410 Chapter 16
aid in emulsifi cation of lipids, thereby
enhancing their absorption along with that of
fat - soluble vitamins and carotenoids.
Phospholipids are considered to protect
gastric mucosa and may even extend protec-
tion from pathogenic microorganisms.
Sphingolipids are another constituent of
milk fat; they occur at a level of only 0.6 mg/g.
Recent studies show sphingolipids are hydro-
lyzed in the gastrointestinal tract to cerami-
des and sphingoid bases, which help in cell
regulation and function. Experimental animal
studies show that they inhibit colon cancer,
reduce serum cholesterol, and elevate
HDL - C, the protective cholesterol. They may
also protect against bacterial toxins and
infection.
Dietary cholesterol. It is now known that
only a minor percentage (less than 25%) of
the blood serum cholesterol arises from
dietary cholesterol. The bulk of blood choles-
terol is synthesized in the liver, which is con-
trolled by the individual genetic makeup of
an individual. The ability to absorb choles-
terol from the gastrointestinal tract and its
excretion in the feces varies widely among
people. In general, the typical cholesterol
content of milk fat is 3 to 4 mg/g.
Bovine milk fat globule membrane. The
envelope surrounding the milk fat contains
several health - promoting factors. Both
protein and non - protein constituents are
potential nutraceuticals. The phospholipid
constituents of the fat globule membrane
protect against colon cancer, gastrointestinal
pathogenic organisms, Alzheimer ’ s disease,
stress - related diseases, and depression. Other
membrane components also exhibit health
properties, including inhibiting the growth of
cancer cells, lowering serum cholesterol,
inhibiting Heliobacter pylori (involved in
stomach ulcers), and suppressing β -
glucuronidase of the intestinal Escherichia
coli. In addition, the membrane - situated
enzyme xanthine oxidase acts as a bacteri-
cidal agent. Butyrophilin is a possible sup-
pressor of multiple sclerosis.products is predominantly the most biologi-
cally active CLA, identifi ed as cis - 9, trans -
11 - 18:2 isomer. CLAs have been demonstrated
to exhibit potent physiological properties.
They are a strong antioxidant constituent of
milk fat and may prevent stomach, colon, and
breast cancers. CLA have been shown to
enhance the immune response and reduce the
risk of heart disease by reducing prostaglan-
din PGE - 2 levels, which otherwise promote
infl ammation, artery constriction, and blood
clotting. Studies have indicated that CLAs
may help in weight reduction, increasing
bone density, reducing chronic infl ammation,
and normalizing blood glucose levels by
increasing insulin sensitivity.
Trans - fatty acids. Trans - fatty acids
(TFAs) are generated from unsaturated fatty
acids by the hydrogenation process in vege-
table oils. The hydrogenation process reduces
the unsaturation level, thereby conferring
shelf life stability. Concomitantly, hydroge-
nation increases the risk of CVD. Trans - fats
raise the LDL - C and simultaneously lower
the protective HDL - C. In this context, the
main trans - fatty acid is identifi ed as elaidic
acid, 18:1, trans - 9.
The milk of cows and other ruminants
contain natural TFAs. Milk fat contains TFAs
at the 3.56% level, but their chemical struc-
ture and physiological effects are opposite to
the TFAs from hydrogenated vegetable oils.
Several studies have shown that TFAs from
milk fat do not increase the risk of CVD. The
TFAs of ruminant milk are trans - vaccenic
acid (18 : 1, trans - 11) and rumenic acid (18:2
cis - 9 trans - 11). The naturally occurring milk
TFAs are classifi ed as CLAs, and as enumer-
ated above, they possess potent benefi cial
effects.
Phospholipids. Phospholipids are present
in the range of 2 to 10 mg/g of milk fat. They
are benefi cial in terms of CVD. Rich in poly-
unsaturated fatty acids, phospholipids are
constituents of membranes. They play an
important role in cell interaction with hor-
mones, antibodies, and mineral ions. They