WATER PLASTICIZATION EFFECTS ON CRYSTALLIZATION BEHAVIOR OF LACTOSE IN A CO-LYOPHILIZED AMORPHOUS POLYSACCHARIDE MATRIX AND ITS RELEVANCE TO THE GLASS TRANSITION

ABSTRACT

Crystallization of lactose in a co-lyophilized amorphous polysaccharide matrix was investigated under various hydration conditions to test the possible relation between the ability of the polymer to raise the glass transition temperature (T_g) of the lactose-pullulan blend, relative to pure lactose, and the crystallization kinetics. Both calorimetric (DSC) non-isothermal measurements and x-ray diffraction analysis of samples stored at a constant temperature revealed a marked retardation in lactose crystallization in the presence of pullulan; i.e., the rate constant values, as determined by the Avrami analysis, declined and the ‘half-time’ (t_1/2c) for lactose crystallization increased with decreasing ratio of lactose/pullulan. The inhibitory action of pullulan on crystallization of lactose could not be solely attributed to T_g-related effects on molecular mobility of the composite systems. At a pullulan weight fraction range of 0.25–0.33 (w/w of total solids) the influence of the polymeric additive on T_g was marginal over the entire water content range examined, although crystallization was delayed as compared with pure lactose. Modeling of the temperature-dependence of t_1/2c for the combined lactose-pullulan systems with the Williams-Landel-Ferry (WLF) equation was feasible only when the coefficients C₁ and C₂ were allowed to vary instead of assuming their ‘universal’ values.     

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.     

Glass transition and crystallization behaviour of freeze-dried lactose-salt mixtures

Glass transition temperatures were determined for dehydrated lactose/salt mixtures with various water contents and water activities, and state diagrams were established. Crystallization behaviour was studied for pure amorphous lactose stored at various relative water vapour pressures (RVP). Furthermore, glass transitions temperatures and time-dependent lactose crystallization of freeze-dried lactose and lactose/CaCl₂, lactose/NaCl, lactose/MgCl₂ and lactose/KCl mixtures in molar ratios of 9:1 were determined. Glass transition temperatures (T_g) of lactose powder as determined by differential scanning calorimetry (DSC) was lower than that of lactose/CaCl₂ (9:1)_, and lactose/MgCl₂ (9:1), but it was slightly higher than the T_g of lactose/NaCl (9:1), and lactose/KCl (9:1). Lactose/KCl had the lowest glass transition temperature, but it had about the same crystallization temperature as lactose/NaCl, and lactose/MgCl₂. The glass transition temperatures decreased as water contents increased. The critical water contents and water activities at 23 °C were predicted using data on glass transition temperature and water sorption. Pure lactose had a different critical water activity and water content from lactose/salt mixtures. The critical values of lactose/CaCl₂ (9:1) were the highest. Loss of sorbed water, indicating lactose crystallization, was observed in lactose and lactose/salt mixtures stored above the critical RVP.     

Characterization of Physical and Mechanical Properties of Miscible Lactose‐Sugars Systems

Lactose‐sugars systems were produced by spray drying. They were lactose, lactose–glucose (4:1) mixtures, lactose–maltose (4:1) mixtures, lactose–sucrose (4:1) mixtures, lactose–trehalose (4:1) mixtures, and lactose–corn syrup solids (CSS) (4:1) mixtures. The physical characteristics, water sorption behavior, glass transition, and mechanical properties of miscible lactose‐sugars systems were investigated. Lactose–glucose mixtures had larger particle size than other lactose‐sugars systems after spray drying. The presence of glucose or sucrose in lactose‐sugars mixtures decreased the glass transition temperatures of amorphous systems, while the presence of maltose and trehalose had only minor impact on the glass transition temperatures. Moreover, glucose accelerated the crystallization of amorphous system at 0.44 a_w, but its presence delayed the loss of sorbed water at higher water activities (≥0.54 a_w). Mechanical property study indicated that glucose and sucrose in amorphous system could result in an increase of molecular mobility, while the presence of CSS could decrease the free volume and maintain the stiffness of the miscible systems.     

