Chemistry Reference
In-Depth Information
of the high content of sugars and low moisture (Ferramondo et al., 1984);
therefore, the shelf life of this product is several months. Several types of DL
are available, the most popular of which, called ''Familiar'', is consumed
mainly at homes. Other types are intended for confectionery, ice cream and
other industrial uses; DL varieties with added cream, chocolate, fruits, etc.
are permitted (C odigo Alimentario Argentino, 2007).
II.2.
Technology
In the manufacture of DL, the initial mixture is composed of milk and
sucrose. The fat content is adjusted by the addition of cream, and the solids
content is often increased by adding whole or skimmed milk powder, in order
to reduce the concentration time. A few additives are allowed: neutralizers to
maintain the pH of milk during concentration, glucose in ''Familiar''-type DL
for partial substitution of sucrose (up to 40%), vanillin or ethylvanillin as
flavours and potassium sorbate (maximum 600 mg kg
-1
) as a fungicide
(C odigo Alimentario Argentino, 2007).
The quantity of nutritive sweeteners added to the milk is calculated to
give 68-70% total solids in the final product, of which milk solids account for
at least 24%. Sucrose is most commonly used in Argentina, but glucose may
also be used, in particular for ''Familiar''-type DL, because it results in a
glossier product and is less expensive than sucrose. The technological advan-
tages and drawbacks of glucose addition will be discussed later.
The mixture of milk and sugars is first neutralized with Ca(OH)
2
or
NaHCO
3
to obtain a pH of 7.0 or a titratable acidity equivalent to 2-10 mg
lactic acid 100 mL
-1
according to the type of DL (Arobba et al., 2002).
Neutralization avoids the destabilization of casein micelles as a consequence
of the decrease in pH during evaporation, which in turn is due to the
concentration of calcium phosphate, the formation of organic acids from
lactose degradation and hydrolysis of phosphoric esters of caseins (Zalazar,
2003). Failures in DL manufacture with the separation of phases (solid
proteins and liquid ''whey'') are due mainly to inadequate neutralization.
The amount of alkali needed for neutralization is calculated taking into
account the pH of the milk, and is added as a solid powder or, preferably,
as an aqueous solution to improve homogeneity. The neutralized blend is
transferred to the evaporation kettle where water is evaporated and the
reactions leading to colour and aroma development occur.
DL can be produced by the traditional process in open kettles or by
semi-continuous or continuous processes. The first is used most frequently
and consists of a classic batch process, which renders the best quality DL
(Figure II.1). The blend is prepared in a mixing tank and then gradually
