分光光度法测定柚子中的维生素C

柚子是一种含维生素C较高的水果,采用2,4-二硝基苯肼法对柚子中的维生素C含量进行测定.先进行波长扫描,确定维生素C的最大吸光度在510nm.然后绘制校准曲线,得到校准曲线方程y=0.0545x+0.053(r=0.9992),测定矮晚柚的平均维生素C含量为75.89mg/100g.并做了3个柚类品种的加标回收实验,回收率都在90％以上,说明此种方法准确率高,方法可行,可用于水果、蔬菜维生素C含量的测定.     

水果、蔬菜中维生素C含量的测定——紫外分光光度快速测定方法探讨

本文利用维生素C具有对紫外产生吸收和对碱不稳定的特性,建立了紫外分光光度快速测定水果、蔬菜维生素C含量的新方法.维生素C浓度在1.00-12.0μg/mL范围内与吸收值呈良好的线性关系;检出限为0.014μg/mL;加标回收率在97.9%-99.0%之间.该法操作简单,结果准确,应用于维生素C含量的测定,结果令人满意.     

气相色谱-质谱联用法测定维生素C泡腾片中的甜蜜素

采用气相色谱-质谱(GC-MS)选择离子监测法(SIM),建立了准确可靠、灵敏度高、快速简便的测定维生素C泡腾片中甜蜜素含量的新方法.样品中的甜蜜素衍生后用有机试剂提取,在选择离子模式下进行测定,以保留时间和特征离子比例进行定性,单离子定量.甜蜜素的线性范围为0.05-10mg/L,检出限为0.6mg/kg,回收率为90.5%-96.9%,相对标准偏差小于4.4%.方法分析所用时间短,结果准确可靠,选择性好,适用于维生素C泡腾片中甜蜜素含量的检验.     

间接原子吸收法测定维生素C的含量

利用银离子可被维生素C还原为银沉淀的原理,建立了原子吸收法间接测定维生素C含量的方法。实验中考察了温度、时间、Ag+用量对反应的影响,选取反应在室温下进行,反应时间为35min,氧化剂用量为1.0μg·mL-1 的Ag+溶液2.0mL。同时优化了测定银的最佳原子吸收条件。建立的方法易于操作,检出限小于1.0μg·mL-1,相对标准偏差为2.04％,线性范围宽,不受样品颜色干扰且其他共存物质干扰也较小,弥补了其他分析维生素C的方法的一些不足,样品测定结果和药典中的碘量法一致,该法的回收率为99.30％～106.06％,结果较为满意。绘制了两种标准曲线,其中绘制以银为标准的工作曲线更简便,而以维生素C为标准的工作曲线相比更准确。     

落葵中硝酸盐、维生素C及胡萝卜素含量的研究

对野生落葵不同生长发育阶段所含的硝酸盐、维生素C及胡萝卜素进行了测定和分析,并将野生落葵和人工栽培落葵所含的以上成分进行了比较.结果表明,落葵富含胡萝卜素,维生素C含量中等,野生落葵硝酸盐含量较低,人工栽培落葵硝酸盐含量比野生落葵高出近1倍,须经煮熟后方可安全食用.     

高效液相色谱法测定内蒙古土默特旗沙棘果中维生素C含量

采用Diamond C18反相柱,以0.01moL/L的磷酸氢二铵缓冲液为流动相,检测波长210nm,应用高效液相色谱外标法测定内蒙古土默特旗沙棘果粒中维生素C的含量.该方法简便、快速、重现性好,维生素C的平均回收率为99%.     

紫外分光光度法快速测定浓缩黑加仑果汁中维生素C含量

本文研究了一种用紫外分光光度法快速测定黑加仑浓缩果汁中维生素C含量的新方法。此法采用室温下Cu~(2 )催化样品中的维生素C做空白样品,在267纳米和pH值为6的条件下测定其吸光度。解决了维生素C分解速度快,影响测定结果的问题。实验结果表明,用紫外分光光度法测定浓缩黑加仑果汁中维生素C的含量,方法简单、快速、准确,且具有较好的准确度和精密度。     

HPLC测定潮州柑果肉中维生素C

利用HPLC测定了潮州柑果肉中维生素C的含量,以Agilent ZORBAX Eclipse XDB-C18为分析柱,柱温为25℃,进样量为10μL,甲醇-0.1%的草酸溶液（5∶95）为流动相,流速为1mL/min,检测波长为254nm进行分析检测,结果表明,维生素C的出峰时间为1.976min,采用外标法进行定量,在维生素C浓度为20—100μg/mL范围内与峰面积有良好的线性关系,相关系数达到0.9995,加标回收率为97.71%—102.16%之间,平均加标回收率为99.78%,RSD为1.68%（n=6）。此方法能快速,准确的测定潮州柑果肉中维生素C的含量,且重复性好。     

鬼针草中维生素K1的研究

样品经丙酮、石油醚提取,用失活磷酸盐处理过的氧化铝进行柱色谱净化处理,用极性不同的洗脱液将样品中VK1分离出来,用C18色谱柱对维生素K1进行定性分析,流动相为甲醇:正己烷(75:25),紫外检测波长为248nm.在流速为1.5mL/min的条件下,用HPLC分析不同生长阶段的鬼针草中维生素K1(VK1)的存在及含量的变化.维生素K1的保留时间为2.18士0.01min,RSD%为2.52%,回收率范围为94.97%-100.49%.鬼针草含有维生素K1,含量随生长阶段的不同有变化.     