Crystallization behavior of lactose/sucrose mixtures during water-induced crystallization

The crystallization behavior of lactose/sucrose mixtures during water-induced crystallization was studied to gain more insight about their crystallization during storage. Solutions with different ratios of lactose and sucrose, 75:25 and 50:50, were spray dried to produce amorphous powders. The powders were kept at a controlled temperature and humidity to study their sorption–desorption behavior. X-ray diffraction and light microscopy analysis were performed to study their crystallization behavior. Two-step desorption was observed after sieving the powders as sample preparation. Sieving decreased the crystallization time for lactose/sucrose mixture 75:25 from 22 days to 2.5 days. Based on the X-ray diffraction analysis during this two-step process of water desorption, it was concluded that lactose crystallizes first and more quickly than sucrose. The degree of crystallization for the lactose crystals increases by 89% (relative to their final level of crystallinity), whereas sucrose crystals increase their level of crystallinity by only 28% during the first step of crystallization in the lactose/sucrose (75:25) mixtures. The light microscopy images also suggested that the crystallization of amorphous lactose/sucrose powders during water-induced crystallization may occur as a solution rather than in the solid phase.     

X-ray diffraction analysis of lactose crystallization in freeze-dried lactose–whey protein systems

Water sorption, time-dependent crystallization and XRD patterns of lactose and lactose–WPI mixtures were studied with glass transition data. The results indicated that the sorbed water of lactose–WPI mixtures was fractional and water content of individual amorphous components in lactose–WPI mixtures at each a_w from 25 °C to 45 °C could be calculated. Crystallization occurred in pure lactose whereas partial crystallization was typical of lactose–WPI mixtures (protein content ≤ 50%) at intermediate and high a_w (> 0.44 a_w) from 25 °C to 45 °C. The extents of crystallization were significantly delayed by WPI. The T_g values of lactose–WPI systems showed the composition-dependent property in systems and might indicate the occurrence of phase separation phenomena during 240 h storage. XRD showed no anhydrous β-lactose and mixed α-/β-lactose with molar ratios of 4:1 crystals in crystallized lactose–WPI systems (70:30 and 50:50 solids ratios). Reduced crystallization in the presence of WPI was more pronounced possibly because of reduced nucleation and diffusion during crystal-growth. The present study showed that WPI could present an important role in preventing sugar crystallization.     

Glass Transition and Crystallization of Amorphous Trehalose-sucrose Mixtures

Our objective was to investigate the glass transition and crystallization of trehalose-sucrose mixtures at various moisture contents. Samples were freeze-dried, rehumidified, and scanned with Differential scanning calorimetry (DSC) to obtain T_g values for all mixtures and pure sugars. Amorphous cotton candy samples for crystallization studies were prepared, humidified, and monitored for crystallinity as a function of time using powder X-ray diffraction (XRD). The T_g of pure dry trehalose was found to be 106 °C, while sucrose had a T_g of 60 °C. Glass transition, as expected, occurred at an intermediate temperature for sucrose-trehalose mixtures. Of the dry samples, only those containing less than 16% trehalose showed sucrose crystallization during scanning. In cotton candy made from a 25% trehalose-75% sucrose mixture, humidified to 33%, sucrose did not crystallize after 30 days, whereas pure sucrose cotton candy at that humidity crystallized completely after 11 days. These data show that trehalose may be a useful crystallization inhibitor in foods with high sucrose content, although small amounts of trehalose did not significantly raise the T_g.     

