Isothermal batch crystallization of alpha-lactose: A kinetic model combining mutarotation,nucleation and growth steps

A kinetic model combining first-order differential equations of the three consecutive steps of lactose crystallization, i.e., mutarotation, nucleation and crystal growth rate, was developed. Numerical solutions successfully fitted the variations of crystal mass growth rate as a function of lactose concentration during unseeded isothermal batch crystallization, at different initial lactose concentrations and temperatures. The model allowed the induction phase and the influence of seeding to be simulated by taking into account the dependency of crystal growth rate on total crystal surface area and, consequently, on nucleation rate. The proposed model highlights the large influence of the mutarotation step, even in unseeded crystallization kinetics. The effects of high lactose supersaturations that prevail at industrial scale during whey powder manufacturing and the effects of alkaline pH (9.5) on lactose crystallization kinetic were successfully predicted.     

Growth Rate Dispersion Effects on Lactose Crystal Size Distributions from a Continuous Cooling Crystallizer

The continuous crystallization kinetics for lactose have been determined. Specifically, a model incorporating the effects of growth rate dispersion (GRD) on particle dynamics has been employed to determine continuous crystallization kinetics from experimentally determined size distributions. The existence of GRD was verified by the excessive number of fines (< 50 μm) observed. Crystal size distributions were successfully modeled using a two component rate distribution indicating the existence of two distinct types of nuclei. These could be classed as fast-growers (product crystals) and slow-growers (fines). Nucleation and growth kinetics of these populations were determined and compared to other methods of determining kinetics.     

Laminar flow continuous settling crystalliser. Part 1. Initial exploration

Conventional lactose crystallisations give large spans that are not suitable for direct use in inhaler grade lactose. The factors causing large spans are successive nucleation events and growth rate dispersion. This paper (Part 1 of 2) explores a novel lactose crystallisation technique, laminar flow continuous settling crystallisation, proposed as a method for directly producing a narrow particle size distribution with a span of less than 1. A theoretical model was developed that modelled the growth and settling of individual crystals with growth rate dispersion within a column full of lactose solution flowing upwards in laminar flow. The model predicted a d₅₀ of 73.2 ± 0.9 μm and a span of 0.47 ± 0.01. In an experimental crystalliser crystals obtained had a d₅₀ between 50 and 90 μm but the span was greater than 1. The difference has been attributed to agglomeration and flow variations from true laminar flow, which is reported in Part 2.     

蔗糖结晶过程的粒度分布及其控制

蔗糖晶体的粒度是衡量其质量的重要指标之一。研究蔗糖结晶过程的晶体粒度分布对提高蔗糖质量和蔗糖连续结晶的实践具有明显的指导意义。本论文通过对晶体粒度的计量及结晶过程粒度分布的研究,着重分析了有关影响晶体生长分散的因素,从而指出控制蔗糖晶体粒度及其分布的途径。     

氨-水体系中硝酸钾结晶的生长特性

采用MSMPR结晶器研究了不同悬浮密度、氨水浓度和过饱和度下,KNO3在氨-水体系中的结晶动力学特性,并得到KNO3在氨水溶液中的结晶动力学模型.研究结果表明:随着悬浮密度的减少,晶体平均粒径增大,粒径分布变得均匀;氨的浓度增加,结晶成核 速率与生长速率均下降,晶体平均粒径减少,但粒径分布变均匀;随着过饱和度的加大,结晶成核速率与生长速率均增加,但晶体平均粒径减小,且粒径分布变差.研究结果可为硝酸钾生产工艺中结晶器的设计提供基础数据.     

