Food Biochemistry and Food Processing (2 edition)

BLBS102-c36 BLBS102-Simpson March 21, 2012 18:47 Trim: 276mm X 219mm Printer Name: Yet to Come

698 Part 6: Health/Functional Foods

conventional batch hydrolysis or continuous hydrolysis using

ultrafiltration membranes.

Ultrafiltration is a pressure-driven membrane process that

generally uses membranes with pore sizes in the range of

0.05μm−1 nm at pressures from 10 to 100 psi to remove both

ionic species and low MW solutes from the stream being pro-

cessed (Short 1995). Ultrafiltration can offer a great advantage

to recover and concentrate a small amount of substances from

a large volume of liquid phase. Since a positive pressure is

employed as a driving force to push the liquid phase through

the membrane pores without involving a phase change, ultra-

filtration is especially suitable for the separation of sensitive

biological substances with activity, such as enzymes. While wa-

ter and particles smaller than membrane pores pass through,

larger molecules, that is, colloids, emulsion droplets, and partic-

ulates, are retained and concentrated. Ultrafiltration processes

have three distinctive characteristics from the conventional fil-

tration process: (1) they are cross-flow systems in which the

solution flows parallel to the membrane surface, clearing away

any particles accumulated on the membrane surface, (2) they are

critically dependent on membrane materials and their nominal

MW cutoff (MWCO), and (3) they depend on membrane ge-

ometry in the actual equipment that highly affects the efficiency

of the entire process (Belter et al. 1988). The mechanism of

separation is complex and is influenced by numerous factors,

such as, method of membrane manufacture, composition of the

membrane, chemical interactions between the feed stream and

the membrane, fluid dynamics of the membrane, pressure, tem-

perature, and velocity of the feed stream (Dziezak 1990). The

main problem in many ultrafiltration processes is fouling or the

buildup of a layer on the membrane surface until the retained

mass offers hydrodynamic resistance and interferes with flux

(Paulson and Wilson 1987). Although conventional pressure-

driven processes have characteristics that make them capable

of performing most of the separations required economically,

their fouling problems dramatically reduce their efficiency and

selectivity when separating similar sized molecules.

In order to improve the yield and selectivity of peptide sepa-

ration from hydrolysates, integrative processes based on the use

of electrodialysis and filtration membrane (EDFM) have been

recently developed (Bazinet et al. 2005, Bazinet and Firdaous

2009). EDFM combines size exclusion capabilities of filtration

membranes with the proper MWCO range with the charge selec-

tivity of electrodialysis. With no pressure applied to the ED cell,

only the charged molecules migrate under the electrical field and

the neutral molecules theoretically stay in the primary solution

and do not pass the filtration membrane. In addition, the ED cell

can be configured into multicompartment to perform simultane-

ous sequential separation of different cationic or anionic peptides

(Fig. 36.3). The application has been tested for the purification

AEM 1 kDaUFM CEM

KC11 KC13 KC14

Anode Cathode

Peptide mixture

Electrode

rinse

solution

UFM

5 kDa

UFM

5 kDa

UFM

1 kDa

A-< 5 kDa

A-< 1 kDa

C+< 5 kDa

C+< 1 kDa

• –

KC12

A−

C+

Neutral

fraction (N°)

Figure 36.3.Configuration of the electrodialysis (ED) cell and filtration membrane (FM) for simultaneous sequential fractionation of anionic

and basic peptides. AEM, anion-exchange membrane; UFM, ultrafiltration membrane; CEM, cation-exchange membrane.