Graininess is a common structural defect in microgel suspensions, e.g., yogurt or fresh cheese. The aim of this study was to investigate the impact of the temperature (23-54°C) and the holding time (1-300 min) on the formation of particle clusters in concentrated, fermented milk (protein content 8.2% (w/w)) during post-processing. Since graininess is correlated with the presence of large protein aggregates, temperature treatment during post-processing was varied systematically to promote particle growth and the particle size d 75.3 was measured. The samples revealed a polydisperse particle size distribution present at all temperatures and holding times. With longer holding times, rearrangement led to larger particle clusters while the number of smaller particles decreased. The increase in the d 75.3 was fitted with a power law function while higher temperatures promoted both the aggregation rate and the particle size. By using the Arrhenius equation, the activation energy, E A , was calculated (26 kJ.mol −1 ), which was in agreement with the aggregation kinetics occurring at smaller scales, e.g., the acid-induced aggregation of casein micelles and the temperature-induced aggregation of casein submicelles. According to the activation energy, the particle growth in microgel suspensions was proposed to be predominantly diffusion-limited. The results of this study imply that particle size during post-processing is adjustable. Furthermore, the particle size increases with increasing temperature load, thus, rapid cooling reduces the Dairy Sci. & Technol. (2012) 92:91-107 DOI 10.1007/s13594-011-0046-
We present a rapid and gentle drying method for the production of high-grade tomato powders from double concentrated tomato paste, comparing results with powders obtained by foam mat air drying and freeze dried powders. The principle of this method consists of drying tomato paste in foamed state at low temperatures in vacuum. The formulations were dried at temperatures of 50, 60, and 70 °C and vacuum of 200 mbar. Foam stability was affected by low serum viscosity and the presence of solid particles in tomato paste. Consequently, serum viscosity was increased by maltodextrin addition, yielding optimum stability at tomato paste:maltodextrin ratio of 2.4:1 (w/w) in dry matter. Material foamability was improved by addition of 0.5% (w/w, fresh weight) egg white. Because of solid particles in tomato paste, foam air filling had to be limited to critical air volume fraction of Φ = 0.7. The paste was first pre-foamed to Φ = 0.2 and subsequently expanded in vacuo. After drying to a moisture content of 5.6% to 7.5% wet base (w.b.), the materials obtained were in glassy state. Qualities of the resulting powders were compared with those produced by freeze and air drying. Total color changes were the least after vacuum drying, whereas air drying resulted in noticeable color changes. Vacuum foam drying at 50 °C led to insignificant carotenoid losses, being equivalent to the time-consuming freeze drying method. In contrast, air drying caused lycopene and β-carotene losses of 18% to 33% and 14% to 19% respectively. Thus, vacuum foam drying enables production of high-grade tomato powders being qualitatively similar to powders obtained by freeze drying.
Liposomes have attracted considerable attention in the food and agricultural, biomedical industries for the delivery of functional components. However, maintaining their stability in aqueous dispersion represents a challenge for their commercialization. Spray drying may promise a solution to that problem. However, prior to this study spray drying of liposomes often led to the loss of structural integrity. Results of this study suggest that spray drying might be used to produce commercially feasible liposomal powders if proper combinations of adsorbing and nonadsorbing polymers are used in the liquid precursor system.
This article presents rapid and gentle-drying method for the preparation of highgrade honey powders from honey-glucose syrup formulation. The honey invertase was used as a marker of final product quality. Honey-glucose syrup ratio was 0.55:0.45 w/w; 1% whey protein isolate was added as surfactant. Drying of honeyglucose syrup formulation was carried out in the foamed state. The material was pre-foamed to an initial air volume fraction of 0.25-0.30, subsequently expanded in vacuo to 0.65-0.70. Drying trials were performed at a vacuum level of 100 mbar in a temperature range of 40-60C chosen in accordance with invertase degradation kinetic data. Powders that were vacuum foam dried at 40C and 50C showed insignificant invertase loss and thus similar quality to powders obtained by the much more time-consuming freeze-drying method. Furthermore, the powders proved very stable as no powder caking was observed after 6 months of storage at ambient conditions. PRACTICAL APPLICATIONSThe vacuum foam-drying method presented in our study is suitable for the preparation of high-grade honey powders for premium products in pharmaceutical or dietary supplements. As a result of gentle-drying conditions, i.e., low temperature and reduced pressure, there is a high retention of valuable thermo-and oxidativesensitive nutrients, indicated by the high residual invertase activity in the dried powders. Regarding the retention of valuable nutrients, this method is comparable with freeze drying, which is currently used in pharmaceutical applications, but vacuum foam drying is faster and less expensive. The composition of the honey formulation also facilitates good powder storage stability.
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