食品中铝含量国标测定法的改进

目的通过优化微波消解试剂和微波消解条件,解决国标推荐方法对生物样品消解不彻底的问题,使其能够准确测定食品中铝含量。方法采用国标推荐的微波消解方法和优化后的微波消解方法迚行样品的前处理,消解河南小麦、芹菜、猪肝、大虾和粉丝粉条等标准参考物质,采用电感耦合等离子体发射光谱法测定铝含量。结果采用国标推荐的微波消解前处理方法,试样测定结果进低于参考值。采用优化的微波消解程序(硝酸-氢氟酸体系),标准参考物质的铝含量测定结果较为接近标准参考值。铝含量在0～10.0μg/mL范围内线性关系良好(r=0.9998),标准参考物质中铝含量的回收率为71.9%～110%,相对标准偏差为1.3%～6.3%。结论硝酸-氢氟酸体系与优化的微波消解程序方法能将样品消解更为彻底,使检测结果更加准确,该法可用于食品中铝含量的测定。     

微波消解制样技术用于生物样品微量分析的研究

叙述了微波消解制样技术直接用于新鲜生物样品消解 -AAS测定 ,取得良好分析结果。HNO3+H2 O2 是最佳消解体系。在密封容器内高温高压消解进一步提高工作效率。与其它无机样品消解特征不同 ,生物样品消解时反应更剧烈且放热 ,释放气体 ,需针对性地设置专门的消解程序。     

重金属元素分析消解技术在镉、砷检测中的应用比较

选择高效、准确的样品消解方法是测定重金属元素含量的关键步骤,直接影响检测结果的准确性和可再现性。概述干灰化法、湿法消解、高压密闭消解及微波消解方法消解效果的影响因素,及在不同样品中镉、砷检测消解时的应用比较。结果表明:灰化温度、时间、消解试剂、消解容器、样品组成等均会影响消解效果;4种消解方法均可应用于镉的检测,其中高压密闭和微波消解效果较好;消解砷的检测主要是微波消解和湿法消解;海洋生物样品的镉检测宜使用敞开体系消解;两种消解方法的联合使用效果可能优于单一消解方法。     

3种不同方法测定食品中铝残留量比较

目的:观察并分析干灰化、湿法消解、微波消解3种方法对食品中铝残留量的测定情况。方法:干灰化法将样品完全灰化,湿法消解采用电热板加热样品,微波消解法将样品于微波消解炉中消解,消解后分别取1 m L样品消解液测定吸光度并计算铝残留量。分析3种方法测定食品中铝残留量的精确度和准确度。结果:干灰化法的相对标准偏差为8.32%~8.91%,湿法消解的相对标准偏差为6.13%~6.90%,微波消解的相对标准偏差为5.64%~7.62%;干灰化法均值为0.184%,湿法消解均值为0.187%,微波消解均值为0.201%。结论 :干灰化、湿法消解、微波消解在食品铝残留量测定当中具有比较良好的精确度和准确度,每种方法有各自优点,根据具体测定情况选择合适的方法。     

微波消解在测定食品中微量元素的应用

总结了食品中微量元素测定时常用的样品处理方法,并重点对微波消解食品时样品的取样量、样品预处理的方法、所用溶剂的种类和数量以及加热时间和压力的选择作了阐述,从而为微波消解食品样品提供了操作依据。     

微波消解光度法测定奶粉中的磷

样品预处理在分析测定过程中具有十分重要的作用。本研究探讨了一种新兴的样品预处理方法——微波消解法在奶粉分析中的应用。考察了微波消解时溶剂的用量、消解液体积、消解时间、功率和压力对消解效果的影响,选择了微波消解的最佳工作参数。与传统方法相比,该方法具有省时、省酸,操作简单,减少沾污,改善工作环境等优点,是一种有效的实用方法。     

微波消解技术在氨基酸分析中的应用研究

目的:建立微波消解法应用于氨基酸分析的水解蛋白方法。方法:以米粉、面粉、燕麦粉、油条粉作为研究对象,分别比较了常规酸水解和微波消解法对4种样品前处理后氨基酸测定结果的影响。实验结果表明,微波消解水解蛋白的最佳条件是150℃,15 min;该微波消解法与常规酸水解法无显著性差异。4种样品采用微波消解法水解蛋白质,氨基酸测定结果RSD值均小于5%。结论:微波消解法的稳定性好、用时短,可替代现有的常规酸水解方法,便于快速检测批量样品。     

