Isothermal Crystallization of Palm Oil-Based Fats with and without the Addition of Essential Oils

The objective of study was to evaluate the crystallization behavior of palm oil-based fats processed with and without the addition of essential oils (5% w/w) obtained from the flowers (EsOF) and stems (EsOS) of Pituranthos scoparius. Palm oil (PO) and a mixture of PO, soybean oil, and sunflower oil (Mix) were tested. The addition of the essential oils did not change the melting points of the fats but affected their crystallization behavior. A delay in crystallization was observed, evidenced by lower crystallization rates, and lower solid fat contents. This delay was comparable in the samples crystallized with EsOF and EsOS for the PO samples but EsOF was more efficient at delaying crystallization in the Mix sample. EsOF generated a less organized crystalline network in both samples (lower enthalpy values) while EsOS generated a more organized crystalline network (high enthalpy values) when used in the Mix sample. The addition of EsO also affected the crystal microstructure in some cases. While a slight increase in crystal size was observed for some PO samples crystallized with EsOF, no change or a decrease in crystal size was observed for the samples crystallized with EsOS. A slight decrease in crystal size was observed for Mix samples crystallized with EsOF while no effect was observed for these samples crystallized with EsOS. Results from this study show that these essential oils can be used as natural additives to modify the crystallization of fats for food applications and therefore widen their functional properties.     

The Effect of Phospholipids on Milkfat Crystallization Behavior

Depending on the production method, the fat component in butter can either be in a continuous phase or entrapped by milk fat globule membranes (MFGM). Phospholipids like those present in the MFGM are known to affect milk fat crystallization behavior. This study examines the effect of MFGM phospholipid concentration on butter crystal structure. Regular raw cream was first concentrated to 85% fat via centrifugation to produce a “plastic” cream, and was then blended with anhydrous milk fat (AMF) and skim milk in order to maintain the total fat-to-water ratio while altering the total amount of MFGM in the butter product. Whereas mixtures of AMF and skim milk contained large spherulites that had finer structures as the degree of supercooling was increased, the addition of globular fat (GF) broke up these structures, eventually producing smaller individual needle-like crystals. However, high levels of GF also lead to the coalescence of the aqueous phase, creating large water pockets that adversely affect sensory properties. Thus, the phospholipid concentration in the final butter product must be controlled in order to obtain optimal crystal structure and product quality.     

Effect of Milk Fat Concentration on Fat Crystallization of Palm Oil-Based Shortenings

The effect of different dosages of anhydrous milk fat (AMF) (25%, 50% and 75%, w/w) on shear-crystallization of fat blends made of refined palm oil, refined palm stearin, and rapeseed oil was studied. Classical techniques as differential scanning calorimetry (DSC), pulsed field gradient nuclear magnetic resonance (pfg-NMR), rheometer, and X-ray diffraction (XRD) were applied to evaluate the crystallization kinetics of fat blends as well as the fat compatibility between components in rapid cooling (15 °C min⁻¹), isothermal crystallization (at 15 °C), and storage (5 °C). Obtained results revealed that the mixtures of palm oils and milk fat had a low compatibility. The co-crystallization between triacylglycerols (TAG) of milk fat and of palm oil occurred during isothermal crystallization and storage resulting in slower crystallization kinetics and the formation of some eutectic mixtures.     

力场下聚合物的结晶行为研究进展

介绍了聚合物在力场作用下结晶行为的研究进展;概述了不同力场(剪切、拉伸、振动)对聚合物结晶形态和结晶动力学的影响;重点论述了剪切力场下,剪切速率、剪切方式、分子量和分子量分布等对聚合物成核和生长的影响,简述了拉伸、振动对结晶的影响。认为力场的加入对聚合物的成核和晶体生长都有促进作用。     

Crystallization Kinetics of Cocoa Fat Systems: Experiments and Modeling

Isothermal crystallization kinetics of unseeded and seeded cocoa butter and milk chocolate is experimentally investigated under quiescent conditions at different temperatures in terms of the temporal increase in the solid fat content. The theoretical equations of Avrami based on one-, two- and three-dimensional crystal growth are tested with the experimental data. The equation for one-dimensional crystal growth represents well the kinetics of unseeded cocoa butter crystallization of form α and β′. This is also true for cocoa butter crystal seeded milk chocolate. The sterical hindrance due to high solids content in chocolate restricts crystallization to lineal growth. In contrast, the equation for two-dimensional crystal growth fits best the seeded cocoa butter crystallization kinetics. However, a transition from three- to one-dimensional growth kinetics seems to occur. Published data on crystallization of a single component involving spherulite crystals are represented well by Avrami’s three-dimensional theoretical equation. The theoretical equations enable the determination of the fundamental crystallization parameters such as the probability of nucleation and the number density of nuclei based on the measured crystal growth rate. This is not possible with Avrami’s approximate equation although it fits the experimental data well. The crystallization can be reasonably well defined for single component systems. However, there is no model which fits the multicomponent crystallization processes as observed in fat systems.     

