Effect of cryoconcentration, reverse osmosis and vacuum evaporation as concentration step of skim milk prior to drying on the powder properties

Abstract

Skim milk was concentrated by cryoconcentration (CC), reverse osmosis (RO) and vacuum evaporation (VE), and the concentrated milks were spray-dried. The powder morphology and shape were observed by electron microscopy and the mean size distribution by a sieve jet method. The resulting powders were reconstituted to 25% total dry matter (TDM) to carry out different measurements such as particle size distribution in solution, zeta-potential, heat stability, color, wettability, solubility and dispersibility. The surface of the particles was smooth with small amount of visible substructures on powder surface concentrated by VE and RO. The CC and RO corresponding powders have less particle fragments than VE powder. The mean particle size was larger for CC, followed by RO and VE powders. At the size of 250nm, the CC-powder occupied three times the volume (%) occupied by the RO-powder and the VE-powder. Analysis of reconstituted powders showed that the mean size distribution of casein micelles was found 190nm, 164 and 164nm for CC, RO and VE reconstituted powders, respectively. Moreover, it has been shown that RO and VE powder produced firm gels when heated whereas the CC powder presented flocs and weak gels. As it, all powders exhibited high solubility index (˃95%). However, depending on the size, the lowest solubility in water was observed at 75nm. Regarding the powder dispersibility, they presented a good dispersibility (<90%). The powders wettability was also size-dependent and was similar for all powders at a given particle size.