Mathematical models of pretreatment processes to utilize purple-fleshed potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) peels for anthocyanin extraction

The effect of particle size on the extraction rate of anthocyanin from Solanum tuberosum L. (purple-fleshed potato) peels (PFPPs) using the stagnant single-stage batch extraction system was investigated. Core pretreatment processes such as drying and grinding were quantitatively evaluated using mathematical models. The drying behavior of PFPP was successfully described using thin layer models (Page model and Midilli-Kucuk model). The effective diffusion coefficient of drying temperature at 40°C was determined to be 1.67x10^?12 m²/s. The grinding time to obtain particles of a specific size was accurately estimated using the grinding kinetic model (R ²=0.97). The extraction rate of anthocyanin increased as the particle size decreased; however, when the particle size was 0.15mm, the anthocyanin content decreased. Our study demonstrated that the grinding kinetic model is useful to estimate the grinding time to produce an optimum particle size for anthocyanin extraction from PFPP.     

Application of in-line monitoring for aiding interpretation and control of dextrose monohydrate crystallization

Two in-line monitoring probes were inserted into a 3.2 L batch cooling crystallizer to monitor the progression of a dextrose monohydrate crystallization and how it was influenced by process variables including impurities, seed size and initial dextrose concentration. The probes used were a K-patents refractometer and a Lasentec FBRM probe. These probes were applied to continuously monitor dextrose concentration in solution and crystal chord length distribution throughout the duration of the crystallization. The influence of process variables on crystallizer performance, as determined by final crystal yield and chord size, may not be intuitive and some unexpected results occurred. The continuous in-line measurement data proved very useful for interpreting how variations in the process variables influenced the crystallizer performance. Supersaturation is a key variable in the control of the crystallization process as it influences both nucleation and crystal growth. In-line monitoring of solution dextrose concentration can be applied to continuously evaluate supersaturation and this can then be applied to control supersaturation so as to achieve a desired crystallizer performance.     

Crystallization Kinetics of Alpha-Lactose Monohydrate in a Continuous Cooling Crystallizer

The crystallization of alpha-lactose monohydrate in a continuous cooling crystallizer was investigated at various temperatures and super-saturations. The population balance model was used to analyze the product crystal size distribution as determined by the Coulter Multi-Sizer for each condition studied. Nucleation and growth values were thereby determined for each temperature and supersaturation. Kinetic models were then developed for both nucleation and growth to demonstrate the effects of the operating parameters. The results showed that the nucleation process had a temperature dependence with an activation energy of 17.0 kcal/mole and that nucleation increased with the 1.9 power of supersaturation and the 1.0 power of the suspension density (mass of crystals). The growth process was found to have a temperature dependence with an activation energy of 22.1 kcal/mole and to be a second order function of the supersaturation.     

Physicochemical characterization and oxidative stability of fish oil encapsulated in an amorphous matrix containing trehalose

Fish oil with 33% omega-3 fatty acids was microencapsulated by spray-drying in a matrix of n-octenylsuccinate-derivatized starch and either glucose syrup or trehalose. Samples showed no difference in physicochemical properties as determined by measurement of particle size, oil droplet size, true density and BET surface. Upon storage at low relative humidity, lipid oxidation was decreased in trehalose containing samples indicating that in the amorphous state trehalose is a more suitable wall material for microencapsulation than glucose syrup. The retarded oxidation of trehalose containing samples may be attributed to the unique binding properties of trehalose to dienes. At 54% relative humidity, a rapid oxidation of the microencapsulated oil was observed upon crystallization of trehalose, which limits the range of applications to products to be stored at low humidity.     

木糖醇介稳区宽度与晶体生长速率测定

用激光散射法测定纯木糖醇水溶液和含有山梨醇和葡萄糖杂质的木糖醇水溶液的结晶介稳区宽度;在介稳区内测得不同结晶温度下纯木糖醇溶液中过饱和度对晶体生长速率的影响,同时研究杂质的添加对木糖醇结晶生长速率的影响。结果表明：相同结晶温度下,生长速率随过饱和度的增大而增大;在相同结晶温度和过饱和度下,木糖醇水溶液中分别加入山梨醇和葡萄糖杂质导致生长速率下降,并随杂质含量的增大而下降,山梨醇对晶体生长的抑制作用比葡萄糖更明显。     

