Influence of temperature on crystallization of lactose in ice-cream

Sandiness in ice-cream due to lactose crystallization can still be a problem in many circumstances. Lactose crystallization occurs in ice-cream as the unfrozen phase becomes supersaturated. However, the effects of storage temperature and temperature fluctuations on lactose crystallization have not been very well quantified. In this work, an accelerated storage apparatus was used to determine the effects of thermal fluctuations (from ±0.01°C to ±2.0°C), at several mean storage temperatures (from −5.0 to −20.0°C), on the onset of lactose nucleation and subsequent crystal growth in a standard vanilla ice-cream. the induction time for nucleation initially decreased as temperature was lowered (for temperature oscillations of ±1.0°C), until a minimum induction time of 3 h was found between −10.0 and −12.0°C. Further decreases in storage temperature caused the induction time to increase. the induction time for nucleation increased as the extent of temperature fluctuations increased, from 0.01 to 2.0°C, while initial lactose crystal growth rate showed the opposite trend. the initial growth rate increased as temperature decreased between −5.0 and −10.0°C, but then decreased for temperatures below −10.0°C. At −20.0°C lactose crystals grew very slowly. At −10.0°C the rate of growth decreased with increasing amplitude of temperature oscillations.     

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.     

An improved model of the seeded batch crystallization of glucose monohydrate from aqueous solutions

The current research has produced an accurate model of the non-nucleating seeded batch crystallization of glucose monohydrate which includes complex phenomena including crystal growth rate dispersion and the effect of the mutarotation reaction. The model is able to predict the population density of crystals in the batch as a function of particle size and batch time, n=n(L,t) as well as total glucose concentration in the mother liquor and the fraction of glucose in the α-d-glucopyranose form. A previous model of similar systems was limited by considering only systems with monosize seed crystals, and where growth rate dispersion had a negligible effect on the particle size distribution. Because of the nature of the ‘common history’ crystals that are produced by the growth of glucose monohydrate, the modifications required to the model to account for these additions to the model are remarkably simple. By predicting the full population density the model produces an accurate mass balance for the crystallization process, since the second moment of the crystal size distribution (CSD) may be calculated analytically at every point in the simulation. This enables the competitive kinetics between the rate of crystal mass deposition of α-glucose and the rate of production of α-glucose via the mutarotation reaction to be more accurately accounted for, and hence the significance of the mutarotation reaction on the crystal growth to be more accurately predicted.     

Effect of galacto-oligosaccharide concentration on the kinetics of lactose crystallisation

Galacto-oligosaccharides (GOS) are said to have a retarding effect on the nucleation and growth of α-lactose monohydrate crystallisation. Studies regarding the kinetic parameters for crystal growth and nucleation were conducted utilising gravimetric analysis and laser light scattering to follow the lactose crystallisation. A statistically significant retarding effect of GOS on lactose crystal growth at concentrations between 0.8 and 3% (w/w) GOS of total solution was observed. A significant nucleation suppressing effect was confirmed further. Studies concerning the change in crystal morphology revealed that as GOS concentration was increased, a transition from the common tomahawk shape to a shape with shortened crystal faces away from the apex to a needle like appearance occurred, strongly suggesting a growth retardation effect on the (010) face. Crystals subjected to high pressure liquid chromatography (HPLC) analysis did confirm an incorporation or inclusion of GOS into the crystal lattice.     

Influence of temperature on accelerated lactose crystallization in dulce de leche

The aims of the present work were to study the crystallization of lactose in dulce de leche and to evaluate the influence of temperature on this process. Samples of approximately 1 g were placed in plastic containers and stored at –5, 5, 20 and 35°C for 25 days. Lactose crystal and lactose crystal agglomerate numbers and size were measured by using an optical microscope. Results suggested that stirring and placing a small sample of dulce de leche in a small container induced lactose crystallization. Lower storage temperatures resulted in an increase of crystal and agglomerate number but in a decrease of crystal and agglomerate size. The effect of temperature on crystal and agglomerate growth rates could be attributed to the effect of temperature on viscosity, as lower temperatures resulted in decreased crystal mobility in dulce de leche and therefore reduced crystal and agglomerate growth rate.     

PARAMETERS THAT DETERMINE TRIPALMITIN CRYSTALLIZATION IN SESAME OIL

The crystallization of tripalmitin (TP) in sesame oil (0.98, 1.80 and 2.62% w/v) was investigated under isothermal conditions using a cooling rate similar to the one achieved by industrial crystallizers (1 K/min) and utilizing a modification of the Avrami equation. It was concluded that z, the crystallization rate constant, and the associated energy of activation (Ea) values determined through Avrami's original equation yield erroneous results. Additional results indicated that the increase in supercooling at constant oil phase viscosity (e.g., 5.25–5.5 dynes/cm²) during crystallization, produced a higher degree of nucleation without an appreciable effect on TP crystal size. In contrast, as viscosity of the oil phase decreased at equal supercooling conditions (e.g., 22.0 - 22.5C) the main crystallization process evaluated through z and Ea was crystal growth. It was also concluded that the characteristic crystallization stages of induction time for nucleation, crystal nucleation and growth, and end of crystallization were evident in the viscosity profile of the solid fraction developed during TP crystallization. The predominance of any of these processes (i.e., nucleation or crystal growth) as a function of supercooling and viscosity of the oil phase determines, to a great extent, the rheological profile during crystallization and the final viscosity value of the crystal suspension.     

