钼蓝比色法测定还原型维生素C

食品中还原型维生素 Ｃ（Ｌ－ＶＣ）能将磷钼酸盐定量还原成蓝色的铝蓝化合物,通过分光比色的方法即可测定出食品中还原型维生素的含量。本文进一步详细的研究了影响显色反应的各种因素,结果表明,在酸性介质中,Ｖｃ与磷钼酸盐的反应速度快,环境因素对其影响小,且反应体系的吸光度稳定。在本实验条件下,ＶＣ浓度在８～２８ｕｇ／ｍｌ的范围内服从比耳定律。在此范围内,回归方程为：Ｙ＝０．０１８９２９２＋３６８６．３１Ｘ（ｍｏｌ／Ｌ）,相关系数ｒ＝０９９８２６,间按摩耳系数为 ３．６８６３１×１０~３,最大吸收波长 ７０５ｎｍ,回收率在９８．５０％～９８．６３％之间,本方法具有简便、快速、准确的特点。     

紫外分光法测定无花果中苯甲醛

建立了一种简便快速的测无花果中苯甲醛的方法。采用乙醇回流提取，水蒸汽蒸馏挥发分离，在紫外２３０ｎｍ和２４９ｎｍ处双波长测定。测得无花果中苯甲醛含量为５９．６μｇ／ｇ，５次测定变异系数为２．４８％，回收率在８５．６％～９２．５％之间。     

食品中还原型抗坏血酸的液相色谱分析

食品中还原型抗坏血酸的液相色谱分析王天丽维生素Ｃ作为强化食品的添加剂已得到了越来越多的应用。现在维生素Ｃ的测定主要用比色法。近年来，色谱工作者也已把液相色谱应用于食品中维生素Ｃ的测定，使维生素Ｃ的分析方法得到了进一步的发展。本实验采用０．００５ＮＨ＿...     

小梅鱼水解过程中的分析方法研究

采用２８０ｎｍ和２６０ｎｍ紫外吸收、双缩脲法、甲醛法、凯氏定量氮法以及６４０ｎｍ可见光吸收法对小酶鱼酶法水解过程中蛋白质，核酸、α氨基氮和总氮含量以及浊芳变化等指标进行了过程监控。实验结果表明可以用２８０ｎｍ紫外吸收法代替凯氏定氮法分析小梅鱼水解过程中清液的总氮含量变化，过程中２８０ｎｍ紫外吸收值的变化呈规律性递增。水解产物中总氮含量与２８０ｎｍ紫外吸收值的关系为Ｙ＝２．０１６Ｘ－０．０４。２６０     

本底校正褪色光度法测定食品中还原型维生素C

还原型维生素C能将Fe3+定量还原 ,通过测定反应中所消耗的Fe3+量 ,即可间接测定样品中还原型维生素C含量。利用KSCN和罗丹明B能与Fe3+形成离子型缔合物的特性和表面活性剂吐温 80 (Tween 80 )的胶束增溶作用 ,使还原型维生素C的测定灵敏度显著提高。利用Cu2 +能将样品中还原型维生素C选择性氧化的特性 ,通过对食品样品的Cu2 +预氧化处理 ,实现对有色样品本底吸收的快速校正 ,建立了一种本底校正褪色光度法测定食品中还原型维生素C的新方法。应用本文方法测定了多种食品样品中还原型维生素C的含量 ,取得了满意的结果     

植酸对柑桔中抗坏血酸（L—ASA）的保护作用

植酸的浓度在０．１％以上，ｐＨ３．５～１０之间时对维生素Ｃ有较好的保护作用，它能抑制金属离子对维生素Ｃ的氧化催化作用，而且在Ｈ２Ｏ２和金属离子存在下对Ｈ２Ｏ２的氧化有抑制作用，尤其是较完全地抑制铁离子存在的Ｈ２Ｏ２的氧化作用，柠檬酸缓冲液能降低植酸对金属离子氧化催化作用的抑制。     

测定巴豆甜菜碱的新方法及其在肉碱研究中的应用

通过对巴豆甜菜碱紫外吸收特性的研究,建立了一种快速、简便的检测方法,最大吸收波长为２６５ｎｍ,检测范围为０．２５－３．５ｇ／Ｌ。由于Ｌ－肉碱是由巴豆甜菜脱水酶作用下不对称水化合成的,转化液主要成分为肉碱与巴豆甜菜碱,而在２６５ｎｍ处肉碱的光吸收相对巴豆甜菜碱而言极低,因此２６５ｎｍ光吸收检测方法也可应用于肉碱在科研,生产上的快速测定,较一航的肉碱检测方法具有简便,经济的优点。     