Crystallization kinetics of palm oil in blends with palm-based diacylglycerol

Crystallization kinetics of palm oil (PO) in the presence of different concentrations (2, 5, 10, 30 and, 50% w/w) of palm-based diacylglycerol (PB-DAG) were investigated over different ranges of crystallization temperatures. Addition of 30 and 50% (w/w) of PB-DAG (high concentrations) increased significantly (P < 0.05) the melting point and crystallization onset while addition of 2 and 5% PB-DAG did not have significant (P > 0.05) effect. PO and PO blends with 2 and 5% of PB-DAG showed crystal transformation at crystallization temperatures (T_Cr) of 26, 26, 26.5 °C, respectively as reflected in corresponding changes of the Avrami parameters at below and above these T_Cr. This was especially evident for the blends containing 2 and 5% of PB-DAG. Individual comparison of induction time (T_i), Avrami exponent (n), Avrami constant (k) and half-time of crystallization (t_1/2) of blends classified under various supercooling ranges based on the supercooling closeness (± 0.1 °C), showed that addition of 5% of PB-DAG in most of the supercooling ranges significantly (P < 0.05) reduced nucleation rate as well as crystal growth velocity of PO. This was reflected in the significantly (P < 0.05) higher T_i and t_1/2 and lower k. Although the presence of 2% of PB-DAG was found to have inhibitory effect on PO crystallization, this effect was not significant (P > 0.05). Mode of crystal growth attributed to n was changed significantly only in presence of 5% of PB-DAG. Furthermore, presence of 10% PB-DAG showed ??'-stabilizing effect on PO. On the other hand, high concentrations of PB-DAG were found to significantly (P < 0.05) reduce T_i as well as t_1/2 and also increase k suggesting their promoting effects on nucleation and crystallization rate of PO even with the close supercoolings. In addition, they changed crystal growth mode of PO. Amongst the different concentrations of PB-DAG investigated, blend containing 50% of PB-DAG as compared to PO, not only, have healthier benefits but also, may have greater potential applications in plastic fat products due to its unique physical properties.     

氯化钠结晶工艺优化设计

2011年我国国内医药用氯化钠产量已超10万t,产品基本采用多效真空蒸发结晶工艺,普通工艺生产的产品结晶在储存过程易出现板结,给流转、使用带来非常大的问题.通过对氯化钠生产过程中的成核、结晶理论进行分析,将套筒隔室武结晶技术和延时结晶技术相结合,使氯化钠产品晶体结构、粒度及品质有了很大的提高.通过研究表明,新工艺生产的氯化钠产品粒径达0.75 mm以上,晶体呈椭圆型（鱼籽状）,产品质量指标优于注射级氯化钠产品标准,是解决氯化钠结晶在储存过程板结、结晶生长致硬块化的很好途径.     

Water sorption and time-dependent crystallization behaviour of freeze-dried lactose-salt mixtures

Water sorption properties of freeze-dried lactose, lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂, and lactose/KCl mixtures in their molar ratio of (9:1) were investigated. Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were used to model water sorption properties. Water is known to function as a plasticizer, depressing the glass transition and facilitating crystallization. Crystallization in the present study resulted in loss of sorbed water from lactose. The crystallization of pure lactose and lactose/salt mixtures was observed at RVP?44.0% within 24 h. At RVP?54.4% water contents were higher in lactose/CaCl₂ and lactose/MgCl₂ mixtures than in pure lactose, lactose/NaCl, and lactose/KCl.Water content in pure lactose after crystallization was ?5.0%, suggesting that lactose crystallized as a mixture of α-lactose monohydrate and various anhydrous forms of α/β-lactose crystals. Anhydrous lactose/CaCl₂ and lactose/MgCl₂ had higher glass transition temperatures than lactose, but other salts (NaCl and KCl) with lactose gave lower glass transition than amorphous lactose. It seems that bivalent salts in mixtures with lactose gave a higher T_g than smaller monovalent ions. Salts delayed lactose crystallization. The effect on lactose crystallization was highest with calcium chloride (CaCl₂) and lowest with potassium chloride (KCl). It seems that different salts interacted with lactose to different extents. For water sorption, GAB model gave a better fit than BET model. Water sorption and time-dependent crystallization properties of lactose/salt mixtures should be considered in manufacturing and storage of dairy-based dehydrated materials.     

