Chemistry Reference
In-Depth Information
The discussion presented above is only an approach to the problem of
lactose crystallization in DL; in the real food matrix, the situation is even
more complex than described. Mutarotation, for example, as well as crystal
formation, may be impaired in DL because of the high viscosity of the
medium. In contrast, the high concentration of sucrose and glucose may
reduce the solubility of lactose significantly, increasing its rate of crystal-
lization. In fact, a sucrose concentration of 70% has been reported to reduce
lactose solubility to 42% of its solubility in water (Nickerson and Moore,
1974) but the combined impact of sucrose and glucose on lactose solubility
has not been studied. In addition, the influence of the products of the
Maillard reaction on the rates of lactose mutarotation and crystallization
has not been reported to date. The available knowledge on lactose crystal-
lization in DL is mainly empirical, based on decades of observation and
experience, but systematic studies on the subject are lacking.
In good quality DL, manufactured according to the standard process,
the formation of lactose crystals larger than 10 mm and detectable in the
mouth does not occur before 120 days of storage at room temperature
(always below 258C). Consequently, industry has adopted this period as the
usual shelf life for the product. However, due to a high demand, the food is
generally consumed earlier.
On the local market, DL is most often retailed in plastic packages.
When packaged in this way, it has been observed that the occurrence of
plastic flavour in the DL is the first observed sensory defect and determines
the shelf life of the product, before the appearance of gritty texture or
''sandiness''. Garitta et al. (2004) reported that the sensory shelf life was
limited to 146 days after storage at 258C as a consequence of a plastic flavour
note developing in the DL; sandiness was not reported in the product during
this period. Premium DL, on the contrary, is often packaged in glass contain-
ers and the shelf life is generally required to be longer (180 days). In this type
of product, sandiness probably determines its sensory shelf life, and its
development should be delayed as much as possible.
One of the most commonly used approaches to avoid lactose crystal-
lization is the enzymatic hydrolysis of lactose to glucose and galactose, which
is performed before manufacture by adding the enzyme,
-galactosidase, to
the milk and incubating for several hours. The hydrolysis of 30% of the
lactose is sufficient to avoid crystallization during a 180-day period. Glucose
and galactose are sweeter than lactose and contribute as nutritive sweeteners
to DL, reducing somewhat the costs; however,
-galactosidase is expensive
and its use is justified only when a premium product with a relatively high
price is manufactured.
It has been reported that lactose crystallization can be retarded by
increasing the proportion of glucose in DL (Ferramondo et al., 1984;
