食盐中氯化钠测定的研究

食盐是人们日常生活中必备的调味品,氯化钠是食用盐的主要成分,是食盐咸味的主要来源。作为食盐生产企业必须控制的指标,氯化钠项目的检测尤为重要,但是不同产品标准规定的氯化钠的检测方法存在着或多或少的差别,常用的氯化钠测定方法为计算法,一个项目涉及到5个项目的检测,且计算过程繁琐。本研究根据食盐中杂质化合物的不同将食用盐分成几个类型,将复杂的计算过程列表表示,使计算过程变得清晰明了。同时汇总了现行食用盐标准中氯化钠含量的测定方法幵迚行了比较分析,以期给管理部门、生产企业及检验人员提供更多的参考和思考。     

氯电极法测定调味品中的氯化钠

目前,食品中氯化钠含量测定方法主要有Mohr 法和Volhard 法;电位滴定法和盐分测定仪法。这些方法有的准确度差,有的操作繁琐,有的受样品色泽及蛋白质影响,有的要消耗贵重的硝酸银试剂。我们采用氯离子选择电极测定调味品中的氯化钠,其准确度与Mohr 法测定确度相符。该法简便、快速、准确,不受样品色泽及蛋白质的影响。     

盖勃法测定乳脂肪

一、盖勃法的基本操作牛奶脂肪含量的测定方法有重量法和容积法。重量法的标准方法是罗兹——哥特里法。容积法有巴布考克法和盖勃法等。容积法较重量法测定速度快、省时、省力。最常用的乳脂肪测定法,在我国是盖勃法(酸法)。现将盖勃法有关问题讨论一下。首     

烟叶中水溶性还原糖的测定

烟叶中还原糖的含量是烟叶品质优劣的重要标志之一。还原糖的测定方法很多,如常用的Somogi比色法;Fehling热滴定法:3,5一二硝基水杨酸法(DNS)等。     

食品中山梨酸的比色测定

<正>山梨酸(SA)及其盐类是食品中常用的防腐剂,测定方法有比色法、薄层色谱法及气相色谱法等。以往的重铬酸盐法虽然灵敏度较高,但缺点是:1)重铬酸钾为强氧化剂,当乙醇     

海带中岩藻聚糖硫酸酯的测定方法比较

比较4种常用的岩藻聚糖硫酸酯定量方法来测定海带岩藻聚糖硫酸酯功效成分的含量,建立海带中岩藻聚糖硫酸酯的测定方法。采用4种常用的多糖测定方法:PMP柱前衍生-HPLC法、Dische法、次甲基蓝染色法、Cameron法进行测定,岩藻糖含量分别是9.23%、10.01%、23.65%、6.75%。经比较分析,Dische比色法简便、快速、准确,不需要昂贵的分析仪器,安全可靠。     

高盐食品中铅测定方法的研究进展

目前,高盐食品中铅的测定方法主要有原子吸收光谱法(包括石墨炉原子吸收法和火焰原子吸收光谱法法)、原子荧光光谱法及双硫腙比色法。此外,还有电感耦合等离子质谱法和电感耦合等离子体发射光谱法。电感耦合等离子体质谱法具有极高的灵敏度与较宽的线性范围,并且不受高盐食品中氯化钠的干扰,对高盐食品中铅的测定具有很强的优势。石墨炉原子吸收光谱法操作简便、灵敏度高,但容易产生基体干扰,主要表现为产生严重的背景吸收,对测定结果造成很大的影响。国家标准方法测定高盐食品的铅含量,通常需加入适当的基体改进剂并优化仪器条件,才能得到准确的实验结果。本文综合概述了上述常用检测方法在高盐食品中铅含量的应用,以期为相关研究提供参考。     