氟,铝,硅杂质对石膏结晶过程的影响

在ＭＳＭＰＲ结晶器中研究磷矿中的常见杂质铝，硅，氟对石膏结晶的影响，发现不同含量的氟，铝，硅存在下，石膏晶体的成核速率和成长速率存在一个极值点，电镜归片表明，只有铝存在时，石膏晶体的外形几乎没有变化，当氟与铝共存时，石膏晶体的外形发生了极大的变化，几乎都形成了球状聚晶，在氟，铝，硅杂质对共存时，石膏晶体的形态与只有氟和铝存在时相似，但较不规则。     

成核剂对LLDPE晶体形态及结晶行为的影响

借助原子力显微镜、偏光显微镜和差示扫描量热仪,研究了山梨糖醇类成核剂对线型低密度聚乙烯(LLDPE)晶体形态及结晶行为的影响。结果表明:随着成核剂用量的增加,LLDPE的晶体形态呈均一化,球晶尺寸逐渐减小;成核剂的加入导致了LLDPE结晶温度和结晶度的提高。     

Effect of CO2 Bubbles on Crystallization Behavior of Anhydrous Milk Fat

A study was designed to observe the effect of bubbles created from dissolved CO₂ (0–2000 ppm) on crystallization and melting behavior, fat polymorphs, microstructure, and hardness of anhydrous milk fat (AMF) under nonisothermal crystallization conditions. Calculated amounts of dry ice were added to generate 2000 ppm CO₂ at low partial pressure, and an ultrasound (205 kHz, 10 s; US) treatment was delivered at 35 °C through a noncontact metal transducer on the molten AMF to generate bubbles (~500 nm) of CO₂. The generated CO₂ bubbles were found to induce a higher onset of crystallization temperature during cooling from 35 to 5°C at the rate of 0.5°C min⁻¹. The changes in crystallization behavior owing to the generation of a smaller and significant number of TAG crystals also increased the hardness of the AMF at room temperature and refrigerated conditions. The work suggested the potential use of CO₂ nanobubbles derived from the dry ice with the emission of low power US to control the crystallization behavior and thereby the physical properties of milk fat-containing dairy products.     

Sonocrystallization of Interesterified Fats with 20 and 30% C16:0 at <Emphasis Type="Italic">sn</Emphasis>-2 Position

The objective of this study was to induce crystallization in enzymatically interesterified fats (IE) with 20 and 30% palmitic acid at the sn-2 position using high intensity ultrasound (HIU). The physical blends (PB) used to prepare these two IE were consisted of tripalmitin and high oleic sunflower oil and contained 13.2 and 27.1% tripalmitin, respectively. Crystallization behavior of IE was compared with PB at supercoolings of 9, 6 and 3 °C. Results show that the melting point, SFC, and crystallization rate of PB were higher than IE and were driven mainly by tripalmitin content. HIU induced crystallization and generated small crystals in the IE samples. At 9 °C supercooling, sonication did not increase the viscosity of IE C16:0 20%, while that of the IE C16:0 30% increased significantly from 192.4 ± 118.9 to 3297.7 ± 1368.6 Pa·s. The elastic modulus (G’) for IE C16:0 30% increased from 12521 ± 2739.8 to 75076.7 ± 18259 Pa upon sonication at 9 °C supercooling, while the G’ of the IE C16:0 20% did not increase. Similar behavior was observed for the other supercoolings tested. This research suggests that HIU can improve the functional properties of IE with low content of C16:0 creating more viscous and elastic materials. These fats with low C16:0 content and improved functional properties could be used as trans-free fat alternatives.     

Effect of High Intensity Ultrasound on Crystallization Behavior of Anhydrous Milk Fat

The need to eliminate trans-fatty acids from foods’ formulation resulted in the exploration of new lipid sources and alternative processing conditions that will improve the physicochemical characteristics and nutritional qualities of lipid-based foods. In general, the physicochemical characteristics of lipid networks depend on the microstructure and crystallization behavior of the system. The objective of this work was to use high intensity ultrasound (HIU) as an additional processing condition to alter the crystallization behavior of a lipid model system (anhydrous milk fat). Results show that HIU application not only decreases the induction time of crystallization (faster crystallization) at a constant crystallization temperature, but also generates smaller crystals. In addition, higher viscosities are obtained when samples are crystallized after HIU application. The degree of supercooling, ultrasound application settings and a combination of both parameters influence the degree of ultrasound effect on the crystallization behavior.     

