Chemistry Reference
In-Depth Information
V.2.1.3.
Condensed Milks
The defect of sandiness and poor texture in concentrated milks can be
overcome by hydrolyzing its lactose. Sabioni et al. (1984) reported less
sandiness in lactose-hydrolyzed sweetened condensed milk compared to the
condensed milk in which lactose was not hydrolyzed.
V.2.2.
Reduction of Lactose by Membrane Technology Techniques
Membrane techniques such as microfiltration and ultrafiltration (UF)
are used commercially to modify the proportion of lactose in milk and milk
products. These processes have resulted in lactose-modified ice creams, milk
powders, yoghurts and a series of fluid milks and dairy beverages. The
addition of UF retentate of milk changes the physical and chemical proper-
ties of all dairy products to which it is added. UF membranes retain all
the fat and practically all the protein in milk. The retention coefficients of
the non-protein nitrogen compounds are generally 20-40%, and higher for
the high-concentration factors (Grandison and Glover, 1997). Urea and
amino acids are mainly lost through the membrane. Retention of lactose
during ultrafiltration may be up to 10%. The minerals and other ions
retained during the membrane processing of milk by ultrafiltration are
those that are attached to the proteins, like calcium, magnesium, phosphate
and citrate, while others pass into the permeate. Likewise, the fat-soluble
and protein-bound vitamins are retained completely. A process in which
lactose can be removed completely from the milk is a modification of
ultrafiltration, referred as diafiltration. During diafiltration, water is
added to the milk or to the ultrafiltration concentrate of milk in order to
wash out components able to pass through the membranes. Diafiltration
helps to remove more permeate and more small molecules and therefore is a
purification process. The combination of ultrafiltration and diafiltration is
a technique for manufacturing milk enriched in protein and fat, and very
low in lactose and salts. During 3X (the most commonly used concentration
factor in industry) ultrafiltration of milk, 66-67% of lactose passes into the
permeate and 33-34% is retained in the UF milk retentate. From the initial
lactose content of 4.8 g/100 g cows' milk, 3.2 g pass into the permeate during
3X UF and 1.6 g are retained in the UF concentrate. When the UF concentrate
is diluted to the level of proteins and fat in the original milk by addition of
water, the lactose content in the reconstituted milk is now only 1.6%. The
residual lactose is then converted to glucose and galactose by treatment with
-
D
-galactosidase. The resulting product is 100% lactose free and has a sweet-
ness similar to that of ordinary whole milk. Select Milk Producers in USA
