姜黄素分光光度法测定广州市售食品中硼含量

目的用姜黄素分光光度法检测广州市售食品中硼含量。方法食品样品用1%Na2CO3调至碱性后灰化,然后在酸性条件下硼转化为硼酸,硼酸与姜黄素生成红色化合物,比色定量。结果硼含量在0～1μg/ml范围内有良好的线性关系,相关系数r=0.999 6,检出限为0.017μg/ml。相对标准偏差在0.09%～6.11%,加标回收率为88.9%～103.6%。用该法测定广州市售68种食品中硼,豆类硼含量范围2.99～34.73 mg/kg,水果类硼含量范围0.10～4.50 mg/kg,蔬菜类硼含量范围0.09～2.91 mg/kg,其他食品大部分硼含量相对较低,有3个样品硼含量远高于同类食品。结论姜黄素分光光度法设备易普及,重现性、灵敏度及准确性能满足分析要求,适用于多类食品中硼含量的测定。豆类、水果、蔬菜等硼含量较高,动物性食品以及多数谷类硼含量较低,部分加工食品可能存在违法添加硼砂或硼酸的情况。     

分光光度法测定胭脂红酸的研究

建立了分光光度法检测胭脂红酸的方法。结果表明,pH4．0浓度为1．0mol／L的磷酸钠缓冲液较适宜作胭脂红酸的溶解剂,胭脂红酸在1．251xg／mL～160μg／mL的浓度范围内的吸光度值线性相关系数达0．9997,方法回收率为104％～110％,平均相对标准偏差为0．78％－2．13％。     

RELATIVE SUITABILITY OF VARIOUS METHODS FOR DETERMINING FREE FATTY ACID (FFA) LEVELS IN FOODS

The relative suitability of analytical methods based on thin-layer chromatographic (TLC), titrimetric and colorimetric determination of free fatty acid (FFA) in foods and oils was determined. For quantitative measurements TLC method was found to be least suitable. For colored vegetable oils and lipids extracted from curried products, colorimetric and titrimetric method based on end-point detection by pH measurements are more precise and reproducible than conventional titrimetric procedure based on phenolpthalein indicator.     

Determination of vitamin C in tropical fruits: A comparative evaluation of methods

Two analytical methods for extracting vitamin C (l-ascorbic and l-dehydroascorbic acids) in tropical fruits [banana, papaya, mango (at three maturity stages) and pineapple] were evaluated. These methods used ion-pair liquid chromatography (LC) for detecting ascorbic acid, but differed in the preparation of the sample (extraction with 3% metaphosphoric acid −8% acetic acid or 0.1% oxalic acid). Results were validated by comparison with ascorbic acid content obtained by the AOAC’s official titrimetric method, by performing a recovery study and by the determination of within-day repeatability and inter-day reproducibility. There were differences in the efficiency of vitamin C extraction related to the fruit matrix and especially to the maturity stage in climacteric fruits. The LC-extraction method using 3% metaphosphoric acid −8% acetic acid shows high mean recoveries (99 ± 6%) for all matrices assayed, while the LC-extraction method with 0.1% oxalic acid proved to be unacceptable in some cases (unripe, half ripe and ripe banana and ripe mango) obtaining mean recoveries of 39.9 ± 9.1% and 72 ± 13% for banana and mango, respectively. The detection limit achieved with the metaphosphoric acid-acetic acid LC-extraction method for ascorbic acid (0.1 mg/l) allowed the determination of this vitamin in fruits analysed with good precision (5.94–12.8%), making its use as a routine analysis method perfectly valid. Recommendations about storage temperature, methods of thawing l-ascorbic acid extracts and the addition of antioxidants to extracts were made.     

A comparison of X-ray fluorescence spectrometry and chemical methods for determining sulphur in plant material

A rapid method for determining total S in plants by X-ray fluorescence spectro-metric analysis of ground pelletised plant material is compared with chemical methods using titrimetric, flame photometric and turbidimetric methods of sulphate determination. Errors in the chemical methods were caused by incomplete oxidation of organic sulphur and by non-reproducibility of the turbidimetric determination of sulphate. A method incorporating the oxidation of the sample with HNO³ and Mg(NO₃)₂ and titration of the reduced sulphate by mercuric acetate gave recoveries accurate to a mean of 1% when determining the sulphur content of sulphur compounds. Taking the results for plant materials determined by the titrimetric method as standard, XRF gave sulphur values with a mean difference of 4%; the flame photometric determination of sulphate after HNO₃ + Mg(NO₃)₂ oxidation gave results with a mean difference of 12%. The effect of absorption of S radiation by silicon is noted.     