维生素C对大鼠急性肺损伤时铁元素水平的干预作用

将ALI实验动物随机分为13组,其中6组为维生素C治疗组,ALI后均立即给予维生素C治疗,依照采集肺组织标本不同时间点分为：6h组、8h组、12h组、16h组和24h组（均12h追加一次维生素C）、36h组;用生理盐水替换维生素C为6组阳性对照组;阴性对照1组。用原子分光光度计检测肺组织铁含量。阴性对照组铁含量为25.1828μg·g-1;损伤期大鼠体内铁元素均比正常值低,治疗组和对照组组内均有明显差异（P〈0.05）;各时间点治疗组与阳性照相比均呈有意义改变（P〈0.01）;各时间点的治疗组、阳性对照组与阴性对照组相比均呈有意义改变（P〈0.05或P〈0.01）。ALI时铁含量降低;用VC后铁有一定程度升高,说明VC对ALI时铁的水平有一定调节作用。     

Effects of natural antioxidants and high-energy fabrication methods on physical properties and oxidative stability of flaxseed oil-in-water nanoemulsions

The effects of high-energy fabrication methods, namely high-pressure homogenization (HPH) and ultrasonication (US), on physicochemical properties of flaxseed oil-in-water nanoemulsions (FNEs) containing clove essential oil (CEO) and/or pomegranate peel extract (PPE) were studied during storage at 4 and 25 °C. Nanoemulsions with relatively similar average droplet size were prepared by HPH and/or US. An increase in droplet size was observed over time. Lower storage temperature and fabrication by US increased Ostwald ripening rate. Higher storage temperature and fabrication by US decreased the centrifugal stability of nanoemulsions. CEO revealed better antioxidant properties than PPE. The oxidative stability was evaluated by determining secondary oxidation products, and fatty acids profile. The absence of antioxidant, fabrication by US, and higher storage temperature decreased the oxidative stability of nanoemulsions. The results of this study might be helpful in controlling the oxidation of FNEs during long-term storage and in designing functional foods and beverages.     

Effects of different levels of vitamin C on UV radiation-induced DNA damage

The Raman spectra of DNA in different levels of vitamin C with 10- and 30-min ultraviolet (UV) radiations were reported. The intensity of UV radiation was 18.68 W/m2. The experimental results proved that vitamin C could alone prevent UV radiation from damaging DNA, but the effects depended on the concentration of vitamin C. When the concentration of vitamin C was about 0.08-0.4 mmol/L, vitamin C decreased UV radiation-induced DNA's damage. When the concentration of vitamin C exceeded 0.4 mmol/L, vitamin C accelerated DNA's damage instead. Maybe the reason is that when DNA in aqueous solution is radiated by UV, free radicals come into being, and vitamin C can scavenge free radicals, so vitamin C in lower concentration can protect DNA. The quantity of free radicals is finite, when vitamin C is superfluous, free radicals have been scavenged absolutely and vitamin C is residual. Vitamin C is a strong reductant. When the mixture of DNA and residual vitamin C is radiated by UV, vitamin C reacts with DNA. The more residual vitamin C and the longer time of UV radiation, the more DNA is damaged.     

Influence of sequential exogenous pretreatment and contact ultrasound-assisted air drying on the metabolic pathway of glucoraphanin in broccoli florets

In this investigation, the combinations of exogenous pretreatment (melatonin or vitamin C) and contact ultrasound-assisted air drying were utilized to dry broccoli florets. To understand the influences of the studied dehydration methods on the conversion of glucoraphanin to bioactive sulforaphane in broccoli, various components (like glucoraphanin, sulforaphane, myrosinase, etc.) and factors (temperature and moisture) involved in the metabolism pathway were analyzed. The results showed that compared with direct air drying, the sequential exogenous pretreatment and contact ultrasound drying shortened the drying time by 19.0–22.7%. Meanwhile, contact sonication could promote the degradation of glucoraphanin. Both melatonin pretreatment and vitamin C pretreatment showed protective effects on the sulforaphane content and myrosinase activity during the subsequent drying process. At the end of drying, the sulforaphane content in samples dehydrated by the sequential melatonin (or vitamin C) pretreatment and ultrasound-intensified drying was 14.4% (or 26.5%) higher than only air-dried samples. The correlation analysis revealed that the exogenous pretreatment or ultrasound could affect the enzymatic degradation of glucoraphanin and the generation of sulforaphane through weakening the connections of sulforaphane-myrosinase, sulforaphane-VC, and VC-myrosinase. Overall, the reported results can enrich the biochemistry knowledge about the transformation of glucoraphanin to sulforaphane in cruciferous vegetables during drying, and the combined VC/melatonin pretreatment and ultrasound drying is conducive to protect bioactive sulforaphane in dehydrated broccoli.     

