476 Part IV: Milk
The exact formulations of infant formulas differ
based on the age and special requirements of the
infant. Formulas for very young (6 months) ba-
bies generally have a high proportion of whey pro-
tein (e.g., 60% of total protein), while follow-on for-
mulas for older infants contain a higher level of
casein. In cases of infants with allergies to milk pro-
teins or, in some cases, proteins in general, formulas
in which milk proteins have been substituted by soy
proteins or in which the proteins have been hydro-
lyzed to small peptides and amino acids, may be
used. Soy-based formulas are also used in cases of
intolerance to lactose.
The exact composition and level of added vita-
mins and minerals also differ based on nutritional
requirements (O’Callaghan and Wallingford 2002).
Certain lipids are of interest as supplements for
infant formulas, such as long-chain polyunsaturated
fatty acids and conjugated linoleic acids. The final
category of additives of interest for infant formulas
is oligosaccharides, which are present at quite high
levels (1 g/L) in human milk. Such oligosaccha-
rides may be produced enzymatically, be chemically
synthesized, or be produced by fermentation.
Two main categories of infant formula are avail-
able in most countries: dry and liquid (UHT). For
dry powder manufacture, the liquid mix is evaporated
and spray-dried to yield a highly agglomerated pow-
der that will disperse readily in warm water (dis-
solving infant formula is probably the most common
dairy powder reconstitution operation practiced by
consumers in the home). Some components may be
dry-blended with the base powder, allowing flexibil-
ity in manufacture for different applications (e.g.,
infant age, dietary requirements, etc.). Powdered for-
mulas are typically packaged in N 2 /CO 2 -flushed cans.
Liquid formulas (ready-to-feed) are generally
subjected to far more severe thermal treatments than
those intended for drying, e.g., UHT processing fol-
lowed by aseptic packaging or retort sterilization of
product in screw-capped glass jars. These products,
which are stable at room temperature, have the obvi-
ous advantage of convenience over their dry coun-
terparts.
NOVEL TECHNOLOGIES FOR
PROCESSING MILK AND DAIRY
PRODUCTS
In recent years, a number of novel processing tech-
niques have been developed for applications in food
processing; major reasons for this trend include con-
sumer demand for minimally processed food prod-
ucts, and ongoing challenges in satisfactorily pro-
cessing certain food products without significant loss
of quality using existing technologies (e.g., deter-
ioration of nutrient content on heating fruit juices,
problems with the safety of shellfish).
One new process that has received particular at-
tention during the last decade is high-pressure (HP)
treatment. The principle of HP processing involves
subjecting food products to a very high pressure
(100–1000 MPa, or 1000–10,000 atm), typically at
room temperature, for a fixed period (e.g., 1–30
minutes); under such conditions, microorganisms
are killed, proteins denatured, and enzymes either
activated (at low pressures) or inactivated (at higher
pressures). The principal advantage of HP process-
ing, which does not rupture covalent bonds, is that
low molecular weight substances, such as vitamins,
are not affected, and hence there are few detrimental
effects on the nutritional or sensory characteristics
of food.
Although first described for the inactivation of
microorgansisms in milk in the 1890s by Bert Hite
at the Agricultural Research Station in Morgans-
town, West Virginia, HP treatment remained unex-
ploited in the food industry for most of the 20th cen-
tury due to lack of available processing equipment.
Only in the late 1990s were HP-processed foods
such as shellfish in the United States, fruit juice in
France, and meat in Spain launched.
To date, no HP-processed dairy products are avail-
able, probably due at least in part to the complex-
ity of the effects of high pressure on dairy sys-
tems, which necessitates considerable fundamental
research to underpin future commercial applications.
In short, high pressure affects the properties of
milk in several, often unique, ways (for reviews see
Huppertz et al. 2002, Trujillo et al. 2002). Key
effects include- Denaturation of the whey proteins, -la and -lg,
at pressures 200 or 600 MPa, respectively,
and interaction of denatured -lg with the casein
micelles. - Increased casein micelle size (by 25%) after
treatment at 250 MPa for about 15 minutes
(Huppertz et al. 2004a) and reductions in micelle
size by about 50% on treatment at 300–800 MPa. - Increased levels of nonmicellar s1-, s2-, - and
-caseins after HP treatment at 200 MPa.