Crystallization behavior of milk fat obtained from linseed-fed cows

Milk with an increased content of unsaturated fatty acids was obtained by incorporating 60% of extruded linseed into the concentrate of cows. Two groups of Holstein cows (3 animals/group) were fed a concentrate (control or linseed enriched) together with the same roughage diet (ad libitum). After an adaptation period of 3 wk, evening and morning milk samples were collected every 7 d for 3 wk. Milk was decreamed and anhydrous milk fat (AMF) was isolated from the fat fraction by using the Bureau of Dairy Industries method. The objective of this study was to investigate if the crystallization mechanism of milk fat changed when the content of unsaturated fatty acids was increased. Therefore, the crystallization behavior of a milk fat enriched with unsaturated fatty acids was compared with that of a control milk fat. Nonisothermal crystallization was investigated with differential scanning calorimetry, and 1-step and 2-step isothermal crystallization behaviors were investigated using pulsed nuclear magnetic resonance, differential scanning calorimetry, and x-ray diffraction. A higher content of unsaturated fatty acids in AMF resulted in an increased proportion of low melting triglycerides. These triglycerides lowered the solid fat content profile, particularly at refrigerator temperatures. Furthermore, they induced some changes in the crystallization and melting behaviors of milk fat compared with a control AMF, although no fundamental changes in the crystallization mechanism could be revealed. Even though a lower melting point could be observed for milk fat with a higher content of unsaturated fatty acids, a similar degree of supercooling was needed to initiate crystallization, resulting in a shift in onset temperature of crystallization toward lower temperatures. In addition, slower crystallization kinetics were measured, such as a lower nucleation rate and longer induction times, although crystallization occurred in a similar polymorphic crystal lattice. During melting, a shift in offset temperature toward lower temperatures could be observed for the 3 melting fractions of AMF in addition to a higher proportion of low melting triglycerides. These results demonstrate that a higher content of unsaturated fatty acids has some effect on the crystallization behavior of milk fat. This knowledge could be used to produce dairy products of similar or superior quality compared with conventional products by intervening in the production process of dairy products.     

现代物理化学方法在油脂质量控制中的应用

介绍了现代物理化学方法(差示扫描量热法、电子显微镜、核磁共振法、X-射线衍射法)的原理及其在油脂质量控制中的应用,并预测了油脂质量控制研究的发展方向。     

现代物化方法在干酪品质研究方面的应用

近年来,世界干酪产量一直保持上升趋势。由于商业竞争及消费者要求的提高,对干酪品质的要求越来越高。要准确判断干酪的品质,就需要一些能够准确判断其品质的仪器。主要探讨了现代的一些物化方法在研究干酪品质方面的应用,主要有:(1)电子显微镜(ElectronMicroscope);(2)差示扫描量热仪(Differentialscanningcalorimetry);(3)核磁共振(NuclearMagneticresonance)。     

Crystallization and Drying in Thin Sucrose Films During Panning

Sucrose crystallization in thin films (50–55 μm) was studied, using a videomicroscopy technique, at conditions encountered during hard panning processes. No nucleation occurred in unseeded films, while a linear increase in seeded crystals occurred during drying. Crystal growth rate increased with temperature (25–30°C) and with air velocity (2.4–12.5 m/sec), but did not change with varying sucrose concentrations (70–76% w/w) and relative humidities (0–66% at 30°C). FD & C Yellow No. 5 food coloring in the dye form (0.05–0.5 g/100 mL) showed no effects while similar concentrations in the lake form inhibited crystal growth rate.     

硫酸钠型矿盐卤水冷冻过程中芒硝结晶动力学的研究

采用连续稳态法对高浓度氯化钠水溶液中十水硫酸钠在MSMPR结晶器中的结晶过程进行了研究,测定了相关动力学参数,成核速率方程为:B0=1.245 E-63exp((-94 396.5)/(RT))ΔC2.907M0.111 5t,生长速率方程为:G=0.206 4exp((-15 825.46)/(RT))ΔC0.549 3.通过实验验证了动力学参数的可靠性,并对冷却结晶的影响因素进行了分析讨论.     

差示扫描量热法对金枪鱼鱼油热氧化动力学研究

利用差示扫描量热法(DSC)研究了金枪鱼鱼油的热氧化动力学.通过对DSC曲线的分析表明,金枪鱼鱼油的酰基甘油组成复杂,脂肪酸种类比较多.用Flynn-Wall-Ozawa法和Kissinger法计算金枪鱼鱼油的热氧化反应动力学参数,两种计算方法得到的动力学参数具有一致性.     