Crystallization Behavior and Kinetics of Chocolate-Lauric Fat Blends and Model Systems

Binary mixtures of cocoa butter and lauric fats have widespread use in chocolates and confections, yet incompatibilities between these fats can present formulation and processing constraints. This study examined the phase behavior and crystallization kinetics of cocoa butter-lauric fat model systems and chocolate-lauric fat blends. Solid fat content (SFC) profiles and isosolid diagrams confirmed eutectic and diluent interactions, indicating a softening of cocoa butter by lauric fat addition. Crystallization kinetics of model systems adhered to an exponential growth model. High lauric fat levels delayed crystal growth and reduced equilibrium SFC of cocoa butter. Coconut and palm kernel oils altered the solidification mechanisms of cocoa butter to a greater extent than fractionated palm kernel oil. Chocolate systems displayed multi-step crystal growth that contrasted with the exponential growth observed in the model systems. At high lauric fat levels (30%), crystallization onset was significantly lengthened. Blends with high lauric fat contents showed low \(G_{{\text {max}} }^{\prime }\) and did not achieve final equilibrium after 60 min of cooling, indicating incomplete crystallization.     

Tailoring Crystalline Structure Using High-Intensity Ultrasound to Reduce Oil Migration in a Low Saturated Fat

The objective of this study was to use high-intensity ultrasound (HIU) to change the crystalline structure of an interesterified soybean oil (IESBO) with 33% of saturated fats and to evaluate how these changes affect oil migration. The IESBO was crystallized at different temperatures (26, 28, 30, and 32 °C) with and without HIU. Results show that oil migration was significantly affected by HIU (P < 0.05). HIU promoted crystallization and induced the formation of harder crystalline networks that were more resistant to oil migration with lower melting peak temperatures and sharper melting profiles. Samples processed with HIU had fewer crystalline clusters as observed by microscopy. Changes observed on the physical properties of the IESBO due to sonication that consequently improved oil migration were attributed to the ability of HIU to induce secondary nucleation and crystallize low-melting point triacyclglycerols (SUU) that would not crystallize without the HIU and to the stronger and stable crystalline network formed capable of entrapping liquid TAG (UUU).     

聚丙烯固相接枝甲基丙烯酸乙酯的非等温结晶行为

利用差示扫描量热法(DSC)研究了聚丙烯(PP)及聚丙烯固相接枝甲基丙烯酸乙酯(PP-g-EMA)在不同冷却速率下的非等温结晶行为,并用Jeiorny法、MO法和Kissinger法处理了数据。结果表明:固相接枝EMA对PP的结晶起到异相成核的作用,提高了PP的结晶温度和结晶度;MO法比较适用于研究本体系的非等温结晶动力学,EMA 的引入提高了PP的结晶速率,改变了成核机理和晶体生长方式;用Kissinger法计算结晶活化能时发现EMA的接枝提高了PP的结晶活化能,表明接枝EMA阻碍了PP分子链在结晶时的运动。     

High-Intensity Ultrasound-Induced Crystallization of Mango Kernel Fat

The crystallization behavior of mango kernel fat (MKF) at 25 °C with and without the application of high-intensity ultrasound (HIU) (20 kHz, 125 W) was studied as a function of ultrasound amplitude level (30%, 50%, and 70% of the maximum amplitude of 180 μm). The irradiation period was fixed at 5 s. It was found that HIU induced MKF crystallization. The crystallization induction time decreased with a decrease in crystal size and an increase in the number of crystals as the HIU amplitude increased. The β' → β transformation was also accelerated with HIU application. This work has shown that there is great potential for the use of HIU in the food industry to achieve a shorter and more controllable crystallization process. In particular, HIU could be used as an efficient tool for controlling the polymorphic transition of fats.     

