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.     

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.     

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.     

Lactose crystallisation in concentrated whey: the influence of vat type

This work aimed to describe the rate of lactose crystallisation in concentrated whey carried out using two different crystallisers, utilising central or lateral stirring. The lactose crystallisation rate differed between treatments, showing high values with use of the central stirrer. Under the experimental conditions, after 4 h of crystallisation, in neither of the vats was 70% lactose crystallisation achieved. With the standardised conditions applied in this study, with soluble solids, time, and stirring and rate cooling being constant, it was possible to verify the influence of the vat type on the rate of lactose crystallisation.     

Effect of solvent and temperature on the size distribution of casein micelles measured by dynamic light scattering

The objectives of this study were to investigate the effect of the solvent on the accuracy of casein micelle particle size determination by dynamic light scattering (DLS) at different temperatures and to establish a clear protocol for these measurements. Dynamic light scattering analyses were performed at 6, 20, and 50°C using a 90Plus Nanoparticle Size Analyzer (Brookhaven Instruments, Holtsville, NY). Raw and pasteurized skim milk were used as sources of casein micelles. Simulated milk ultrafiltrate, ultrafiltered water, and permeate obtained by ultrafiltration of skim milk using a 10-kDa cutoff membrane were used as solvents. The pH, ionic concentration, refractive index, and viscosity of all solvents were determined. The solvents were evaluated by DLS to ensure that they did not have a significant influence on the results of the particle size measurements. Experimental protocols were developed for accurate measurement of particle sizes in all solvents and experimental conditions. All measurements had good reproducibility, with coefficients of variation below 5%. Both the solvent and the temperature had a significant effect on the measured effective diameter of the casein micelles. When ultrafiltered permeate was used as a solvent, the particle size and polydispersity of casein micelles decreased as temperature increased. The effective diameter of casein micelles from raw skim milk diluted with ultrafiltered permeate was 176.4 ± 5.3 nm at 6°C, 177.4 ± 1.9 nm at 20°C, and 137.3 ± 2.7 nm at 50°C. This trend was justified by the increased strength of hydrophobic bonds with increasing temperature. Overall, the results of this study suggest that the most suitable solvent for the DLS analyses of casein micelles was casein-depleted ultrafiltered permeate. Dilution with water led to micelle dissociation, which significantly affected the DLS measurements, especially at 6 and 20°C. Simulated milk ultrafiltrate seemed to give accurate results only at 20°C. Results obtained in simulated milk ultrafiltrate at 6°C could not be explained based on the known effects of temperature on the casein micelle, whereas at 50°C, precipitation of amorphous calcium phosphate affected the DLS measurement.     

CRYSTALLIZATION IN SOLUTIONS SUPERSATURATED WITH SUCROSE AND LACTOSE

Changes in properties of sucrose solutions as a result of substituting lactose for a portion of the sucrose were studied at room temperature (27°C). The influence of a seeding regimen on the properties also was investigated. Seeding with sucrose or lactose favored crystallization of the sugar of higher concentration, whereas seeding a mixture of sucrose and lactose to less supersaturated solutions resulted in rapid crystallization of both sugars. Crystal habit of each sugar was influenced by increasing the concentration of the other. Solution viscosity following complete crystallization increased with the percentage of lactose. As the percentage of lactose in the supersaturated solution was increased, the proportion of lactose in the crystalline mass also increased, the proportion of sucrose decreased, and the hardness of the crystalline mass decreased. Type of seeding influenced the type and number of crystals and therefore influenced the properties of the system, but this was minor compared to the influence of composition. Application of this work to produce softer, smoother sugar products is suggested.     