Crystallization Kinetics of Lactose and Sucrose Based On Isothermal Differential Scanning Calorimetry

Isothermal Differential Scanning Calorimetry (DSC) was used to study the crystallization kinetics of freeze-dried samples of lactose and sucrose at several temperatures between Tg and Tm. The sample was rapidly heated to the required temperature. After subtraction of an induction time, the Avrami equation was used to model the data and a Lauritzen-Hoffman like expression used to fit the derived rates of crystallization over the temperature range Tg相似文献   

Physical State Study of (Sugar Mixture)-Polymer Model Systems

The physical state of components in the unfrozen solute phase of frozen solutions was determined by using differential scanning calorimetry (DSC) for mixtures of lactose, sucrose, and trehalose with albumin, gelatine, or cornstarch. An equal weight ratio (1:1) of lactose-sucrose, lactose-trehalose and sucrose-trehalose mixtures with polymer systems (sugar mixture-albumen (1:1:1), gelatine (1:1:1), and cornstarch (1:1:1), as well as cornstarch-gelatine (1:1:1:1) was used. Mixed sugar mixture (lactose/sucrose)-polymer systems were further studied for maximum freeze-concentration in complex systems. A comparative thermal study between sugar-polymer and mixed sugar-polymer systems was conducted. The sugar-polymer and mixed sugar-polymer systems showed similarities and differences in thermal behaviour. The similarities included maximum freeze-concentration of a frozen system at an annealing temperature (T_m´-1) °C, constant initial concentration independent onset of glass transition T_g´, and onset of ice melting temperature T_m´, and increased in temperature difference between T_g´ and T_m´ or increase in broadness of transition with the addition of polymeric compound.     

Crystallization and X-ray Diffraction of Crystals Formed in Water-Plasticized Amorphous Spray-dried and Freeze-dried Lactose/Protein Mixtures

ABSTRACT: Effects of proteins (whey protein isolate [WPI], Na-caseinate, and gelatin), drying method, storage relative vapor pressure (RVP), and time on lactose crystallization and crystals formed were investigated using x-ray diffraction (XRD). Crystallization was observed from increasing peak intensities of XRD patterns. Lactose in lactose/protein (5:1,3:1) mixtures crystallized in samples stored at RVP of 44.1% and above in both spray-dried and freeze-dried materials, except in freeze-dried lactose/Na-caseinate and lactose/gelatin mixtures, which showed lactose crystallization at 54.5% RVP and above. The rate of crystallization increased with increasing RVP and storage time. The rate of crystallization in spray-dried materials was higher than in freeze-dried materials, and the crystallization rate decreased with increasing protein content. Lactose crystallized mainly as α-lactose monohydrate in spray-dried lactose/WPI and lactose/gelatin mixtures. Crystals formed in freeze-dried lactose/WPI and lactose/gelatin mixtures were anhydrous β-lactose and α-lactose monohydrate crystals. Lactose crystallized as a-lactose monohydrate in both spray-dried and freeze-dried lactose/Na-caseinate mixtures. Trace amounts of anhydrous β-lactose were present in spray-dried lactose/WPI (5:1) and lactose/gelatin (5:1) mixtures. Peak intensities of XRD patterns for anhydrous β-lactose decreased with increasing protein content and storage time. The crystallization data were successfully modeled using Avrami equation at an RVP of 65.6% and above. These data are important in understanding and predicting storage stability of lactose- and protein-containing food and pharmaceutical materials.     

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.     

Structural strength and crystallization of amorphous lactose in food model solids at various water activities

Freeze-dried lactose and lactose/whey protein isolate (WPI) mixtures were used as amorphous food models at various a_w, and the effects of temperature and water and WPI contents on physical state were analyzed. Thermal behavior and mechanical properties were studied and Williams-Landel-Ferry (WLF) model was fitted to structural relaxation times (τ). The WLF-analysis gave a strength parameter (S) that was used to describe structural strength of the food solids. Our results showed that lactose and WPI in mixtures exhibited fractional water sorption. Thermal properties and structural strength of the solids were affected by water and WPI while T_g measured for the lactose/WPI systems followed that of the lactose component and showed phase separation of lactose and proteins. A relationship between S and water content was established, whereas the crystallization of amorphous lactose was more rapid in systems with a smaller S. Therefore, S provided a simple and convenient measure of τ controlling structure formation in food processing as well as to control lactose crystallization.Industrial relevanceSugars are common ingredients and often used as a mixture with other components, e.g., proteins, in the food and pharmaceutical industries. Thus, understanding the physical state and thermal behavior of sugar containing food materials has a great importance in the development of processing and shelf life control procedures for such ingredients and relevant products. This study provides physicochemical information about thermal and mechanical properties of freeze-dried lactose/whey protein systems used as food models at various water activities. Data on water sorption, time-dependent lactose crystallization, calorimetric glass transition and crystallization temperatures, and structural relaxation times can be used to understand and predict structural changes during processing and storage of relevant foods. Moreover, the structural strength concept, described in this study, allows of the control of crystallization behavior as a physical state and time-dependent phenomenon, and therefore, stability of food and pharmaceutical materials     

