one and (E,E)-2,4-decadienal. Strecker degradation of methionine, phenylalanine and proline, as well as autoxidation of phospholipid-bound linoleic and arachidonic acids are proposed as the major factors for egg yolk flavour formation.     

Determination of potent odorants in apple by headspace gas dilution analysis

Gas chromatography-olfactometry with headspace gas dilution analysis was used to evaluate the odor potencies of volatile compounds in Fuji apple. To improve the resolution of volatile compounds, the dilution analysis was conducted on two types of capillary columns with different polarities. Thirty three and 20 compounds were identified on DB-WAX and DB-5 columns, respectively. Methyl 2-methylbutanoate, isobutyl acetate, ethyl butanoate, ethyl 2-methylbutanoate, isopentyl formate, butyl acetate and hexyl acetate as well as hexanal were important odor contributors in the headspace gas of apple on the basis of high Flavor Dilution (FD) factors. Threshold values-in-air of these compounds were also estimated from the relationships between their FD factors and concentrations. Methyl 2-methylbutanoate and ethyl 2-methylbutanote were considered as the most potent odorants because of their lowest threshold values. In addition, the threshold values-in-air of isopentyl formate, isopentyl acetate and butyl isobutanoate, which have never been reported, were estimated at 0.149, 1.95 and 0.00607 μl/l, respectively.     

The applicability of digital PCR for the assessment of detection limits in GMO analysis

We investigate the applicability of using digital PCR to estimate absolute limits of detection and quantitation associated with the validation of traditional real-time PCR methods for analysis of genetically modified (GM) ingredients. We also demonstrate the use of dynamic arrays as a precursor in selecting suitable sample dilution levels for accurate copy number assessment using the aforementioned digital PCR. Additionally, we further explore the relevance of digital PCR in accurately quantifying plasmid copy numbers associated with a commercially available Certified Reference Material. The use of digital PCR has the advantage of facilitating absolute single molecule detection, therefore negating the necessity for standards on a calibration curve, and reducing associated matrix effects. The approaches described in this paper enable pre-existing validated protocols to be re-examined, and estimates based on an alternative approach using digital PCR to be used in order to objectively characterise sensitivity limits.