Physical and mechanical properties of lactose/WPI mixtures: Effect of pre-crystallisation

This study investigated the physical and mechanical properties of spray-dried lactose/whey protein isolate (WPI) (4:1) mixtures with different contents of α-lactose monohydrate (1.0%, 11.2%, 29.2%, and 46.8%, w/w). Particle size of samples with 11.2%, 29.2%, and 46.8% crystallinity was significantly (P < 0.05) larger compared with the sample with 1.0% crystallinity. The presence of less than 46.8% crystalline lactose in lactose/WPI mixtures had only a minor effect on water sorption behaviour at a_w 0.11–0.44, whereas samples with higher crystallinity had higher stable water content after showing lactose crystallisation. Moreover, samples with lower crystallinity showed higher initial sorption rates. Increasing the amount of crystalline lactose had no significant influence on the glass transition temperature and the initial crystallisation temperatures at a_w 0.11–0.44. Furthermore, dairy powders with higher crystallinity had higher stiffness and water plasticisation showed a stronger effect on the structural relaxation of dairy powders with lower crystallinity.     

Casein glycomacropeptide pH-driven self-assembly and gelation upon heating

Casein glycomacropeptide (CMP) found in cheese whey is a C-terminal hydrophilic glycopeptide released from κ-casein by the action of chymosin during cheese making. In a previous work a self-assembly model for CMP at room temperature was proposed, involving a first step of hydrophobic assembly followed by a second step of electrostatic interactions which occurs below pH 4.5. The objective of the present work was to study, by dynamic light scattering (DLS), the effect of heating (35–85 °C) on the pH-driven CMP self-assembly and its impact on the dynamics of CMP gelation. The concentration of CMP was 3% w/w for DLS and 12% w/w for rheological measurements. The solutions at pH 4.5 and 6.5 did not show any change in the particle size distributions upon heating. In contrast the solutions at pH lower than 4.5 that showed electrostatic self-assembly at room temperature were affected by heating. The mean diameter of assembled CMP increased by decreasing pH. For all solutions with pH lower than 4.5, the particle size did not change on cooling, suggesting that the assembled CMP forms formed during heating were stable. The gel point determined as G′–G″ crossover, occurred in all systems at 70 °C, but at different times. The rate of self-assembly determined by DLS as well as the rate of gelation increased with increasing temperature and decreasing pH from 4 to 2. Increasing temperature and decreasing pH, the first step of CMP self-assembly by hydrophobic interactions is speed out. All the self-assembled structures and the gels formed at different temperatures were pH-reversible but did not revert to the initial size (monomer) but to associated forms that correspond mainly to CMP dimers.     

The influence of formulation and cooling rate on the rheological properties of chocolate

Rheological properties of chocolate play a relevant role either in process design or texture definition. Nevertheless, only flow properties of molten product or mechanical properties of samples cooled at fixed temperature (usually 20 °C) are measured, whilst testing conditions close to the industrial applications (temperature close to 30 °C) are less common to be used. In this work, chocolate samples (cooled at 1 and 5 °C min⁻¹) were characterised at 30 °C by using small-amplitude oscillations and low-stress creep tests, aiming at establishing how material properties are related to the chocolate microstructure. The effects of either 3 anhydrous milk fats (AMF), having different melting points, or sugar particle size were evaluated. It was found that addition of AMFs, owing to their solid content, can yield an increase in consistency; however, this effect is less relevant when coarse sugar is used, because of the broader particle size distribution, and it depends on the thermal history because of the different fat crystallisation time. Finally, creep tests resulted to be very sensitive in detecting changes in chocolate rheological properties.     

Characterization and functional properties of soybean high-molecular-mass polysaccharide complex

