Microbiological Aspects of Dairy Ingredients 87quorum sensing. Lactobacillus acidophilus
has also been shown to be inhibitory both in
vitro and in vivo to infection with H. pylori,
the major etiological factor in human gastri-
tis, gastric ulcers, gastric atrophy, and gastric
carcinoma.
Prebiotics, which are non - digestible food
ingredients and can be oligosaccharides
designed with different linkages and different
degrees of polymerization, may be used to
stimulate the growth of probiotic bacteria in
the gut. The combined administration of a
prebiotic and probiotic bacterium is termed
synbiotic. Prebiotics should neither be hydro-
lyzed nor absorbed in the gastrointestinal
tract, provide a selective substrate to stimu-
late the growth of probiotic bacteria, and be
capable of inducing luminal or systemic
effects benefi cial to host health.Concentrated Milk
Concentrated milk can take a number of
forms: evaporated, concentrated, condensed,
and sweetened condensed milk. Each of
these products are dealt with individually in
this chapter. More general information can be
obtained from Clark (2001) and Robinson
and Itsaranuwat (2002).
Evaporated milk differs from the other
concentrated milks mainly because of the
inclusion of a sterilization stage either before
or usually after fi nal packaging. In some
countries with low internal milk production,
especially in the tropics, evaporated milk is
still a general - use milk product.
The Codex Alimentarius standard requires
evaporated milk to have at least 7.5% milk
fat and 25% total milk solids (Nieuwenhuijse,
2002 ). Initially the milk can be clarifi ed cen-
trifugally to remove some bacteria, princi-
pally heavy spores. In order to stabilize the
proteins in the fi nal product, the milk is pre-
heated, usually on a continuous fl ow basis,
at 110 ° C to 130 ° C for 1 to 3 minutes to kill
vegetative bacteria and some spores. The
evaporation or concentration stage is usually- Aiding the prevention and management of
allergies which are thought to be due to the
delayed colonization of the gut by LAB
For a bacterium to be considered a probiotic,
it must (Salminen and Ouwehand, 2003 ):
- Be nonpathogenic
- Be genetically stable
- Retain viability during manufacture and
storage of the product into which it is
incorporated - Survive in the gut
- Possess desirable physiological traits as
listed above
Probiotic cultures usually do not grow
well in milk and are often used as co - cultures
along with Strep. thermophilus and Lb. del-
brueckii subsp. bulgaricus, which reduce the
fermentation time necessary to achieve the
required acidity.
Two typical examples of probiotic bacte-
ria are Bifi dobacterium bifi dum and Lb.
acidophilus.
Bifi dobacterium bifi dum. Bifi dobacterium
bifi dum is isolated from human dental caries,
feces, and vagina as well as the intestinal
tract of animals. It possesses a metabolic
pathway that allows production of acetic acid
in addition to lactic acid in the molar ratio
3 : 2. This is important because acetic acid is
more bacteriostatic than lactic acid at the
same pH value. In addition, the production of
organic acids by the organism is thought to
stimulate peristalsis and aid normal bowel
movement in patients with constipation or
irregular bowel movements.
Lactobacillus acidophilus. Lactobacillus
acidophilus occurs naturally in the mouth,
vagina, and gastrointestinal tract of humans
and animals. Alone and in combination with
Bifi do. bifi dum it has been shown to alleviate
the symptoms of patients with irritable bowel
syndrome. The organism has also been shown
to be effective against E. coli O157 : H7
infection by interfering with the transcrip-
tion of genes involved in colonization and