Use of a turbidity sensor to characterize micellar casein powder rehydration: influence of some technological effects (original) (raw)
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Use of a turbidity sensor to determine dairy powder rehydration properties
Powder Technology, 2009
A method using a turbidity sensor has been developed to study rehydration of dairy powders. The process involved dispersing powder in a stirred vessel equipped with a turbidity sensor under standardized conditions. The changes of turbidity occurring during powder rehydration highlighted several stages including particles wetting, then swelling as the water penetrates into the powder bed, followed by a slow dispersion of the particles. The following information was obtained: wetting time (Tw), swelling time (Ts) and rehydration time (Tr). The results are in agreement with static light scattering and optic microscopy analyses. Finally, the method was used for the characterization of two powders (native phosphocaseinate and whey proteins isolate) differing in their rehydration properties.
International Dairy Journal, 2002
Enrichment of milk with micellar casein decreases water transfer during the rehydration of milk powders. In this study, the effects of the ion environment and the ion addition method on the rehydration kinetics were found to be dependent on the changes in the micellar casein. For example, adding citrate or phosphate solution to the micellar casein suspension before drying considerably increased rehydration rates and this was related to the destruction of the micelle structure. Water transfer in the casein suspension was improved by adding NaCl during rehydration: this effect may be explained by the more hygroscopic nature of NaCl rather than by extensive modification of the micellar structure. The addition of CaCl 2 considerably affected micelle organization and led to the formation of insoluble structures during spray drying.
Dairy Science & Technology, 2009
Rehydration is an essential quality attribute of dairy powders. Before industrial use, most powders are generally dissolved in mechanically stirred tanks in order to obtain a homogeneous solution as quickly as possible. The purpose of the present study was to investigate the effect of stirring conditions on the rehydration properties of a micellar casein powder. The powder particle size distribution was initially monitored during rehydration process under various conditions: hydrodynamic (400-1000 rpm), temperature (26-30°C) and solid concentration (4.8-12% [w/w]) conditions. Then, the time required to achieve a predetermined rehydration value was determined. Finally, rehydration times were correlated to hydrodynamic conditions using a process relationship obtained from experimental data and dimensional analysis. The results showed that increasing temperature and/or agitation resulted in decreasing the rehydration time and analysis of the data enabled their respective influences to be compared. For example, increasing the temperature by only 4°C has the same influence on rehydration time as doubling the stirring speed. Therefore, it could be concluded that temperature has a major effect on rehydration behaviour. The process relationship suggested that for the mixing system investigated, under isothermal conditions and for the range of flow conditions and suspensions studied, the number of revolutions required to achieve a desired degree of rehydration is independent of the impeller rotational speed. However, increasing the solid concentration from 4.8% to 12% significantly increased the number of revolutions required. These results are consistent with the hydrodynamic theory that higher stirring speeds are required at higher solid concentrations in freshly suspended powders. rehydration time / micellar casein / mixing / temperature / solid concentration 摘要-搅拌速度温度和固形物浓度对酪蛋白粉再水化作用的影响○ 再水化能力是乳粉最基 本的质量特性○ 过去，在工业生产中为了获得均匀的溶液通常采用机械搅拌的方法将 乳粉快速溶解○ 本文目的是研究搅拌条件对酪蛋白胶束粉再水化性质的影响○ 在流体力
Five common high protein dairy powders and their agglomerates produced by fluidised bed granulation were evaluated and compared for their rehydration characteristics in this study. Wettability of powders was measured by immersion wetting time, capillary rise wetting and contact angles methods, while dispersion and solubilisation processes were quantified by the change of particle size and the sediment height after centrifugation. The results showed that these high protein dairy powders generally had poor wettability, especially for whey protein isolate and the caseinates, which formed an impermeable layer separating the water surface and powders just after they contacted the water. However, the casein-micellar dominant powders exhibited prolonged dispersion due to strong interactions inside the micellar structures. The agglomerates with large particle size and high porosity are expected to exhibit increased wettability. However, agglomeration only caused the external structural modification and thus is difficult to accelerate the dispersion process of micellar casein, which can be explained by the milk protein isolate rehydration mechanism. The micellar structure inhibits the release of materials into surrounding liquid phase, which is mainly responsible for the extended rehydration time.