Water Mobility and Crystallization Action of Lactose-water Systems by Oxygen-17 and Carbon-13 NMR

Systems ranging in concentration from 10-60g lactose/100g water were investigated by fully proton decoupled ¹⁷O and fully proton decoupled ¹³C Nuclear Magnetic Resonance (NMR). The relation between ¹⁷O NMR transverse relaxation rate measurements and lactose concentration showed water mobility decreased linearly with increasing lactose concentration up to 25g lactose/100g water and decreased rapidly and nonlinearly above that level. Water mobility was used to monitor lactose crystallization in supersaturated solutions with time. The 13 C NMR showed no significant differences in chemical shifts of carbon atom peaks in lactose molecules during crystallization. However, depending on the method of sample preparation, mutarotation could be observed.     

Sugar crystallization in food products

A review of the recent literature on crystallization of the commercial sugars (fructose, glucose, lactose, and sucrose) is presented. Topics include: NUCLEATION--The formation of the crystalline phase from supersaturated solutions can occur by either a spontaneous or a forced nucleation mechanism. Recent work on the mechanisms, kinetics, and impact of both heterogeneous and secondary (contact) nucleation is discussed. GROWTH--Recent studies on the mechanisms and kinetics of crystal growth will be reviewed. This discussion includes work on the growth rate dispersion exhibited by these sugars. EFFECTS OF IMPURITIES AND ADDITIVES--The presence of impurities and additives (including mixed sugar systems) affects both the nucleation and growth steps. A discussion of the recent work in this area is included. Emphasis is placed on the relationship between these crystallization phenomena and the solution structure for comparison purposes.     

Influence of shear on fat crystallization

Processing conditions greatly impact fat crystallization kinetics and growth mechanisms. Recently, there has been increased interest in elucidating the role of shear on fat crystallization. This review provides an overview of fat crystallization under static conditions followed by a summary of the current body of work pertaining to the effects of shear on fat crystallization, namely its effects on nucleation and growth, crystal network formation, polymorphic transitions, and microstructure modification at different length scales. The effects of shear are usually tied to critical shear rates but shear generally enhances nucleation and growth, accelerates crystallization and polymorphic transitions, and can cause orientation and structuring of fat crystal networks.     

Rates of Crystallization of Dried Lactose-sucrose Mixtures

The isothermal crystallization kinetics of glassy lactose/sucrose mixtures were studied at several storage temperatures (close to T_g and T_m). The kinetic parameters implicit in the Avrami equation were determined. Activation energies for transport (E_D) and surface nucleation (W*) were also found and correlated to the molar composition of the lactose/sucrose mixtures. A monotonic increase in the half crystallization time (t_1/z), Avrami index (n), % crystallization per day, activation energy for transport (E_D) and surface nucleation energy (W*) and a decrease in the crystallization velocity constants (K) were related to the increase in the lactose content of lactose/sucrose mixtures.     

Drying of Whey

The properties of lactose in whey powder and the effect of crystallization are assessed and the process of mutarotation described. Concentration in an evaporator and the influence of heat­treatment in the process of whey is considered and the action of proteins on viscosity shown. Thermoplasticity in the drying of whey concentrate and the possibility of producing a high-quality non­caking powder are discussed. Editor's summary     

Crystallization kinetics of emulsified triglycerides

Nucleation and crystal growth process of triglycerides in water emulsions composed of trimyristin (c l4:0) admixed with 0, 40, and 80 ml litre^?1 trilaurin (c 12:0) (expressed v per total v emulsion) were followed with NMR (nuclear magnetic resonance) and DSC (differential scanning calorimetry). Mathematical analysis of the time dependence of the phase changes and thermal data distinguished two distinct ‘apparent’ kinetic phases. These phases were tentatively referred to as nucleation and crystal growth. With 40 and 80 ml litre^?1 trilaurin (NMR data at 293 K) nucleation and crystal growth phases of trimyristin were simulated with zero order and second order rate expressions, respectively. Relative to these mixtures, pure trimyristin nucleation was delayed in the initial phase, but crystal growth occurred with fast homogeneous nucleation and slower growth in the second phase. Statistical analyses indicated that homogeneous nucleation similarly occurred when 40 or 80 ml litre^?1 trilaurin was admixed with trimyristin. NMR resolution made it possible to follow the crystallization phenomena in different locations of the crystallization vessel effectively in situ and undisturbed. Statistical analyses in this case revealed a significant trilaurin-location interaction confirming that the rate of nucleation processes was affected both by the concentration of trilaurin and the heat transfer properties of the sample and vessel. The time-location interactions were not significant, confirming the hypothesis that in the absence of tilaurin, zero order nucleation did not occur in the first phase.     