卤代磷脂的合成研究

以大豆磷脂为原料,利用有机卤代试剂制备出一种新型的卤代磷脂。通过正交试验确定了该反应的最佳反应条件：温度７５℃,引发剂量４％,溶剂量１５０ｍｌ,反应时间１．５ｈ。     

Effects of Fat Content and Solid Fat Content on Caramel Texture Attributes

Fat plays an important role in caramel quality attributes, yet there is very little published work on how fat type and level influence caramel characteristics. Fat content was increased from 0 to 20 % to determine the effects of total fat content on caramel texture attributes such as cold flow, hardness, stickiness and tensile strength. Solid fat content (SFC) was also varied, from 3 to 90 %, by using commercially‐available fats with varied SFC at 22 °C. Cold flow decreased significantly with increased fat content, with greater effect for fats with higher SFC. Changes in caramel hardness with fat content were dependent on SFC. Hardness generally decreased with increasing fat content for the fats with low SFC, with the 3 % SFC fat softening the most. Hardness increased slightly with fat content for the hardest fat (90 % SFC). Stickiness generally decreased with increasing fat content although the effect was significantly higher with higher SFC fats. These results document that both fat content and SFC significantly influence caramel texture attributes.     

Morphology, reorganization and stability of mesomorphic nanocrystals in isotactic polypropylene

The morphology and thermodynamic stability of crystals of isotactic polypropylene (iPP) were analyzed as a function of the path of crystallization by atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Samples were melt-crystallized at different rates of cooling using a “controlled rapid cooling technique”, and subsequently annealed at elevated temperature. Mesomorphic equi-axed domains with a size less than 20 nm were obtained by fast cooling from the melt at a rate larger about 100 K s⁻¹. These domains stabilize on heating by growing in chain direction and cross-chain direction, to reach a maximum size of about 40-50 nm at a temperature of 433 K, with the quasi-globular shape preserved. Annealing at 433 K additionally triggers formation of different types of lamellae. It is suggested that these lamellae either develop by coalescence of nodules, or by recrystallization from the melt. The transition from the disordered mesomorphic structure, evident at ambient temperature after fast crystallization, to monoclinic structure on heating at about 340 K occurs at local scale within existing crystals, and cannot be linked to complete melting of mesomorphic domains and recrystallization of the melt. The temperature of melting of initial mesomorphic domains, after reorganization at elevated temperature, is identical to the temperature of melting of rather perfect lamellae, obtained by initial slow melt-crystallization, followed by annealing. The close-to-identical temperatures of melting of these crystals of largely different shapes are confirmed by model calculations, using the Gibbs-Thomson equation. Modeling of the melting temperature reveals that nodular crystals, stabilized by annealing at high temperature, exhibit a similar fold-surface as lamellar crystals.     

Crystallization of high purity ammonium meta-tungstate for production of ultrapure tungsten metal

The growth mechanism of Ammonium Meta-Tungstate (AMT) crystal was interpreted as two-step model. Growth rates of AMT crystals were measured in a fluidized bed crystallizer. The effects of temperature, supersaturation and crystal size on the crystal growth were investigated. The contribution of the diffusion step increased with the increase of temperature, crystal size and supersaturation. The nucleation kinetics from measurements on the width of the metastable region of Ammonium Meta-Tungstate (AMT) was also evaluated. The crystal size distribution from a programmed cooling crystallization system was predicted by the numerical simulation of a mathematical model using the kinetics of nucleation and crystal growth. It was also observed that the shape of AMT crystals was changed during the growth period. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

Crystallization and Drying of Milk Powder in a Multiple-Stage Fluidized Bed Dryer

The rationale of this study has been to use fluidized beds to crystallize amorphous spray-dried skim milk powders with multiple stages of processing at different temperatures and humidities with the aim of rapidly making mostly crystalline powders. This paper discusses the performance of a multiple-stage fluidized bed dryer, and a combination of crystallization of lactose in spray drying at high humidity (lactose nuclei formation) and subsequent fluidized bed drying. Two different combinations of spray dryer and multi-stage fluidized-bed dryer have been suggested to crystallize lactose in skim milk powder. The results show significant improvements in the crystallinity of the powders. Moisture sorption test and X-ray diffraction analysis were used to assess the crystallinity of the powders. The processed powders that were crystallized in a humid-loop spray drying combined with a two-stage fluidized-bed dryer/crystallizer showed 92% improvement in lower amorphicity by processing at different stages of 70°C, 50% RH and 80°C, 50% RH for 15 minutes. The conventionally spray-dried powders that were crystallized in a three-stage fluidized-bed dryer/crystallizer showed 87% improvement in lower amorphicity (less moisture sorption) by processing at different stages of 60°C, 50% RH; 70°C, 40% RH; and 80°C, 40% RH for 20 minutes. The multiple-stage fluidized bed system showed distinctive potential to crystallize lactose significantly in skim milk powder using an industrial-feasible process.