BLBS102-c25 BLBS102-Simpson March 21, 2012 13:23 Trim: 276mm X 219mm Printer Name: Yet to Come
25 Biochemistry of Milk Processing 481Other EnzymesOther enzymes that have been used in dairy processing include
catalase, lactoperoxidase and lysozyme. All of these are added
for preservative reasons, and their use is more common in some
countries than others. Lysozyme may be added to milk for mak-
ing certain cheese varieties (e.g., Edam, Emmental) to prevent
growth ofClostridium tyrobutyricumand gas blowing, although
its use is not widespread. Catalase and lactoperoxidase may
be used in milk preservation strategies (particularly in tropical
countries), with the latter (either the indigenous activity present
or added purified enzyme) acting on hydrogen peroxide (which
may be added to the milk) and the former being used to destroy
excess hydrogen peroxide and terminate the enzymatic reaction
(Brennan and McSweeney 2011).MILK LIPIDS
Production of Fat-Based Dairy ProductsMilk fat is a complex mixture of triglycerides that, in milk,
is maintained as a stable o/w emulsion by the MFGM, which
surrounds milk fat globules and protects the lipids therein from
physical or enzymatic damage.
As mentioned earlier, separation of milk, either slowly under
the influence of gravity or more rapidly under centrifugal force,
readily produces a fraction (cream) enriched in the less dense
milk fat globules, separated from the fat-depleted skim milk.
Cream products of varying fat content (12–40%) are produced
industrially for a range of applications, including dessert, coffee
and as a food ingredient. The technology of cream products was
reviewed by Smiddy et al. (2009).
One of the oldest dairy products is butter, a fat-continuous
(water-in-oil, w/o) emulsion containing 80–81% fat, not more
than 16% H 2 O and, usually, 1.5% added salt. The production of
butter from cream requires destabilisation of the emulsion and
phase inversion, followed by consolidation of the fat and removal
of a large part of the aqueous phase (Frede and Buchheim 1994,
Frede 2002a). The manufacture of butter has been the subject
of several reviews (e.g., Keogh 1995, Lane 1998; Ranjith and
Rajah 2001, Frede 2002a, Wilbey 2009).
In traditional butter manufacture, cream is churned (mixed)
in a large partially filled rotating cylindrical, conical or cubical
churn, which damages the MFGM. Mechanically damaged fat
globules become adsorbed on the surfaces of air bubbles (flota-
tion churning) and gradually coalesce, being bound together by
expressed free fat, to form butter grains. Eventually, the air en-
trapped within such grains is expelled and churning generally
progresses until the grains have grown to approximately the size
of a pea (Frede and Buchheim 1994, Vanapilli and Coupland
2001). In a batch process, growth of grains is monitored visually
and audibly (impact of masses of grains on the churn walls);
at this point, the buttermilk (essentially, skim milk but with a
high content of sloughed off MFGM components such as phos-
pholipids) is drained off and the butter worked by repeated falls
and impaction within the rotating churn. After a set time, salt is
added and worked throughout the butter.With the exception of very small-scale plants, most modern
dairy factories use continuous rather than batch buttermakers.
In the most common system, the Fritz system, each stage of
the process occurs in a separate horizontal cylindrical chamber,
with product passing vertically between stages. In the churning
cylinder, rotating impellers churn the cream very rapidly in the
first stage, and in the second stage, butter grains are consolidated
and the buttermilk drained off. In the final stage, the butter mass
is worked; this chamber is sloped upwards and, while augers
transport the butter and squeeze it through a series of perfo-
rated plates, the buttermilk drains off in the opposite direction.
Midway through the working stage, salt (generally as a concen-
trated brine) is added, and becomes distributed in small mois-
ture droplets with a high local salt concentration (∼12.5% S/M),
which acts to flavour and microbiologically stabilise the butter.
The moisture present in the final droplets comes originally from
milk serum, with a small contribution from water added in brine.
The by-product buttermilk is rich in MFGM materials, in-
cluding phospholipids, and is commonly dried and used as an
ingredient in many food products; however, due to its high con-
tent of polyunsaturated fatty acids, it deteriorates quite rapidly
due to oxidation (O’Connell and Fox 2000). In recent years, there
has been increasing interest in the fact that buttermilk contains
high levels of biologically active (e.g., anticarcinogenic, antic-
holesterolemic) membrane-derived lipids, including glycosphin-
golipids and gangliosides (Jensen 2002, Dewettinck et al. 2008).
Buttermilk isolates may also have potential application as emul-
sifying agents (Corrideg and Dalgleish 1997, Singh 2006). In
addition, proteins in the MFGM such as butyrophilin may have
anticancer and antimicrobial properties, and may play a role in
diseases including multiple sclerosis and autism (Dewettinck
et al. 2008).
Traditionally, butter was produced from cream that was nat-
urally soured, and, today, in some countries, cream for butter
manufacture is ripened with LAB (lactic or fermented butter).
Bacterial acidification enhances the keeping quality of butter
and changes the flavour, through production of diacetyl. How-
ever, the production of lactic butter leads to the production of
acidic buttermilk as an unwanted by-product, and in recent years
alternative technologies have been developed for the production
of lactic butter. One of the most successful is the NIZO method,
in which a sweet (non-lactic) cream is used, and a concentrated
starter permeate is added to the butter grains midway through
the process. This process leads to production of normal butter-
milk, gives a well-flavoured product, which is very resistant to
autoxidation (Walstra et al. 1999).
In the second half of the nineteenth century, the high cost
of butter led to the development of alternatives to butter, such
as margarine; consumer preference for reduced-fat (i.e., higher
perceived ‘healthiness’) products has strengthened this trend.
A further significant disadvantage of butter for domestic ap-
plications is the fact that at typical refrigeration temperatures,
butter behaves essentially as a solid and has poor spreadabil-
ity; moreover, at room temperature, it oils off and exudes water.
The spreadability of butter may be improved by blending with
vegetable oils, or by modifications such as interesterification
(Marangoni and Rousseau 1998).