Soybean soluble polysaccharide (SSPS), extracted from the by-product obtained during isolation of soybean protein, is an anionic polysaccharide that stabilizes milk proteins under acidic conditions. We developed a high-molecular-mass complex of SSPS cross-linked via phosphate (SSPS-HC; absolute molecular weight = 2850 kg/mol, radius of gyration = 106 nm), and found that it has different protein stabilization properties when compared with the original SSPS (absolute molecular weight = 550 kg/mol, radius of gyration = 36 nm). The objective of this work was not only to study the rheological properties of SSPS-HC, but also clarify its protein-stabilizing properties in comparison with SSPS; if molecular mass or negative charge affected protein dispersion. Irrespective of high-molecular-mass, SSPS-HC possessed similar rheological properties to SSPS such as low viscosity in aqueous solution. The absolute negative charges of SSPS-HC measured by a zeta potential analyzer at pH range of 2.0–7.0 were higher than those of SSPS. Acidified milk drinks prepared with 8.4% non-fat milk solids and 0.4% SSPS-HC or SSPS showed low viscosity and small protein particle size, and did not aggregate for 14 days. The thickness of the hydrated layer, which was formed on the surface of protein particles by SSPS molecules measured after hemicellulase treatment with DLS (dynamic light scattering), was estimated to be about 89 nm for SSPS-HC and 33 nm for SSPS. These numerical values were in good relation to the molecular diameter of SSPS-HC and SSPS in aqueous solution measured by DLS and AFM image, and suggested that protein particles were dispersed and the hydrated monolayer made on the surface of protein particles by SSPS-HC or SSPS molecules prevented aggregation. However, stabilizing pH ranges were different with stability of SSPS-HC at pH range of 4.0–4.8 and stability for SSPS at pH range of 3.6–4.2. In addition to the difference in the molecular mass and absolute negative charge, the phosphate groups of SSPS-HC were possibly influenced on the protein-dispersing property approximately at isoelectric point of milk protein; SSPS-HC prevent aggregation of casein by accelerating solubility of calcium phosphate under acidic conditions as is already reported in the starches phosphorylated.     

Heat-triggered thermo-irreversible gelation of curdlan to control crystallisation and in vitro release of nobiletin

Many kinds of flavonoids with poor water solubility and high crystallisation properties tend to crystallise in the system, which negatively affects their processing, storage and bioavailability. Hence, controlling crystal growth is an effective pathway to achieve stabilisation. Inspired by the properties of heat-triggered gelation of curdlan (Cur), the nobiletin (NOB) supersaturated solution was mixed with Cur gel under heating treatment, following which the formation of Cur gel might control NOB crystallisation process in situ. The results showed that different proportions of Cur could change the size of the crystals, of which a concentration higher than 4% could better control the crystallisation of NOB. The effect on texture and rheological properties after the addition of NOB was investigated in detail. Finally, in vitro release experiments showed that the gel played a great role in sustained release, greatly improving the release efficiency compared with pure NOB samples. Taken together, this study proposes a simple stabilisation method that initially attempts to overcome some of the bottlenecks in storage and processing of hydrophobic substances.     

The prediction of moisture sorption isotherms for dairy powders

Moisture sorption isotherms were measured for whey protein isolate, high micellar casein and a milk protein concentrate powder. No temperature dependence was observed over the temperature range of 4–37 °C. At 50 °C the powders absorbed less moisture than observed at the lower temperatures. These isotherms were used to predict the isotherms for freeze-dried amorphous lactose/casein/whey protein powders. An isotherm for micellar casein was predicted using a simple additive isotherm model and was used along with isotherms for whey protein and amorphous lactose to predict moisture sorption isotherms for commercial dairy powders. Predicted isotherms compared well with measured isotherms indicating that this simple additive isotherm model is suitable for predicting moisture sorption isotherms of dairy powders. Delayed lactose crystallisation was observed in lactose/whey protein powders when compared to lactose/casein powders over the same water activity range.     

Prediction of Lactose Crystals Present in Supersaturated Lactose and Whey Solutions by Measuring the Water Activity

Linear models based on water activity measurement were developed to predict the crystalline fraction of lactose present in the supersaturated crystal-solution mixture of lactose and whey. By this method, it was possible to measure the crystalline fraction in the mixture even if the sample is opaque or coloured, which would be difficult to measure by the conventional refractometric method. To calculate the fraction of lactose crystallized, the differential water activity of the crystallized mixture and non-crystalline supersaturated solution needs to be determined. For the pure lactose, the predictive linear equation was Δ?L = 1874.4 Δ?a_w, whereas for whey it was Δ?L = 1155.2 Δ a_w, where Δ L is the amount of α-lactose monohydrate crystals (g 100g^?1 water) that is in the crystallized solution, and Δ a_w is the differential water activity after and prior to crystallization. Other equations such as Raoult's. Norrish, and Money-Born were also tested to predict the water activity of supersaturated solutions of lactose or whey.     

