2009_Book_FoodChemistry

10.2 Dairy Products 521
Fig. 10.19. Schematic presentation of milk processing
10.2 Dairy Products
Milk processing is illustrated schematically in
Fig. 10.19.
10.2.1 Fermented Milk Products
All sour milk products have undergone fermentation,
which can involve not only lacticacid bacteria,
but also other microorganisms, e. g., yeasts.
To the lactic acid bacteria count the genera Lactobacillus,
Lactococcus, Leuconostoc, andPediococcus.
The most important species are presented
in Table 10.25.
Depending on the microorganisms involved,
fermentation proceeds via the glycolysis path-
way with the almost exclusive formation of
lactic acid (homofermentation), via the pentose
phosphate pathway with formation of lactic
acid, acetic acid (ethanol), and possibly CO 2
(heterofermentation) or via both pathways. These
metabolic pathways are shown in Fig. 10.20.
Organisms that are obligatorily homofermentative
have fructose-bisphosphate aldolase, but
not glucose 6-phosphate dehydrogenase and
6-phosphogluconate dehydrogenase. However,
organisms that are obligatorily heterofermentative
have both dehydrogenases, but no aldolase.
Facultatively homofermentative organisms have
all three enzymes and can use both metabolic
pathways.
Apart from the type of fermentation, the configuration
of the lactic acid formed also depends on
Fig. 10.20. Glucose metabolism in lactic acid bacteria. A: homofermentation, B: Bifidus pathway, and C: heterofermentation
(6-phosphogluconate pathway)