果蔬抗氧化活性测定方法的比较

采用DPPH法、硫氰酸铁(FTC)法、β-胡萝卜素-亚油酸乳化液法3种常用果蔬抗氧化活性测定方法,对杭州市场常见的20种果蔬进行了抗氧化活性测定,比较3种果蔬抗氧化活性测定方法的差异,寻求合适的果蔬抗氧化活性测定方法。结果表明:DPPH法测定果蔬抗氧化活性简便,重现性好;FTC法测定结果与DPPH法较为接近,但操作相对复杂;而β-胡萝卜素-亚油酸乳化液法虽筒捷方便,但测定结果与前2种相比差异较大。     

制革常用蛋白酶活力测定方法及结果的比较

介绍了制革蛋白酶活力常用的测定方法LVU法、福林法和胰酶转化倍数法的测定原理和方法。对21种制革中常用的胰蛋白酶、高浓度的细菌蛋白酶和制革工业用酶制剂，分别用三种方法进行了活力检测，结果表明，在相同的反应pH和温度下(LVU标准条件pH 8．2，37℃)，福林法和LVU法两种测定方法的结果基本一致。活力1：24倍国产胰酶的LVU法活力为2．4万左右。以此为基础，在确定酶制剂用量时，对于用不同活力测定方法表征的酶制剂可更方便地换算。     

食品用塑料包装薄膜中氧气透过量测定方法的比较

<正>塑料包装薄膜是最为常用的食品保鲜方法,因成本较低、加工方便等优点,已被广泛应用于食品加工业。氧气透过量是衡量食品用塑料包装薄膜性能及质量的重要指标之一,要想选择最为合适的食品用塑料包装薄膜就需要准确测定其氧气通过量。当前最为常用的测定方法有压差法和等压法两种,本文从测定原理、测定过程、     

高压液相色谱同时快速测定饮料中苯甲酸、糖精钠、咖啡因方法的研究

<正> 前言 近年来,市售的饮料种类和数量大量增加,如何快速、准确地检测饮料中添加剂的含量成为一个亟待解决的问题。高压液相色谱测定食品添加剂苯甲酸、糖精钠和咖啡因的方法,国内外均有报道,但有的方法要求专用柱、专用试剂,有的方法测定时间长,影响因索多。本方法根据被测物特性,提出采用甲醇——0.02M醋酸铵(pH4) 为流动相,分离效果好,饮料中蔗糖、柠檬酸、色素均不影响测定结果。苯甲酸、糖精钠、咖啡因的最低检测量分别可达1.1×10~(-9)、8.9×10~(-10)、2×10~(-9)g/ml。试样只经滤膜过滤直接进样,无须复杂的提取、净化等步骤,整个测定过程大约30分钟即可完成。     

离子色谱法测定糖蜜样品中氯离子、硫酸根和硝酸根含量

目的 建立离子色谱法测定糖蜜样品中氯离子、硫酸根离子和硝酸根离子含量的方法。方法 使用去离子水对样品进行准确定容的稀释,之后对稀释后样品溶液过IC Na柱净化后上机测定样品的氯离子、硫酸根和硝酸根含量。使用Ion Pac _^TMAS19(4 mm × 50 mm)为分析柱,KOH淋洗液的浓度为35.0 mmol/L,流速1.0 mL/min,进样体积50 μL,外标法定量。结果 氯离子、硫酸根、和硝酸根标准溶液在0.05 ~ 2.0 mg/L浓度范围内呈现良好线性关系,R_²大于0.99,检出限0.02 ~0.1mg/L。在1.0 ~ 4.0 mg/L添加浓度上,回收率范围为85.4%~102.6%,相对标准偏差3.63%~10.64%。结论 该方法操作简便且快速准确,能够有效测定糖蜜中的氯离子、硫酸根和硝酸根含量,满足糖蜜中氯离子、硫酸根和硝酸根的检测需求以及样品的分析测定。     