Precipitation of β-carotene microparticles from SEDS technique using supercritical CO2

This work investigates the application of the Solution-Enhanced Dispersion by supercritical fluids technique for the precipitation of β-carotene. The effect of pressure (8.0–12.0 MPa), temperature (293–313 K) anti-solvent flow rate (20–40 mL/min), solution flow rate (1–4 mL/min) and concentration of β-carotene in the dichloromethane solution (4 and 8 mg/mL) on the precipitation yield, particle morphology and particle size and size distribution was examined. Precipitated powders presented mean particle size varying from 3.2 μm to 96.8 μm with morphology of β-carotene microparticles changing from plate-like to leaf-like particles. The statistical analysis of the experimental results revealed that pressure, organic solution concentration and CO₂ flow rate had a significant effect on particle size. The precipitation yield was observed to be within the range of 71–94% and was statistically influenced by system temperature and pressure, and anti-solvent flow rate.     

Aqueous citric acid as a promising cleaning agent of whey evaporators

Scale in evaporators for lactose production was identified as mainly calcium citrate tetrahydrate with phosphate contaminations. Dissolution of 3.00 g of scale in aqueous solutions of 0.100, 0.500, and 1.00 mol L⁻¹ citric acid with final volumes of 100, 50, and 25 mL was investigated. The highest concentration of citric acid was the most effective for all the investigated volumes. From the citric acid solutions, spontaneously supersaturated in calcium citrate tetrahydrate during scale dissolution in the smaller volumes for all citric acid concentrations, calcium citrate tetrahydrate slowly precipitated in acceptable purity for technical use. Dissolution efficiency of aqueous solutions of 0.200 mol L⁻¹ nitric acid combined with 0.100, 0.500, and 1.00 mol L⁻¹ citric acid with final volumes of 100, 50, and 25 mL showed synergistic effect especially for the higher concentrations and lower volumes of two acids.     

The influence of different water types and brewing durations on the colloidal properties of green tea infusion

Green tea infusions were prepared with three different water types: distilled water, commercial mineral water and CaCl₂ added distilled water (at 20 mg L^?1). The impact of different water type on the colloidal particle parameters, namely size, polydispersity index (PDI) and zeta potential, was examined within 24 h. Our results indicate that distilled water green tea infusion (DWT) brewed at 80 °C for 5 min contained the smallest particles (242.17 ± 11.78 nm) as examined by dynamic light scattering (DLS). Moreover, DWT showed smaller size increase during the 24 h storage than that of mineral water tea and CaCl₂ added water tea infusion. The morphology characteristics of green tea infusion particles were visualised by transmission electron microscope (TEM) which revealed that green tea infusion particles had heteromorphic shapes. Our results suggest that mineral composition of water impacts the colloidal size and stability of green tea infusion. Additionally, DLS and TEM could be useful tools to provide colloidal information which is important to understand quality characteristics of green tea infusion during processing and storage.     

β-Carotene nanodispersions: preparation,characterization and stability evaluation

The aim of the present study was to investigate the preparation of β-carotene nanodispersions as potential active ingredients for food formulations. Nanodispersions containing β-carotene were obtained by a process based on an emulsification–evaporation technique. The preparation method consisted of emulsifying an organic solution of β-carotene in an aqueous solution containing emulsifier using two different homogenizers (a conventional homogenizer and a microfluidizer), followed by direct solvent evaporation under reduced pressure. The influence of different homogenizing conditions (pressure and cycle) and two organic/aqueous phase ratios on particle size parameters and content of β-carotene was investigated. In addition, the stability of β-carotene nanodispersions was carried out at a storage temperature of 4 °C. The particle size distribution of β-carotene in nanodispersions was demonstrated with a laser diffraction particle size analyzer and the retention of β-carotene in the prepared nanodispersions was studied by high-pressure liquid chromatography. In general, homogenization pressure and cycle had significant (P < 0.05) effects on various particle size parameters. A volume-weighted mean diameter (D_4,3) of β-carotene nanoparticles, ranging from 60 to 140 nm, was observed in this study.     