高效毛细管电泳法测定胭脂虫提取物中胭脂红酸

建立高效毛细管电泳法(HPCE)测定胭脂虫提取物中胭脂红酸含量的方法以含5% 乙腈、5% 乙二醇的40mmol/LNa2HPO4-Na2B4O7·10H2O 混合缓冲液(pH9.434)为背景电解质,60cm × 75μm 未涂层毛细管柱为分离泳道,分离电压20kV,0.5psi × 10s 压力进样,柱温25℃,检测波长239nm,此条件下,采用峰面积内标法定量;在选定的电泳条件下,胭脂红酸质量浓度在50～500mg/L 范围内线性关系良好,线性相关系数R=0.9958,加标回收率为100.86%,方法检出限(RSN=3)为5.00μg/mL。本方法测定胭脂红酸含量试剂用量少,简便、快速、准确,可应用于实际生产中胭脂红酸的测定。     

Al3+荧光增敏快速检测酸奶和乳酸菌饮料中的胭脂虫红酸（英文）

研究溶剂、浓度、pH值以及金属离子对胭脂虫红酸荧光性能的影响,表明胭脂虫红酸在pH 4且其物质的量浓度为2.0×10^-4 mol/L的水溶液中荧光最强;而胭脂虫红酸对金属离子选择性识别的结果显示,Al^3+能使胭脂虫红酸的荧光强度显著增强从而提高检测的灵敏度。以Al^3+(2.0×10^-3 mol/L)为标准溶液检测样品中胭脂虫红酸含量时,胭脂虫红酸的物质的量浓度在1.0×10^-5~8.0×10^-5 mol/L范围内与其荧光强度呈良好的线性关系,检测限为5.0×10^-6 mol/L。实际应用结果表明,用荧光法检测不同酸奶和乳酸菌饮料中添加的胭脂虫红酸的含量,样品回收率在96.6%~110.5%之间,相对标准偏差小于5.9%。本研究为快速、有效、定量地检测食品中的胭脂虫红酸提供了一种有效的方法。     

A comparison of selected methods for determining eicosapentaenoic acid and docosahexaenoic acid in cereal-based foods

The accuracy of four transesterification methods and four extraction methods for determining the eicosapentaenoic acid and docosahexaenoic acid contents of cereal-based foods enriched with fish oil containing these fatty acids was investigated. The four enriched test foods were a flaked breakfast cereal, a snack bar, bread and muffins. The accuracy of the transesterification methods was tested using several commercial fish oils. The recovery of eicosapentaenoic acid and docosahexaenoic acid in the fish oils ranged from 97% to 104% depending on the transesterification method used. For the extraction methods, the recovery of eicosapentaenoic acid and docosahexaenoic acid across all food products ranged from 59% to 101% and 74% to 98% respectively depending on the extraction method used. Overall, the solvent mixture direct method was the most accurate extraction method across all the foods. However, the application of different extraction methods for different food types may be optimal when accurate analysis of eicosapentaenoic acid and docosahexaenoic acid in foods is required.     

蛋白饮料中胭脂红酸的高效液相色谱-荧光法检测技术研究

建立了高效液相色谱．荧光法定量检测蛋白饮料中胭脂红酸的方法。样品经过8mol／LNFLOH溶液处理5min,过滤后直接进高校液相色谱。色谱条件：流动相：乙腈和1．19mol／L的甲酸（19：81,v／v）;流速0．8mL／min,进样量：20此,荧光检测的激发波长hx=470nm,发射波长hm=600nm。该方法条件下,胭脂红酸在浓度5斗g,mL-80μg/mL线性关系良好,检测限为0．1mg／kg,相对标准偏差（RSD）小于4．25％,加标回收率为90．34％-95．15％。该方法在多种人工合成红色素的存在的条件下,可以实现对胭脂红酸进行准确的定量检测。     

Comparison of four different methods for the determination of sulfites in foods marketed in South Korea

Sulfites in foods were analysed using four methods: optimised Monier–Williams (official method), modified Rankine, HPLC and ion-exchange chromatography (IEC). The modified Rankine and HPLC methods were performed according to the previously reported methods but with some modifications. The IEC method was carried out through a combination of a modified Rankine apparatus and an anion-exchange column for the first time. In false-positive response tests, false-positive results with acetic acid and propionic acid were not observed in the modified Rankine, HPLC or IEC methods, unlike the optimised Monier–Williams method. All methods were evaluated for accuracy, precision and simple correlations. Modified Rankine, HPLC and IEC methods were determined to be suitable for foods with less than 10 mg kg^–1 of sulfur dioxide (SO₂). The modified Rankine and HPLC methods were suggested to be the most appropriate for the determination of sulfites in foods due to their high correlation coefficient with the optimised Monier–Williams method (R² = 0.9138 and 0.9011, respectively).     