A novel method for the determination of sodium chloride in salted fish

A novel, simple and reliable spectrophotometric method to determine sodium chloride in salted fish was developed and validated. The method was based on the reaction of chloride with silver nitrate and the determination of turbidity of silver chloride formed. The absorbance was measured at 385 nm. The method was tested under various conditions, and we confirmed an optimal operation with 2 mL 1:4 (v/v) nitric acid, 2 mL 1.5 g L^?1 gelatin, 5 mL 0.5% silver nitrate in a total volume of 50 mL, mixed and heated at 60 °C for 10 min. The range of linearity and the detection limit were 0.4–24 mg L^?1 and 0.2 mg L^?1, respectively. The relative standard deviations and the recovery were 0.83% to 2.87% and 93.74% to 103.6%, respectively. The accuracy of this method was comparable with Volhard method, and it was cheap and successfully applied to determine sodium chloride in salted fish.     

Bridging the gap between macroscopic and spectroscopic studies of metal ion sorption at the oxide/water interface: Sr(II), Co(II), and Pb(II) sorption to quartz

Metal sorption mechanisms were investigated for strontium, cobalt, and lead using sodium chloride, sodium nitrate, and sodium perchlorate as background electrolytes and quartz as the adsorbent. Spectroscopic analyses of concentrated sorption samples were evaluated for their ability to provide insight into the controlling sorption process for more dilute systems. For strontium, outer-sphere complexes identified using X-ray absorption spectroscopy (XAS) of concentrated samples were consistent with macroscopic sorption data collected in more dilute systems. XAS results indicated that cobalt formed a new solid phase upon sorption to silica. Macroscopic studies of cobalt sorption supported the spectroscopic data for total cobalt concentrations of 10(-5) M, regardless of the background electrolyte composition or concentration. At a lower total cobalt concentration (10(-7) M), adsorption appeared to be the prevailing mechanism of cobalt removal. Spectroscopic results suggested that lead adsorbed as an inner-sphere complex on silica. The decrease of lead removal with increasing chloride concentration was attributed to competition with aqueous lead-chloride complexes, based on thermodynamic calculations.     

Partial purification and characterization of polyphenoloxidase from peppermint (Mentha piperita)

Polyphenoloxidase (PPO) of peppermint leaves ( Mentha piperita) was isolated by (NH₄)₂SO₄ precipitation and dialysis. Its pH and temperature optima were 7.0 and 30°C, respectively. On heat-inactivation, half of the activity was lost after 6.5 and 1.5 min of treatment at 70 and 80°C, respectively. Sucrose, (NH₄)₂SO₄, NaCl and KCl appeared to be protective agents of peppermint PPO against thermal denaturation. Km of this enzyme ranged from 6.25×10⁻³ M with catechol to 9.00×10⁻³ M with L-dopa. The I₅₀ values of inhibitors studied on PPO were determined by means of activity percentage (I) diagrams. Values were 1.4×10⁻⁴ M, 1.7×10⁻⁴ M, 9.7×10⁻⁵ M, 2.45×10⁻⁴ M, 2.16×10⁻¹ M, 1.83×10⁻⁵ M, 6.5×10⁻⁵ M, 1.4×10⁻² M, 7.5×10⁻⁵ M, for potassium cyanide, glutathione, ascorbic acid, thiourea, sodium azide, sodium metabisulfite, dithioerythritol, β-mercaptoethanol and sodium diethyl dithiocarbamate respectively. Therefore, sodium metabisulfite was the most effective inhibitor.     

Fractionation of Starch Amylopectin and Amylose by High Performance Gel Filtration Chromatography

A gel filtration chromatographic method has been developed which is capable of fractionating amylose and amylopectin in starch. Three GFC columns (2 × 4000 A and 1 × 300A PL Separation Sciences, Polymer Laboratories Ltd,) are used in series using sodium chloride solution as eluent. Minimal sample preparation is involved which includes a preliminary wetting of powder starch with ethanol followed by dissolution with sodium hydroxide. Since the solvent system is aqueous, cooked starch samples are analysed by direct dissolution with sodium hydroxide. The method shows promise as a rapid technique in elucidating starch structure.     

