The objective of this study was to assess the effects of three storage temperatures (11, 20 and 26 7C) on the migration kinetics and equilibrium states of a model filled confection consisting of dark chocolate and a hazelnut oil-based filling. HPLC, atomic force microscopy and X-ray diffraction were used to study the migration behaviour of hazelnut oil into simulated filled confections and the associated changes in microstructure. Using a Fickean model, the mechanism for the migration of foreign triacylglycerols (TAG) into chocolate was evaluated. Deviations from Fickian diffusion were noted with increasing temperature, and resulted from the breakdown of the chocolate matrix. At higher temperatures, filled dark chocolate exhibited accelerated fat bloom formation due to the increased ingress of foreign incompatible TAG. The rate of migration and the diffusion coefficient increased 20 and 400 times, respectively, when the storage temperature was raised from 11 to 26 7C. The amplified rate of migration at elevated temperatures resulted in a confectionary product with a severe loss in quality. There was significant degradation in the texture and gloss of the product within 24 h of storage at 26 7C. However, the storage of filled dark chocolate at 11 and 20 7C showed negligible deterioration over 8 wk. Overall, the results from this study offer some insight into the optimisation for the production and storage of filled chocolates.
Commercially available butter, regular-fat margarine, and a fat-reduced margarine (38% fat w/w) were stored between 10 and 35°C for up to 4 d to elaborate on the relationship between droplet size and solid fat content (SFC) that exists in these spreads. At 10°C, the mean volume-weighted droplet size for butter was 4.22 ± 0.40 µm followed by margarine (6.22 ± 0.10 µm) and fat-reduced margarine (12.62 ± 0.28 µm). At higher temperatures, as a result of decreasing SFC, the mean droplet size increased as did the droplet size distribution, leading to eventual coalescence and destabilization in all spreads. In butter, the critical SFC was ~9%, whereas in margarine notable coalescence occurred at ~5% SFC. The fat-reduced margarine destabilized at lower temperatures than the other spreads (~20°C vs. ~30°C), at an SFC of ~6.5%. In these spreads, two different mechanisms influenced dispersed phase stability: (i) steric stabilization against coalescence via fat crystals located at the droplet interface, known as Pickering stabilization, and (ii) stabilization against droplet sedimentation (and droplet encounters) due to the presence of the fat crystal network.Paper no. J10475 in JAOCS 80, 957-961 (October 2003).Table spreads are multiphase colloidal systems consisting of an aqueous phase dispersed as fine droplets (typically 1-20 µm) within a continuous oil phase and fat crystal network. In butter and margarine, the aqueous phase (16% w/w) usually consists of water and salt, and in the case of margarine, milk protein (usually buttermilk or whey) and preservatives are dispersed in an oil and fat network (80% w/w total). The stability of table spreads may depend on two mechanisms: (i) Pickering stabilization, whereby interfacially absorbed colloidal particles sterically stabilize dispersed droplets (1), and (ii) the presence of a fat crystal network that physically "locks" the water droplets in place within the spread matrix, thereby preventing droplets from migrating, flocculating, coalescing, and eventually creaming (2). This is in contrast to fat-reduced spreads (≤40% w/w fat), where the kinetic stability of the dispersed phase, although still dependent on the presence of a fat crystal network, also relies on the composition of the aqueous phase. Thickeners such as gelatin or polysaccharide gums are often added to fat-reduced spreads to hinder droplet-droplet coalescence by increasing the viscosity of the dispersed phase. Furthermore, surfactants such as MAG are added to such systems to increase stability. Few studies on the differing mechanisms involved in table spread stability have been reported in the literature. Borwankar et al.(3) and Borwankar and Buliga (4) examined the emulsion properties of low-fat spreads and margarines and the relationship between rheology and meltability. Heertje (5) investigated the relationship between structure and functionality in numerous spreads, commenting on the differences in network structures between spreads of differing compositions and processing conditions. Conspicuously lacking, ...
Microtopographical roughening and fat phase melting of milk chocolate subjected to three temperature cycles between 20 and 28, 30, 32, or 34°C were examined using optical profilometry and differential scanning calorimetry (DSC). Cycling to any of these temperatures did not lead to immediate visual bloom, though significant effects on microstructure and fat phase melting behavior were noted. The initial chocolate topography was lightly mottled and consisted of small asperities. DSC indicated the presence of form V crystals in control chocolates kept isothermally, with form VI crystals appearing with cycling to 30 and 32°C. The fat phase of the chocolates cycled to 34°C existed only in the form IV polymorph. As a result of cycling, the surface roughness of all samples increased, with the smallest rise seen with cycling to 28°C. Decomposition of the roughness into low and highfrequency components revealed a significant contribution of waviness (the low-frequency component) to overall roughness, particularly with cycling to 34°C. Furthermore, with the fat phase fully molten, the backbone structure consisting of the dispersed particulates also contributed to overall roughness. This study demonstrated that significant microstructural changes and deformation take place within chocolate as a result of temperature fluctuations prior to the onset of visible surface fat bloom.
Genipin-crosslinked gelatin-maltodextrin phase-separated hydrogels consisting of gelatin-continuous or bicontinuous microstructures were developed to regulate swelling and release behavior of four fluorescent markers of varying molecular weights [(fluorescein (332 Da) and FITC-dextrans (FD) (4000-250,000 Da)]. Bicontinuous hydrogels showed significantly greater swelling than gelatin-continuous hydrogels under all conditions (at pH 1.5 and 7.4 and three genipin/gelatin crosslinking ratios) (P < 0.05). With both microstructures, fluorescein showed the largest release rate and total release followed by FD 4000 Da, FD 40,000 Da, and FD 250,000 Da (P < 0.05). Marker molecular weight, pH, and crosslink ratio all affected the rate and amount of release. The mode of transport for the solvent and all markers was Fickian or slightly anomalous, with diffusional exponent (n) values ranging from 0.35 to 0.64. These results demonstrated that with the proper combination of crosslink density, solvent pH, and microstructure, hydrogels with a specified swelling behavior may be developed. This, coupled with a marker of appropriate size, can lead to controllable levels and rates of release.
We report the results of timing and spectral analysis of the x-ray pulsar EXO2030+375. The observations were made using the Rossi x-ray timing explorer space satellite. The spectral analysis is carried out for the flux of x-ray energy range 3-30 keV. The x-ray continuum spectra of proportional counter array could be represented by a two-component model, a power law with an exponential cutoff at higher energies and a blackbody. An iron line at about 6.4-6.6 keV was also detected.
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