Crystallization and pressure filtration of anhydrous milk fat: Mixing effects

Abstract

Melt crystallization of anhydrous milk fat and subsequent filtration of the slurry is a common process for obtaining milk fat fractions with different physical and chemical properties. The crystallization mechanism is very complex and little is known about how the crystallizer conditions and the crystal size distribution (CSD) affect the filtration process. The objective of this study was to characterize the fractionation process and determine which geometric parameters of the crystallizer affect the filtration step. Two scales of fractionation were studied, 0.6 L and 3.6 L, with crystallization at 28°C. The slurry was pressure-filtered after 24 h at 500 kPa in a 1-L chamber. Impeller diameters and speeds were varied for both scales. Photomicroscopy and spectrophotometry were used to characterize the crystallization process, and filtration rates were measured by weighing the amount of filtrate passing through the filter. Filtration resistance values, calculated using the constant pressure filtration equation, as well as photomicroscopy results indicated that the agglomerates and crystals that formed had different morphological characteristics for the different mixing and flow regimes in the crystallizer. Crystallization conditions that provide an optimal filtration time, a solid fraction with minimal liquid entrainment, and a CSD with an intermediate range of sizes (80-500 µm) having good packing properties for filtration were found.Paper no. J9087 in JAOCS 76, 585-594 (1999).

Synchrotron study on crystallization kinetics of milk fat under shear flow

“…Milk fat can form compound or mixed crystals (cocrystallization) during crystallization/fractionation, as discussed in previous publications (Breitschuh & Windhab, 1996;Marangoni & Lencki, 1998). Of particular interest are the studies carried out under shear (Breitschuh & Windhab, 1998;Grall & Hartel, 1992;Herrera & Hartel, 2000a;Mazzanti et al, 2003;Patience, Hartel, & Illingworth, 1999;Van Aken & Visser, 2000;Vanhoutte, Dewettinck, Vanlerberghe, & Huyghebaert, 2002), of which only our preliminary work (Mazzanti et al, 2003) followed the crystalline structure in situ. Herrera et al (Herrera & Hartel, 2000a, 2000b, 2000c showed that blends of HMF in LMF mixed at high shear lead to the formation of smaller crystals, as did faster cooling rates (Herrera & Hartel, 2000a, 2000bHerrera & Hartel, 2000c).…”

Application of laser backscattering for monitoring of palm oil crystallisation from melt

“…Among the key aspects in particle characterisation during crystallisation are crystal size distribution (CSD) and crystal population. It has been shown that the separation efficiency of crystals during the filtration process is largely determined by the CSD and this in turn directly affects the quality and quantity of the resultant filtration products [2][3][4][5].…”

Monitoring milk fat fractionation: Effect of agitation, temperature, and residence time on physical properties

“…Samples crystallized at the highest shear rates produced the smallest crystals and the narrowest particle size distribution (6,7). At low agitation, agglomeration took place, whereas at high shear rates, smaller crystals were formed because of an enhanced nucleation rate (6,8) and breakdown of crystals by the shear forces of the impeller (5,9). Grall and Hartel (8) found the same effect at 30 and 20°C but the opposite at 15°C.…”

“…Deffense (4) discussed four factors that influence crystallization of milk fat during fractionation: oil composition, polymorphism, rate of cooling, and intersolubility. In addition, the technique used to crystallize milk fat (type of crystallizer, impeller, and operating conditions) can significantly affect the process (5). Several process parameters will be discussed in more detail.…”

“…This phenomenon was explained by the crystal habit: The uniform spheres formed at 15°C did not seem to be sensitive to shear forces. Patience et al (5) investigated the effects of stirring and type of impeller on filtration properties and crystal size distribution. Breitschuh and Windhab (7) showed that higher agitation promotes cocrystallization, probably due to an enhanced heat transfer.…”