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。     

Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that (E_a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E_a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage (G′) and loss (G′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G′ and G′′ increased with the increase in gum concentration. Dynamic rheological data of ln (G′, G′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G′ greater than G′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.     

Effect of protein concentration on the surface composition,water sorption and glass transition temperature of spray-dried skim milk powders

The effects of dilution of protein content in skim milk (34–8.5% protein content), by lactose addition, on the surface composition, water sorption property and glass transition temperatures of spray-dried powders were investigated. The X-ray photoelectron spectroscopy (XPS) study of spray-dried powders showed preferential migration of proteins toward the surface of the milk particles whereas the lactose remained in the bulk. Sorption studies showed that the lower protein concentration in milk powders is linked to an increased water adsorption property and lowering of water activity (a_w) for lactose crystallization. Analysis of glass transition temperature (T_g) of the powders sorbed at different humidities showed no distinct change in T_g values, indicating the dominant effect of lactose on the glass transition temperature of all the powders.     

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.     

Optimization of Combined Microwave–Hot Air Roasting of Malt Based on Energy Consumption and Neo-Formed Contaminants Content

ABSTRACT: To produce specialty malt, malts were roasted by combined microwave–hot air at various specific microwave powers (SP = 2.5 to 3 W/g), microwave heating times (t_mw = 3.3 to 3.5 min), oven temperatures (T_oven = 180 to 220 °C), and oven heating times (t_oven = 60 to 150 min). The response variables, color, energy consumption by microwave (E_mw) and oven (E_oven), total energy consumption (E_tot), quantity of neo-formed contaminants (NFCs), which include hydroxymethylfurfural, furfural, furan, and acrylamide were determined. Response surface methodology (RSM) was performed to analyze and predict the optimum conditions for the specialty malt. Production using combined microwave–hot air roasting process based on minimum energy consumption and level of NFCs. At 95% confident level, SP, T_oven, and t_oven were the most influencing effects with regard to E_tot, whereas t_mw did not affect E_tot. T_oven and t_oven significantly affected malt color. Only T_oven significantly influenced the NFCs content. The optimum parameters were: SP = 2.68 W/g for 3.44 min, T_oven = 206 °C for 136 min for coffee malt, SP = 2.5 W/g for 3.48 min, T_oven = 214 °C for 136 min for chocolate malt, and SP = 2.5 W/g for 3.48 min, T_oven = 211 °C for 150 min for black malt. Comparing with conventional process, combined microwave–hot air reduced E_tot by approximately 40%, 26%, and 26% for coffee, chocolate, and black malts, respectively, and reduced HMF, furfural, furan, and acrylamide contents by 40%, 18%, 23%, and 95%, respectively, for black malt. Practical Application: An important goal for research institutions and the brewery industry is to produce colored malt by combining microwave and hot air roasting, while saving energy, getting desirable color, and avoiding the formation of carcinogenic and toxic neo-formed contaminants (NFCs). Therefore, one objective of this study was to compare energy consumption and content of NFCs during roasting of malt by hot air-only and combined microwave–hot air processes as well as to determine the effect of specific power, microwave processing time, oven temperature, and oven processing time during combined microwave–hot air roasting. Another objective was to predict the optimum conditions for the production of coffee, chocolate, and black malts.     