Water transfer during rehydration of micellar casein powders
Le Lait, 2007
Rehydration is an essential quality attribute of a dairy powder, as most powders are dissolved before use. However, there can be problems associated with the different stages of the rehydration process: i.e. wettability, sinkability, dispersibility and solubility. Many sensors and analytical methods such as the insolubility index, NMR spectroscopy, turbidity, viscosity and particle size distribution can be used to study water transfer in dairy protein concentrates during rehydration. Micellar casein (MC) powder, obtained by tangential membrane microfiltration of milk followed by spray-drying, is an interesting dairy powder due to its high protein content, and it is a valuable model of milk micelles. However, enrichment of milk in micellar casein decreases water transfer during rehydration of MC powder. The slow water transfer during MC powder rehydration is timeconsuming. Some studies have shown that insolubility is related to a decrease in the water transfer during rehydration and not to thermal denaturation. Other studies have also shown that the decrease in water transfer might be related to the micellar structure. In the present study, the destructuration of micelle induced by addition of phosphate or citrate solution to MC increased water transfer during rehydration. Water transfer in the dairy protein concentrate during rehydration was found to be related to the aqueous environment, the nature of the mineral salts, the structure of the dairy proteins, the size of the powder particle and the rehydration conditions. micellar casein / powder / rehydration / wettability / dispersibility / solubility
Dairy powder rehydration: influence of protein state, incorporation mode, and agglomeration
Journal of dairy science, 2007
A simplified method to study rehydration was used on different dairy powders. The method involved dispersing powder in a stirred vessel equipped with a turbidity sensor. The changes of turbidity occurring during powder rehydration highlighted the rehydration stage, and the influence of the proteins' state on rehydration was clarified. Casein powders had a quick wetting time but very slow dispersion, making the total rehydration process time-consuming. On the other hand, whey powders were found to have poor wettability but demonstrated immediate dispersion after wetting. Mixing casein (80%) and whey (20%) before spray drying greatly improved rehydration time compared with casein powder; whereas mixing whey powder with casein powder at the same ratio after spray drying caused a dramatic deterioration in the rehydration properties. Moreover, agglomeration was found to significantly improve the rehydration time of whey protein powder and to slow down the rehydration time of casein p...
Assessment of measurement characteristics for rehydration of milk protein based powders
Rehydration is an important powder property and is regarded as a critical issue by the dairy industry. Traditional powder rehydration measurements are relatively empirical with poor reproducibility. Thus, more reliable techniques tailored for dairy powders should be developed based on varied rehydration behaviours and applications. In this paper, a critical assessment to identify the measurement characteristics of milk protein powder rehydration is presented. Milk protein based powders were used as model systems. Four different wettability measurements (Immersion, Capillary rise, Condensation and Spreading) and four different dispersibility measurements (Dispersibility Index, Light scattering of particles in suspension, Light transmission and Conductivity of suspension) are compared and analysed. The results show that the method based on immersional wetting procedure is only appropriate for skimmed milk powder while the method for capillary rise wetting is more useful for the agglomerated milk protein powders with porous structures. Contact angle changes in the spreading wetting approach is found to be a straightforward technique to show the hydrophobicity or hydrophilicity of milk protein powders. If compared with traditional dispersibility measurements, light transmission of suspension is suitable to reflect optical properties of slow dispersion process. Light scattering methods can also be used to measure the dynamic size change of particles during the dispersion process. Furthermore, the conductivity of suspensions is a useful indicator to quantify the dispersibility indirectly by the release of minerals during rehydration. In summary, it is necessary to understand the specialities and applications of dairy powders before choosing the appropriate rehydration measurement methods.
Dairy Science & Technology, 2010
As dissolution of powdered milk proteins is necessary for the expression of their functional properties, it is regarded as a critical property by the dairy industry. However, milk proteins exhibit a progressive loss of solubility during storage in the dry form, especially in the case of high-protein-containing powders such as milk protein concentrate (MPC). To further understand the mechanisms responsible for this loss of solubility, the rehydration process of MPC powder before and after storage at 23% equilibrium relative humidity and 24°C for up to two months was studied. This work clearly showed that the storage-induced loss of milk protein powder solubility was due to changed rehydration kinetics and not to the formation of insoluble material in the course of storage. The concentrations of the various constituents of MPC (caseins, whey proteins, lactose, calcium, magnesium, phosphorus, sodium and potassium) were determined in the dispersed phase during the powder dissolution process. The results suggest that the release of micelles from powder particles is the rate-limiting step of the MPC rehydration process and is inhibited upon storage. In contrast, water penetration into the powder particles is shown not to be a rate-limiting factor as molecules larger than water (whey proteins and lactose) were freely released out of the powder structure in both fresh and aged MPCs.
Towards a better control of dairy powder rehydration processes
International Dairy Journal, 2013
The present study investigated the effect of flow conditions (temperature, agitators and stirring speed) on particle size reduction during the reconstitution process of milk powders. Images acquired with a granulomorphometer during reconstitution showed that the mixing system design had a strong influence on the course of the rehydration process. Laser light scattering data obtained for each temperature of reconstitution and agitator revealed that whatever the powder tested, the number of agitator revolutions required to achieve a given level of rehydration was constant and independent of the stirring speed. Kinetics of rehydration were shown to be much more sensitive to temperature than to stirring speed. Inversely, as expected, it was shown that granulation did not always improve rehydration time, depending on surface composition. This result revealed that both granulation/composition and flow should be considered in controlling the reconstitution process.