*3.3. Enrichment of Milk Phospholipids via Filtration*

BM or BS is composed of milk fat, casein and whey protein, lactose, and ash. The particle sizes range from 0.4–4 μm for MFGM fragments or phospholipid micelles [98], 0.02–0.3 μm for casein, 0.03–0.06 μm for whey protein, and 0.002 μm for lactose and ash, respectively [99]. The size of MFG is around 0.2–15 μm [3]. As illustrated in Figure 4, the MF unit removes lactose and whey protein, and UF separates the smaller casein proteins from MPLs. Due to the size overlap of casein micelles and MPL particles, their separation is usually incomplete. Casein micelles disintegrate into peptides and amino acids in the proteolysis unit [34,42], and hydrolysates enter into the permeate stream during the subsequent UF operation [42,96]. Alcalase (E.E. 3.4.21.62), a serine-type endoprotease with esterase activity, catalyzes amino esters at pH 7.5 and 35–60 ◦C [96], while tryptic and peptic hydrolysis may be carried out at 42 ◦C for 2–16 h, at a pH of 7.7 and 2.0, respectively [42].

**Figure 4.** Filtration to enrich milk phospholipids (MPLs): (**a**) microfiltration (MF) [98] and (**b**) ultrafiltration (UF) [96]. BM, buttermilk; BMC, BM concentrate; TS, total solid; R, retentate.

Membrane filtration is a typical process for enriching BM (Figure 4a). Proteolytic treatment plus UF, as illustrated in Figure 4b, successfully differentiates MFGM from protein particles and yields product purities of 14 ± 3.4% (DM) [42] and 11.05 ± 0.02% (DM) [96]. The combined process of proteolysis and membrane separation can yield a 100% recovery rate of MPLs from BM, as illustrated in Table 3. Considering membrane units exist in most dairy factories [99,100], the process remains the most effective method for concentrating MPLs, requiring less investment than the other processes [101]. As illustrated in Table 3, this method [96] recovered more MPLs than the other processes.


**Table 3.** Process to purify MPLs and achieved purity (g MPLs/100 g dry product).

BM, buttermilk; BS, beta serum; BMP, BM powder; BSP, BS powder; CWBM, cheese whey BM; WPPC, whey protein phospholipid concentrate; BMC, BM concentrate; DME, dimethyl ether; SFE, supercritical fluid extraction; MF/UF/DF, micro/ultra/dia-filtration; TA, thermal aggregation.