2种消解方法-原子吸收分光光度法检测大米粉中铜、锌、镉含量

采用微波消解法和湿法消解2种消解方法对大米粉样品进行前处理,利用原子吸收光谱法测定各组样品中Cu、Zn和Cd 3种元素的含量,探讨简单、快捷、准确地测定大米粉中元素的前处理方法。结果表明:微波消解和湿法消解均符合分析要求,但从准确度、精密度、耗时、试剂消耗等方面比较,微波消解优于湿法消解。     

微波消解—硝酸银滴定法测定肉制品中食盐

建立了用微波消解技术进行样品前处理,硝酸银标准溶液滴定法测定高温肉制品中氯化钠含量的方法。方法:在样品中加入过量的硝酸银固定住样品中的氯离子,加入硝酸用微波消解仪消解。消解液在转移至容量瓶中后加入与硝酸银等物质的量的氯化钠溶液,混匀后定容。然后以铬酸钾为指示液,用硝酸银标准滴定溶液滴定,根据硝酸银消耗量计算食盐含量。结果:微波消解技术可将样品快速消解完全,该法与国家标准湿化学方法相比无显著性差异。结论:该法操作简单,试剂用量少、重现性好,用微波消解技术大大缩短了样品前处理时间,适于肉制品中食盐含量的测定。     

不同前处理方法对火焰原子吸收光谱法测定饲料中铜含量的影响

目的通过比较不同的样品前处理方法,建立一种火焰原子吸收光谱法测定饲料中铜的含量。方法以饲料样品为原料,微波消解、湿法消解和干法灰化前处理方法分别对样品前处理后,采用火焰原子吸收光谱法测定饲料样品中铜的含量。结果 3种前处理方法测得的饲料中铜含量的加标回收率为92.0%~108%,在测定质控样品时,微波消解和湿法消解测定结果的相对标准偏差为1.3%~2.3%,符合要求;但干法灰化测定结果的相对标准偏差最大值为11.0%,超出标准范围。结论微波消解和湿法消解均能得到准确的检测结果,但湿法消解存在试剂消耗多、消解时间长等问题,而微波消解相对快速、准确、精密度高,更适合作为日常实验时饲料中铜的测定分析方法。     

微波消解-原子吸收法测定海鸭蛋中微量元素的含量

用微波消解的方法处理样品，采用空气-乙炔火焰原子吸收法测定海鸭蛋中6种微量元素的含量。结果各元素的回收率在99.2％～101．5％之间，RSD〈3．6％。建立了优化的仪器测试条件，方法简便、准确，消化完全，干扰小，是高蛋白食品微量元素较为理想的测定方法。     

原子荧光法测定富硒米中的硒含量

采用微波密闭H2O2-HNO3消解样品中的硒,以氢化物发生原子荧光光谱法测定富硒米中微量硒元素的含量.方法的检出限为0.0558ng/mL,线性范围为0～300ng/mL,回收率为86.7%～102.0%.方法适用于富硒米中硒含量的测定,结果令人满意.     

自动凯氏定氮仪测定烟草及其制品中的总氮

为了替代烟草及其制品中总氮含量测定过程中使用的有毒消解剂氧化汞,考察了消解剂用量对烟草及其制品中总氮含量测定结果的影响,并采用自动水蒸气蒸馏滴定仪测定样品中的总氮含量.结果表明,用硫酸铜替代氧化汞,当用0.4 g硫酸铜、6.0 g硫酸钾和12 mL浓硫酸消解烟草样品时,总氮含量测试变异系数小于2%,回收率在97.90%～103.85%之问.该法的测试结果与YC/T161-2002规定的方法无显著性差异.该法适合烟草及其制品中总氮含量的快速分析.     