Chemical and molecular dynamics analysis of crystallization properties of honey

Honey crystallization is a natural phenomenon commonly found in honey products. To better understand the characteristics of honey crystallization, the concentrations of the four major compositions (namely glucose, fructose, sucrose, and maltose) were determined in the liquid, crystal, and mixed forms of honey. Our study revealed the contents of glucose and fructose in three forms varied significantly (p < 0.05). Molecular dynamics simulation was performed to investigate honey crystallization process. All the simulation systems had a tendency to form a cubic crystal. When the ratio of glucose/fructose is 2.5:1, which is the same as the crystal found in honey, a shorter time and lower root-mean-square deviation were found compared to the ratios at 2:1, 1:1, and pure glucose. It infers that glucose/fructose at 2.5:1 is the most stable honey crystallization, relatively. The morphology of crystals found in honey, which was observed under an environment scanning electron microscope, looked like sticky balls with indistinct edges, different from that plates or granule of glucose crystal with flattened edges. These results indicated that the relative content of glucose and fructose had a significant effect on the crystallization of honey. The glucose/fructose at 2.5:1 probably is the critical ratio of honey crystallization, at which honey can form stable crystalline deposit speedily.     

Estimation of crystalline phase present in the glucose crystal–solution mixture by water activity measurement

The amount of crystalline fraction present in monohydrate glucose crystal–solution mixture up to 110% crystal in relation to solution (crystal:solution=110:100) was determined by water activity measurement. It was found that the water activity had a strong linear correlation (R²=0.994) with the amount of glucose present above saturation. Difference in the water activities of the crystal–solution mixture (a_w1) and the supersaturated solution (a_w2) by re-dissolving the crystalline fraction allowed calculation of the amount of crystalline phase present (ΔG) in the mixture by an equation ΔG=846.97(a_w1−a_w2). Other methods such as Raoult's, Norrish and Money–Born equations were also tested for the prediction of water activity of supersaturated glucose solution.     

Determining the physical stability and water–solid interactions responsible for caking during storage of alpha-anhydrous glucose

Typically, a crystalline powder is considered reasonably stable below it deliquescence point (RH₀), however, caking has been reported for some materials below their RH₀. The critical relative humidity (RH) values for caking and hydrate formation in alpha-anhydrous glucose (α-AG) and α-AG partitioned into three particle sizes were assessed using saturated salt slurries ranging from 0 to 84 % RH at 25 °C for 20 weeks. The degree of caking was determined by a five-point visual physical stability scale, from free flowing with minimal clumping (1) to fully caked (5), and X-ray powder diffraction was used to determine the composition of the samples. Caking was observed in α-AG during storage at 68 % RH at 25 °C and the severity of caking increased with increasing RH. Fine particle α-AG caked during storage at 64 % RH, whereas medium and large particle α-AG caked at 68 and 75 % RH, respectively, at 25 °C. Caking was observed in the absence of deliquescence, amorphous content, and hydrate formation; therefore, it is proposed that capillary condensation leads to caking in α-AG below its RH₀. Capillary condensation caking occurs at a specific RH (termed RH_cc) where direct condensation of moisture into confined spaces, such as particle contact points or surface defects, causes the formation of liquid bridges, which may solidify over time without changes in RH or temperature. To avoid caking, α-AG should be stored below its RH_cc, which is highly dependent on particle size; and to avoid conversion to glucose monohydrate, α-AG, regardless of particle size, should be stored below 64 % RH at 25 °C.     