Water Sorption and Plasticization Behavior of Spray-dried Lactose/Protein Mixtures

ABSTRACT: Water sorption properties, effects of proteins on glass transition temperature, and time-dependent lactose crystallization of spray-dried lactose and lactose in lactose/WPI (3:1), lactose/Na-caseinate (3:1), lactose/albumin (3:1), and lactose/gelatin (3:1) mixtures were investigated. Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were used to model water sorption. Lactose/protein mixtures sorbed high amounts of water at low relative vapor pressure (RVP) up to 23.1%. Above 23.1% RVP levels, water sorbed by pure lactose was higher, up to 44.1% RVP, except in the case of the lactose/gelatin mixture. Lactose/ gelatin also sorbed a high amount of water at 33.2% RVP. Loss of sorbed water resulting from crystallization of amorphous lactose was observed. Crystallization of pure lactose and lactose crystallization in lactose/protein mixtures occurred at RVP ≥ 44.1% within 24 h. After crystallization at RVP ≥ 54.5%, water contents remained higher for lactose/protein mixtures than for pure lactose. The rate of lactose crystallization was less in all lactose/protein mixtures than was observed for pure lactose. WPI had the lowest effect on lactose crystallization. Crystallization occurred most slowly in lactose/gelatin mixtures. Both GAB and BET models fitted to water sorption data up to 0.441 a_w. It seems that different proteins interact with lactose differently. Water sorption and time-dependent lactose crystallization of lactose/protein mixtures have important consequences to processing and storage behavior of lactose-protein based products.     

Kinetic analysis of isothermal crystallization in hydrogenated palm kernel stearin with emulsifier mixtures

The kinetics of isothermal crystallization of hydrogenated palm kernel stearin (HPKS) with emulsifiers was evaluated by applying the Avrami equation. Effects of five commercial emulsifiers (lecithin, monoglyceride, polyglycerol polyricinoleate, Span 60, and Tween 60) on crystallization behaviors were tested at four different isothermal temperatures (15, 20, 25, and 30 °C). It is shown that, as temperature increases, induction time for HPKS samples generally increased especially from 25 to 30 °C. Meanwhile, different nucleation mechanisms were observed according to Avrami exponent (n) values. The addition of emulsifiers generally accelerated crystallization rate without changing the growth mechanism (plate-like growth) under 25 °C. However, when the temperature increased to 30 °C, n ranged from 1.0 to 5.1, which indicated different nucleation mechanisms induced by different emulsifiers. Avrami constant (k) (indicating the crystallization rate) decreased as the temperature increased except for samples with Span 60. At higher temperatures, values of t_1/2 were significantly higher which reflects the decrease in k at higher temperatures. Crystal microstructures at 30 °C were obtained by using polarized light microscope. Lecithin and Span 60 samples showed large and dense crystals compared with the control sample. Tween 60 sample showed very small crystals which aggregated in a line trend. However, small differences were observed in fractal dimension results except for Tween 60 sample.     

Amorphous lactose crystallisation kinetics

Amorphous lactose crystallisation kinetics were investigated at different relative humidity and temperature combinations. Amorphous lactose was equilibrated to a water activity of 33%, then placed in sealed pans with a saturated magnesium chloride solution to maintain a constant relative humidity (33%). The temperature was raised to 10–40 °C above the glass transition temperature (T_g). The degree of crystallisation was measured using isothermal microcalorimetry. Crystallisation was shown to be an all-or-nothing event, such that direct measurement of the kinetics was not possible. This was not expected from the Avrami model. The rapid crystallisation could be an autocatalytic effect, as moisture is released during crystallisation, or a showering event as seen in highly supersaturated lactose solutions. Experiments using a blend of crystalline and amorphous lactose, produced by spray drying a lactose crystal slurry, showed crystallisation occurring at lower T_g conditions than was required for the crystallisation of 100% amorphous lactose.