BLBS102-c24 BLBS102-Simpson March 21, 2012 13:47 Trim: 276mm X 219mm Printer Name: Yet to Come
24 Chemistry and Biochemistry of Milk Constituents 4450510Solubility (galactose/100 g water)204010020020 40
Temperature (°C)602.1LabileIntermediate
MetastableNot saturated1.6^1βα80 100Figure 24.2.Initial solubility ofα- andβ-lactose, final solubility at
equilibrium (line 1) and supersaturation by a factor of 1.6 and 2.1
(α-lactose excluding water of crystallisation) (Fox and McSweeney
1998).powder with coarser, more easily wetted particles; such pow-
ders are said to be ‘instantised’ and are produced by agglom-
erating the fine powder particles, in effect by controlling the
caking process. In the case of whole milk powder, instantisa-
tion processes must also overcome the intrinsic hydrophobic
nature of milk fat; this is normally achieved by adding the am-
phiphilic agent, lecithin. Although lactose is hygroscopic when
it crystallises, properly crystallised lactose has very low hygro-
scopicity and, consequently, is a very effective component of
icing sugar.
The crystallisation of lactose in frozen milk products results
in destabilisation of the casein, which aggregates when the prod-
uct is thawed. In this case, the effect of lactose is indirect; when
milk is frozen, pure water freezes and the concentration of so-
lutes in the unfrozen water is increased. Since milk is super-
saturated with calcium phosphate (∼66% and∼57% of the Ca
and PO 4 , respectively, are insoluble and occur in the casein mi-
celles, known as colloidal calcium phosphate (CCP); see Section
‘Milk Salts’), when the amount of water becomes limiting, sol-
uble Ca(H 2 PO 4 ) 2 and CaHPO 4 crystallise as Ca 3 (PO 4 )2,with
the concomitant release of H+and a decrease in pH to ap-
proximately 5.8. During frozen storage, lactose crystallises as
α-lactose monohydrate, thus, reducing the amount of solvent
water and aggravating the problems of calcium phosphate solu-
bility and pH decline. Thorough crystallisation of lactose before
freezing alleviates, but does not eliminate, this problem. Pre-
heating milk prior to freezing also alleviates the problem, but
pre-hydrolysis of lactose to the more soluble sugars, glucose and
galactose, usingβ-galactosidase, appears to be the best solution.Lactose has low sweetness (16% as sweet as sucrose in a 1%
solution). This limits its usefulness as a sweetener (the principal
function of sugars in foods) but makes it is a very useful diluent,
for example for food colours, flavours or enzymes, when a high
level of sweetness is undesirable.
Being a reducing sugar, lactose can participate in the Mail-
lard (non-enzymatic) browning reaction, with very undesirable
consequences in all dairy products, for example brown colour,
off-flavours, reduced solubility and reduced nutritional value.
The Maillard reaction, and factors that affect it, has been studied
extensively for around 100 years and the relevant literature has
been reviewed frequently (see O’Brien 2009, Nursten 2011).Food Applications of LactoseTotal milk production (∼ 600 × 106 tonnes/annum) contains
∼ 30 × 106 tonnes of lactose. Most of this lactose is consumed
as a constituent of milk but whey, a by-product of the man-
ufacture of cheese and, to a lesser extent, of casein, contains
8–9× 106 tonnes of lactose. About 400,000 tonnes of lac-
tose are isolated/prepared per annum. A number of high-lactose
food products are also produced, for example approximately
2,000,000 tonnes of whey powder, electrodialysed whey pow-
der and whey permeate powder; these serve as crude sources
of lactose for several food products, including infant formulae.
Thus, most available lactose is now utilised in some form and
little is wasted. The production of lactose is basically similar
to that for other sugars, involving concentration, crystallisation,
recovery, washing and drying of the crystals (see Paterson 2009,
2011).
Although some of its properties, especially its low sweetness
and low solubility, limit the usefulness of lactose as a sugar,
other properties, that is very low hygroscopicity if properly crys-
tallised, low sweetness and reducing properties, make it a valu-
able ingredient for the food and pharmaceutical industries. In the
pharmaceutical industry, lactose is widely used as a diluent in
pelleting operations. The principal application of lactose in the
food industry is in the humanisation of infant formulae; human
milk contains approximately 7% lactose, compared to approxi-
mately 4.8% in bovine milk. For this application, demineralised
whey is widely used; it is cheaper and more suitable than puri-
fied lactose because it also supplies whey proteins, which help
bring the casein:whey protein ratio of the formulae closer to
the value 40:60, found in human milk, compared with 80:20
in bovine milk. It is necessary to demineralise the whey be-
cause bovine milk contains approximately 4 times as much inor-
ganic salts as human milk. Demineralisation is accomplished by
electrodialysis, ion exchange or nanofiltration or combinations
of these.
Lactose is also used as an agglomerating/free-flowing agent
in foods (e.g., butter powders), in the confectionery industry
to improve the functionality of shortenings, as an anti-caking
agent in icing mixtures at high humidity, or as a reducing sugar
if Maillard browning is desired. The low sweetness of lactose
limits its widespread use as a sugar but is advantageous in many
applications. Lactose absorbs compounds and may be used as a
diluent for food flavours and colours or to trap flavours.