Effect of Span 60 on the Microstructure,Crystallization Kinetics,and Mechanical Properties of Stearic Acid Oleogels: An In‐Depth Analysis

Modulation of crystallization of stearic acid and its derivatives is important for tuning the properties of stearate oleogels. The present study delineates the crystallization of stearic acid in stearate oleogels in the presence of Span 60. Microarchitecture analysis revealed that stearic acid crystals in the oleogels changed its shape from plate‐like structure to a branched architecture in the presence of Span 60. Consequently, a significant variation in the mobility of the solute molecules inside the oleogel (Fluorescence recovery after photobleaching studies, FRAP analysis) was observed. Thermal analysis (gelation kinetics and DSC) revealed shortening of nucleation induction time and secondary crystallization with an increase in the Span 60 concentration. Furthermore, isosolid diagram suggested better physical stability of the formulations at higher proportions of Span 60. XRD analysis indicated that there was a decrease in the crystal size and the crystallinity of the stearic acid crystals with an increase in Span 60 concentration in the Span 60 containing oleogels. However, crystal growth orientation was unidirectional and found unaltered with Span 60 concentration (Avarmi analysis using DSC data). The mechanical study indicated a composition‐dependent variation in the viscoelastic properties (instantaneous [τ₁], intermediate [τ₂], and delayed [τ₃] relaxation times) of the formulations. In conclusion, Span 60 can be used to alter the kinetics of the crystallization, crystal habit and crystal structure of stearic acid. This study provides a number of clues that could be used further for developing oleogel based formulation.     

The effect of agitation on the nucleation of α-lactose monohydrate

Nucleation in an industrial crystallisation process determines how many crystals are formed and defines the final particle size distribution. This parameter plays a critical role in determining the success of an industrial lactose crystallisation, impacting yield, throughput and product quality. Previous studies on lactose crystallisation have reported that mixing can influence the nucleation kinetics of α-lactose monohydrate. This work looked to authenticate this by measuring the induction time required for nucleation of supersaturated lactose solutions across a range of agitation rates. Increasing agitation increased the rate of nucleation at a given supersaturation. The results show that this is a result of an increase in the frequency of activated molecular collisions and not a change in the critical nucleus size, which remains constant at a defined supersaturation.     

Development of Novel Methods to Determine Crystalline Glucose Content of Honey Based on DSC,HPLC, and Viscosity Measurements,and Their Use to Examine the Setting Propensity of Honey

Crystallization must occur in honey in order to produce set or creamed honey; however, the process must occur in a controlled manner in order to obtain an acceptable product. As a consequence, reliable methods are needed to measure the crystal content of honey (? expressed as kg crystal per kg honey), which can also be implemented with relative ease in industrial production facilities. Unfortunately, suitable methods do not currently exist. This article reports on the development of 2 independent offline methods to measure the crystal content in honey based on differential scanning calorimetry and high‐performance liquid chromatography. The 2 methods gave highly consistent results on the basis of paired t‐test involving 143 experimental points (P > 0.05, r² = 0.99). The crystal content also correlated with the relative viscosity, defined as the ratio of the viscosity of crystal containing honey to that of the same honey when all crystals are dissolved, giving the following correlation: . This correlation can be used to estimate the crystal content of honey in industrial production facilities. The crystal growth rate at a temperature of 14 °C—the normal crystallization temperature used in practice—was linear, and the growth rate also increased with the total glucose content in the honey.     

PREDICTING AVAILABLE LYSINE LOSSES DURING HEAT PROCESSING1

Mathematical models, which are amalgams of empirical equations and reaction kinetics, were used to predict the destruction of available lysine in proteins. R²-values for plots of predicted versus observed values ranged from 0.8 to 0.9. Changes in water activity, sugar, salt, oil, pH, time and temperature are considered by the model. The model can adjust for different sugars by employing an algorithm based upon the mutarotation constant for a specific sugar. A plot of sugar mutarotation constant against the appropriate loss rate coefficient demonstrated the relation between these two measures (R²= 0.8). Nomograms for predicting the loss rate coefficient and the activation energy, which can be used in an industrial application, are presented.