20 Biochemistry of Milk Processing 467repositioned as a valuable source of a range of food
ingredients, rather than as a disposal problem. While
part of the impetus for this strategic reevaluation of
the potential of whey was driven by environmental
and other concerns about the disposal of a product
of such a high biological oxygen demand, it has
resulted in a previously unsuspected richness and
diversity of products, and a significant new process-
ing sector of the dairy industry (see Sienkiewicz and
Riedel 1990, Jelen 2002).
The first stage in the production of any whey prod-
uct is preliminary purification of the crude whey,
recovered after cheese or casein manufacture. Fresh
whey is classified as either sweet, with a pH5.6
and a low calcium content, or acid, with a pH of
around 4.6 and a high calcium content; the difference
in calcium content arises from the solubilization of
colloidal calcium phosphate (CCP) as pH decreases.
Common pretreatments include centrifugal clarifica-
tion to remove curd particles (fines) and pasteuriza-
tion (to inactivate starter lactic acid bacteria). For
many whey protein–based products, removal of all
lipids is desirable; this can be achieved by centrifu-
gal separation to produce whey cream, which may be
churned into whey butter. To obtain a very low level
of lipids, calcium chloride may be added to the whey,
with adjustment of the pH to more alkaline values,
followed by heating and cold storage to precipitate
and remove lipoprotein complexes (thermocalcic ag-
gregation; Karleskind et al. 1995).
The next level of processing technology applied
to the pretreated whey depends on the end product
to be manufactured. The simplest whey products
are probably whey beverages, consisting of clarified
whey, typically blended with natural or concentrated
fruit juices. Whey beverages have a nutritionally
beneficial amino acid profile, plus an isotonic na-
ture; although not widely commercialized, such
drinks have been successful in some European coun-
tries (e.g., Rivella in Switzerland).
Whey may be concentrated by evaporation and
spray-dried to whey powders. The key consideration
in spray-drying whey is the constraints imposed by
the fact that the major constituent of whey is lactose
(typically75% of whey solids). Thus, processes for
drying whey must include controlled crystallization
of lactose to yield small crystals (30–50m). This is
typically achieved by controlled cooling of concen-
trated (i.e., supersaturated with respect to lactose)
whey under a programmed temperature regime, with
careful stirring and addition of seed crystals, typically
of-lactose monohydrate, followed by holding under
conditions sufficient to allow crystallization to pro-
ceed. In general, only about 70% of the lactose pres-
ent will crystallize at this stage, and processes often
include a postdrying crystallization stage, for exam-
ple, on a belt attached to the spray-dryer, where the
remainder crystallizes (Mulvihill and Ennis 2003).
The simplest dried whey product is whey powder,
which is produced in a single-stage spray-dryer.
Additional care must be taken in drying acid whey
products, which may be sticky; the corrosive nature
of the acids (e.g., HCl) used in their manufacture
may also present processing difficulties, and such
products may be neutralized prior to drying.
Whey powders may be unsuitable for use in cer-
tain food applications (e.g., infant formulas) due to
their high mineral content; in such cases, whey is
demineralized by ion exchange or electrodialysis
before concentration and dialysis (for a discussion
of the technologies involved, see Burling 2002).
Demineralization of whey is also desirable for use in
ice cream production, to reduce the salty taste of
normal whey powder.WHEYPROTEIN–RICHPRODUCTSWhey powder has a low protein content (12–15%)
and a high lactose content (75%); many whey
products have undergone at least some degree of
purification to increase the level of a particular con-
stituent, usually protein (Matthews, 1984). There is a
family of protein-enriched whey-derived powders,
which are differentiated based on the level of protein:
whey protein concentrates (WPCs), with a protein
content in the range 35–80%, and whey protein iso-
lates (WPIs), with a protein content88%. Typ-
ically, WPCs are produced by ultrafiltration (UF),
with protein being progressively concentrated in the
retentate, while lactose, salts, and water are removed
in the permeate (Ji and Haque 2003). Higher protein
levels can be achieved by diafiltration, that is, dilution
of the retentate followed by UF. The use of ion
exchangers to adsorb the proteins from whey, fol-
lowed by selective release into suitable buffer solu-
tions, is required to achieve the high degree of purity
required of WPIs.LACTOSEPROCESSINGWhey or whey permeate, produced as a by-product
of UF processing, contains a high level of lactose.