Page 284 - Natural Antioxidants, Applications in Foods of Animal Origin

Application of Natural Antioxidants in Dairy Foods 263
VetBooks.ir protein digestibility corrected amino acid score (PDCAAS) as 2.5, 3.2; 77,

104; 76, 92; and 1.00, 1.00, respectively, while these values for milk are 2.5,
91, 82, and 1.00, respectively. As can be noticed, the PDCAAS for casein,
whey protein and milk is 1.00 which is highest for a protein (Puranik & Rao,
1996; Sarwar, 1997; United States Dairy Export Council, 1999; Hoffman
& Falvo, 2004). The biological function of casein is to carry calcium and
phosphate. It forms a gel or clot in the stomach which leads to continuous
but slow release of amino acids into the blood stream (Boirie et al., 1997;
Hoffman & Falvo, 2004). Some bioactive peptides are also released from
casein on digestion that have physiological significance like, antithrombotic
peptides, antihypertensive peptides, opioid peptides, immune modulatory
peptides, antimicrobial peptides, casein phosphopeptides, glycomacropep-
tides, and so forth. Unlike casein, the plasma appearance of amino acids is
fast, high, and transient upon ingestion of whey proteins (Boirie et al., 1997;
Hoffman & Falvo, 2004). Whey proteins are rich source of branched chain
amino acids (BCAAs) that are metabolized directly into the muscle tissue
leading to replenishment of the exhausted levels followed by repairing and
rebuilding of lean muscle tissue. These are, thus important for athletes and
alike. Whey proteins are also rich and balanced source of sulfur-containing
amino acid cysteine that help boost body’s antioxidant levels as cysteine,
along with glycine and glutamic acid is a precursor of glutathione which is
the potent intracellular antioxidant and it gets oxidized to glutathione disul-
fide (GSSG) (oxidized glutathione) leading to removal of reactive oxygen
species (ROS), thus regulating the level of ROS in the cells (Haug et al.,
2007; Smithers, 2008).
The milk lipids, similar to the milk proteins, are important dietary
components for supplying nutrients as contain certain bioactive components
like short chain fatty acids, conjugated linoleic acid (CLA), branched chain
fatty acids, and so forth, and are present as emulsified droplets in globules
coated with membrane. Butyric acid (4:0) is reported to be a modulator
of gene function (German, 1999), besides inhibiting colon and mammary
tumors (Parodi, 2003). Caprylic (8:0) and capric (10:0) acids are reported
to have antiviral activities; however, caprylic acid is also reported to delay
tumor growth (Thormar et al., 1994). Sun et al. (2002) reported that lauric
acid (12:0) may have antiviral and antibacterial function, while Schuster
et al. (1980) reported that it may act as an anticaries and antiplaque agent.
An interesting observation was reported by Henry et al. (2002) that capric
and lauric acid inhibit cyclooxygenase, that is, COX-I and COX-II. Milk
fat naturally contains CLA which is shown to be anticarcinogenic and anti-
atherogenic and it has effects on body composition and fat metabolism