偶氮胂Ⅲ催化动力学光度法测定食品中微量铜的研究

研究了痕量铜对抗坏血酸还原偶氮胂Ⅲ的催化作用,发现其在ＨＡＣ－ＮａＡＣ介质中具有高灵敏的反应,Ｃｕ（Ⅱ）量在０．０２～０．１２μｇ／２５ｍｌ内符合比耳定律,检出限为４．５３×１０－１０ｇ／ｍｌ,可用于测定食品及饮用水中的痕量铜。     

Impedimetric Determinaton of Total, Mesophilic and Psychrotrophic Zounts in Raw Milk

A rapid impedimetric determination for total, mesophilic and psychrotrophic counts in raw milk showed correlations (between impedance detection times and standard plate counts) of -0.96, -0.95, and 0.96, respectively. Mesophiles were most often seen as the predominant population, the impedimetric method allowed for these samples containing above 1.0 × 10⁵ CFU/ml to be screened out within 4 hr. Psychrotrophic levels of 1 × 10⁵ CFU/ml and above were screened within 21 hr, while total concentration of samples containing above 1 × 10⁵ CFU/ml were screened within 16 hr.     

Computer aided boar semen motility analysis for cereulide detection in different food matrices

Computer Aided Semen Analysis (CASA) study of the boar semen motility has been demonstrated to be an appropriate assay for detection of cereulide (Bacillus cereus emetic toxin). Application of the boar semen bio-assay to detect cereulide directly in foods requires investigation of potential interference of food components, preservatives and other microbial and chemical food contaminants with the bio-assay. Current study provides evidence that none of included Staphylococcus aureus enterotoxins A, B, C and D nor B. cereus Hemolysin BL (HBL) and non-hemolytic enterotoxin (NHE) and three mycotoxins (Sterigmatocystin, Fumonisin B1 and Patulin) exhibited a toxic impact on semen progressive motility. Aflatoxin M1, M3 and zearalenone impaired semen motility only at concentrations (0.004 mg ml(-1), 0.1 mg ml(-1) and 10 mg ml(-1), respectively) much higher than those found in foods and those permitted by legislation, in comparison to cereulide which induces motility cease at concentrations lower than 20 ng ml(-1). Ten commonly used preservatives, namely potassium sorbate, sodium benzoate, (DL) malic acid, citric acid, (L+) tartaric acid, acetic acid, (DL) lactic acid, (L+) ascorbic acid, sodium chloride and sucrose induced no cease in spermatozoa motility even at preservative concentrations higher than permitted by legislation. Dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and acrylamide had no acute effect on spermatozoa motility at concentrations of 500 and 10,000 mg ml(-1), respectively. Robustness of computer aided boar semen motility analysis, tested with 14 different foods inoculated with cereulide producing B. cereus, showed distinct cereulide production in seven samples (although B. cereus growth to counts higher than 8 log CFU g(-1) was noted in 11 samples), in amounts close to those reported in foodborne outbreaks. Test evaluation in 33 samples suspected to hold cereulide showed actual cereulide presence in ten samples and no interference of food matrix with the assay.     

The effect of added L-ascorbic acid,and sodium chloride on the change in concentration of some volatiles in pressurised peach homogenate during storage

White peach (Prunus persica L cv Yamane) homogenates with sugar (20%), or with sugar (20%) and/or L -ascorbic acid (0·1%) and/or sodium chloride (0·5%), were packed in plastic bottles, pressurised (400 MPa, 20°C, 10 min), and then stored at 0 and 25°C for various periods. The headspace volatiles which were absorbed on Tenax TA using dynamic headspace sampling were heat desorbed and analysed by capillary gas chromatography mass spectrometry. Enzymatic formation of benzaldehyde during storage was observed in all samples. The homogenate with L -ascorbic acid showed the highest level of benzaldehyde formation. The flavour quality and colour of the pressurised homogenates with ascorbic acid stored at lower temperature were excellent. © 1997 SCI.