Effect of temperature,calcium and protein concentration on aggregation of whey protein isolate: Formation of gel-like micro-particles

Protein aggregation occurs in biological systems and industrial processes, affecting protein solubility and functional properties. In this study, whey protein isolate (WPI) obtained from bovine milk was used as a model to study the dependence of aggregation on pre-heating temperature and on protein and calcium concentrations. WPI solutions (0.1–5.0%, w/v) were heated at 25–85 °C for 30 min prior to cooling and calcium addition. Tryptophan shifted to a more hydrophilic environment as WPI concentrations and pre-heating temperatures increased. Pre-heated WPI solutions yielded soluble particles, which aggregated to form porous gel-like particles by addition of calcium chloride. WPI microgel particles could be prepared by using a cold gelation method and preheated the protein above 65 °C. The particle size was monodisperse with sizes of about 190 nm and 255 nm, respectively in solutions pre-heated to 75 or 85 °C and containing 5 mm calcium.     

Digestibility and structural parameters of spray-dried casein clusters under simulated gastric conditions

The digestibility of casein clusters prepared from sodium caseinate solution (plain or pH-adjusted (pH = 6.0)) was studied. The prepared solutions were spray-dried at different inlet air temperatures (150 °C and 180 °C), and the properties (i.e. encapsulation efficiency, surface hydrophobicity, and digestibility) of the resultant powders were investigated. The specimens obtained from the pH-adjusted solution had higher encapsulation efficiencies than the specimens obtained from the plain solution. A higher spray-drying temperature resulted in lower encapsulation efficiencies and higher surface hydrophobicities. Simulated gastric digestion tests were carried out to study the digestibility of the obtained casein clusters, which was analyzed in terms of reaction kinetics and structural changes during digestion. The effects of drying temperature and pH on the amount of casein digested were not significant; that is, approximately 30% of casein was digested in 120 min for all specimens. Small-angle and ultra-small-angle X-ray scattering measurements were used to analyze the structure of the obtained clusters and their changes during digestion. The results suggested that all the obtained casein clusters, with an average size of approximately 428 nm, had a rough, fractal-structured surface with many dense primary clusters. These structures changed during digestion; specifically, the cluster size increased both in the overall diameter and on the primary structure scale. The fractal characteristics changed from surface to mass fractals, and simultaneously, the cluster density decreased. The drying temperature affected the cluster size during digestion, and the trends were different in the specimens obtained from the plain and pH-adjusted solutions. These results could be useful in the design of protein-based encapsulation systems with desirable digestibility and bioavailability.     

Characterisation of sodium caseinate as a function of ionic strength, pH and temperature using static and dynamic light scattering

Extensive static and dynamic light scattering (DLS) measurements were done on sodium caseinate solutions as a function of the ionic strength (3–500 mM NaCl), pH (5–8) and temperature (10–70 °C). DLS results were analysed in terms of two populations: the caseinate and a small weight fraction of large particles with a hydrodynamic radius (R_h) of about 65 nm that was independent of the ionic strength, pH and temperature. Caseinate was present as individual molecules at low ionic strength (3 mM), but formed small aggregates (R_h=11 nm) at high ionic strength (>100 mM). The aggregation number (N_agg) increased weakly with decreasing pH between pH 8 and 6, but extensive acid-induced aggregation occurred below pH 5.4 at 250 mM and below pH 6.0 at 3 mM. N_agg increased reversibly with increasing temperature.