Determination and modelling of the particle size dependent residence time distribution in a pilot plant spray dryer

[EN] The residence time distribution (RTD) in a pilot plant spray dryer was characterised for two kinds of air distributors (centrifugal and parallel flow) and for different atomizing air pressures. To determine the RTD - and the RTD of different particle size fractions - the particle concentration and size at the dryer outlet was measured continuously using a particle counter. Results were modelled using the Bodenstein number and the CSTR in series model. An increasing nozzle pressure leads to a decrease in mean residence time and a more narrow distribution. The influence of nozzle pressure is more pronounced than of air distributor and particle size fraction.Ruprecht, N.; Kohlus, R. (2018). Determination and modelling of the particle size dependent residence time distribution in a pilot plant spray dryer. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 1775-1782. https://doi.org/10.4995/IDS2018.2018.7740OCS1775178

Demineralised skim milk concentrates by means of dynamic cross-flow microfiltration

At ambient temperature and native pH of milk, approx. 66 % of milk containing calcium is bound onto the casein micelles (micellar calcium), whereas approx. 34 % is in the serum phase presented as free serum calcium (Koutina et al. 2014). In membrane filtration processes such as microfiltration (nominal pore size 0.1 µm), the casein fraction is retained so that micellar calcium is enriched in the retentate and is subsequently in the final product. Micellar calcium can be solubilised by reducing pH and/or temperature. This can be applied to reduce the calcium content of the retentate via membrane fractionation. However, under certain temperature and pH combinations, casein micelles change from sol to the gel state and an enhanced gel layer is built up on the membrane surface and flux decreases rapidly (Brandsma & Rizvi 1999). We combined small amplitude oscillation shear rheology and photon correlation spectroscopy to examine the sol-gel-transition behaviour of pasteurised skim milk (protein content = 3.4 %) and microfiltrated (nominal pore size = 0.1 µm) skim milk retentates (protein content = 6 to 12 %) between pH 4.6 and 6.8 at temperatures ranging from 1 to 65 °C. The aim of this study was to predict pH-temperature-protein content combinations for membrane separation while maintaining adequate flux to get skim milk retentates with defined calcium content without macroscopic aggregated casein micelles. To proof the concept filtration experiments comparing appropriate and unappropriate pH-temperature combinations to get particle free calcium degraded skim milk retentates by means of a novel dynamic cross-microfiltration (nominal pore size: 0.06 and 0.2 µm) were carried out. Results will be shown and discussed. [1] Brandsma, R. L.; Rizvi, S.S.H. (1999): Depletion of Whey Proteins and Calcium by Microfiltration of Acidified Skim Milk Prior to Cheese Making. In: Journal of Dairy Science 82 (10), p. 2063–2069. [2] Koutina, G.; Knudsen, J. C.; Andersen, U.; Skibsted, L. H. (2014): Temperature effect on calcium and phosphorus equilibria in relation to gel formation during acidification of skim milk. In: International Dairy Journal 36 (1), p. 65–73

Identification of key factors determining the surface oil concentration of encapsulated lipid particles produced by spray drying

[EN] Potential factors leading to surface oil were investigated by analyzing the impact of emulsion properties, atomization and drying conditions separately. An increased oil load, droplet size and in particular the size of droplet aggregates led to significant more surface oil. Increasing the viscosity, inlet temperature and relative humidity resulted in larger particles with a higher encapsulation efficiency. The results indicate that the probability of oil droplets being in contact with the particle surface determines the amount of surface oil. Oil diffusion towards the surface was excluded due to the short residence times and high viscosities.This work was supported by a grant for Annika Linke from the Ministry of Science, Research and the Arts of Baden-Württemberg (MWK) Az: 7533-10-5-87. Furthermore, the author acknowledges generous support by the bioeconomy graduate program BBW ForWerts, supported by the MWKLinke, A.; Balke, T.; Kohlus, R. (2018). Identification of key factors determining the surface oil concentration of encapsulated lipid particles produced by spray drying. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 1013-1020. https://doi.org/10.4995/IDS2018.2018.7739OCS1013102

Influence of Levan on the Thermally Induced Gel Formation of β-Lactoglobulin

In this study, the influence of levan on the phase behavior and the thermally induced gelation of the mixed β-lactoglobulin—levan gels as a function of polymer content, molecular weight and ionic strength was characterized. For this purpose, rheology was used to study the mechanical properties of the gels and the water binding of the network structure was investigated by time domain nuclear magnetic resonance. Phase behavior and network type were analyzed by optical observation and electron microscopy. Levan enhanced the aggregation and gel formation of β-lg due to segregative forces between the polymer species. Segregation was caused by the excluded volume effect and was more pronounced at lower ionic strength, higher levan contents and higher levan molecular weights. The presence of levan increased the water binding of the gel networks. However, this effect decreased with increasing levan content. At high ionic strength and high levan content, phase separated gels were formed. While segregative forces enhanced network formation, and therefore, increased the gel strength of mixed gels at low ionic strength, levan had also antagonistic effects on the network formation at high ionic strength and high polymer contents