河南烤烟(40级)氮组分含量及规律性研究

测定了河南烤烟（４０级）各等级烟叶的总氮、不溶性氮、水溶性氮、总生物碱氮、氨态氮的含量。结果表明：各等级烟叶总氮含量集中在１．５％～２．５％之间，不溶性氮含量集中在０．８％～１．５％之间，水溶性氮含量集中在０．６％～１．２％之间，总生物碱氮含量集中在０．２％～０．８％之间，氨态氮含量集中在０．０２％～０．０８％之间。进一步分析了上述测定结果与烟叶部位、颜色、等级的关系，找出了规律性，为研究氮组分对烟草品质的影响提供了参考依据。     

硅钼兰分光光度法测定微量L—抗坏血酸棕榈酸酯

研究了Ｌ－抗坏血酸棕榈酸酯在硅钼杂多兰形成反应中的影响，优选了测定条件，建立了测定其含量的硅钼分光光度法。本法显色体系的最大吸收波长在７２０ｎｍ，检测范围为０．２５－２．０ｍｇ／５０ｍｌ，相对标准偏差为０．４３％，回收率为９９．４％－１００．４％。     

紫外分光光度法测定维多康中维生素C的含量

目的:建立紫外分光光度法直接测定维多康中维生素C含量的方法。方法:以Cu2+为催化剂加速维生素C的氧化,以EDTA络合校正背景作参比,利用氧化前后吸光度差值(△A)直接测定维生素C的含量。测得还原型维生素C在265nm处有最大吸收峰。结果:维生素C的浓度在30～70μg/ml范围内吸光度与浓度呈良好的线性关系r=0.99922(n=5),回收率在105.77%～109.50%之间。结论:操作简单,测定快速,结果准确,精密度高,检测范围大,适合于维多康中维生素C的含量测定。     

采用褪色光度法测定维生素C

在硫酸介质中,利用维生素C（L-VC）对高锰酸钾的褪色效应建立了褪色光度法测定维生素C的方法。在最大吸收波长为526nm,表观摩尔吸收系数为6.71×103L·mol-1·cm-1时,维生素C浓度在0～20μg/ml范围内与溶液的褪色程度（△A）服从比尔定律,最小检出限为0.91mg/L,相对标准偏差为0.54%～0.96%,回收率为92.5%～101.8%。     

雪莲果防褐变技术的研究

从雪莲果块茎中提取多酚氧化酶(Polyphenol Oxidase,PPO),采用分光光度法对其最大吸收波长最适反应温度进行研究,还研究了VC、氯化钠、柠檬酸、柠檬汁、橘子汁对雪莲果PPO活性的影响。结果表明:雪莲果多酚氧化酶最大吸收波长为400nm,最佳反应温度为30℃。氯化钠、抗坏血酸、柠檬酸、柠檬汁、橘子汁都有抑制褐变的效果。组合抑制剂抑制褐变效果比单一抑制剂好且最佳组合抑制剂为1.5%氯化钠+0.5%抗坏血酸+1.5%柠檬酸+10%柠檬汁。     

二苯胺磺酸钠褪色光度法测定饮料中还原型维生素C

在硫酸介质中,二苯胺磺酸钠可被过氧化氢氧化生成二苯联苯胺磺酸紫。利用在酸性条件下还原型维生素C（L—VC）对二苯联苯胺磺酸紫的褪色效应建立了褪色光度法测定还原型维生素C的方法。最大吸收波长为780nm,还原型维生素C浓度在0～24μg／ml范围内与溶液的褪色程度（ΔA）服从比耳定律,回收率为94．5％-100．8％     

荧光分光光度计法测定腊肉中维生素C

样品中的VC用偏磷酸钠提取,经2,6-二氯靛酚氧化成脱氢型抗坏血酸后与邻苯二胺(OPDA)反应,生成具有荧光的喹喔啉(quinoxaline),其荧光强度与脱氢抗坏血酸的浓度在一定条件下成正比,以此测定腊肉中VC含量.荧光分光光度计在激发波长360nm,发射波长430nm测定喹喔啉荧光强度.该方法VC的检出限为0.95mg.kg-1,相对标准偏差(RSD) 2.4％,回收率在87.2％～94.3％之间.用荧光分光光度计法和2,4-二硝基苯肼比色法同时测定腊肉中VC,发现二者结果无显著差异,但荧光分光光度计法精密度高于2,4-二硝基苯肼比色法.实验证明,荧光分光光度计法测量腊肉中VC具有灵敏度高、快速、准确等优点.     

