Chemistry Reference
In-Depth Information
14.2.2. Processing-Induced Changes
14.2.2.1. Heat-Induced Changes
Thermal treatment of fluid milk, such as pasteurization or the produc-
tion of various concentrated/dried milk products, leads to a whole series of
desirable, and undesirable, chemical changes which can have major conse-
quence for the texture, taste and flavour. Selected changes, which directly
influence the flavour/off-flavour of milk and milk products, are
Thermal degradation of lipids (e.g., accelerated degradation of
hydroperoxides resulting in the formation of 2-alkanones). (For
more information on the thermal degradation of lipids, see Nawar,
1989; Yoo et al., 1989).
Thermal reactions involving amino acid side chains (e.g., generation
H
2
S and other S-compounds).
Maillard reactions: e.g., reaction of lactose, a reducing sugar, with
"
-amino groups on the side chain of lysine residues in milk proteins
(e.g., resulting in the formation of a wide variety of odorants, namely
furfurals, 3-/4-furanones, Strecker aldehydes, pyrazines, pyrroles,
thiazoles maltol, furaneol, etc., see Chapter 7), (Figure 14.3).
Limited information is available on the interaction of lipid oxidation
and Maillard reaction products on the flavour and off-flavour chem-
istry of milk and milk products. These reactions also contribute to
non-enzymatic browning in food systems, which may or may not be
desirable (see details in review by Zamora and Hidalgo, 2005; see also
Chapter 7).
This is not a complete list of thermally induced reactions in milk and
milk products. Other reactions such as hydrolysis of peptide bonds, dephos-
phorylation of proteins, etc., also occur but are not important from a flavour
point of view.
14.2.2.2.
Changes Induced by Non-Thermal Processing Technologies
New technologies are needed to process milk without compromising its
flavour. Several non-thermal processing technologies have been explored to
achieve microbial safety and minimize the formation of off-flavour. Some
promising technologies are
Membrane filtration
High pressure processing
Pulsed electric field treatment
