Chemistry Reference
In-Depth Information
The use of Streptococcus thermophilus, which cannot metabolize galac-
tose, and galactose-negative strains of lactobacilli may produce sufficient
galactose to cause browning-related problems in certain types of cheese and
especially in whey therefrom during drying. The crystallization characteristics
of galactose are quite different from those of lactose (see Chapter 2) and may
cause problems in whey powders.
The monosaccharides, glucose and galactose, are much more reactive
than lactose, and hence dairy products containing hydrolysed lactose are
particularly susceptible to Maillard browning. The hydrolysis of lactose by
-galactosidase markedly increases the heat stability of milk and concen-
trated milk, especially around the pH of minimum solubility; hydrolysis of
20% has a significant effect (Tan and Fox, 1996). The mechanism of
stabilization has not been elucidated fully but is probably due to the carbo-
nyls formed in the Maillard reaction; unfortunately, such lactose-hydrolysed
milk products are very susceptible to intense browning, which may render
them non-viable commercially.
1.5.
Conclusion
Lactose is one of the principal naturally occurring disaccharides. For reasons
which are not fully clear, lactose is the principal saccharide in mammalian
milks, which are the only significant sources of lactose. As for other sugars,
the chemical and physico-chemical properties of lactose are well established
after more than 200 years of research. However, lactose continues to be the
subject of considerable research and new discoveries continue to be made and
will be described in the following chapters. Moreover, lactose has become a
valuable commodity, which stimulates further studies.
References
Aider, M., de Halleux, D. 2007. Isomerization of lactose and lactulose production: review. Trends
Food Sci. Technol. 18, 356-364.
Brew, K. 2003.
-Lactalbumin. In: Advanced Dairy Chemistry,Vol.1,Proteins, 3rd edn., (P.F. Fox
and P.L.H. McSweeney, eds.), pp. 387-419, Kluwer Academic/Plenum Publishers, New York.
de Boer, R., Dijksterhuis, J. 1998. Permeate, milk sugar, and derivatives - An overview. In: Whey,
pp. 220-226, Special Issue, SI 9804. International Dairy Federation, Brussels.
Doreau, M., Boudots, S. 1989. Recent knowledge on mare's milk production: A review. Livestock
Prod. Sci. 22, 213-235.
Fox, P.F. (ed.) 1985. Developments in Dairy Chemistry, Vol. 3, Lactose and Minor Constituents.
Elsevier Applied Science, London.
Fox, P.F. (ed.) 1997. Advanced Dairy Chemistry, Vol. 3, Lactose, Water, Salts and Vitamins, 2nd
edn, Chapman & Hall, London.