Avrami法研究微量司盘85对棕榈油结晶动力学的影响

采用差示扫描量热仪（differential scanning calorimetry,DSC）分析棕榈油及其与司盘85混合物的等温结晶及熔融行为,通过Hoffman-Weeks法计算出样品的平衡熔点。采用Avrami方程进一步研究样品的等温结晶动力学,从而得到与结晶动力学相关的参数。结果表明：DSC分析显示司盘85可明显降低棕榈油的结晶率和成核速率。通过Hoffman-Weeks法和Avrami方程求得的温度数据具有良好的线性关系,表明Avrami方程适用于棕榈油结晶过程的研究,但在结晶后期出现偏离。拟合得到的Avrami指数（n）在2.37～2.77之间,可知样品二维和三维晶体生长同时存在;结晶速率（k）和半结晶时间（t1/2）随着添加剂的添加均变小。     

Glass formation and dormancy in bacterial spores

Summary Differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) techniques were used to obtain evidence whether a glassy state exists within fully hydrated dormant Bacillus subtilis spores. DSC thermograms of hydrated dormant spores contained two major transitions; one at ∼60 °C assigned to be associated with the initial 'activation' stage for germination, and the other at ∼120 °C assigned to be associated with the 'inactivation' process (i.e. killing of the spores). The peak at ∼60 °C had characteristics which were all consistent with at least some region of the compartmentalised structure of fully hydrated dormant spores being in a glassy state. Solid (CPMAS) and liquid state (SPMAS) mobility resolved ¹³C NMR spectroscopy studies on the calcium dipicolinic acid (CaDPA) resonances, which are only present in the central protoplast of bacterial spores, showed it to be present in an amorphous solid-like environment. The DSC and NMR results were both found to be consistent with the hypothesis that the dormancy of bacterial spores is due to at least the central protoplast region being maintained in a low moisture content glassy state.     

Experimental design applied to the formulation of lipsticks with particular features

In our work a non-classical experimental design was applied to obtain lipsticks endowed with particular characteristics. Our aim was to formulate lipsticks that leave a brilliant and shiny colour application and have a transparent look. The emollient substances and the waxes (consistency factors) were identified as the main variables of the system. A two phase experimental strategy was thought out: the optimal quantities of consistency factors were selected using a Doehlert experimental matrix, whereas the correct mixtures of emollients were determined using a Scheffé simplex-centroid design. These two design were combined and a set of 49 experiments was obtained. The experiments carried out allowed the definition of a zone of two phases in which the objectives were attained: the correct types and appropriate quantities of emollients and waxes were determined. To find a possible correlation between some mixtures and the lipsticks' sensorial behaviour, differential scanning calorimetry was used. These results, in addition to those obtained using the experimental design allowed us to select the best lipstick formula. (c) Rapid Science Ltd. 1998.     

Pasting,rheological properties and gelatinization kinetics of tapioca starch with sucrose or glucose

Effects of sugars (sucrose and glucose) on the pasting, rheological and thermal properties of tapioca starch (TS) were studied. Rapid visco-analyser (RVA) and differential scanning calorimetry (DSC) showed that pasting and gelatinization temperature of TS increased with increased sugar concentration in the order of sucrose > glucose. Peak, breakdown, final and setback viscosities tended to increase with increased sugar content. Rheological parameters calculated from Herschley–Bulkley model showed sugar addition increased the yield stress and consistency coefficient, while decreased the thixotropy of TS gels. Loss tangent determined from dynamic viscoelastic tests revealed that sugars increased the solid-like characteristics of TS gels. Kinetics analysis showed E_a raised and rate constants declined in the presence of sugars, suggesting the same sugar effect as the experiments of RVA and DSC. And thus kinetics analysis could provide new evidences for the influence of sugars on starch gelatinization.     

差示扫描量热法及其在猪肉凝胶机理探索中的应用

通过差示扫描量热法研究不同压力水平下凝胶的形成过程,初步探索凝胶形成机理。结果表明,凝胶的主要成分为肌球蛋白,200MPa蛋白质已经变性,400MPa蛋白质聚集,600MPa蛋白质凝胶形成。本研究结果能够为超高压诱导猪肉凝胶品质控制提供理论依据。     

猪不同部位脂肪理化检测及结晶特性分析

对猪腹部、皮下和肌间等不同部位的7种脂肪理化性质进行分析,并利用差示扫描量热法(DSC)、X-射线衍射法及偏光显微镜对其热力学性质、结晶特性和晶体微观形态进行对比研究。结果表明:不同部位猪脂熔点变化范围为28. 2～46. 3℃,胆固醇含量变化范围在654～2 189mg/kg之间,差异较大;腹部内脂肪的固体脂肪含量(SFC)及饱和脂肪酸含量比皮下脂肪和肌间脂肪的高;网油和冠油在熔化及结晶过程中主要有两种晶型的变化,常温下以β型为主,晶体颗粒粗大;板油、五花油和前腿油以β晶型为主,后腿油和背膘油中α、β'、β晶型都存在,这5种油脂结晶网络相较于网油和冠油,球晶大小不一,无规则性,前腿油和后腿油中存在部分游离片状晶体。由于猪不同部位脂肪的性能差异大,在生产应用中可根据实际需要选择不同的猪脂原料。     

