差示扫描量热法测定谷氨酸纯度

目的:研究差示扫描量热法(DSC)测定谷氨酸纯度的可行性。方法:以铟和锌校正仪器,考察样品粒径、试验气氛、升温速率和样品质量等因素对DSC测定结果的影响,并在最佳条件下测定谷氨酸纯度;比较DSC法和中国药典2015版滴定法的测定结果。结果:当称样量为3 mg,升温速率为40℃/min时,DSC测得谷氨酸纯度为99.74%,精密度为0.07%。滴定法测得谷氨酸纯度为99.72%。结论:DSC法准确度高、操作简便,可用于谷氨酸的纯度测定。     

差示扫描量热法测定番茄红素的纯度

差示扫描量热法（differential scanning calorimetry,简称DSC）是法定的药物纯度测试手段之一,可以快速、方便、准确地测定高纯度化工、医药产品。本文应用此项技术对纯化出的番茄红素晶体进行了纯度测定。并将测定结果与HPLC法和分光光度法做了比较,结果表明DSC法具有较高的准确度。     

应用差示扫描量热法测定胶原蛋白热滞活性

采用酶法从猪皮中制备胶原蛋白,并对其纯度进行了鉴定。在此基础上,利用差示扫描量热法对制备的胶原蛋白进行热滞活性的测定,考察了保留温度(-0.18、-0.088、0.013、0.13、0.23℃)、胶原蛋白浓度(0.1、0.5、1、2.5、5、10、15、20、50 mg/ml)及升降温速率(0.5、1、2.5、5、10℃/min)对热滞活性的影响。结果表明:所制备猪皮胶原蛋白为典型的Ⅰ型胶原蛋白,纯度较高,其分子量约为330 kD;当胶原蛋白浓度为20 mg/mL,保留温度为0.12℃,升降温速率为10℃/min时胶原蛋白热滞活性最高,为0.61℃。测定胶原蛋白热滞活性时保留温度的选取至关重要,而升降温速率对热滞活性无显著影响。     

用差示扫描量热法测定聚酯切片的熔融热,结晶度和熔点

本实验是根据热量差示扫描的原理建立了一种用来测定成纤高聚物对苯二甲酸乙二醇酯切片的熔融热（△Ｈ）、结晶度（Ｘｃ）和熔点（Ｔｍ）的快速而方便的方法。经反复试验证明其可靠性、重复性较好。     

用差示扫描量热法测定高性能材料的比热

用差示扫描量热法测定高性能材料,如聚合物、玻璃、陶瓷的比热,操作简便、准确,为高性能材料在航空、军工及民用领域中耐热性和保温性的合理应用提供了科学依据。     

差示扫描量热法测定钛合金的相变温度

采用差示扫描量热法测定了四种不同钛合金TC27、TA15、TC4、TB6的β相变温度。四种不同钛合金的测试曲线体现出类似的规律,TG线一直保持不变说明升温过程中没有发生氧化反应,在500℃前由于释放残余应力呈现放热现象,而在后向吸热方向偏移,这个过程发生了相变。通过对DSC曲线求一阶导数,其峰值即为β相变温度。通过对比四种不同钛合金差示扫描量热法和金相法的测试结果,两者相当接近,因此差示扫描量热法也是一种有效的测试钛合金β相变温度的方法。     

差示扫描量热法及其发展趋势

差示扫描量热仪可以测定多种热力学和动力学参数,如比热容、反应热、转变热、相图、反应速率、结晶速率、高聚物结晶度及样品纯度等。该仪器具有使用温度范围宽(-175~500℃)、分辨率高和试样用量少的优点。本文论述了差示扫描量热仪的特点、目前我国与差示扫描量热法相关的标准以及方法的未来发展趋势。未来在聚合物的结晶性研究和相变材料的热焓变化测量方面,差示扫描量热法(differential scanning calorimetry,DSC)会有更广泛的应用。在物质的鉴别方面,熔点的精确测量也会起到很重要的辅助作用。未来期待温度范围更宽的DSC仪器的出现,同时,红外-气相-差式扫描联用技术及热重-差式扫描量热联用仪器的更进一步发展会使得联用技术在未来得到更多的重视。     

用差示扫描量热法测定调温针织物的热性能

介绍了差示扫描量热法（DSC）的原理、用途及用法,测定了罗纹空气层织物的相变温度和相变焓,得到了其DSC曲线图。结果表明该织物具有良好的温度调节功能。     

用差示扫描量热法研究维生素C的热稳定性及热动力学

用差示扫描量热法(DSC)测定了VC的熔点、热分解点,研究了热分解动力学.结果表明:VC熔点为193.457℃.融化热焓为258.73 J/g;VC分解的起始温度为221.620℃,分解热焓为-58.768 J/g;计算得到其热分解动力学参数Ea=1710.067±239.309 kJ/mol,并据此推算出在等温条件下反映热稳定性的分解率、时间、温度之间的关系.     