Comparative Study of Different Milk Samples Preservation Procedures for Bacteriologic Examination

The control of pathogenic bacteria present in foods, as well as scientific data concerning their behavior, are closely linked to analytical methods used and the way they are implemented. To assess the capacity of the laboratories to conduct correctly microbiological analyses, national and international proficiency testing schemes are organized. To set up these inter-laboratory studies (ILS), it is necessary to prepare artificially contaminated samples, which contamination level is sufficiently stable regarding their transportation conditions to the participating laboratories. In this context, we tested several procedures to maintain the concentration of Listeria monocytogenes and coagulase-positive staphylococci in milk samples: freezing temperature and addition of bacteriostatic agents at refrigeration temperatures, such as nystatin, boric acid, sodium azide, the lactoperoxidase system, or a boric acid mixture. Through this study we selected preservation procedures, which could be used to stabilize the contamination level of artificially contaminated milk samples during transportation without preventing the growth of the target bacteria during the analysis and after the initial dilution step. Boric acid mixture and boric acid were found to be effective in stabilizing the contamination level of Staphylococcus aureus in milk samples, whereas freezing, a boric acid mixture, and boric acid were suitable for milk samples containing L. monocytogenes, depending on the samples’ contamination rate. An erratum to this article can be found at     

A comparative study of titrimetric and gravimetric methods for the determination of organic carbon in soil

Two gravimetric procedures for determining carbon in soil, one a dry combustion method and the other a wet oxidation method, were compared with seven variants of the titrimetric method, all based on titrimetric determination of the dichromate consumed when soil is heated with dichromate and acid. The coefficients of variation of the methods were, as percentages: dry combustion, 0.76; wet combustion, 1.1; Tinsley I, 1.3; Tinsley II, 1.8; Tinsley III, 0.8; Anne, 1.3; Mebius, 1.8; Walkley and Black, 1.6 and Tyurin, 8.5. Taking the dry combustion method as standard, the percentage recovery of organic carbon from 22 soils was 99 for wet combustion, 95 for Tinsley I, 95 for Tinsley II, 97 for Tinsley III, 93 for Anne, 95 for Mebius, 77 for Walkley and Black and 93 for the Tyurin method. A variant of the Tinsley method (Tinsley III) is proposed as a quick procedure when the accuracy of dry combustion is not essential.     

白灵菇菌丝体多糖两种测定方法的比较

为选出一种比较准确、方便的测定食用菌菌丝体多糖方法,以白灵菇菌丝体提取的粗多糖为原料,对苯酚-硫酸法、蒽酮-比色法2种方法进行比较。苯酚-硫酸法和蒽酮-硫酸法的稳定性实验RSD分别为0.71%和1.40%,精密度实验RSD分别为2.10%和9.53%,回收率平均值分别125.41%和154.88%;苯酚-硫酸法具有稳定性好、精密度高,而且回收率实验也较为理想,是测定食用菌菌丝体多糖含量较为理想的方法。     

硼酸-柠檬酸比色法测银杏枝叶中黄酮苷含量

用硼酸-柠檬酸比色法测定了银杏枝叶不同季节黄酮苷的含量,结果表明:硼酸-柠檬酸比色法测定银杏枝叶中的黄酮苷含量稳定性好,精度高,标准差为0.06,黄酮苷测定回收率为98.3%～101.1%,测定结果不受脂溶性杂质的干扰;银杏枝叶中的黄酮苷含量随季节的变化而变化,8月黄酮苷含量最高。     

食品中硼酸及硼酸盐污染分布研究

目的了解市售食品中硼酸及硼酸盐的污染及分布情况,发现危险因素。方法采集市售食品面粉制品、豆制品、米制品、水产品及其他类食品共335件,采用分光光度法测定样品中硼酸的含量。结果面粉制品中硼酸及硼酸盐的检出率为40%;豆类及制品中全部检出,其含量主要集中在200mg/kg以下范围;水产品中检出率达84%;米制品中检出率最低为11%。结论市售食品中存在不同程度的硼酸及硼酸盐的污染,有一定安全隐患,相关部门应针对性加强监管,预防食源性疾病的发生,同时科学、合理区分本底和违法添加。     