Monoacylglycerols in dairy recombined cream: I. The effect on milk fat crystallization

The effect of monoacylglycerols (rich in oleic acid, stearic acid or lauric acid) on milk fat crystallization in recombined cream is examined using differential scanning calorimetry to study crystallization kinetics, nuclear magnetic resonance to measure solid fat content during storage and interfacial tension analyses to analyze interfacial properties. The long-chain saturated monoacylglycerols (stearic acid) form upon cooling a two-dimensional crystal at the interface, called chain crystallization, which induces interfacial heterogeneous nucleation. Also, the crystal growth and α–β′ polymorphic transition were accelerated. On the contrary, long-chain unsaturated monoacylglycerols (oleic acid) didn't affect the crystallization behavior while mid-chain saturated monoacylglycerols (lauric acid) showed intermediate behavior. None of the monoacylglycerols influenced the solid fat content after storage for 5 days at 5 °C. The observed differences in nucleation mechanism and crystallization kinetics may influence the microstructural arrangement of the milk fat inside the fat globules and consequently the partial coalescence rate and hence the whipping properties of recombined cream.     

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.     

搅拌速度对氯化钾结晶影响的研究

通过MSMPR结晶器系统对纯氯化钾及加入光卤石母液后的溶液,采用不同的搅拌速度及不同的桨叶材料进行了氯化钾结晶动力学的研究,计算出了不同的搅拌速度及不同的桨叶材料下氯化钾结晶的基本动力学关系式,分析了氯化钾结晶过程中成核与生长速率的影响程度,为用光卤石生产氯化钾产品,提高其取得率及增大晶体粒度提供了理论依据.     

Crystallization in Lactose Refining—A Review

In the dairy industry, crystallization is an important separation process used in the refining of lactose from whey solutions. In the refining operation, lactose crystals are separated from the whey solution through nucleation, growth, and/or aggregation. The rate of crystallization is determined by the combined effect of crystallizer design, processing parameters, and impurities on the kinetics of the process. This review summarizes studies on lactose crystallization, including the mechanism, theory of crystallization, and the impact of various factors affecting the crystallization kinetics. In addition, an overview of the industrial crystallization operation highlights the problems faced by the lactose manufacturer. The approaches that are beneficial to the lactose manufacturer for process optimization or improvement are summarized in this review. Over the years, much knowledge has been acquired through extensive research. However, the industrial crystallization process is still far from optimized. Therefore, future effort should focus on transferring the new knowledge and technology to the dairy industry.     

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.     

Lactose Solubility and Crystal Growth as Affected by Mineral Impurities

Single crystal growth method was applied to determine lactose solubility, growth rate and morphology of lactose crystals grown in model lactose solutions containing various salts and in whey ultrafiltration (UF) permeate solutions. Salts either increased or decreased the lactose crystal growth rate, due to effects on lactose solubility. Addition of LiCl led to a maximum increase in growth rate and a maximum decrease in lactose solubility, while K₂HPO₄ had opposite effects. Growth rates of individual lactose crystals in whey UF permeate solutions were lower and lactose solubility higher than those in pure lactose solutions.     

Effect of cytoskeleton on ice crystal growth in cells during freezing

The factors affecting intracellular ice formation (IIF) and growth is essential to the mechanistic understanding of cellular damage through freezing. In the aid of high speed and high-resolution cryo-imaging technology, the broad bean intracellular ice formation and growth processes were successfully captured during freezing. Cytochalasin B（CB）was used to solubilize the cytoskeleton. Images of IIF were compared between cells with and without cytoskeleton. The behavior of intracellular ice crystal formation in plant tissues with or without CB was evaluated using changes of cell areas, the probability of crystallization, and growing rate of intracellular ice crystal. Moreover, light intensity figures were used to determine cell damage. This study showed that the cytoskeleton was involved in ice crystal nucleation mechanism during freezing responses of the plant cells.     

Crystallization kinetics of lactose in sytems co-lyofilized with trehalose. Analysis by differential scanning calorimetry

The objective of the present work was to study by differential scanning calorimetry phase/state transitions in model systems of amorphous lactose and lactose co-lyophilized with trehalose. The obtained parameters, such as glass transition temperatures (T_g) and enthalpies of crystallization were employed to test the applicability of different proposed models to predict the behavior of these systems. Thermograms of low moisture lactose–trehalose mixtures showed only one glass transition temperature indicating that compatibility exists between both sugars. The increase of trehalose concentration in the mixture promoted a delay of lactose crystallization in isothermal runs, and of the crystallization temperature (T_cr) in dynamic experiments. The presence of trehalose delayed lactose crystallization, without affecting the T_g value. Several factors (thermodynamic, geometric, kinetics) may modify the molecular environment in the combined systems, affecting nucleation and/or crystal growth. Three models [Arrhenius, Williams–Landel–Ferry (WLF) and Vogel–Tamman–Fulcher (VTF)] were used to study the temperature dependence of the crystallization time. Although experimental points were fitted fairly well by all these models in the range of temperature from 14 to 59 °C above T_g value, the VTF equation appears to apply better for sugars.