差示扫描量热技术在淀粉研究中的应用

差示扫描量热技术(ＤＳＣ)是一种使用最为普遍的热分析技术,主要用来直接测量程序控制温度下物质的物理性质与温度的关系———热分析曲线,特别适合于研究伴随有焓变或比热容变化的现象。淀粉作为大多数高等植物的主要储藏物,是由直链淀粉和支链淀粉构成,它的许多性质如糊化、老化、玻璃化相变等都与热有关,都伴随着热焓或比热容的变化。故而许多研究人员都采用ＤＳＣ来检测淀粉在热相变过程中的热流变化,为深入研究淀粉颗粒在热相变过程中的结构变化提供有价值的参考资料[1]。1　淀粉的糊化性质淀粉糊化是食品加工过程中的一种重要现象,如…     

掺假藕粉中木薯淀粉和甘薯淀粉的鉴别-差示扫描量热法

为了对掺入藕粉中的其他淀粉种类进行鉴别,本研究通过差示扫描量热仪对藕粉等常见几种淀粉的糊化过程进行考察发现,藕粉与其他淀粉在糊化吸热峰上有着明显的差别。根据藕粉与木薯淀粉和甘薯淀粉等在糊化吸热峰上的差异,以糊化吸热峰作为特征指标,对掺假藕粉中掺入的木薯淀粉和甘薯淀粉进行定性或定量鉴别实验。同理,此方法也可用于检验与藕粉在糊化吸热峰上有明显差异的用于藕粉掺假的其他淀粉种类,如马铃薯淀粉,玉米淀粉等。此方法将弥补前期发表的基于淀粉颗粒超微形貌特征的可食用淀粉种类扫描电镜鉴别方法的不足。     

高效液相色谱法分析原料乳和奶粉中三聚氰胺

建立了二极管阵列检测器-高效液相色谱测定原料乳及奶粉中三聚氰胺的方法。奶粉样品经三氯乙酸超声提取,乙酸铅沉淀蛋白,三氯甲烷除去脂肪和非极性杂质,PROELUTPXCSPE阳离子交换固相萃取小柱进一步除去样品基质干扰,氨化甲醇洗脱。实验对色谱分离条件进行了优化,三聚氰胺的质量浓度在1.0～100.0μg/mL范围内与色谱峰面积呈良好的线性关系,回归方程为y=89.763x-113.72,相关系数为R2=0.9988。加标回收率为90.5%～105.0%,相对标准偏差(RSD)小于4.0%。该方法简单、快速,结果准确可靠。     

比色法检测奶粉中的糊精

研究了奶粉中糊精质量浓度的检测方法。样品经过乙醇溶液处理，利用苯酚-硫酸法检测提取液中糊精的质量浓度。结果表明，该方法用于检测提取液中糊精质量浓度在5～100mg／L范围内具有良好的重现性和回收率，同时方法操作简单，结果准确。     

饲料含水率对淀粉糊化及蛋白变性温度的影响

在过量水的条件下,用DSC测定了小麦淀粉、小麦面粉、大豆粕、鱼粉,以及用这些组分配合而成的对虾饲料等试样加热时的吸热曲线,并以此辩认了这些原料中所含淀粉及蛋白质的吸热峰值。在不同的水分含量条件下,测定了这些峰值的变化,其结果被引用于解释常用制粒条件(水分17%,温度93℃)下所得颗粒饲料的糊化度仅为35%左右的原因。     

乳粉中核苷酸的检测方法

建立了用超声波进行提取,采用高效液相色谱仪、紫外检测器方法,检测出乳粉中CMP,UMP,AMP,GMP4种核苷酸的含量。色谱柱为C—18柱,在室温条件下采用磷酸盐缓;中溶液作为流动相,测得的4种核苷酸标准曲线的相关系数均大于0．9995,回收率为在95．7％～106．8％之间,该方法的变异系数为1．61％,满足使用要求。     

Activity and thermal stability of antioxidants by differential scanning calorimetry and electron spin resonance spectroscopy

Heat flux differential scanning calorimetry (DSC) and electron spin resonance spectroscopy (ESR) were used to assess the activity and the thermal stability of antioxidants in four vegetable oils. Sunflower oil (SO) and high oleic sunflower oil (HOSO), both rich in diunsaturated fatty acids (FA), low trans oil (LT) and partially hydrogenated palm oil (PHPO), both containing monounsaturated FA, were analyzed by isothermal heat flux DSC, with or without 300 mg/kg of antioxidant: ascorbyl palmitate (AP), α-tocopherol (αT), δ-tocopherol (δT) and propyl gallate (PG). DSC experiments showed that δT is the most effective antioxidant for SO and PG for the less unsaturated oils. SO and PHPO were also analyzed by ESR at 120 and 145 °C, respectively. ESR results confirm the strongest antioxidant activity of δT and PG for SO and PHPO, respectively. Therefore, the present study demonstrates that DSC and ESR are valuable technologies to study activity and stability of antioxidants at high temperature. Moreover, experiments performed in the presence of the spin-trap N-tert-butyl-α-phenylnitrone (PBN), suggest that δT delay lipid oxidation through a different reaction mechanism when compared to αT. A different mechanism between tocopherols isomers in delaying lipid oxidation has been hypotized.     