非水滴定法快速测定食品中的糖精钠

建立了在非水条件下快速测定食品中糖精钠的方法，以冰乙酸为溶剂，用高氯酸的冰乙酸标准溶液滴定，经过反复试验，相对标准误差0．92%-2．93％，加标回收率97．13％-100．3％，结果表明；该法定量分析准确，精确度高，可靠性和重现性好。     

基于计算机色度学小麦粉中硼砂的快速检测方法研究

根据硼砂在酸性条件下转化为硼酸,硼酸与姜黄素显色的原理,利用自主设计的图像采集传感器,采集硼砂与显色液显色后的图像,用Lab VIEW设计图像处理软件,建立了基于计算机色度学小麦粉中硼砂的快速筛查方法。优化了显色体系的显色条件和软件的操作功能。结果表明:显色体系的亮度I值与硼酸在0~4 mg/L范围内呈线性关系,并得到测定的硼砂含量与I值的关系曲线。将关系曲线公式植入数据分析系统,通过采集显色后溶液的图像,软件可自动得出硼砂的实际添加量。该法用于实际样品分析,加标回收率为96.6%~102.9%,相对标准偏差(RSD)为1.18%~3.14%。     

Determination of ammonia nitrogen in the urine of small ruminants

The objective of the present work was to compare colorimetric and distillation–titration methods to determine the ammonia-nitrogen (NH₃-N) concentration in sheep and goat urine samples. Colorimetric methods used were based on the indophenol reaction, whereas titrimetric methods were based on the alkali distillation of ammonia from the urine and its titrimetric determination with a standard acid. Colorimetric methods were only reliable when urine samples were diluted at least 1: 20. Both colorimetric and alkali-distillation methods gave quantitative recoveries with standard NH₃-N solutions, but when NH₃-N was determined in urine samples there was a significant discrepancy between analytical methods on the measured concentrations. These were between 1·3 and 10-fold (on average 2·6-fold) higher with alkali distillation than with the colorimetric method. The difference between concentrations measured by both analytical methods was significantly related (R² = 0·990; P < 0·001) to the concentration of urea in the urine samples. To study the effect of urea concentration, standard solutions containing variable concentrations of urea and NH₃-N were prepared, and NH₃-N concentration determined by both methods. Concentrations measured by colorimetry were similar to the actual concentrations irrespective of the urea concentration of the solutions. In urea-free solutions, alkali-distillation methods gave values similar to the actual concentrations, but when urea was present observed values were consistently higher than the expected concentrations. The overestimation increased with the urea concentration of the solutions, with a significant (P < 0·001) relationship between both variables. Colorimetric methods were more reliable to measure NH₃-N concentrations in urine samples containing high urea concentrations. © 1998 Society of Chemical Industry.     

A comparative study on the determination of lactic acid in silage juice by colorimetric,high-performance liquid chromatography and enzymatic methods

The determination of lactic acid in the silage juice of artichokes with different additives (formid acid, molasses and NaCl) by the colorimetric method and its comparision with the high-performance liquid chromatography and enzymatic methods was investigated. The lactic acid content of the artichoke with molasses (62.1 g kg⁻¹) was higher than that of those with formic acid, or NaCl and without any additive (39.3, 33.0 and 43.2 g kg⁻¹, respectively). However, this effect was not significant (P > 0.05). There were significant differences on the method of measuring lactic acid of the artichoke silages (P < 0.001). The use of the enzymatic method resulted in a higher (75.6 g kg⁻¹) lactic acid content than when the colorimetric or HPLC methods were employed (with results of 42.0 and 28.9 g kg⁻¹, respectively). However, the levels of lactic acid in silage juices found using the colorimetric and HPLC methods were not different, and recovery percentages, by using the colorimetric method, were satisfactory (103.78%), when the detection limit at maximum level (30 µg ml⁻¹) was not exceeded. © 1999 Society of Chemical Industry     

Quantitative Bestimmung von Citronensaure in Citratstärken

Quantitative Determination of Citric Acid in Citrate Starches Both colorimetric and titrimetric methods for determination of the esterlike bounded citric acid in citrate starches are described. Both methods give comparable results. The titrimetric method is preferred because of its lower expenditure and rapid performance.