Dairy Ingredients for Food Processing

118 Chapter 4

trates solids by removing water. Nanofi ltration

(NF) can concentrate organic components by

removing monovalent ions such as sodium

and chloride, thereby resulting in demineral-

ization. Ultrafi ltration (UF) is the process in

which macromolecules are concentrated; the

major macromolecules in milk are fat and

proteins. Microfi ltration (MF) removes bac-

teria and can separate macromolecules.

These techniques use a cross fl ow mem-

brane in which the feed solution is forced

through the membrane under pressure Figure

4.16 ). The solution fl ows over the membrane

and solids are retained (retentate) while the

removed materials are present in the perme-

ate. The membranes are classifi ed according

to their molecular weight cutoff, supposedly

20 MPa. In this process, 4% milk, which has
an average fat globule diameter of 9 μ , is
reduced to 1.6 μ. The protein that is adsorbed
onto the newly formed surfaces is casein.
Approximately 75% of the surface area is
covered with casein. Larger micelles are
preferentially adsorbed over smaller ones.
Protein adsorption is greatest on smaller
globules. The surface concentration of protein
has been measured at 10 mg.m^2.

Membrane Technology

Membrane technology is useful for selec-
tively enriching certain components. Mem-
brane technology consists of four distinct
processes: Reverse osmosis (RO) concen-

Figure 4.16. Different membrane processes and their characteristics. Reproduced with permission from Tetra
Pak.

Pressure Bar

Membrane

pore size mm

Reverse Osmosis (RO)

Nanofiltration (NF)

Ultrafiltration (UF)

Microfiltration (MF)

30 – 60^10 –4–10–3

20 – 40

1 – 10

<1

10 –3–10–2

10 –2–10–1

10 –1–10^1

Bacteria, fat

Proteins

Lactose

Minerals (calts)

Water Permeate

(filtrate)

Feed

Retentate

(concentrate)