A theoretical analysis on microwave heating of food slabs attached with ceramic plates: Role of distributed microwave incidence

A detailed analysis has been carried out to study efficient heating processes due to microwaves for one dimensional food samples placed on ceramic plates with various distributions of microwave incidence. The enhanced heating effects due to microwave propagation within samples have been illustrated via average power within a sample vs sample thickness diagram. The maxima in power, also termed as ‘resonances’ is observed for specific sample thicknesses. The spatial temperature distributions illustrate the presence of local thermal heating effects for various cases. Either one side incidence or both sides incidence with suitable distribution of microwave incidence may be preferred for various food materials attached with ceramic plates. One side incidence may cause overall larger heating rates for beef samples and the heating rates for oil samples would remain invariant irrespective of various distributions of microwave incidence. It is observed that beef samples would exhibit greater thermal runaway specially with SiC plate in presence of both sides distributed microwave incidence whereas oil sample would exhibit smaller thermal runaway effects with both sides equi-distributed microwave incidence irrespective of any ceramic plates. Current analysis has been illustrated for low and high dielectric food materials (beef and oil) and based on our analysis, a generalized heating strategy for any materials due to uniform plane waves may be derived.     

黄花菜组合干燥法工艺条件研究

本论文主要研究了组合干燥法在黄花菜干制过程中的应用.首先采用远红外杀青,然后再进行微波干燥.通过单因素试验和正交试验确定了最佳的组合干燥条件为:远红外杀青温度100℃,远红外杀青时间60min,远红外杀青功率400W,微波干燥功率200W,微波干燥时间25min,进样量0.3kg/m2.采用上述工艺参数干燥后的黄花菜感官质量好,蛋白质保留率为87.3%.     

Efficient microwave processing of oil–water emulsion cylinders with lateral and radial irradiations

A detailed theoretical analysis has been carried out to assess the role of lateral and radial irradiations on the microwave heating of 2D cylinders for both o/w and w/o emulsion samples. Lateral irradiation represents the sample incident at one direction with the source at infinity whereas radial irradiation represents the situation where the sample is incident with microwave radiations from the coaxial cylindrical cavity at infinity. For both of lateral and radial irradiations, the effective microwave incidence from the source is assumed to be identical. A preliminary analysis on the microwave heating of samples has been carried out via average power within a sample vs. sample diameter for emulsions with various values (volume fraction of the disperse phase). The samples with smaller diameter are found to have larger average power with radial irradiation for both o/w and w/o emulsion samples. The hot spot formation within a sample is found to be a strong function of lateral/radial irradiation for various emulsion compositions. The radial irradiation or conventional microwave heating with turntable rotation in ovens is not favorable especially for large w/o samples as the hot spot occurs at the center resulting in larger thermal gradient. The present work provides guideline on the heating policy based on either lateral or radial irradiation depending on the sample size and emulsion dielectric properties.     

TRIAL METHOD FOR MEASURING THE EFFECT OF LIPIDS ON THE RHEOLOGICAL PROPERTIES OF STARCH PASTE DURING THE GELATION PROCESS

An attempt was made to measure the effect of lipid components on the viscosity and thixotropy of wheat starch paste in a short aging time after gelatinization. Viscometry was used to follow periodically the changes in apparent viscosity (at 76.8 s⁻¹) of the mixed paste of wheat starch and one of a series of lipids in a cone-plate viscometer for 210 min after gelatinization, i.e. a procedure of eight cycles of measurement with a sample. Each cycle of the measurement consisted of viscometry for 3 min and a rest period for 27 min at 30°C. The apparent viscosity of all the samples decreased greatly during the 3 min measurement due to thixotropic breakdown of the macroscopic structure in the samples. The results suggest that the presence of a small amount of free fatty acid and monoglyceride may play a role in reducing starch paste gelation.     

Recovery of fecal chromium used as a digestibility marker in cattle

Chromium content of fecal samples that were mixed with Cr-mordanted rumen contents at 5 or 10 g/200 g feces in Experiment 1 and at 5 or 10 g/300 and 200 g feces in Experiment 2 was determined by atomic absorption spectroscopy. Recovery of Cr was estimated after digesting fecal samples, which were frozen fresh and later thawed or dried in either a forced draft oven at 60 degrees C or in a microwave oven in Experiment 1. Experiment 2 evaluated the efficacy of each of three methods of digestion in recovery of Cr from fecal samples. Recoveries of Cr from feces were calculated relative to the Cr content of the Cr-mordanted rumen contents, which were determined by atomic absorption spectroscopy of samples digested with concentrated nitric acid in the presence or absence of the wetting agent Tween 80. Recovery of Cr from fecal samples frozen fresh and later thawed was greater than that from either forced draft oven or from microwave oven-dried samples, especially when the concentrated nitric acid digestion was used. Neither the double ashing procedure nor the digestion with the weaker nitric acid did not improve Cr recoveries from the samples.