Differential Scanning Calorimetry of Beef/Kappa-Carrageenan Mixtures

The thermal properties of kappa-carrageenan (KC) and/or beef under various ionic conditions were evaluated using Differential Scanning Calorimetry (DSC). The single endotherm observed for 2% aqueous KC (Tmax at 53°C) shifted to 54–59°C with addition of 1–3% NaCl and 0.35% sodium tripolyphosphate. Three endotherms were observed for post-rigor bovine semimembranosus meat (Tmax at 57, 66 and 80°C). Addition of salt/phosphate to beef had greater effects on Tmax than did 2% KC. On rescanning following 24 hr refrigerated storage, beef samples showed no thermal response, while KC treatments and beef/KC mixtures showed single endotherms at 53–63 and 69–76°C, respectively, indicating a wide shift in melting temperature of KC both in the presence of meat and at higher ionic strength.     

Moisture‐Absorption and Water Dynamics in the Powder of Egg Albumen Peptide,Met‐Pro‐Asp‐Ala‐His‐Leu

Moisture absorbed into the powder of Met‐Pro‐Asp‐Ala‐His‐Leu (MPDAHL)—a novel egg albumen antioxidant peptide—profoundly affects its properties. In this study, we elucidated water dynamics in MPDAHL using DVS, DSC, and low‐field ¹H NMR. Based on the DVS data, we found that MPDAHL sorption kinetics obey a parallel exponential model. DSC results indicated that both water and heating could change the microstructure of MPDAHL. The T₂ parameters of NMR reflected the different phases of moisture absorption revealed that there were 4 categories of water with different states or mobility in the MPDAHL during the moisture absorption process. The fastest fraction T_2b mainly dominated the hygroscopicity of MPDAHL and the absorbed water significantly changed the proton distribution and structure of MPDAHL. Thus, this study shows that DVS, DSC, and low‐field ¹H NMR are effective methods for monitoring water mobility and distribution in synthetic peptides. It can be used to improve the quality assurance of functional peptides.     

Nonisothermal kinetics of acrylamide elimination and its acceleration by table salt--a model study

ABSTRACT:  Acrylamide was applied onto table salt and heated in a glass reaction vessel within the temperature range 50 to 210 °C with a heating rate of 2 °C/min in order to study the influence of temperature and table salt on acrylamide elimination. For comparison purposes, pure acrylamide was also heated at the same conditions to 190 °C. Both systems were analyzed for acrylamide amount by GC-MS. During heating, the amount of acrylamide in contact with table salt decreased from 99.9 to 67.7 μg while the amount of acrylamide without table salt decreased from 99.9 to 81.3 μg, obviously due to polymerization reactions taking place in both studied systems. Comparing the results it was found that table salt has substantial catalytic effects on the polymerization reactions. Based on the treatment of experimental results, the parameters characterizing the kinetics of acrylamide polymerization, for example, the rate of its elimination at nonisothermal conditions, have been obtained, also making possible the calculation of rate constant values for any temperature in isothermal regime. As concluded, the polymerization may represent one of conceivable pathways of acrylamide elimination in a real food matrix.     

Hydration of heat-treated soy protein isolate and its effect on the molten flow properties at an elevated temperature

The relationship between the flow properties of soy protein isolate (SPI) at 140°C, measured using an extrusion viscometer, and changes in the hydration state were investigated. The state of the water in SPI was analysed by measurement of the freezable water content using differential scanning calorimetry (DSC) and by spin-spin relaxation rate (R₂) measurements using pulsed nuclear magnetic resonance (NMR). The dependence of the flow properties on the state of water was indicated by the correspondence between the water content at which the flow characteristics of molten SPI changed, and the critical water content indicated by DSC measurement of the minimum freezable water content, and by the inflection point in NMR measurement of the spin-spin relaxation rate (R₂).     

茶多酚磁性白蛋白微球的制备

探索茶多酚磁性白蛋白微球的制备工艺,用作治疗肿瘤的新型动脉栓塞制剂。采用喷雾干燥法,以无抗原性的白蛋白为骨架材料,制备茶多酚微球。再将其加入一定的壳聚糖溶液中,同时加入适量磁粉,利用超声波混匀,加入少量戊二醛进行固化,真空干燥后得到茶多酚磁性微球。通过差示扫描量热法对茶多酚微球进行热分析,确认微球制备过程中茶多酚未发生变性。制备茶多酚白蛋白微球的最佳条件为:进风温度110℃、进料速度3.13mL/min、芯壁材比为2∶1、总固形物含量为2%,此时微球包封率最大。通过差示扫描量热法对茶多酚微球和茶多酚原样进行热分析,得到两者有相似的相变峰,表明在微球制备过程中茶多酚未发生变性。茶多酚磁性白蛋白微球的粒径为30μm,符合动脉栓塞制剂要求。采用本方法制备茶多酚磁性微球可行,有望成为新型治疗肿瘤动脉栓塞制剂。     

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。