2009_Book_FoodChemistry

10.3 Aroma of Milk and Dairy Products 539
10.2.10.4 Hydrolyzed Whey Syrups
The production of sweet whey syrups is becoming
increasingly important due to the
use of carrier-bound lactase (β-galactosidase,
EC. 3.2.1.23). In these syrups, lactose is hydrolyzed
to glucose and galactose. Concentration
to 60–75% solids is achieved by evaporation.
10.2.11 Lactose
For lactose production the whey is evaporated to
55–65% solid content, and the concentrate is then
seeded and cooled slowly to induce sugar crystallization.
The raw lactose (food quality) is recrystallized
to yield a raffinade (pharmaceuticalgrade
lactose). Lactose is used in manufacturing
of drugs (tablet filler), dietetic food products,
baked products, dehydrated foods, cocoa products,
beverages and ice creams.
10.2.12 Cholesterol-Reduced Milk
and Milk Products
In the production of milk products with a reduced
cholesterol content, more than 90% of the cholesterol
is removed from water-free milk fat by extraction
with supercritical carbon dioxide or by
steam distillation. The fat is then recombined with
skim milk to give low-cholesterol milk, which is
used to make the usual milk products. The extent
of cholesterol reduction in a series of products is
listed in Table 10.37.
Recombined milk does not have the same properties
as the original milk because, e. g., the membrane
composition of the fat globule changes in
the process. Cheese made from milk of this type
can exhibit texture defects. Since skim milk with
a fat content of 0.2% still contains about 18 mg/l
of cholesterol, skim milk must also be freed of
cholesterol for the production of cholesterol-free
products.
10.3 Aroma of Milk
and Dairy Products
10.3.1 Milk, Cream
Raw or gently pasteurized milk has a mild but
characteristic taste.
In the AEDA of UHT milk (Table 10.38),
δ-decalactone, which contributes to the aroma
of butter (Table 10.40) as well as unripened and
ripened cheese (cf. 10.3.5), is the predominant
aroma substance. Apart from other lactones,
2-acetyl-1-pyrroline, methional, 2-acetyl-2-thioazoline
and 4,5-epoxy-2-decenal are among the
identified aroma substances.
A higher thermal exposure of milk, e. g., by sterilization,
allows the accumulation of Maillard
products, such as methylpropanal, 2- and 3-
methyl butanal and 4-hydroxy-2,5-dimethyl-
3(2H)-furanone.
Table 10.37. Effects of a 90% reduction of cholesterol
in butter oil on the cholesterol content of recombined
milk and its products
Food Fat (%) Cholesterol (mg/kg)
I a
II a
Whole milk 3.3 135 26
Butter 81 2400 300
Yoghurt 3.5 124 26
Ice cream 10.8 450 41
Cottage cheese 4.6 150 12
Mozzarella 21.6 786 68
Brie 20.8 1000 75
Camembert 24.6 714 57
Roquefort 30.6 929 107
Cheddar 33.1 1071 114
a Product before (I) and after (II) cholesterol reduction.
10.3.2 Condensed Milk, Dried Milk Products
During the concentration and drying of milk,
reactions that are similar to those described
for heat-treated milk (cf. 10.1.3.5 and 10.3.1)
occur, but to a greater extent. Therefore, like the
aroma of UHT milk (cf. 10.3.1 and Table 10.38),
the aroma of condensed milk is also caused
by Maillard reaction products. The stale flavor
that appears when condensed milk is stored for
longer periods is due especially to the presence
of the degradation product of tryptophan,
o-aminoacetophenone, which is aroma active
in concentrations ≥1µg/kg. A rubbery aroma
defect results from higher concentrations of
benzothiazole.