Experimental Investigations on Latent Heat Storage Unit using Paraffin Wax as Phase Change Material

Thermal performance of a latent heat storage unit is evaluated experimentally. The latent heat thermal energy storage system analyzed in this work is a shell-and-tube type of heat exchanger using paraffin wax (melting point between 58°C and 60°C) as the phase change material. The temperature distribution in the phase change material is measured with time. The influence of mass flow rate and inlet temperature of the heat transfer fluid on heat fraction is examined for both the melting and solidification processes. The mass flow rate of heat transfer fluid (water) is varied in the range of 0.0167 kg/s to 0.0833 kg/s (1 kg/min to 5 kg/min), and the fluid inlet temperature is varied between 75°C and 85°C. The experimental results indicate that the total melting time of the phase change material increases as the mass flow rate and inlet temperature of heat transfer fluid decrease. The fluid inlet temperature influences the heat fraction considerably as compared to the mass flow rate of heat transfer fluid during the melting process of the phase change material.     

非稳态人口温度下相变材料蓄热性能研究

太阳能辐射强度随时间发生变化,造成蓄热单元入口处传热流体温度呈现非稳态变化。为了分析非稳态的入口温度对相变材料蓄热特性的影响,假设传热流体入口温度1 h内随时间呈线性变化,并且1 h内的平均温度恒定在60℃。讨论了入口温度随时间线性增加及线性降低两种变化形式,对相变材料的熔化速率、熔化分数、蓄热量、固液界面位置等参数的影响。结果表明,当1 h内平均入口温度不变,而初始入口温度在30～90℃的范围内变化时,随初始入口温度增加,尽管熔化速率增加,熔化时间从42.75 min减小到20.58 min;但1 h内的总蓄热量却从72.6 kW减小到45.3 kW。     

低温液体甲烷无损储存规律研究

液体甲烷是易燃易爆的低温液体,在封闭容器中压力的上升是它安全储存所面临的关键问题。文中列出了无损储存计算用模型,并以40m~3液化天然气储罐为研究对象计算了甲烷的无损储存规律,得到了0．1518MPa和标准大气压下环境温度分别为30℃,50℃和80℃下的无损储存规律,以及液体甲烷安全无损储存天数。     

黄芩素稳定性研究

用紫外光谱研究了光、温度、pH、Na2SO3、FeSO4及抗坏血酸对黄芩素稳定性的影响.在室温条件下,黄芩素溶液的吸光度值在6h内强度有明显的下降;当温度升高或在避光条件下,偏酸性黄芩素溶液的吸光度值在6h内强度不变,而碱性条件下依然有下降趋势;但黄芩素溶液加入抗坏血酸或Na2SO3后,吸光度值可稳定不变.本文研究提示:黄芩素对光和pH稳定性差;抗坏血酸和Na2SO3具有提高黄芩素溶液稳定性的作用.     

Study on the properties of a novel shape-stable epoxy resin sealed expanded graphite/paraffin composite PCM and its application in buildings

In this study, a novel phase change material (PCM) of epoxy resin sealed expanded graphite/paraffin composite was developed as an independent attachment for building applications. A relatively high thermal energy storage density and a high thermal conductivity (2.141?W/(m·K)) were obtained in the composite PCM. The mass fraction of paraffin in the composite PCM could reach 94% without leakage of liquid paraffin when being heated at 50°C for more than 3 h, and the thermal cycle stability was good. Moreover, the thermal storage and release properties of this composite PCM with different thicknesses were studied by numerical simulation. The results showed that the thermal storage and release time are proportional to the thickness of the composite PCM, and there was almost no temperature gradient during the thermal storage and release process, which indicated that the thermal conductivity of this kind of composite PCM was high enough for building applications.     

多孔介质高温蓄热的热性能分析

高温蓄热是太阳能热发电、高温热利用中的重要组成部分。本文对基于多孔介质和熔融盐流体的高温蓄热过程进行了计算分析,对蓄热时间、流体进口温度、进口速度对斜温层温度分布的影响进行了分析。结果表明进口温度对斜温层厚度的影响较小,进口速度的增加会导致斜温层厚度的增加。同时对流体和多孔介质的温度差进行了分析,得到了应用于局部热平衡和非热平衡的雷诺数判据。     

分离式螺旋热管管外融冰放冷特性分析

在提出分离式螺旋热管蓄冷空调系统的基础上,建立了螺旋热管管外融冰放冷过程的理论模型;分析了蓄冷桶内融冰量及放冷量随时间的变化关系。研究结果表明,在蓄冷桶进口水温一定的情况下,外融冰的循环水流量越大,其融冰放冷过程就越快;在外融冰循环水流量一定的情况下,放冷过程随蓄冷桶进口水温的升高而加快。