高效液相色谱法快速测定乳粉中叶黄素的质量分数

建立一种测定配方奶粉中叶黄素质量分数的高效液相色谱方法。采用Diamonsil C18色谱柱(5μm,250 mm×4.6 mm),流动相为甲醇-水(97∶3),流速1.0 mL/min,检测波长445 nm,采用空白基质加标实验绘制标准曲线,该方法在0.5～100 mg/L的质量浓度范围内线性关系良好(R=0.9987),加标水平为0.50,1.00,5.00μg/g时,回收率分别介于96.8%～98.4%之间,相对标准偏差介于4.27%～6.73%之间,该方法检测限低于0.10μg/g。该方法操作简便,灵敏度高、准确度高、重现性好,适合于配方奶粉中叶黄素的测定。     

Storage stability of coconut milk powder

Spray-dried coconut milk powder prepared with additions of skim milk and dextrin was stored in packages for 6 months at room temperature (30°C and 80% RH). The packaging materials used were aluminum laminate (vacuum and air packed) and polypropylene. The sorption isotherm of the powder showed that the monolayer of water molecules was complete when the relative humidity was 27% which corresponded to a moisture content of 5%. Measurements of water activity, moisture content, peroxide value and solubility index indicated that lipid oxidation is the limiting factor in the stability of the powder. Its maximum shelf-life was 4 months when air or vacuum packaged in aluminum laminates and 1 1/2 months in polypropylene.     

Comparative study on the characteristics and oxidation stability of commercial milk powder during storage

The quality of milk powder can decrease during storage. In this study, the characteristics of 12 kinds of commercial milk powder from China were investigated. Changes in various indicators were tracked to comprehensively estimate the oxidation stability of different commercial milk powders. The components of the commercial milk powder were different. The percentages of milk fat, protein, and carbohydrates ranged from 9.8 to 28.5 g/100 g, 15.0 to 24.0 g/100 g, and 32.0 to 67.5 g/100 g, respectively. The water activities ranged from 0.2394 to 0.5286. The diameters of the milk fat globules in different commercial milk powder ranged from 13.99 to 41.09 nm. At the same time, the peroxide value of the control sample was low (≤0.14 mEq/kg). After 3 mo of storage, the peroxide values of some of the commercial milk powder increased significantly. The changes in the thiobarbituric acid values during storage did not follow a common trend. The contents of free fat in the different control samples were 0.21 to 1.67 g/100 g, and these values did not increase during storage. After 3 mo of storage, the hydroxymethyl furfural values and b color values of the different commercial milk powder reached their highest levels. The concentrations of typical oxidized flavor compounds in different commercial milk powder increased greatly with prolonged storage time. The level of hexanal was the highest, and the contents in all the samples ranged from 28.56 to 4,071.28 μg/kg after 6 mo of storage and from 5.91 to 6,281.37 μg/kg after 12 mo of storage. Free radicals were found in some of the stored milk powder, and these were shown as single peaks or multiple peaks. The ratios of the peak areas and masses reached 12.42 × 10⁶ to 14.26 × 10⁸. However, the presence of free radicals in the commercial milk powder was not consistent. The water activities and diameters of the fat globules in the commercial milk powder were highly correlated with their oxidation stabilities during storage.     

Impact of source and level of calcium fortification on the heat stability of reconstituted skim milk powder

Calcium enrichment of food and dairy products has gained interest with the increased awareness about the importance of higher calcium intake. Calcium plays many important roles in the human body. Dairy products are an excellent source of dietary calcium, which can be further fortified with calcium salts to achieve higher calcium intake per serving. However, the addition of calcium salts can destabilize food systems unless conditions are carefully controlled. The effect of calcium fortification on the heat stability of reconstituted skim milk was evaluated, using reconstituted skim milks with 2 protein levels: 1.75 and 3.5% (wt/wt) prepared using low and high heat powders. Calcium carbonate, phosphate, lactate, and citrate were used for fortification at 0.15, 0.18, and 0.24% (wt/wt). Each sample was analyzed for solubility, heat stability, and pH. The addition of phosphate and lactate salts lowered the pH of milk, citrate did not have any major effect, and carbonate for the 1.75% protein samples increased the pH. In general, changes in solubility and heat stability were associated with changes in pH. Calcium addition decreased the solubility and heat stability. However, interestingly, the presence of carbonate salt greatly increased the heat stability for 1.75% protein samples. This is due to the neutralizing effect of calcium carbonate when it goes into solution. The results suggested that the heat stability of milk can be affected by the type of calcium salt used. This may be applied to the development of milk-based calcium enriched beverages.