High-pressure liquid chromatographic determination of ascorbic acid in cooked sausages

The purpose of this paper was to study and optimize both extraction and high-pressure liquid chromatography (HPLC)-UV detection procedures to develop a proper method for the determination of ascorbic acid content in cooked sausages. A simple and sensitive reversed-phase HPLC method for the NH2-bonded phase has been described for the determination of ascorbic acid content in cooked sausages. Various extracting agents were tested to solubilize the vitamin, with 5% (wt/vol) metaphosphoric acid giving the best results. Samples were chromatographed with UV detection at 248 nm on a 25-cm Spherisorb NH2 cartridge with a 0.4-cm inside diameter with a mixture of 0.02 M potassium phosphate buffer solution (pH 3.6) and acetonitrile (40:60, vol/vol) for the mobile phase. The method's precision within a day was 1.2%, and its precision between days was 3.8%. The detection limit was 1.6 mg/100 g. Recovery ranged from 91.4 to 96.2% for ascorbic acid added to meat samples. Twenty samples of six different products were analyzed in duplicate. For the samples analyzed, the mean value for ascorbic acid ranged between 21.555 and 24.899 mg/100 g of fresh weight.     

Ascorbic Acid Effects on Bovine Muscle Pigments in the Presence of Radiant Energy

Untreated and treated (dipped in ascorbic acid solutions of 0, 0.5, 1.0, or 5.0%) raw psoas major muscle samples were exposed to radiant energy in a model system (500W Hg lamp, 577 nm, 2°± 1°C, 20% 02) with spectral reflectance measured every 30 min. Results varied with reflectance ratios or differences at 572/525, 630-582, 630/582, or 630-614 nm. Differences between 0 and 4 hr exposure indicated that ascorbic acid retarded pigment oxidation. The K/S ratio at 572/525 nm indicated that 5% ascorbic acid solution retarded pigment oxidation and protected muscle color most. Ascorbic acid retarded lipid oxidation (TBA values) in muscle stored at ?26°C from 3–10 wk; a 5% solution gave the least protection of the solutions tested.     

Determinations of Organic Acids in Potatoes by High Performance Liquid Chromatography

A high performance liquid chromatographic method has been developed to quantify the major organic acids in potatoes oxalic, citric, malic, fumaric and ascorbic acids. Tubers were extracted with 95% ethanol:water:concentrated sulfuric acid 60:40:0.2 followed by injection on an Aminex HPX-87 column with a mobile phase of 0.018N sulfuric acid. Ascorbic acid was detected at 260 nm while the other four acids were quantified at 210 nm unless fructose was present at a concentration of 6 mg/g or higher, in which case 220 or 230 nm was used. Greater than 90% recovery was observed for all acids with most recoveries near 100%. The method has been shown to be very reproducible with the CV% ranging from 1.3-12.3 while the majority were below 4%. Analyses of several potato varieties have shown a wide variation in acid content among varieties.     

Determination of ascorbic acid in vegetables and fruits by differential pulse polarography

A method for the determination of ascorbic acid in vegetables and fruits using differential pulse polarography has been developed. The extraction medium recommended is a mixture of oxalic acid (1%), trichloroacetic acid (2%) and sodium sulphate (1%), and simple filtration is used to remove the residue. An acetate buffer (2M) is recommended to keep the pH at 4.5. The polarograms were recorded using a modulation amplitude of 50mV, a scan rate of 2mVs^?1, and a drop time of 1 s. The precision of the procedure was found to be 1.4% at the 1 mg litre^?1 level of ascorbic acid. The calibration graph was linear in the range of 0–20 mg litre ^?1 of ascorbic acid with a slope of 0.48μA mg litre^?1. Most common anions and cations did not interfere, however, Fe³⁺ and EDTA interfered, and Br^? and I^? seriously interfered with the determination. The method was applied to determine the ascorbic acid content of a number of vegetables and fruits using the standard-addition calibration.